erlang - The Erlang BIFs and predefined types.
Please see following description for synopsis
erlang(3) Erlang Module Definition erlang(3)
NAME
erlang - The Erlang BIFs and predefined types.
DESCRIPTION
By convention, most Built-In Functions (BIFs) and all predefined types
are included in this module. Some of the BIFs and all of the predefined
types are viewed more or less as part of the Erlang programming lan-
guage and are auto-imported. Thus, it is not necessary to specify the
module name. For example, the calls atom_to_list(erlang) and
erlang:atom_to_list(erlang) are identical.
Auto-imported BIFs are listed without module prefix. BIFs listed with
module prefix are not auto-imported.
Predefined types are listed in the Predefined datatypes section of this
reference manual and in the Types and Function Specifications section
of the Erlang Reference Manual.
BIFs can fail for various reasons. All BIFs fail with reason badarg if
they are called with arguments of an incorrect type. The other reasons
are described in the description of each individual BIF.
Some BIFs can be used in guard tests and are marked with "Allowed in
guard tests".
DATA TYPES
Predefined datatypes
any() = any()
All possible Erlang terms. Synonym for term().
arity() = arity()
The arity of a function or type.
atom() = atom()
An Erlang atom.
binary() = <<_:_*8>>
An Erlang binary, that is, a bitstring with a size divisible by
8.
bitstring() = <<_:_*1>>
An Erlang bitstring.
boolean() = true | false
A boolean value.
byte() = 0..255
A byte of data represented by an integer.
char() = 0..1114111
An ASCII character or a unicode codepoint presented by an inte-
ger.
float() = float()
An Erlang float.
function() = function()
An Erlang fun.
identifier() = pid() | port() | reference()
An unique identifier for some entity, for example a process,
port or monitor.
integer() = integer()
An Erlang integer.
iodata() = iolist() | binary()
A binary or list containing bytes and/or iodata. This datatype
is used to represent data that is meant to be output using any
I/O module. For example: file:write/2 or gen_tcp:send/2.
To convert an iodata() term to binary() you can use
iolist_to_binary/2. To transcode a string() or unicode:char-
data() to iodata() you can use unicode:characters_to_binary/1.
iolist() =
maybe_improper_list(byte() | binary() | iolist(),
binary() | [])
A list containing bytes and/or iodata. This datatype is used to
represent data that is meant to be output using any I/O module.
For example: file:write/2 or gen_tcp:send/2.
In most use cases you want to use iodata() instead of this type.
list() = list()
An Erlang list containing terms of any type.
list(ContentType) = [ContentType]
An Erlang list containing terms of the type ContentType.
map() = #{any() => any()}
An Erlang map containing any number of key and value associa-
tions.
maybe_improper_list() = maybe_improper_list(any(), any())
An Erlang list that is not guaranteed to end with a [], and
where the list elements can be of any type.
maybe_improper_list(ContentType, TerminationType) =
maybe_improper_list(ContentType, TerminationType)
An Erlang list, that is not guaranteed to end with a [], and
where the list elements are of the type ContentType.
mfa() = {module(), atom(), arity()}
A three-tuple representing a Module:Function/Arity function sig-
nature.
module() = atom()
An Erlang module represented by an atom.
neg_integer() = integer() =< -1
A negative integer.
nil() = []
The empty list().
no_return() = none()
The type used to show that a function will never return a value,
that is it will always throw an exception.
node() = atom()
An Erlang node represented by an atom.
non_neg_integer() = integer() >= 0
A non-negative integer, that is any positive integer or 0.
none() = none()
This type is used to show that a function will never return a
value; that is it will always throw an exception. In a spec, use
no_return() for the sake of clarity.
nonempty_binary() = <<_:8, _:_*8>>
A binary() that contains some data.
nonempty_bitstring() = <<_:1, _:_*1>>
A bitstring() that contains some data.
nonempty_improper_list(ContentType, TerminationType) =
nonempty_improper_list(ContentType, TerminationType)
A maybe_improper_list/2 that contains some items.
nonempty_list() = [any(), ...]
A list() that contains some items.
nonempty_list(ContentType) = [ContentType, ...]
A list(ContentType) that contains some items.
nonempty_maybe_improper_list() =
nonempty_maybe_improper_list(any(), any())
A maybe_improper_list() that contains some items.
nonempty_maybe_improper_list(ContentType, TerminationType) =
nonempty_maybe_improper_list(ContentType, TerminationType)
A maybe_improper_list(ContentType, TerminationType) that con-
tains some items.
nonempty_string() = [char(), ...]
A string() that contains some characters.
number() = integer() | float()
An Erlang number.
pid() = pid()
An Erlang process identifier.
port() = port()
An Erlang port identifier.
pos_integer() = integer() >= 1
An integer greater than zero.
reference() = reference()
An Erlang reference.
string() = [char()]
A character string represented by a list of ASCII characters or
unicode codepoints.
term() = any()
All possible Erlang terms. Synonym for any().
timeout() = infinity | integer() >= 0
A timeout value that can be passed to a receive expression.
tuple() = tuple()
An Erlang tuple.
Other Datatypes
ext_binary() = binary()
A binary data object, structured according to the Erlang exter-
nal term format.
ext_iovec() = iovec()
A term of type iovec(), structured according to the Erlang
external term format.
iovec() = [binary()]
A list of binaries. This datatype is useful to use together with
enif_inspect_iovec.
message_queue_data() = off_heap | on_heap
See process_flag(message_queue_data, MQD).
monitor_option() =
{alias, explicit_unalias | demonitor | reply_demonitor} |
{tag, term()}
See monitor/3.
timestamp() =
{MegaSecs :: integer() >= 0,
Secs :: integer() >= 0,
MicroSecs :: integer() >= 0}
See erlang:timestamp/0.
time_unit() =
integer() >= 1 |
second | millisecond | microsecond | nanosecond | native |
perf_counter |
deprecated_time_unit()
Supported time unit representations:
PartsPerSecond :: integer() >= 1:
Time unit expressed in parts per second. That is, the time
unit equals 1/PartsPerSecond second.
second:
Symbolic representation of the time unit represented by the
integer 1.
millisecond:
Symbolic representation of the time unit represented by the
integer 1000.
microsecond:
Symbolic representation of the time unit represented by the
integer 1000_000.
nanosecond:
Symbolic representation of the time unit represented by the
integer 1000_000_000.
native:
Symbolic representation of the native time unit used by the
Erlang runtime system.
The native time unit is determined at runtime system start,
and remains the same until the runtime system terminates. If
a runtime system is stopped and then started again (even on
the same machine), the native time unit of the new runtime
system instance can differ from the native time unit of the
old runtime system instance.
One can get an approximation of the native time unit by
calling erlang:convert_time_unit(1, second, native). The
result equals the number of whole native time units per sec-
ond. If the number of native time units per second does not
add up to a whole number, the result is rounded downwards.
Note:
The value of the native time unit gives you more or less no
information about the quality of time values. It sets a limit
for the resolution and for the precision of time values, but
it gives no information about the accuracy of time values.
The resolution of the native time unit and the resolution of
time values can differ significantly.
perf_counter:
Symbolic representation of the performance counter time unit
used by the Erlang runtime system.
The perf_counter time unit behaves much in the same way as
the native time unit. That is, it can differ between runtime
restarts. To get values of this type, call
os:perf_counter/0.
deprecated_time_unit():
Deprecated symbolic representations kept for backwards-com-
patibility.
The time_unit/0 type can be extended. To convert time values
between time units, use erlang:convert_time_unit/3.
deprecated_time_unit() =
seconds | milli_seconds | micro_seconds | nano_seconds
The time_unit() type also consist of the following deprecated
symbolic time units:
seconds:
Same as second.
milli_seconds:
Same as millisecond.
micro_seconds:
Same as microsecond.
nano_seconds:
Same as nanosecond.
dist_handle()
An opaque handle identifing a distribution channel.
nif_resource()
An opaque handle identifing a NIF resource object .
spawn_opt_option() =
link | monitor |
{monitor, MonitorOpts :: [monitor_option()]} |
{priority, Level :: priority_level()} |
{fullsweep_after, Number :: integer() >= 0} |
{min_heap_size, Size :: integer() >= 0} |
{min_bin_vheap_size, VSize :: integer() >= 0} |
{max_heap_size, Size :: max_heap_size()} |
{message_queue_data, MQD :: message_queue_data()}
Options for spawn_opt().
priority_level() = low | normal | high | max
Process priority level. For more info see process_flag(priority,
Level)
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
Process max heap size configuration. For more info see
process_flag(max_heap_size, MaxHeapSize)
message_queue_data() = off_heap | on_heap
Process message queue data configuration. For more information,
see process_flag(message_queue_data, MQD)
stacktrace() =
[{module(),
atom(),
arity() | [term()],
[stacktrace_extrainfo()]} |
{function(), arity() | [term()], [stacktrace_extrainfo()]}]
stacktrace_extrainfo() =
{line, integer() >= 1} |
{file, unicode:chardata()} |
{error_info,
#{module => module(), function => atom(), cause => term()}} |
{atom(), term()}
An Erlang stacktrace as described by Errors and Error Handling
section in the Erlang Reference Manual.
EXPORTS
abs(Float) -> float()
abs(Int) -> integer() >= 0
Types:
Int = integer()
Returns an integer or float that is the arithmetical absolute
value of Float or Int, for example:
> abs(-3.33).
3.33
> abs(-3).
3
Allowed in guard tests.
erlang:adler32(Data) -> integer() >= 0
Types:
Data = iodata()
Computes and returns the adler32 checksum for Data.
erlang:adler32(OldAdler, Data) -> integer() >= 0
Types:
OldAdler = integer() >= 0
Data = iodata()
Continues computing the adler32 checksum by combining the previ-
ous checksum, OldAdler, with the checksum of Data.
The following code:
X = erlang:adler32(Data1),
Y = erlang:adler32(X,Data2).
assigns the same value to Y as this:
Y = erlang:adler32([Data1,Data2]).
erlang:adler32_combine(FirstAdler, SecondAdler, SecondSize) ->
integer() >= 0
Types:
FirstAdler = SecondAdler = SecondSize = integer() >= 0
Combines two previously computed adler32 checksums. This compu-
tation requires the size of the data object for the second
checksum to be known.
The following code:
Y = erlang:adler32(Data1),
Z = erlang:adler32(Y,Data2).
assigns the same value to Z as this:
X = erlang:adler32(Data1),
Y = erlang:adler32(Data2),
Z = erlang:adler32_combine(X,Y,iolist_size(Data2)).
alias() -> Alias
alias(Opts) -> Alias
Types:
Alias = reference()
Opts = [explicit_unalias | reply]
Create an alias which can be used when sending messages to the
process that created the alias. When the alias has been deacti-
vated, messages sent using the alias will be dropped. An alias
can be deactivated using unalias/1. Currently available options
for alias/1:
explicit_unalias:
The alias can only be deactivated via a call to unalias/1.
This is also the default behaviour if no options are passed
or if alias/0 is called.
reply:
The alias will be automatically deactivated when a reply
message sent via the alias is received. The alias can also
still be deactivated via a call to unalias/1.
Example:
server() ->
receive
{request, AliasReqId, Request} ->
Result = perform_request(Request),
AliasReqId ! {reply, AliasReqId, Result}
end,
server().
client(ServerPid, Request) ->
AliasReqId = alias([reply]),
ServerPid ! {request, AliasReqId, Request},
%% Alias will be automatically deactivated if we receive a reply
%% since we used the 'reply' option...
receive
{reply, AliasReqId, Result} -> Result
after 5000 ->
unalias(AliasReqId),
%% Flush message queue in case the reply arrived
%% just before the alias was deactivated...
receive {reply, AliasReqId, Result} -> Result
after 0 -> exit(timeout)
end
end.
Note that both the server and the client in this example must be
executing on at least OTP 24 systems in order for this to work.
For more information on process aliases see the Process Aliases
section of the Erlang Reference Manual .
erlang:append_element(Tuple1, Term) -> Tuple2
Types:
Tuple1 = Tuple2 = tuple()
Term = term()
Returns a new tuple that has one element more than Tuple1, and
contains the elements in Tuple1 followed by Term as the last
element. Semantically equivalent to
list_to_tuple(tuple_to_list(Tuple1) ++ [Term]), but much faster.
Example:
> erlang:append_element({one, two}, three).
{one,two,three}
apply(Fun, Args) -> term()
Types:
Fun = function()
Args = [term()]
Calls a fun, passing the elements in Args as arguments.
If the number of elements in the arguments are known at compile
time, the call is better written as Fun(Arg1, Arg2, ... ArgN).
Warning:
Earlier, Fun could also be specified as {Module, Function},
equivalent to apply(Module, Function, Args). This use is depre-
cated and will stop working in a future release.
apply(Module, Function, Args) -> term()
Types:
Module = module()
Function = atom()
Args = [term()]
Returns the result of applying Function in Module to Args. The
applied function must be exported from Module. The arity of the
function is the length of Args. Example:
> apply(lists, reverse, [[a, b, c]]).
[c,b,a]
> apply(erlang, atom_to_list, ['Erlang']).
"Erlang"
If the number of arguments are known at compile time, the call
is better written as Module:Function(Arg1, Arg2, ..., ArgN).
Failure: error_handler:undefined_function/3 is called if the
applied function is not exported. The error handler can be rede-
fined (see process_flag/2). If error_handler is undefined, or if
the user has redefined the default error_handler so the replace-
ment module is undefined, an error with reason undef is gener-
ated.
atom_to_binary(Atom) -> binary()
Types:
Atom = atom()
The same as atom_to_binary(Atom, utf8).
atom_to_binary(Atom, Encoding) -> binary()
Types:
Atom = atom()
Encoding = latin1 | unicode | utf8
Returns a binary corresponding to the text representation of
Atom. If Encoding is latin1, one byte exists for each character
in the text representation. If Encoding is utf8 or unicode, the
characters are encoded using UTF-8 where characters may require
multiple bytes.
Note:
As from Erlang/OTP 20, atoms can contain any Unicode character
and atom_to_binary(Atom, latin1) may fail if the text represen-
tation for Atom contains a Unicode character > 255.
Example:
> atom_to_binary('Erlang', latin1).
<<"Erlang">>
atom_to_list(Atom) -> string()
Types:
Atom = atom()
Returns a list of unicode code points corresponding to the text
representation of Atom, for example:
> atom_to_list('Erlang').
"Erlang"
> atom_to_list('').
[20320,22909]
See unicode(3) for how to convert the resulting list to differ-
ent formats.
binary_part(Subject, PosLen) -> binary()
Types:
Subject = binary()
PosLen = {Start :: integer() >= 0, Length :: integer()}
Extracts the part of the binary described by PosLen.
Negative length can be used to extract bytes at the end of a
binary, for example:
1> Bin = <<1,2,3,4,5,6,7,8,9,10>>.
2> binary_part(Bin,{byte_size(Bin), -5}).
<<6,7,8,9,10>>
Failure: badarg if PosLen in any way references outside the
binary.
Start is zero-based, that is:
1> Bin = <<1,2,3>>
2> binary_part(Bin,{0,2}).
<<1,2>>
For details about the PosLen semantics, see binary(3).
Allowed in guard tests.
binary_part(Subject, Start, Length) -> binary()
Types:
Subject = binary()
Start = integer() >= 0
Length = integer()
The same as binary_part(Subject, {Start, Length}).
Allowed in guard tests.
binary_to_atom(Binary) -> atom()
Types:
Binary = binary()
The same as binary_to_atom(Binary, utf8).
binary_to_atom(Binary, Encoding) -> atom()
Types:
Binary = binary()
Encoding = latin1 | unicode | utf8
Returns the atom whose text representation is Binary. If Encod-
ing is utf8 or unicode, the binary must contain valid UTF-8
sequences.
Note:
As from Erlang/OTP 20, binary_to_atom(Binary, utf8) is capable
of decoding any Unicode character. Earlier versions would fail
if the binary contained Unicode characters > 255.
Note:
The number of characters that are permitted in an atom name is
limited. The default limits can be found in the efficiency
guide (section Advanced).
Note:
There is configurable limit on how many atoms that can exist and
atoms are not garbage collected. Therefore, it is recommended to
consider whether binary_to_existing_atom/2 is a better option
than binary_to_atom/2. The default limits can be found in effi-
ciency guide (section Advanced).
Examples:
> binary_to_atom(<<"Erlang">>, latin1).
> binary_to_atom(<<1024/utf8>>, utf8).
binary_to_existing_atom(Binary) -> atom()
Types:
Binary = binary()
The same as binary_to_existing_atom (Binary, utf8).
binary_to_existing_atom(Binary, Encoding) -> atom()
Types:
Binary = binary()
Encoding = latin1 | unicode | utf8
As binary_to_atom/2, but the atom must exist.
The Erlang system has a configurable limit for the total number
of atoms that can exist, and atoms are not garbage collected.
Therefore, it is not safe to create many atoms from binaries
that come from an untrusted source (for example, a file fetched
from the Internet), for example, using binary_to_atom/2. This
function is thus the appropriate option when the input binary
comes from an untrusted source.
An atom exists in an Erlang system when included in a loaded
Erlang module or when created programmatically (for example, by
binary_to_atom/2). See the next note for an example of when an
atom exists in the source code for an Erlang module but not in
the compiled version of the same module.
Failure: badarg if the atom does not exist.
Note:
Note that the compiler may optimize away atoms. For example, the
compiler will rewrite atom_to_list(some_atom) to "some_atom". If
that expression is the only mention of the atom some_atom in the
containing module, the atom will not be created when the module
is loaded, and a subsequent call to binary_to_exist-
ing_atom(<<"some_atom">>, utf8) will fail.
Note:
The number of characters that are permitted in an atom name is
limited. The default limits can be found in the efficiency
guide (section Advanced).
binary_to_float(Binary) -> float()
Types:
Binary = binary()
Returns the float whose text representation is Binary, for exam-
ple:
> binary_to_float(<<"2.2017764e+0">>).
2.2017764
The float string format is the same as the format for Erlang
float literals except for that underscores are not permitted.
Failure: badarg if Binary contains a bad representation of a
float.
binary_to_integer(Binary) -> integer()
Types:
Binary = binary()
Returns an integer whose text representation is Binary, for
example:
> binary_to_integer(<<"123">>).
123
binary_to_integer/1 accepts the same string formats as
list_to_integer/1.
Failure: badarg if Binary contains a bad representation of an
integer.
binary_to_integer(Binary, Base) -> integer()
Types:
Binary = binary()
Base = 2..36
Returns an integer whose text representation in base Base is
Binary, for example:
> binary_to_integer(<<"3FF">>, 16).
1023
binary_to_integer/2 accepts the same string formats as
list_to_integer/2.
Failure: badarg if Binary contains a bad representation of an
integer.
binary_to_list(Binary) -> [byte()]
Types:
Binary = binary()
Returns a list of integers corresponding to the bytes of Binary.
binary_to_list(Binary, Start, Stop) -> [byte()]
Types:
Binary = binary()
Start = Stop = integer() >= 1
1..byte_size(Binary)
As binary_to_list/1, but returns a list of integers correspond-
ing to the bytes from position Start to position Stop in Binary.
The positions in the binary are numbered starting from 1.
Note:
The one-based indexing for binaries used by this function is
deprecated. New code is to use binary:bin_to_list/3 in STDLIB
instead. All functions in module binary consistently use zero-
based indexing.
binary_to_term(Binary) -> term()
Types:
Binary = ext_binary()
Returns an Erlang term that is the result of decoding binary
object Binary, which must be encoded according to the Erlang
external term format.
> Bin = term_to_binary(hello).
<<131,100,0,5,104,101,108,108,111>>
> hello = binary_to_term(Bin).
hello
Warning:
When decoding binaries from untrusted sources, the untrusted
source may submit data in a way to create resources, such as
atoms and remote references, that cannot be garbage collected
and lead to Denial of Service attack. In such cases, consider
using binary_to_term/2 with the safe option.
See also term_to_binary/1 and binary_to_term/2.
binary_to_term(Binary, Opts) -> term() | {term(), Used}
Types:
Binary = ext_binary()
Opt = safe | used
Opts = [Opt]
Used = integer() >= 1
As binary_to_term/1, but takes these options:
safe:
Use this option when receiving binaries from an untrusted
source.
When enabled, it prevents decoding data that can be used to
attack the Erlang runtime. In the event of receiving unsafe
data, decoding fails with a badarg error.
This prevents creation of new atoms directly, creation of
new atoms indirectly (as they are embedded in certain struc-
tures, such as process identifiers, refs, and funs), and
creation of new external function references. None of those
resources are garbage collected, so unchecked creation of
them can exhaust available memory.
> binary_to_term(<<131,100,0,5,"hello">>, [safe]).
** exception error: bad argument
> hello.
hello
> binary_to_term(<<131,100,0,5,"hello">>, [safe]).
hello
Warning:
The safe option ensures the data is safely processed by the
Erlang runtime but it does not guarantee the data is safe to
your application. You must always validate data from untrusted
sources. If the binary is stored or transits through untrusted
sources, you should also consider cryptographically signing
it.
used:
Changes the return value to {Term, Used} where Used is the
number of bytes actually read from Binary.
> Input = <<131,100,0,5,"hello","world">>.
<<131,100,0,5,104,101,108,108,111,119,111,114,108,100>>
> {Term, Used} = binary_to_term(Input, [used]).
{hello, 9}
> split_binary(Input, Used).
{<<131,100,0,5,104,101,108,108,111>>, <<"world">>}
Failure: badarg if safe is specified and unsafe data is decoded.
See also term_to_binary/1, binary_to_term/1, and list_to_exist-
ing_atom/1.
bit_size(Bitstring) -> integer() >= 0
Types:
Bitstring = bitstring()
Returns an integer that is the size in bits of Bitstring, for
example:
> bit_size(<<433:16,3:3>>).
19
> bit_size(<<1,2,3>>).
24
Allowed in guard tests.
bitstring_to_list(Bitstring) -> [byte() | bitstring()]
Types:
Bitstring = bitstring()
Returns a list of integers corresponding to the bytes of Bit-
string. If the number of bits in the binary is not divisible by
8, the last element of the list is a bitstring containing the
remaining 1-7 bits. Examples:
> bitstring_to_list(<<433:16>>).
[1,177]
> bitstring_to_list(<<433:16,3:3>>).
[1,177,<<3:3>>]
erlang:bump_reductions(Reductions) -> true
Types:
Reductions = integer() >= 1
This implementation-dependent function increments the reduction
counter for the calling process. In the Beam emulator, the
reduction counter is normally incremented by one for each func-
tion and BIF call. A context switch is forced when the counter
reaches the maximum number of reductions for a process (4000
reductions in Erlang/OTP 19.2 and later).
Warning:
This BIF can be removed in a future version of the Beam machine
without prior warning. It is unlikely to be implemented in other
Erlang implementations.
byte_size(Bitstring) -> integer() >= 0
Types:
Bitstring = bitstring()
Returns an integer that is the number of bytes needed to contain
Bitstring. That is, if the number of bits in Bitstring is not
divisible by 8, the resulting number of bytes is rounded up.
Examples:
> byte_size(<<433:16,3:3>>).
3
> byte_size(<<1,2,3>>).
3
Allowed in guard tests.
erlang:cancel_timer(TimerRef) -> Result
Types:
TimerRef = reference()
Time = integer() >= 0
Result = Time | false
Cancels a timer. The same as calling erlang:cancel_timer(Timer-
Ref, []).
erlang:cancel_timer(TimerRef, Options) -> Result | ok
Types:
TimerRef = reference()
Async = Info = boolean()
Option = {async, Async} | {info, Info}
Options = [Option]
Time = integer() >= 0
Result = Time | false
Cancels a timer that has been created by erlang:start_timer or
erlang:send_after. TimerRef identifies the timer, and was
returned by the BIF that created the timer.
Options:
{async, Async}:
Asynchronous request for cancellation. Async defaults to
false, which causes the cancellation to be performed syn-
chronously. When Async is set to true, the cancel operation
is performed asynchronously. That is, cancel_timer() sends
an asynchronous request for cancellation to the timer ser-
vice that manages the timer, and then returns ok.
{info, Info}:
Requests information about the Result of the cancellation.
Info defaults to true, which means the Result is given. When
Info is set to false, no information about the result of the
cancellation is given.
* When Async is false: if Info is true, the Result is
returned by erlang:cancel_timer(). otherwise ok is
returned.
* When Async is true: if Info is true, a message on the form
{cancel_timer, TimerRef, Result} is sent to the caller of
erlang:cancel_timer() when the cancellation operation has
been performed, otherwise no message is sent.
More Options may be added in the future.
If Result is an integer, it represents the time in milliseconds
left until the canceled timer would have expired.
If Result is false, a timer corresponding to TimerRef could not
be found. This can be either because the timer had expired,
already had been canceled, or because TimerRef never corre-
sponded to a timer. Even if the timer had expired, it does not
tell you if the time-out message has arrived at its destination
yet.
Note:
The timer service that manages the timer can be co-located with
another scheduler than the scheduler that the calling process is
executing on. If so, communication with the timer service takes
much longer time than if it is located locally. If the calling
process is in critical path, and can do other things while wait-
ing for the result of this operation, or is not interested in
the result of the operation, you want to use option {async,
true}. If using option {async, false}, the calling process
blocks until the operation has been performed.
See also erlang:send_after/4, erlang:start_timer/4, and
erlang:read_timer/2.
ceil(Number) -> integer()
Types:
Number = number()
Returns the smallest integer not less than Number. For example:
> ceil(5.5).
6
Allowed in guard tests.
check_old_code(Module) -> boolean()
Types:
Module = module()
Returns true if Module has old code, otherwise false.
See also code(3).
check_process_code(Pid, Module) -> CheckResult
Types:
Pid = pid()
Module = module()
CheckResult = boolean()
The same as check_process_code(Pid, Module, []).
check_process_code(Pid, Module, OptionList) -> CheckResult | async
Types:
Pid = pid()
Module = module()
RequestId = term()
Option = {async, RequestId} | {allow_gc, boolean()}
OptionList = [Option]
CheckResult = boolean() | aborted
Checks if the node local process identified by Pid executes old
code for Module.
Options:
{allow_gc, boolean()}:
Determines if garbage collection is allowed when performing
the operation. If {allow_gc, false} is passed, and a garbage
collection is needed to determine the result of the opera-
tion, the operation is aborted (see information on CheckRe-
sult below). The default is to allow garbage collection,
that is, {allow_gc, true}.
{async, RequestId}:
The function check_process_code/3 returns the value async
immediately after the request has been sent. When the
request has been processed, the process that called this
function is passed a message on the form
{check_process_code, RequestId, CheckResult}.
If Pid equals self(), and no async option has been passed, the
operation is performed at once. Otherwise a request for the
operation is sent to the process identified by Pid, and is han-
dled when appropriate. If no async option has been passed, the
caller blocks until CheckResult is available and can be
returned.
CheckResult informs about the result of the request as follows:
true:
The process identified by Pid executes old code for Module.
That is, the current call of the process executes old code
for this module, or the process has references to old code
for this module, or the process contains funs that refer-
ences old code for this module.
false:
The process identified by Pid does not execute old code for
Module.
aborted:
The operation was aborted, as the process needed to be
garbage collected to determine the operation result, and the
operation was requested by passing option {allow_gc, false}.
Note:
Up until ERTS version 8.*, the check process code operation
checks for all types of references to the old code. That is,
direct references (e.g. return addresses on the process stack),
indirect references (funs in process context), and references to
literals in the code.
As of ERTS version 9.0, the check process code operation only
checks for direct references to the code. Indirect references
via funs will be ignored. If such funs exist and are used after
a purge of the old code, an exception will be raised upon usage
(same as the case when the fun is received by the process after
the purge). Literals will be taken care of (copied) at a later
stage. This behavior can as of ERTS version 8.1 be enabled when
building OTP, and will automatically be enabled if dirty sched-
uler support is enabled.
See also code(3).
Failures:
badarg:
If Pid is not a node local process identifier.
badarg:
If Module is not an atom.
badarg:
If OptionList is an invalid list of options.
erlang:convert_time_unit(Time, FromUnit, ToUnit) -> ConvertedTime
Types:
Time = ConvertedTime = integer()
FromUnit = ToUnit = time_unit()
Converts the Time value of time unit FromUnit to the correspond-
ing ConvertedTime value of time unit ToUnit. The result is
rounded using the floor function.
Warning:
You can lose accuracy and precision when converting between time
units. To minimize such loss, collect all data at native time
unit and do the conversion on the end result.
erlang:crc32(Data) -> integer() >= 0
Types:
Data = iodata()
Computes and returns the crc32 (IEEE 802.3 style) checksum for
Data.
erlang:crc32(OldCrc, Data) -> integer() >= 0
Types:
OldCrc = integer() >= 0
Data = iodata()
Continues computing the crc32 checksum by combining the previous
checksum, OldCrc, with the checksum of Data.
The following code:
X = erlang:crc32(Data1),
Y = erlang:crc32(X,Data2).
assigns the same value to Y as this:
Y = erlang:crc32([Data1,Data2]).
erlang:crc32_combine(FirstCrc, SecondCrc, SecondSize) ->
integer() >= 0
Types:
FirstCrc = SecondCrc = SecondSize = integer() >= 0
Combines two previously computed crc32 checksums. This computa-
tion requires the size of the data object for the second check-
sum to be known.
The following code:
Y = erlang:crc32(Data1),
Z = erlang:crc32(Y,Data2).
assigns the same value to Z as this:
X = erlang:crc32(Data1),
Y = erlang:crc32(Data2),
Z = erlang:crc32_combine(X,Y,iolist_size(Data2)).
date() -> Date
Types:
Date = calendar:date()
Returns the current date as {Year, Month, Day}.
The time zone and Daylight Saving Time correction depend on the
underlying OS. The return value is based on the OS System Time.
Example:
> date().
{1995,2,19}
erlang:decode_packet(Type, Bin, Options) ->
{ok, Packet, Rest} |
{more, Length} |
{error, Reason}
Types:
Type =
raw | 0 | 1 | 2 | 4 | asn1 | cdr | sunrm | fcgi | tpkt |
line | http | http_bin | httph | httph_bin
Bin = binary()
Options = [Opt]
Opt =
{packet_size, integer() >= 0} |
{line_length, integer() >= 0}
Packet = binary() | HttpPacket
Rest = binary()
Length = integer() >= 0 | undefined
Reason = term()
HttpPacket =
HttpRequest | HttpResponse | HttpHeader | http_eoh |
HttpError
HttpRequest = {http_request, HttpMethod, HttpUri, HttpVer-
sion}
HttpResponse =
{http_response, HttpVersion, integer(), HttpString}
HttpHeader =
{http_header,
integer(),
HttpField,
UnmodifiedField :: HttpString,
Value :: HttpString}
HttpError = {http_error, HttpString}
HttpMethod =
'OPTIONS' | 'GET' | 'HEAD' | 'POST' | 'PUT' | 'DELETE' |
'TRACE' | HttpString
HttpUri =
'*' |
{absoluteURI,
http | https,
Host :: HttpString,
Port :: inet:port_number() | undefined,
Path :: HttpString} |
{scheme, Scheme :: HttpString, HttpString} |
{abs_path, HttpString} |
HttpString
HttpVersion =
{Major :: integer() >= 0, Minor :: integer() >= 0}
HttpField =
'Cache-Control' | 'Connection' | 'Date' | 'Pragma' |
'Transfer-Encoding' | 'Upgrade' | 'Via' | 'Accept' |
'Accept-Charset' | 'Accept-Encoding' | 'Accept-Language'
|
'Authorization' | 'From' | 'Host' | 'If-Modified-Since' |
'If-Match' | 'If-None-Match' | 'If-Range' |
'If-Unmodified-Since' | 'Max-Forwards' |
'Proxy-Authorization' | 'Range' | 'Referer' | 'User-
Agent' |
'Age' | 'Location' | 'Proxy-Authenticate' | 'Public' |
'Retry-After' | 'Server' | 'Vary' | 'Warning' |
'Www-Authenticate' | 'Allow' | 'Content-Base' |
'Content-Encoding' | 'Content-Language' | 'Content-
Length' |
'Content-Location' | 'Content-Md5' | 'Content-Range' |
'Content-Type' | 'Etag' | 'Expires' | 'Last-Modified' |
'Accept-Ranges' | 'Set-Cookie' | 'Set-Cookie2' |
'X-Forwarded-For' | 'Cookie' | 'Keep-Alive' |
'Proxy-Connection' | HttpString
HttpString = string() | binary()
Decodes the binary Bin according to the packet protocol speci-
fied by Type. Similar to the packet handling done by sockets
with option {packet,Type}.
If an entire packet is contained in Bin, it is returned together
with the remainder of the binary as {ok,Packet,Rest}.
If Bin does not contain the entire packet, {more,Length} is
returned. Length is either the expected total size of the
packet, or undefined if the expected packet size is unknown.
decode_packet can then be called again with more data added.
If the packet does not conform to the protocol format,
{error,Reason} is returned.
Types:
raw | 0:
No packet handling is done. The entire binary is returned
unless it is empty.
1 | 2 | 4:
Packets consist of a header specifying the number of bytes
in the packet, followed by that number of bytes. The length
of the header can be one, two, or four bytes; the order of
the bytes is big-endian. The header is stripped off when the
packet is returned.
line:
A packet is a line-terminated by a delimiter byte, default
is the latin-1 newline character. The delimiter byte is
included in the returned packet unless the line was trun-
cated according to option line_length.
asn1 | cdr | sunrm | fcgi | tpkt:
The header is not stripped off.
The meanings of the packet types are as follows:
asn1 - ASN.1 BER:
sunrm - Sun's RPC encoding:
cdr - CORBA (GIOP 1.1):
fcgi - Fast CGI:
tpkt - TPKT format [RFC1006]:
http | httph | http_bin | httph_bin:
The Hypertext Transfer Protocol. The packets are returned
with the format according to HttpPacket described earlier. A
packet is either a request, a response, a header, or an end
of header mark. Invalid lines are returned as HttpError.
Recognized request methods and header fields are returned as
atoms. Others are returned as strings. Strings of unrecog-
nized header fields are formatted with only capital letters
first and after hyphen characters, for example, "Sec-Web-
socket-Key". Header field names are also returned in Unmodi-
fiedField as strings, without any conversion or formatting.
The protocol type http is only to be used for the first line
when an HttpRequest or an HttpResponse is expected. The fol-
lowing calls are to use httph to get HttpHeaders until
http_eoh is returned, which marks the end of the headers and
the beginning of any following message body.
The variants http_bin and httph_bin return strings (Http-
String) as binaries instead of lists.
Options:
{packet_size, integer() >= 0}:
Sets the maximum allowed size of the packet body. If the
packet header indicates that the length of the packet is
longer than the maximum allowed length, the packet is con-
sidered invalid. Defaults to 0, which means no size limit.
{line_length, integer() >= 0}:
For packet type line, lines longer than the indicated length
are truncated.
Option line_length also applies to http* packet types as an
alias for option packet_size if packet_size itself is not
set. This use is only intended for backward compatibility.
{line_delimiter, 0 =< byte() =< 255}:
For packet type line, sets the delimiting byte. Default is
the latin-1 character $\n.
Examples:
> erlang:decode_packet(1,<<3,"abcd">>,[]).
{ok,<<"abc">>,<<"d">>}
> erlang:decode_packet(1,<<5,"abcd">>,[]).
{more,6}
erlang:delete_element(Index, Tuple1) -> Tuple2
Types:
Index = integer() >= 1
1..tuple_size(Tuple1)
Tuple1 = Tuple2 = tuple()
Returns a new tuple with element at Index removed from tuple
Tuple1, for example:
> erlang:delete_element(2, {one, two, three}).
{one,three}
delete_module(Module) -> true | undefined
Types:
Module = module()
Makes the current code for Module become old code and deletes
all references for this module from the export table. Returns
undefined if the module does not exist, otherwise true.
Warning:
This BIF is intended for the code server (see code(3)) and is
not to be used elsewhere.
Failure: badarg if there already is an old version of Module.
demonitor(MonitorRef) -> true
Types:
MonitorRef = reference()
If MonitorRef is a reference that the calling process obtained
by calling monitor/2, this monitoring is turned off. If the mon-
itoring is already turned off, nothing happens.
Once demonitor(MonitorRef) has returned, it is guaranteed that
no {'DOWN', MonitorRef, _, _, _} message, because of the moni-
tor, will be placed in the caller message queue in the future.
However, a {'DOWN', MonitorRef, _, _, _} message can have been
placed in the caller message queue before the call. It is there-
fore usually advisable to remove such a 'DOWN' message from the
message queue after monitoring has been stopped. demonitor(Moni-
torRef, [flush]) can be used instead of demonitor(MonitorRef) if
this cleanup is wanted.
Note:
Before Erlang/OTP R11B (ERTS 5.5) demonitor/1 behaved completely
asynchronously, that is, the monitor was active until the
"demonitor signal" reached the monitored entity. This had one
undesirable effect. You could never know when you were guaran-
teed not to receive a DOWN message because of the monitor.
The current behavior can be viewed as two combined operations:
asynchronously send a "demonitor signal" to the monitored entity
and ignore any future results of the monitor.
Failure: It is an error if MonitorRef refers to a monitoring
started by another process. Not all such cases are cheap to
check. If checking is cheap, the call fails with badarg, for
example if MonitorRef is a remote reference.
demonitor(MonitorRef, OptionList) -> boolean()
Types:
MonitorRef = reference()
OptionList = [Option]
Option = flush | info
The returned value is true unless info is part of OptionList.
demonitor(MonitorRef, []) is equivalent to demonitor(Monitor-
Ref).
Options:
flush:
Removes (one) {_, MonitorRef, _, _, _} message, if there is
one, from the caller message queue after monitoring has been
stopped.
Calling demonitor(MonitorRef, [flush]) is equivalent to the
following, but more efficient:
demonitor(MonitorRef),
receive
{_, MonitorRef, _, _, _} ->
true
after 0 ->
true
end
info:
The returned value is one of the following:
true:
The monitor was found and removed. In this case, no 'DOWN'
message corresponding to this monitor has been delivered
and will not be delivered.
false:
The monitor was not found and could not be removed. This
probably because someone already has placed a 'DOWN' mes-
sage corresponding to this monitor in the caller message
queue.
If option info is combined with option flush, false is
returned if a flush was needed, otherwise true.
Note:
More options can be added in a future release.
Failures:
badarg:
If OptionList is not a list.
badarg:
If Option is an invalid option.
badarg:
The same failure as for demonitor/1.
disconnect_node(Node) -> boolean() | ignored
Types:
Node = node()
Forces the disconnection of a node. This appears to the node
Node as if the local node has crashed. This BIF is mainly used
in the Erlang network authentication protocols.
Returns true if disconnection succeeds, otherwise false. If the
local node is not alive, ignored is returned.
Note:
This function may return before nodedown messages have been
delivered.
erlang:display(Term) -> true
Types:
Term = term()
Prints a text representation of Term on the standard output.
Warning:
This BIF is intended for debugging only.
erlang:dist_ctrl_get_data(DHandle) -> {Size, Data} | Data | none
Types:
Size = integer() >= 0
DHandle = dist_handle()
Data = iovec()
Get distribution channel data from the local node that is to be
passed to the remote node. The distribution channel is identi-
fied by DHandle. If no data is available, the atom none is
returned. One can request to be informed by a message when more
data is available by calling erlang:dist_ctrl_get_data_notifica-
tion(DHandle).
The returned value when there are data available depends on the
value of the get_size option configured on the distribution
channel identified by DHandle. For more information see the doc-
umentation of the get_size option for the
erlang:dist_ctrl_set_opt/3 function.
Note:
Only the process registered as distribution controller for the
distribution channel identified by DHandle is allowed to call
this function.
This function is used when implementing an alternative distribu-
tion carrier using processes as distribution controllers. DHan-
dle is retrived via the callback f_handshake_complete. More
information can be found in the documentation of ERTS User's
Guide How to implement an Alternative Carrier for the Erlang
Distribution Distribution Module.
erlang:dist_ctrl_get_opt(DHandle, Opt :: get_size) -> Value
Types:
DHandle = dist_handle()
Value = boolean()
Returns the value of the get_size option on the distribution
channel identified by DHandle. For more information see the doc-
umentation of the get_size option for the
erlang:dist_ctrl_set_opt/3 function.
Note:
Only the process registered as distribution controller for the
distribution channel identified by DHandle is allowed to call
this function.
This function is used when implementing an alternative distribu-
tion carrier using processes as distribution controllers. DHan-
dle is retrived via the callback f_handshake_complete. More
information can be found in the documentation of ERTS User's
Guide How to implement an Alternative Carrier for the Erlang
Distribution Distribution Module.
erlang:dist_ctrl_get_data_notification(DHandle) -> ok
Types:
DHandle = dist_handle()
Request notification when more data is available to fetch using
erlang:dist_ctrl_get_data(DHandle) for the distribution channel
identified by DHandle. When more data is present, the caller
will be sent the message dist_data. Once a dist_data messages
has been sent, no more dist_data messages will be sent until the
dist_ctrl_get_data_notification/1 function has been called
again.
Note:
Only the process registered as distribution controller for the
distribution channel identified by DHandle is allowed to call
this function.
This function is used when implementing an alternative distribu-
tion carrier using processes as distribution controllers. DHan-
dle is retrived via the callback f_handshake_complete. More
information can be found in the documentation of ERTS User's
Guide How to implement an Alternative Carrier for the Erlang
Distribution Distribution Module.
erlang:dist_ctrl_input_handler(DHandle, InputHandler) -> ok
Types:
DHandle = dist_handle()
InputHandler = pid()
Register an alternate input handler process for the distribution
channel identified by DHandle. Once this function has been
called, InputHandler is the only process allowed to call
erlang:dist_ctrl_put_data(DHandle, Data) with the DHandle iden-
tifing this distribution channel.
Note:
Only the process registered as distribution controller for the
distribution channel identified by DHandle is allowed to call
this function.
This function is used when implementing an alternative distribu-
tion carrier using processes as distribution controllers. DHan-
dle is retrived via the callback f_handshake_complete. More
information can be found in the documentation of ERTS User's
Guide How to implement an Alternative Carrier for the Erlang
Distribution Distribution Module.
erlang:dist_ctrl_put_data(DHandle, Data) -> ok
Types:
DHandle = dist_handle()
Data = iodata()
Deliver distribution channel data from a remote node to the
local node.
Note:
Only the process registered as distribution controller for the
distribution channel identified by DHandle is allowed to call
this function unless an alternate input handler process has been
registered using erlang:dist_ctrl_input_handler(DHandle,
InputHandler). If an alternate input handler has been regis-
tered, only the registered input handler process is allowed to
call this function.
This function is used when implementing an alternative distribu-
tion carrier using processes as distribution controllers. DHan-
dle is retrived via the callback f_handshake_complete. More
information can be found in the documentation of ERTS User's
Guide How to implement an Alternative Carrier for the Erlang
Distribution Distribution Module.
erlang:dist_ctrl_set_opt(DHandle, Opt :: get_size, Value) ->
OldValue
Types:
DHandle = dist_handle()
Value = OldValue = boolean()
Sets the value of the get_size option on the distribution chan-
nel identified by DHandle. This option controls the return value
of calls to erlang:dist_ctrl_get_data(DHandle) where DHandle
equals DHandle used when setting this option. When the get_size
option is:
false:
and there are distribution data available, a call to
erlang:dist_ctrl_get_data(DHandle) will just return Data to
pass over the channel. This is the default value of the
get_size option.
true:
and there are distribution data available, a call to
erlang:dist_ctrl_get_data(DHandle) will return Data to pass
over the channel as well as the Size of Data in bytes. This
is returned as a tuple on the form {Size, Data}.
All options are set to default when a channel is closed.
Note:
Only the process registered as distribution controller for the
distribution channel identified by DHandle is allowed to call
this function.
This function is used when implementing an alternative distribu-
tion carrier using processes as distribution controllers. DHan-
dle is retrived via the callback f_handshake_complete. More
information can be found in the documentation of ERTS User's
Guide How to implement an Alternative Carrier for the Erlang
Distribution Distribution Module.
element(N, Tuple) -> term()
Types:
N = integer() >= 1
1..tuple_size(Tuple)
Tuple = tuple()
Returns the Nth element (numbering from 1) of Tuple, for exam-
ple:
> element(2, {a, b, c}).
b
Allowed in guard tests.
erase() -> [{Key, Val}]
Types:
Key = Val = term()
Returns the process dictionary and deletes it, for example:
> put(key1, {1, 2, 3}),
put(key2, [a, b, c]),
erase().
[{key1,{1,2,3}},{key2,[a,b,c]}]
erase(Key) -> Val | undefined
Types:
Key = Val = term()
Returns the value Val associated with Key and deletes it from
the process dictionary. Returns undefined if no value is associ-
ated with Key. The average time complexity for the current
implementation of this function is O(1) and the worst case time
complexity is O(N), where N is the number of items in the
process dictionary. Example:
> put(key1, {merry, lambs, are, playing}),
X = erase(key1),
{X, erase(key1)}.
{{merry,lambs,are,playing},undefined}
error(Reason) -> no_return()
Types:
Reason = term()
Raises an exception of class error with the reason Reason. As
evaluating this function causes an exception to be thrown, it
has no return value.
The intent of the exception class error is to signal that an
unexpected error has happened (for example, a function is called
with a parameter that has an incorrect type). See the guide
about errors and error handling for additional information.
Example:
> catch error(foobar).
{'EXIT',{foobar,[{shell,apply_fun,3,
[{file,"shell.erl"},{line,906}]},
{erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,677}]},
{erl_eval,expr,5,[{file,"erl_eval.erl"},{line,430}]},
{shell,exprs,7,[{file,"shell.erl"},{line,687}]},
{shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
{shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]}}
error(Reason, Args) -> no_return()
Types:
Reason = term()
Args = [term()] | none
Raises an exception of class error with the reason Reason. Args
is expected to be the list of arguments for the current function
or the atom none. If it is a list, it is used to provide the
arguments for the current function in the stack back-trace. If
it is none, the arity of the calling function is used in the
stacktrace. As evaluating this function causes an exception to
be raised, it has no return value.
The intent of the exception class error is to signal that an
unexpected error has happened (for example, a function is called
with a parameter that has an incorrect type). See the guide
about errors and error handling for additional information.
Example:
test.erl:
-module(test).
-export([example_fun/2]).
example_fun(A1, A2) ->
erlang:error(my_error, [A1, A2]).
Erlang shell:
6> c(test).
{ok,test}
7> test:example_fun(arg1,"this is the second argument").
** exception error: my_error
in function test:example_fun/2
called as test:example_fun(arg1,"this is the second argument")
error(Reason, Args, Options) -> no_return()
Types:
Reason = term()
Args = [term()] | none
Options = [Option]
Option = {error_info, ErrorInfoMap}
ErrorInfoMap =
#{cause => term(), module => module(), function =>
atom()}
Raises an exception of class error with the reason Reason. Args
is expected to be the list of arguments for the current function
or the atom none. If it is a list, it is used to provide the
arguments for the current function in the stack back-trace. If
it is none, the arity of the calling function is used in the
stacktrace. As evaluating this function causes an exception to
be raised, it has no return value.
If the error_info option is given, the ErrorInfoMap will be
inserted into the stacktrace. The information given in the
ErrorInfoMap is to be used by error formatters such as erl_error
to provide more context around an error.
The default module of the ErrorInfoMap is the module that the
call to error/3 is made. The default function is format_error.
See format_error/2 for more details on how this Module:Func-
tion/2 is to be used
The intent of the exception class error is to signal that an
unexpected error has happened (for example, a function is called
with a parameter that has an incorrect type). See the guide
about errors and error handling for additional information.
exit(Reason) -> no_return()
Types:
Reason = term()
Raises an exception of class exit with exit reason Reason. As
evaluating this function causes an exception to be raised, it
has no return value.
The intent of the exception class exit is that the current
process should be stopped (for example when a message telling a
process to stop is received).
This function differ from error/1,2,3 by causing an exception of
a different class and by having a reason that does not include
the list of functions from the call stack.
See the guide about errors and error handling for additional
information.
Example:
> exit(foobar).
** exception exit: foobar
> catch exit(foobar).
{'EXIT',foobar}
Note:
If a process calls exit(kill) and does not catch the exception,
it will terminate with exit reason kill and also emit exit sig-
nals with exit reason kill (not killed) to all linked processes.
Such exit signals with exit reason kill can be trapped by the
linked processes. Note that this means that signals with exit
reason kill behave differently depending on how they are sent
because the signal will be untrappable if a process sends such a
signal to another process with erlang:exit/2.
exit(Pid, Reason) -> true
Types:
Pid = pid() | port()
Reason = term()
Sends an exit signal with exit reason Reason to the process or
port identified by Pid.
The following behavior applies if Reason is any term, except
normal or kill, and P is the process or port identified by Pid:
* If P is not trapping exits, P exits with exit reason Reason.
* If P is trapping exits, the exit signal is transformed into
a message {'EXIT', From, Reason}, where From is the process
identifier of the process that sent the exit signal, and
delivered to the message queue of P.
The following behavior applies if Reason is the term normal and
Pid is the identifier of a process P which is not the same as
the process that invoked erlang:exit(Pid, normal) (the behavior
when a process sends a signal with the normal reason to itself
is described in the warning):
* If P is trapping exits, the exit signal is transformed into
a message {'EXIT', From, normal}, where From is the process
identifier of the process that sent the exit signal, and
delivered to P's message queue.
* The signal has no effect if P is not trapping exits.
If Reason is the atom kill, that is, if exit(Pid, kill) is
called, an untrappable exit signal is sent to the process that
is identified by Pid, which unconditionally exits with exit rea-
son killed. The exit reason is changed from kill to killed to
hint to linked processes that the killed process got killed by a
call to exit(Pid, kill).
Note:
The functions erlang:exit/1 and erlang:exit/2 are named simi-
larly but provide very different functionalities. The
erlang:exit/1 function should be used when the intent is to stop
the current process while erlang:exit/2 should be used when the
intent is to send an exit signal to another process. Note also
that erlang:exit/1 raises an exception that can be caught while
erlang:exit/2 does not cause any exception to be raised.
Warning:
The only scenario that has not been covered by the description
above is when a process P sends an exit signal with reason nor-
mal to itself, that is erlang:exit(self(), normal). The behavior
in this scenario is as follows:
* If P is trapping exits, the exit signal is transformed into
a message {'EXIT', From, normal}, where From is P's process
identifier, and delivered to P's message queue.
* P exits with reason normal if P is not trapping exits.
Note that the behavior described above is different from when a
process sends an exit signal with reason normal to another
process. This is arguably strange but this behavior is kept for
backward compatibility reasons.
erlang:external_size(Term) -> integer() >= 0
Types:
Term = term()
Calculates, without doing the encoding, the maximum byte size
for a term encoded in the Erlang external term format. The fol-
lowing condition applies always:
> Size1 = byte_size(term_to_binary(Term)),
> Size2 = erlang:external_size(Term),
> true = Size1 =< Size2.
true
This is equivalent to a call to:
erlang:external_size(Term, [])
erlang:external_size(Term, Options) -> integer() >= 0
Types:
Term = term()
Options = [{minor_version, Version :: integer() >= 0}]
Calculates, without doing the encoding, the maximum byte size
for a term encoded in the Erlang external term format. The fol-
lowing condition applies always:
> Size1 = byte_size(term_to_binary(Term, Options)),
> Size2 = erlang:external_size(Term, Options),
> true = Size1 =< Size2.
true
Option {minor_version, Version} specifies how floats are
encoded. For a detailed description, see term_to_binary/2.
float(Number) -> float()
Types:
Number = number()
Returns a float by converting Number to a float, for example:
> float(55).
55.0
Allowed in guard tests.
Note:
If used on the top level in a guard, it tests whether the argu-
ment is a floating point number; for clarity, use is_float/1
instead.
When float/1 is used in an expression in a guard, such as
'float(A) == 4.0', it converts a number as described earlier.
float_to_binary(Float) -> binary()
Types:
Float = float()
The same as float_to_binary(Float,[{scientific,20}]).
float_to_binary(Float, Options) -> binary()
Types:
Float = float()
Options = [Option]
Option =
{decimals, Decimals :: 0..253} |
{scientific, Decimals :: 0..249} |
compact
Returns a binary corresponding to the text representation of
Float using fixed decimal point formatting. Options behaves in
the same way as float_to_list/2. Examples:
> float_to_binary(7.12, [{decimals, 4}]).
<<"7.1200">>
> float_to_binary(7.12, [{decimals, 4}, compact]).
<<"7.12">>
> float_to_binary(7.12, [{scientific, 3}]).
<<"7.120e+00">>
float_to_list(Float) -> string()
Types:
Float = float()
The same as float_to_list(Float,[{scientific,20}]).
float_to_list(Float, Options) -> string()
Types:
Float = float()
Options = [Option]
Option =
{decimals, Decimals :: 0..253} |
{scientific, Decimals :: 0..249} |
compact
Returns a string corresponding to the text representation of
Float using fixed decimal point formatting.
Available options:
* If option decimals is specified, the returned value contains
at most Decimals number of digits past the decimal point. If
the number does not fit in the internal static buffer of 256
bytes, the function throws badarg.
* If option compact is specified, the trailing zeros at the
end of the list are truncated. This option is only meaning-
ful together with option decimals.
* If option scientific is specified, the float is formatted
using scientific notation with Decimals digits of precision.
* If Options is [], the function behaves as float_to_list/1.
Examples:
> float_to_list(7.12, [{decimals, 4}]).
"7.1200"
> float_to_list(7.12, [{decimals, 4}, compact]).
"7.12"
> float_to_list(7.12, [{scientific, 3}]).
"7.120e+00"
> float_to_list(0.1+0.2)
"3.00000000000000044409e-01"
In the last example, float_to_list(0.1+0.2) evaluates to
"3.00000000000000044409e-01". The reason for this is explained
in Representation of Floating Point Numbers.
floor(Number) -> integer()
Types:
Number = number()
Returns the largest integer not greater than Number. For exam-
ple:
> floor(-10.5).
-11
Allowed in guard tests.
erlang:fun_info(Fun) -> [{Item, Info}]
Types:
Fun = function()
Item =
arity | env | index | name | module | new_index |
new_uniq |
pid | type | uniq
Info = term()
Returns a list with information about the fun Fun. Each list
element is a tuple. The order of the tuples is undefined, and
more tuples can be added in a future release.
Warning:
This BIF is mainly intended for debugging, but it can sometimes
be useful in library functions that need to verify, for example,
the arity of a fun.
Two types of funs have slightly different semantics:
* A fun created by fun M:F/A is called an external fun. Call-
ing it will always call the function F with arity A in the
latest code for module M. Notice that module M does not even
need to be loaded when the fun fun M:F/A is created.
* All other funs are called local. When a local fun is called,
the same version of the code that created the fun is called
(even if a newer version of the module has been loaded).
The following elements are always present in the list for both
local and external funs:
{type, Type}:
Type is local or external.
{module, Module}:
Module (an atom) is the module name.
If Fun is a local fun, Module is the module in which the fun
is defined.
If Fun is an external fun, Module is the module that the fun
refers to.
{name, Name}:
Name (an atom) is a function name.
If Fun is a local fun, Name is the name of the local func-
tion that implements the fun. (This name was generated by
the compiler, and is only of informational use. As it is a
local function, it cannot be called directly.) If no code is
currently loaded for the fun, [] is returned instead of an
atom.
If Fun is an external fun, Name is the name of the exported
function that the fun refers to.
{arity, Arity}:
Arity is the number of arguments that the fun is to be
called with.
{env, Env}:
Env (a list) is the environment or free variables for the
fun. For external funs, the returned list is always empty.
The following elements are only present in the list if Fun is
local:
{pid, Pid}:
Pid is the process identifier of the process that originally
created the fun.
It might point to the init process if the Fun was statically
allocated when module was loaded (this optimisation is per-
formed for local functions that do not capture the environ-
ment).
{index, Index}:
Index (an integer) is an index into the module fun table.
{new_index, Index}:
Index (an integer) is an index into the module fun table.
{new_uniq, Uniq}:
Uniq (a binary) is a unique value for this fun. It is calcu-
lated from the compiled code for the entire module.
{uniq, Uniq}:
Uniq (an integer) is a unique value for this fun. As from
Erlang/OTP R15, this integer is calculated from the compiled
code for the entire module. Before Erlang/OTP R15, this
integer was based on only the body of the fun.
erlang:fun_info(Fun, Item) -> {Item, Info}
Types:
Fun = function()
Item = fun_info_item()
Info = term()
fun_info_item() =
arity | env | index | name | module | new_index | new_uniq |
pid | type | uniq
Returns information about Fun as specified by Item, in the form
{Item,Info}.
For any fun, Item can be any of the atoms module, name, arity,
env, or type.
For a local fun, Item can also be any of the atoms index,
new_index, new_uniq, uniq, and pid. For an external fun, the
value of any of these items is always the atom undefined.
See erlang:fun_info/1.
erlang:fun_to_list(Fun) -> String :: string()
Types:
Fun = function()
Returns String that represents the code that created Fun.
String has the following form, if Fun was created by a fun
expression of the form fun ModuleName:FuncName/Arity:
"fun ModuleName:FuncName/Arity"
The form of String when Fun is created from other types of fun
expressions differs depending on if the fun expression was exe-
cuted while executing compiled code or if the fun expression was
executed while executing uncompiled code (uncompiled escripts,
the Erlang shell, and other code executed by the erl_eval mod-
ule):
compiled code:
"#Fun<M.I.U>", where M, I and U correspond to the values
named module, index and uniq in the result of
erlang:fun_info(Fun).
uncompiled code:
All funs created from fun expressions in uncompiled code
with the same arity are mapped to the same list by
fun_to_list/1.
Note:
Generally, one can not use fun_to_list/1 to check if two funs
are equal as fun_to_list/1 does not take the fun's environment
into account. See erlang:fun_info/1 for how to get the environ-
ment of a fun.
Note:
The output of fun_to_list/1 can differ between Erlang implemen-
tations and may change in future versions.
Examples:
-module(test).
-export([add/1, add2/0, fun_tuple/0]).
add(A) -> fun(B) -> A + B end.
add2() -> fun add/1.
fun_tuple() -> {fun() -> 1 end, fun() -> 1 end}.
> {fun test:add/1, test:add2()}.
{fun test:add/1,#Fun<test.1.107738983>}
Explanation: fun test:add/1 is upgradable but test:add2() is not
upgradable.
> {test:add(1), test:add(42)}.
{#Fun<test.0.107738983>,#Fun<test.0.107738983>}
Explanation: test:add(1) and test:add(42) has the same string
representation as the environment is not taken into account.
>test:fun_tuple().
{#Fun<test.2.107738983>,#Fun<test.3.107738983>}
Explanation: The string representations differ because the funs
come from different fun experssions.
> {fun() -> 1 end, fun() -> 1 end}. >
{#Fun<erl_eval.45.97283095>,#Fun<erl_eval.45.97283095>}
Explanation: All funs created from fun expressions of this form
in uncompiled code with the same arity are mapped to the same
list by fun_to_list/1.
erlang:function_exported(Module, Function, Arity) -> boolean()
Types:
Module = module()
Function = atom()
Arity = arity()
Returns true if the module Module is current and contains an
exported function Function/Arity, or if there is a BIF (a built-
in function implemented in C) with the specified name, otherwise
returns false.
garbage_collect() -> true
Forces an immediate garbage collection of the executing process.
The function is not to be used unless it has been noticed (or
there are good reasons to suspect) that the spontaneous garbage
collection will occur too late or not at all.
Warning:
Improper use can seriously degrade system performance.
garbage_collect(Pid) -> GCResult
Types:
Pid = pid()
GCResult = boolean()
The same as garbage_collect(Pid, []).
garbage_collect(Pid, OptionList) -> GCResult | async
Types:
Pid = pid()
RequestId = term()
Option = {async, RequestId} | {type, major | minor}
OptionList = [Option]
GCResult = boolean()
Garbage collects the node local process identified by Pid.
Option:
{async, RequestId}:
The function garbage_collect/2 returns the value async imme-
diately after the request has been sent. When the request
has been processed, the process that called this function is
passed a message on the form {garbage_collect, RequestId,
GCResult}.
{type, 'major' | 'minor'}:
Triggers garbage collection of requested type. Default value
is 'major', which would trigger a fullsweep GC. The option
'minor' is considered a hint and may lead to either minor or
major GC run.
If Pid equals self(), and no async option has been passed, the
garbage collection is performed at once, that is, the same as
calling garbage_collect/0. Otherwise a request for garbage col-
lection is sent to the process identified by Pid, and will be
handled when appropriate. If no async option has been passed,
the caller blocks until GCResult is available and can be
returned.
GCResult informs about the result of the garbage collection
request as follows:
true:
The process identified by Pid has been garbage collected.
false:
No garbage collection was performed, as the process identi-
fied by Pid terminated before the request could be satis-
fied.
Notice that the same caveats apply as for garbage_collect/0.
Failures:
badarg:
If Pid is not a node local process identifier.
badarg:
If OptionList is an invalid list of options.
get() -> [{Key, Val}]
Types:
Key = Val = term()
Returns the process dictionary as a list of {Key, Val} tuples.
The items in the returned list can be in any order. Example:
> put(key1, merry),
put(key2, lambs),
put(key3, {are, playing}),
get().
[{key1,merry},{key2,lambs},{key3,{are,playing}}]
get(Key) -> Val | undefined
Types:
Key = Val = term()
Returns the value Val associated with Key in the process dictio-
nary, or undefined if Key does not exist. The expected time com-
plexity for the current implementation of this function is O(1)
and the worst case time complexity is O(N), where N is the num-
ber of items in the process dictionary. Example:
> put(key1, merry),
put(key2, lambs),
put({any, [valid, term]}, {are, playing}),
get({any, [valid, term]}).
{are,playing}
erlang:get_cookie() -> Cookie | nocookie
Types:
Cookie = atom()
Returns the magic cookie of the local node if the node is alive,
otherwise the atom nocookie.
erlang:get_cookie(Node) -> Cookie | nocookie
Types:
Node = node()
Cookie = atom()
Returns the magic cookie for node Node if the local node is
alive, otherwise the atom nocookie.
get_keys() -> [Key]
Types:
Key = term()
Returns a list of all keys present in the process dictionary.
The items in the returned list can be in any order. Example:
> put(dog, {animal,1}),
put(cow, {animal,2}),
put(lamb, {animal,3}),
get_keys().
[dog,cow,lamb]
get_keys(Val) -> [Key]
Types:
Val = Key = term()
Returns a list of keys that are associated with the value Val in
the process dictionary. The items in the returned list can be in
any order. Example:
> put(mary, {1, 2}),
put(had, {1, 2}),
put(a, {1, 2}),
put(little, {1, 2}),
put(dog, {1, 3}),
put(lamb, {1, 2}),
get_keys({1, 2}).
[mary,had,a,little,lamb]
group_leader() -> pid()
Returns the process identifier of the group leader for the
process evaluating the function.
Every process is a member of some process group and all groups
have a group leader. All I/O from the group is channeled to the
group leader. When a new process is spawned, it gets the same
group leader as the spawning process. Initially, at system
startup, init is both its own group leader and the group leader
of all processes.
group_leader(GroupLeader, Pid) -> true
Types:
GroupLeader = Pid = pid()
Sets the group leader of Pid to GroupLeader. Typically, this is
used when a process started from a certain shell is to have
another group leader than init.
The group leader should be rarely changed in applications with a
supervision tree, because OTP assumes the group leader of their
processes is their application master.
Setting the group leader follows the signal ordering guarentees
described in the Processes Chapter in the Erlang Reference Man-
ual .
See also group_leader/0 and OTP design principles related to
starting and stopping applications.
halt() -> no_return()
The same as halt(0, []). Example:
> halt().
os_prompt%
halt(Status) -> no_return()
Types:
Status = integer() >= 0 | abort | string()
The same as halt(Status, []). Example:
> halt(17).
os_prompt% echo $?
17
os_prompt%
halt(Status, Options) -> no_return()
Types:
Status = integer() >= 0 | abort | string()
Options = [Option]
Option = {flush, boolean()}
Status must be a non-negative integer, a string, or the atom
abort. Halts the Erlang runtime system. Has no return value.
Depending on Status, the following occurs:
integer():
The runtime system exits with integer value Status as status
code to the calling environment (OS).
Note:
On many platforms, the OS supports only status codes 0-255. A
too large status code is truncated by clearing the high bits.
string():
An Erlang crash dump is produced with Status as slogan. Then
the runtime system exits with status code 1. The string will
be truncated if longer than 200 characters.
Note:
Before ERTS 9.1 (OTP-20.1) only code points in the range 0-255
was accepted in the string. Now any unicode string is valid.
abort:
The runtime system aborts producing a core dump, if that is
enabled in the OS.
For integer Status, the Erlang runtime system closes all ports
and allows async threads to finish their operations before exit-
ing. To exit without such flushing, use Option as {flush,false}.
For statuses string() and abort, option flush is ignored and
flushing is not done.
hd(List) -> term()
Types:
List = [term(), ...]
Returns the head of List, that is, the first element, for exam-
ple:
> hd([1,2,3,4,5]).
1
Allowed in guard tests.
Failure: badarg if List is the empty list [].
erlang:hibernate(Module, Function, Args) -> no_return()
Types:
Module = module()
Function = atom()
Args = [term()]
Puts the calling process into a wait state where its memory
allocation has been reduced as much as possible. This is useful
if the process does not expect to receive any messages soon.
The process is awaken when a message is sent to it, and control
resumes in Module:Function with the arguments specified by Args
with the call stack emptied, meaning that the process terminates
when that function returns. Thus erlang:hibernate/3 never
returns to its caller. The resume function Module:Function/Arity
must be exported (Arity =:= length(Args)).
If the process has any message in its message queue, the process
is awakened immediately in the same way as described earlier.
In more technical terms, erlang:hibernate/3 discards the call
stack for the process, and then garbage collects the process.
After this, all live data is in one continuous heap. The heap is
then shrunken to the exact same size as the live data that it
holds (even if that size is less than the minimum heap size for
the process).
If the size of the live data in the process is less than the
minimum heap size, the first garbage collection occurring after
the process is awakened ensures that the heap size is changed to
a size not smaller than the minimum heap size.
Notice that emptying the call stack means that any surrounding
catch is removed and must be re-inserted after hibernation. One
effect of this is that processes started using proc_lib (also
indirectly, such as gen_server processes), are to use
proc_lib:hibernate/3 instead, to ensure that the exception han-
dler continues to work when the process wakes up.
erlang:insert_element(Index, Tuple1, Term) -> Tuple2
Types:
Index = integer() >= 1
1..tuple_size(Tuple1) + 1
Tuple1 = Tuple2 = tuple()
Term = term()
Returns a new tuple with element Term inserted at position Index
in tuple Tuple1. All elements from position Index and upwards
are pushed one step higher in the new tuple Tuple2. Example:
> erlang:insert_element(2, {one, two, three}, new).
{one,new,two,three}
integer_to_binary(Integer) -> binary()
Types:
Integer = integer()
Returns a binary corresponding to the text representation of
Integer, for example:
> integer_to_binary(77).
<<"77">>
integer_to_binary(Integer, Base) -> binary()
Types:
Integer = integer()
Base = 2..36
Returns a binary corresponding to the text representation of
Integer in base Base, for example:
> integer_to_binary(1023, 16).
<<"3FF">>
integer_to_list(Integer) -> string()
Types:
Integer = integer()
Returns a string corresponding to the text representation of
Integer, for example:
> integer_to_list(77).
"77"
integer_to_list(Integer, Base) -> string()
Types:
Integer = integer()
Base = 2..36
Returns a string corresponding to the text representation of
Integer in base Base, for example:
> integer_to_list(1023, 16).
"3FF"
iolist_size(Item) -> integer() >= 0
Types:
Item = iolist() | binary()
Returns an integer, that is the size in bytes, of the binary
that would be the result of iolist_to_binary(Item), for example:
> iolist_size([1,2|<<3,4>>]).
4
iolist_to_binary(IoListOrBinary) -> binary()
Types:
IoListOrBinary = iolist() | binary()
Returns a binary that is made from the integers and binaries in
IoListOrBinary, for example:
> Bin1 = <<1,2,3>>.
<<1,2,3>>
> Bin2 = <<4,5>>.
<<4,5>>
> Bin3 = <<6>>.
<<6>>
> iolist_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6>>
erlang:iolist_to_iovec(IoListOrBinary) -> iovec()
Types:
IoListOrBinary = iolist() | binary()
Returns an iovec that is made from the integers and binaries in
IoListOrBinary. This function is useful when you want to flatten
an iolist but you do not need a single binary. This can be use-
ful for passing the data to nif functions such as
enif_inspect_iovec or do more efficient message passing. The
advantage of using this function over iolist_to_binary/1 is that
it does not have to copy off-heap binaries. Example:
> Bin1 = <<1,2,3>>.
<<1,2,3>>
> Bin2 = <<4,5>>.
<<4,5>>
> Bin3 = <<6>>.
<<6>>
%% If you pass small binaries and integers it works as iolist_to_binary
> erlang:iolist_to_iovec([Bin1,1,[2,3,Bin2],4|Bin3]).
[<<1,2,3,1,2,3,4,5,4,6>>]
%% If you pass larger binaries, they are split and returned in a form
%% optimized for calling the C function writev.
> erlang:iolist_to_iovec([<<1>>,<<2:8096>>,<<3:8096>>]).
[<<1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,...>>,
<<0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
...>>,
<<0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,...>>]
is_alive() -> boolean()
Returns true if the local node is alive (that is, if the node
can be part of a distributed system), otherwise false. A node is
alive if it is started with:
* "erl -name LONGNAME" or,
* "erl -sname SHORTNAME".
A node can also be alive if it has got a name from a call to
net_kernel:start/1 and has not been stopped by a call to
net_kernel:stop/0.
is_atom(Term) -> boolean()
Types:
Term = term()
Returns true if Term is an atom, otherwise false.
Allowed in guard tests.
is_binary(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a binary, otherwise false.
A binary always contains a complete number of bytes.
Allowed in guard tests.
is_bitstring(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a bitstring (including a binary), other-
wise false.
Allowed in guard tests.
is_boolean(Term) -> boolean()
Types:
Term = term()
Returns true if Term is the atom true or the atom false (that
is, a boolean). Otherwise returns false.
Allowed in guard tests.
erlang:is_builtin(Module, Function, Arity) -> boolean()
Types:
Module = module()
Function = atom()
Arity = arity()
This BIF is useful for builders of cross-reference tools.
Returns true if Module:Function/Arity is a BIF implemented in C,
otherwise false.
is_float(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a floating point number, otherwise
false.
Allowed in guard tests.
is_function(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a fun, otherwise false.
Allowed in guard tests.
is_function(Term, Arity) -> boolean()
Types:
Term = term()
Arity = arity()
Returns true if Term is a fun that can be applied with Arity
number of arguments, otherwise false.
Allowed in guard tests.
is_integer(Term) -> boolean()
Types:
Term = term()
Returns true if Term is an integer, otherwise false.
Allowed in guard tests.
is_list(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a list with zero or more elements, oth-
erwise false.
Allowed in guard tests.
is_map(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a map, otherwise false.
Allowed in guard tests.
is_map_key(Key, Map) -> boolean()
Types:
Key = term()
Map = map()
Returns true if map Map contains Key and returns false if it
does not contain the Key.
The call fails with a {badmap,Map} exception if Map is not a
map.
Example:
> Map = #{"42" => value}.
#{"42" => value}
> is_map_key("42",Map).
true
> is_map_key(value,Map).
false
Allowed in guard tests.
is_number(Term) -> boolean()
Types:
Term = term()
Returns true if Term is an integer or a floating point number.
Otherwise returns false.
Allowed in guard tests.
is_pid(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a process identifier, otherwise false.
Allowed in guard tests.
is_port(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a port identifier, otherwise false.
Allowed in guard tests.
is_process_alive(Pid) -> boolean()
Types:
Pid = pid()
Pid must refer to a process at the local node.
Returns true if the process exists and is alive, that is, is not
exiting and has not exited. Otherwise returns false.
If process P1 calls is_process_alive(P2Pid) it is guaranteed
that all signals, sent from P1 to P2 (P2 is the process with
identifier P2Pid) before the call, will be delivered to P2
before the aliveness of P2 is checked. This guarantee means that
one can use is_process_alive/1 to let a process P1 wait until a
process P2, which has got an exit signal with reason kill from
P1, is killed. Example:
exit(P2Pid, kill),
% P2 might not be killed
is_process_alive(P2Pid),
% P2 is not alive (the call above always return false)
See the documentation about signals and erlang:exit/2 for more
information about signals and exit singnals.
is_record(Term, RecordTag) -> boolean()
Types:
Term = term()
RecordTag = atom()
Returns true if Term is a tuple and its first element is Record-
Tag. Otherwise returns false.
Note:
Normally the compiler treats calls to is_record/2 especially. It
emits code to verify that Term is a tuple, that its first ele-
ment is RecordTag, and that the size is correct. However, if
RecordTag is not a literal atom, the BIF is_record/2 is called
instead and the size of the tuple is not verified.
Allowed in guard tests, if RecordTag is a literal atom.
is_record(Term, RecordTag, Size) -> boolean()
Types:
Term = term()
RecordTag = atom()
Size = integer() >= 0
RecordTag must be an atom.
Returns true if Term is a tuple, its first element is RecordTag,
and its size is Size. Otherwise returns false.
Allowed in guard tests if RecordTag is a literal atom and Size
is a literal integer.
Note:
This BIF is documented for completeness. Usually is_record/2 is
to be used.
is_reference(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a reference, otherwise false.
Allowed in guard tests.
is_tuple(Term) -> boolean()
Types:
Term = term()
Returns true if Term is a tuple, otherwise false.
Allowed in guard tests.
length(List) -> integer() >= 0
Types:
List = [term()]
Returns the length of List, for example:
> length([1,2,3,4,5,6,7,8,9]).
9
Allowed in guard tests.
link(PidOrPort) -> true
Types:
PidOrPort = pid() | port()
Sets up and activates a link between the calling process and
another process or a port identified by PidOrPort. We will from
here on call the identified process or port linkee. If the lin-
kee is a port, it must reside on the same node as the caller.
If one of the participants of a link terminates, it will send an
exit signal to the other participant. The exit signal will con-
tain the exit reason of the terminated participant. Other cases
when exit signals are triggered due to a link are when no linkee
exist (noproc exit reason) and when the connection between
linked processes on different nodes is lost or cannot be estab-
lished (noconnection exit reason).
An existing link can be removed by calling unlink/1. For more
information on links and exit signals due to links, see the Pro-
cesses chapter in the Erlang Reference Manual :
* Links
* Sending Exit Signals
* Receiving Exit Signals
For historical reasons, link/1 has a strange semi-synchronous
behavior when it is "cheap" to check if the linkee exists or
not, and the caller does not trap exits. If the above is true
and the linkee does not exist, link/1 will raise a noproc error
exception. The expected behavior would instead have been that
link/1 returned true, and the caller later was sent an exit sig-
nal with noproc exit reason, but this is unfortunately not the
case. The noproc exception is not to be confused with an exit
signal with exit reason noproc. Currently it is "cheap" to check
if the linkee exists when it is supposed to reside on the same
node as the calling process.
The link setup and activation is performed asynchronously. If
the link already exists, or if the caller attempts to create a
link to itself, nothing is done. A detailed description of the
link protocol can be found in the Distribution Protocol chapter
of the ERTS User's Guide .
Failure:
* badarg if PidOrPort does not identify a process or a node
local port.
* noproc linkee does not exist and it is "cheap" to check if
it exists as described above.
list_to_atom(String) -> atom()
Types:
String = string()
Returns the atom whose text representation is String.
As from Erlang/OTP 20, String may contain any Unicode character.
Earlier versions allowed only ISO-latin-1 characters as the
implementation did not allow Unicode characters above 255.
Note:
The number of characters that are permitted in an atom name is
limited. The default limits can be found in the efficiency
guide (section Advanced).
Note:
There is configurable limit on how many atoms that can exist and
atoms are not garbage collected. Therefore, it is recommended to
consider if list_to_existing_atom/1 is a better option than
list_to_atom/1. The default limits can be found in the effi-
ciency guide (section Advanced).
Example:
> list_to_atom("Erlang").
list_to_binary(IoList) -> binary()
Types:
IoList = iolist()
Returns a binary that is made from the integers and binaries in
IoList, for example:
> Bin1 = <<1,2,3>>.
<<1,2,3>>
> Bin2 = <<4,5>>.
<<4,5>>
> Bin3 = <<6>>.
<<6>>
> list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6>>
list_to_bitstring(BitstringList) -> bitstring()
Types:
BitstringList = bitstring_list()
bitstring_list() =
maybe_improper_list(byte() | bitstring() | bitstring_list(),
bitstring() | [])
Returns a bitstring that is made from the integers and bit-
strings in BitstringList. (The last tail in BitstringList is
allowed to be a bitstring.) Example:
> Bin1 = <<1,2,3>>.
<<1,2,3>>
> Bin2 = <<4,5>>.
<<4,5>>
> Bin3 = <<6,7:4>>.
<<6,7:4>>
> list_to_bitstring([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6,7:4>>
list_to_existing_atom(String) -> atom()
Types:
String = string()
Returns the atom whose text representation is String, but only
if there already exists such atom. An atom exists if it has been
created by the run-time system by either loading code or creat-
ing a term in which the atom is part.
Failure: badarg if there does not already exist an atom whose
text representation is String.
Note:
Note that the compiler may optimize away atoms. For example, the
compiler will rewrite atom_to_list(some_atom) to "some_atom". If
that expression is the only mention of the atom some_atom in the
containing module, the atom will not be created when the module
is loaded, and a subsequent call to list_to_exist-
ing_atom("some_atom") will fail.
list_to_float(String) -> float()
Types:
String = string()
Returns the float whose text representation is String, for exam-
ple:
> list_to_float("2.2017764e+0").
2.2017764
The float string format is the same as the format for Erlang
float literals except for that underscores are not permitted.
Failure: badarg if String contains a bad representation of a
float.
list_to_integer(String) -> integer()
Types:
String = string()
Returns an integer whose text representation is String, for
example:
> list_to_integer("123").
123
> list_to_integer("-123").
-123
> list_to_integer("+123234982304982309482093833234234").
123234982304982309482093833234234
String must contain at least one digit character and can have an
optional prefix consisting of a single "+" or "-" character
(that is, String must match the regular expression
"^[+-]?[0-9]+$").
Failure: badarg if String contains a bad representation of an
integer.
list_to_integer(String, Base) -> integer()
Types:
String = string()
Base = 2..36
Returns an integer whose text representation in base Base is
String, for example:
> list_to_integer("3FF", 16).
1023
> list_to_integer("+3FF", 16).
1023
> list_to_integer("3ff", 16).
1023
> list_to_integer("3fF", 16).
1023
> list_to_integer("-3FF", 16).
-1023
For example, when Base is 16, String must match the regular
expression "^[+-]?([0-9]|[A-F]|[a-f])+$".
Failure: badarg if String contains a bad representation of an
integer.
list_to_pid(String) -> pid()
Types:
String = string()
Returns a process identifier whose text representation is a
String, for example:
> list_to_pid("<0.4.1>").
<0.4.1>
Failure: badarg if String contains a bad representation of a
process identifier.
Warning:
This BIF is intended for debugging and is not to be used in
application programs.
list_to_port(String) -> port()
Types:
String = string()
Returns a port identifier whose text representation is a String,
for example:
> list_to_port("#Port<0.4>").
#Port<0.4>
Failure: badarg if String contains a bad representation of a
port identifier.
Warning:
This BIF is intended for debugging and is not to be used in
application programs.
list_to_ref(String) -> reference()
Types:
String = string()
Returns a reference whose text representation is a String, for
example:
> list_to_ref("#Ref<0.4192537678.4073193475.71181>").
#Ref<0.4192537678.4073193475.71181>
Failure: badarg if String contains a bad representation of a
reference.
Warning:
This BIF is intended for debugging and is not to be used in
application programs.
list_to_tuple(List) -> tuple()
Types:
List = [term()]
Returns a tuple corresponding to List, for example
> list_to_tuple([share, ['Ericsson_B', 163]]).
{share, ['Ericsson_B', 163]}
List can contain any Erlang terms.
load_module(Module, Binary) -> {module, Module} | {error, Reason}
Types:
Module = module()
Binary = binary()
Reason = badfile | not_purged | on_load
If Binary contains the object code for module Module, this BIF
loads that object code. If the code for module Module already
exists, all export references are replaced so they point to the
newly loaded code. The previously loaded code is kept in the
system as old code, as there can still be processes executing
that code.
Returns either {module, Module}, or {error, Reason} if loading
fails. Reason is one of the following:
badfile:
The object code in Binary has an incorrect format or the
object code contains code for another module than Module.
not_purged:
Binary contains a module that cannot be loaded because old
code for this module already exists.
on_load:
The code in Binary contains an on_load declaration that must
be executed before Binary can become the current code. Any
previous current code for Module will remain until the
on_load call has finished.
Warning:
This BIF is intended for the code server (see code(3)) and is
not to be used elsewhere.
erlang:load_nif(Path, LoadInfo) -> ok | Error
Types:
Path = string()
LoadInfo = term()
Error = {error, {Reason, Text :: string()}}
Reason =
load_failed | bad_lib | load | reload | upgrade |
old_code
Loads and links a dynamic library containing native implemented
functions (NIFs) for a module. Path is a file path to the share-
able object/dynamic library file minus the OS-dependent file
extension (.so for Unix and .dll for Windows). Notice that on
most OSs the library has to have a different name on disc when
an upgrade of the nif is done. If the name is the same, but the
contents differ, the old library may be loaded instead. For
information on how to implement a NIF library, see erl_nif(3).
LoadInfo can be any term. It is passed on to the library as part
of the initialization. A good practice is to include a module
version number to support future code upgrade scenarios.
The call to load_nif/2 must be made directly from the Erlang
code of the module that the NIF library belongs to. It returns
either ok, or {error,{Reason,Text}} if loading fails. Reason is
one of the following atoms while Text is a human readable string
that can give more information about the failure:
load_failed:
The OS failed to load the NIF library.
bad_lib:
The library did not fulfill the requirements as a NIF
library of the calling module.
load | upgrade:
The corresponding library callback was unsuccessful.
reload:
A NIF library is already loaded for this module instance.
The previously deprecated reload feature was removed in OTP
20.
old_code:
The call to load_nif/2 was made from the old code of a mod-
ule that has been upgraded; this is not allowed.
erlang:loaded() -> [Module]
Types:
Module = module()
Returns a list of all loaded Erlang modules (current and old
code), including preloaded modules.
See also code(3).
erlang:localtime() -> DateTime
Types:
DateTime = calendar:datetime()
Returns the current local date and time, {{Year, Month, Day},
{Hour, Minute, Second}}, for example:
> erlang:localtime().
{{1996,11,6},{14,45,17}}
The time zone and Daylight Saving Time correction depend on the
underlying OS. The return value is based on the OS System Time.
erlang:localtime_to_universaltime(Localtime) -> Universaltime
Types:
Localtime = Universaltime = calendar:datetime()
Converts local date and time to Universal Time Coordinated
(UTC), if supported by the underlying OS. Otherwise no conver-
sion is done and Localtime is returned. Example:
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}).
{{1996,11,6},{13,45,17}}
Failure: badarg if Localtime denotes an invalid date and time.
erlang:localtime_to_universaltime(Localtime, IsDst) ->
Universaltime
Types:
Localtime = Universaltime = calendar:datetime()
IsDst = true | false | undefined
Converts local date and time to Universal Time Coordinated (UTC)
as erlang:localtime_to_universaltime/1, but the caller decides
if Daylight Saving Time is active.
If IsDst == true, Localtime is during Daylight Saving Time, if
IsDst == false it is not. If IsDst == undefined, the underlying
OS can guess, which is the same as calling erlang:local-
time_to_universaltime(Localtime).
Examples:
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, true).
{{1996,11,6},{12,45,17}}
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, false).
{{1996,11,6},{13,45,17}}
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, undefined).
{{1996,11,6},{13,45,17}}
Failure: badarg if Localtime denotes an invalid date and time.
make_ref() -> reference()
Returns a unique reference. The reference is unique among con-
nected nodes.
Warning:
Before OTP-23 when a node is restarted multiple times with the
same node name, references created on a newer node can be mis-
taken for a reference created on an older node with the same
node name.
erlang:make_tuple(Arity, InitialValue) -> tuple()
Types:
Arity = arity()
InitialValue = term()
Creates a new tuple of the specified Arity, where all elements
are InitialValue, for example:
> erlang:make_tuple(4, []).
{[],[],[],[]}
erlang:make_tuple(Arity, DefaultValue, InitList) -> tuple()
Types:
Arity = arity()
DefaultValue = term()
InitList = [{Position :: integer() >= 1, term()}]
Creates a tuple of size Arity, where each element has value
DefaultValue, and then fills in values from InitList. Each list
element in InitList must be a two-tuple, where the first element
is a position in the newly created tuple and the second element
is any term. If a position occurs more than once in the list,
the term corresponding to the last occurrence is used. Example:
> erlang:make_tuple(5, [], [{2,ignored},{5,zz},{2,aa}]).
{[],aa,[],[],zz}
map_get(Key, Map) -> Value
Types:
Map = map()
Key = Value = any()
Returns value Value associated with Key if Map contains Key.
The call fails with a {badmap,Map} exception if Map is not a
map, or with a {badkey,Key} exception if no value is associated
with Key.
Example:
> Key = 1337,
Map = #{42 => value_two,1337 => "value one","a" => 1},
map_get(Key,Map).
"value one"
Allowed in guard tests.
map_size(Map) -> integer() >= 0
Types:
Map = map()
Returns an integer, which is the number of key-value pairs in
Map, for example:
> map_size(#{a=>1, b=>2, c=>3}).
3
Allowed in guard tests.
erlang:match_spec_test(MatchAgainst, MatchSpec, Type) ->
TestResult
Types:
MatchAgainst = [term()] | tuple()
MatchSpec = term()
Type = table | trace
TestResult =
{ok, term(), [return_trace], [{error | warning,
string()}]} |
{error, [{error | warning, string()}]}
Tests a match specification used in calls to ets:select/2 and
erlang:trace_pattern/3. The function tests both a match specifi-
cation for "syntactic" correctness and runs the match specifica-
tion against the object. If the match specification contains
errors, the tuple {error, Errors} is returned, where Errors is a
list of natural language descriptions of what was wrong with the
match specification.
If Type is table, the object to match against is to be a tuple.
The function then returns {ok,Result,[],Warnings}, where Result
is what would have been the result in a real ets:select/2 call,
or false if the match specification does not match the object
tuple.
If Type is trace, the object to match against is to be a list.
The function returns {ok, Result, Flags, Warnings}, where Result
is one of the following:
* true if a trace message is to be emitted
* false if a trace message is not to be emitted
* The message term to be appended to the trace message
Flags is a list containing all the trace flags to be enabled,
currently this is only return_trace.
This is a useful debugging and test tool, especially when writ-
ing complicated match specifications.
See also ets:test_ms/2.
max(Term1, Term2) -> Maximum
Types:
Term1 = Term2 = Maximum = term()
Returns the largest of Term1 and Term2. If the terms compare
equal with the == operator, Term1 is returned.
The Expressions section contains descriptions of the == opera-
tor and how terms are ordered.
Examples:
> max(1, 2).
2
> max(1.0, 1).
1.0
> max(1, 1.0).
1
> max("abc", "b").
"b"
erlang:md5(Data) -> Digest
Types:
Data = iodata()
Digest = binary()
Computes an MD5 message digest from Data, where the length of
the digest is 128 bits (16 bytes). Data is a binary or a list of
small integers and binaries.
For more information about MD5, see RFC 1321 - The MD5 Message-
Digest Algorithm.
Warning:
The MD5 Message-Digest Algorithm is not considered safe for
code-signing or software-integrity purposes.
erlang:md5_final(Context) -> Digest
Types:
Context = Digest = binary()
Finishes the update of an MD5 Context and returns the computed
MD5 message digest.
erlang:md5_init() -> Context
Types:
Context = binary()
Creates an MD5 context, to be used in the following calls to
md5_update/2.
erlang:md5_update(Context, Data) -> NewContext
Types:
Context = binary()
Data = iodata()
NewContext = binary()
Update an MD5 Context with Data and returns a NewContext.
erlang:memory() -> [{Type, Size}]
Types:
Type = memory_type()
Size = integer() >= 0
memory_type() =
total | processes | processes_used | system | atom |
atom_used | binary | code | ets
Returns a list with information about memory dynamically allo-
cated by the Erlang emulator. Each list element is a tuple
{Type, Size}. The first element Type is an atom describing mem-
ory type. The second element Size is the memory size in bytes.
Memory types:
total:
The total amount of memory currently allocated. This is the
same as the sum of the memory size for processes and system.
processes:
The total amount of memory currently allocated for the
Erlang processes.
processes_used:
The total amount of memory currently used by the Erlang pro-
cesses. This is part of the memory presented as processes
memory.
system:
The total amount of memory currently allocated for the emu-
lator that is not directly related to any Erlang process.
Memory presented as processes is not included in this mem-
ory. instrument(3) can be used to get a more detailed break-
down of what memory is part of this type.
atom:
The total amount of memory currently allocated for atoms.
This memory is part of the memory presented as system mem-
ory.
atom_used:
The total amount of memory currently used for atoms. This
memory is part of the memory presented as atom memory.
binary:
The total amount of memory currently allocated for binaries.
This memory is part of the memory presented as system mem-
ory.
code:
The total amount of memory currently allocated for Erlang
code. This memory is part of the memory presented as system
memory.
ets:
The total amount of memory currently allocated for ETS
tables. This memory is part of the memory presented as sys-
tem memory.
maximum:
The maximum total amount of memory allocated since the emu-
lator was started. This tuple is only present when the emu-
lator is run with instrumentation.
For information on how to run the emulator with instrumenta-
tion, see instrument(3) and/or erl(1).
Note:
The system value is not complete. Some allocated memory that is
to be part of this value is not.
When the emulator is run with instrumentation, the system value
is more accurate, but memory directly allocated for malloc (and
friends) is still not part of the system value. Direct calls to
malloc are only done from OS-specific runtime libraries and per-
haps from user-implemented Erlang drivers that do not use the
memory allocation functions in the driver interface.
As the total value is the sum of processes and system, the error
in system propagates to the total value.
The different amounts of memory that are summed are not gathered
atomically, which introduces an error in the result.
The different values have the following relation to each other.
Values beginning with an uppercase letter is not part of the
result.
total = processes + system
processes = processes_used + ProcessesNotUsed
system = atom + binary + code + ets + OtherSystem
atom = atom_used + AtomNotUsed
RealTotal = processes + RealSystem
RealSystem = system + MissedSystem
More tuples in the returned list can be added in a future
release.
Note:
The total value is supposed to be the total amount of memory
dynamically allocated by the emulator. Shared libraries, the
code of the emulator itself, and the emulator stacks are not
supposed to be included. That is, the total value is not sup-
posed to be equal to the total size of all pages mapped to the
emulator.
Also, because of fragmentation and prereservation of memory
areas, the size of the memory segments containing the dynami-
cally allocated memory blocks can be much larger than the total
size of the dynamically allocated memory blocks.
Note:
As from ERTS 5.6.4, erlang:memory/0 requires that all
erts_alloc(3) allocators are enabled (default behavior).
Failure: notsup if an erts_alloc(3) allocator has been disabled.
erlang:memory(Type :: memory_type()) -> integer() >= 0
erlang:memory(TypeList :: [memory_type()]) ->
[{memory_type(), integer() >= 0}]
Types:
memory_type() =
total | processes | processes_used | system | atom |
atom_used | binary | code | ets
Returns the memory size in bytes allocated for memory of type
Type. The argument can also be specified as a list of mem-
ory_type() atoms, in which case a corresponding list of {mem-
ory_type(), Size :: integer >= 0} tuples is returned.
Note:
As from ERTS 5.6.4, erlang:memory/1 requires that all
erts_alloc(3) allocators are enabled (default behavior).
Failures:
badarg:
If Type is not one of the memory types listed in the
description of erlang:memory/0.
badarg:
If maximum is passed as Type and the emulator is not run in
instrumented mode.
notsup:
If an erts_alloc(3) allocator has been disabled.
See also erlang:memory/0.
min(Term1, Term2) -> Minimum
Types:
Term1 = Term2 = Minimum = term()
Returns the smallest of Term1 and Term2. If the terms compare
equal with the == operator, Term1 is returned.
The Expressions section contains descriptions of the == opera-
tor and how terms are ordered.
Examples:
> min(1, 2).
1
> min(1.0, 1).
1.0
> min(1, 1.0).
1
> min("abc", "b").
"abc"
module_loaded(Module) -> boolean()
Types:
Module = module()
Returns true if the module Module is loaded, otherwise false. It
does not attempt to load the module.
Warning:
This BIF is intended for the code server (see code(3)) and is
not to be used elsewhere.
monitor(Type :: process, Item :: monitor_process_identifier()) ->
MonitorRef
monitor(Type :: port, Item :: monitor_port_identifier()) ->
MonitorRef
monitor(Type :: time_offset, Item :: clock_service) -> MonitorRef
Types:
MonitorRef = reference()
registered_name() = atom()
registered_process_identifier() =
registered_name() | {registered_name(), node()}
monitor_process_identifier() =
pid() | registered_process_identifier()
monitor_port_identifier() = port() | registered_name()
Sends a monitor request of type Type to the entity identified by
Item. If the monitored entity does not exist or it changes moni-
tored state, the caller of monitor/2 is notified by a message on
the following format:
{Tag, MonitorRef, Type, Object, Info}
Note:
The monitor request is an asynchronous signal. That is, it takes
time before the signal reaches its destination.
Type can be one of the following atoms: process, port or
time_offset.
A process or port monitor is triggered only once, after that it
is removed from both monitoring process and the monitored
entity. Monitors are fired when the monitored process or port
terminates, does not exist at the moment of creation, or if the
connection to it is lost. If the connection to it is lost, we do
not know if it still exists. The monitoring is also turned off
when demonitor/1 is called.
A process or port monitor by name resolves the RegisteredName to
pid() or port() only once at the moment of monitor instantia-
tion, later changes to the name registration will not affect the
existing monitor.
When a process or port monitor is triggered, a 'DOWN' message is
sent that has the following pattern:
{'DOWN', MonitorRef, Type, Object, Info}
In the monitor message MonitorRef and Type are the same as
described earlier, and:
Object:
The monitored entity, which triggered the event. When moni-
toring a process or a local port, Object will be equal to
the pid() or port() that was being monitored. When monitor-
ing process or port by name, Object will have format {Regis-
teredName, Node} where RegisteredName is the name which has
been used with monitor/2 call and Node is local or remote
node name (for ports monitored by name, Node is always local
node name).
Info:
Either the exit reason of the process, noproc (process or
port did not exist at the time of monitor creation), or
noconnection (no connection to the node where the monitored
process resides).
Monitoring a process:
Creates monitor between the current process and another
process identified by Item, which can be a pid() (local or
remote), an atom RegisteredName or a tuple {RegisteredName,
Node} for a registered process, located elsewhere.
Note:
Before ERTS 10.0 (OTP 21.0), monitoring a process could fail
with badarg if the monitored process resided on a primitive
node (such as erl_interface or jinterface), where remote
process monitoring is not implemented.
Now, such a call to monitor will instead succeed and a monitor
is created. But the monitor will only supervise the connec-
tion. That is, a {'DOWN', _, process, _, noconnection} is the
only message that may be received, as the primitive node have
no way of reporting the status of the monitored process.
Monitoring a port:
Creates monitor between the current process and a port iden-
tified by Item, which can be a port() (only local), an atom
RegisteredName or a tuple {RegisteredName, Node} for a reg-
istered port, located on this node. Note, that attempt to
monitor a remote port will result in badarg.
Monitoring a time_offset:
Monitors changes in time offset between Erlang monotonic
time and Erlang system time. One valid Item exists in combi-
nation with the time_offset Type, namely the atom clock_ser-
vice. Notice that the atom clock_service is not the regis-
tered name of a process. In this case it serves as an iden-
tifier of the runtime system internal clock service at cur-
rent runtime system instance.
The monitor is triggered when the time offset is changed.
This either if the time offset value is changed, or if the
offset is changed from preliminary to final during finaliza-
tion of the time offset when the single time warp mode is
used. When a change from preliminary to final time offset is
made, the monitor is triggered once regardless of whether
the time offset value was changed or not.
If the runtime system is in multi time warp mode, the time
offset is changed when the runtime system detects that the
OS system time has changed. The runtime system does, how-
ever, not detect this immediately when it occurs. A task
checking the time offset is scheduled to execute at least
once a minute, so under normal operation this is to be
detected within a minute, but during heavy load it can take
longer time.
The monitor is not automatically removed after it has been
triggered. That is, repeated changes of the time offset
trigger the monitor repeatedly.
When the monitor is triggered a 'CHANGE' message is sent to
the monitoring process. A 'CHANGE' message has the following
pattern:
{'CHANGE', MonitorRef, Type, Item, NewTimeOffset}
where MonitorRef, Type, and Item are the same as described
above, and NewTimeOffset is the new time offset.
When the 'CHANGE' message has been received you are guaran-
teed not to retrieve the old time offset when calling
erlang:time_offset(). Notice that you can observe the change
of the time offset when calling erlang:time_offset() before
you get the 'CHANGE' message.
Making several calls to monitor/2 for the same Item and/or Type
is not an error; it results in as many independent monitoring
instances.
The monitor functionality is expected to be extended. That is,
other Types and Items are expected to be supported in a future
release.
Note:
If or when monitor/2 is extended, other possible values for Tag,
Object, and Info in the monitor message will be introduced.
monitor(Type :: process,
Item :: monitor_process_identifier(),
Opts :: [monitor_option()]) ->
MonitorRef
monitor(Type :: port,
Item :: monitor_port_identifier(),
Opts :: [monitor_option()]) ->
MonitorRef
monitor(Type :: time_offset,
Item :: clock_service,
Opts :: [monitor_option()]) ->
MonitorRef
Types:
MonitorRef = reference()
registered_name() = atom()
registered_process_identifier() =
registered_name() | {registered_name(), node()}
monitor_process_identifier() =
pid() | registered_process_identifier()
monitor_port_identifier() = port() | registered_name()
Provides an option list for modification of monitoring function-
ality provided by monitor/2. The Type and Item arguments have
the same meaning as when passed to monitor/2. Currently avail-
able options:
{alias, UnaliasOpt}:
The returned monitor reference will also become an alias for
the calling process. That is, the returned reference can be
used for sending messages to the calling process. See also
alias/0. The UnaliasOpt determines how the alias should be
deactivated.
explicit_unalias:
Only an explicit call to unalias/1 will deactivate the
alias.
demonitor:
The alias will be automatically deactivated when the moni-
tor is removed. This either via an explicit call to demon-
itor/1 or when it is automatically removed at the same
time as a 'DOWN' message is delivered due to the monitor.
The alias can also still be deactivated via a call to una-
lias/1.
reply_demonitor:
The alias will be automatically deactivated when the moni-
tor is removed (see demonitor option above) or a reply
message sent via the alias is received. When a reply mes-
sage is received via the alias the monitor will also be
automatically removed. This is useful in client/server
scenarios when a client monitors the server and will get
the reply via the alias. Once the response is received
both the alias and the monitor will be automatically
removed regardless of whether the response is a reply or a
'DOWN' message. The alias can also still be deactivated
via a call to unalias/1. Note that if the alias is removed
using the unalias/1 BIF, the monitor will still be left
active.
Example:
server() ->
receive
{request, AliasReqId, Request} ->
Result = perform_request(Request),
AliasReqId ! {reply, AliasReqId, Result}
end,
server().
client(ServerPid, Request) ->
AliasMonReqId = monitor(process, ServerPid, [{alias, reply_demonitor}]),
ServerPid ! {request, AliasMonReqId, Request},
%% Alias as well as monitor will be automatically deactivated if we
%% receive a reply or a 'DOWN' message since we used 'reply_demonitor'
%% as unalias option...
receive
{reply, AliasMonReqId, Result} ->
Result;
{'DOWN', AliasMonReqId, process, ServerPid, ExitReason} ->
error(ExitReason)
end.
Note that both the server and the client in this example
must be executing on at least OTP 24 systems in order for
this to work.
For more information on process aliases see the Process
Aliases section of the Erlang Reference Manual .
{tag, UserDefinedTag}:
Replace the default Tag with UserDefinedTag in the monitor
message delivered when the monitor is triggered. For exam-
ple, when monitoring a process, the 'DOWN' tag in the down
message will be replaced by UserDefinedTag.
An example of how the {tag, UserDefinedTag} option can be
used in order to enable the new selective receive optimiza-
tion, introduced in OTP 24, when making multiple requests to
different servers:
server() ->
receive
{request, From, ReqId, Request} ->
Result = perform_request(Request),
From ! {reply, self(), ReqId, Result}
end,
server().
client(ServerPids, Request) when is_list(ServerPids) ->
ReqId = make_ref(),
lists:foreach(fun (ServerPid) ->
_ = monitor(process, ServerPid,
[{tag, {'DOWN', ReqId}}]),
ServerPid ! {request, self(), ReqId, Request}
end,
ServerPids),
receive_replies(ReqId, length(ServerPids), []).
receive_replies(_ReqId, 0, Acc) ->
Acc;
receive_replies(ReqId, N, Acc) ->
%% The compiler will detect that we match on the 'ReqId'
%% reference in all clauses, and will enable the selective
%% receive optimization which makes the receive able to
%% skip past all messages present in the message queue at
%% the time when the 'ReqId' reference was created...
Res = receive
{reply, ServerPid, ReqId, Result} ->
%% Here we typically would have deactivated the
%% monitor by a call to demonitor(Mon, [flush]) but
%% we ignore this in this example for simplicity...
{ok, ServerPid, Result};
{{'DOWN', ReqId}, _Mon, process, ServerPid, ExitReason} ->
{error, ServerPid, ExitReason}
end,
receive_replies(ReqId, N-1, [Res | Acc]).
In order for this example to work as intended, the client
must be executing on at least an OTP 24 system, but the
servers may execute on older systems.
monitor_node(Node, Flag) -> true
Types:
Node = node()
Flag = boolean()
Monitor the status of the node Node. If Flag is true, monitoring
is turned on. If Flag is false, monitoring is turned off.
Making several calls to monitor_node(Node, true) for the same
Node is not an error; it results in as many independent monitor-
ing instances.
If Node fails or does not exist, the message {nodedown, Node} is
delivered to the process. If a process has made two calls to
monitor_node(Node, true) and Node terminates, two nodedown mes-
sages are delivered to the process. If there is no connection to
Node, an attempt is made to create one. If this fails, a node-
down message is delivered.
The delivery of the nodedown signal is not ordered with respect
to other link or monitor signals from the node that goes down.
If you need a guarantee that all signals from the remote node
has been delivered before the nodedown signal is sent, you
should use net_kernel:monitor_nodes/1.
Nodes connected through hidden connections can be monitored as
any other nodes.
Failure: notalive if the local node is not alive.
erlang:monitor_node(Node, Flag, Options) -> true
Types:
Node = node()
Flag = boolean()
Options = [Option]
Option = allow_passive_connect
Behaves as monitor_node/2 except that it allows an extra option
to be specified, namely allow_passive_connect. This option
allows the BIF to wait the normal network connection time-out
for the monitored node to connect itself, even if it cannot be
actively connected from this node (that is, it is blocked). The
state where this can be useful can only be achieved by using the
Kernel option dist_auto_connect once. If that option is not
used, option allow_passive_connect has no effect.
Note:
Option allow_passive_connect is used internally and is seldom
needed in applications where the network topology and the Kernel
options in effect are known in advance.
Failure: badarg if the local node is not alive or the option
list is malformed.
erlang:monotonic_time() -> integer()
Returns the current Erlang monotonic time in native time unit.
This is a monotonically increasing time since some unspecified
point in time.
Note:
This is a monotonically increasing time, but not a strictly
monotonically increasing time. That is, consecutive calls to
erlang:monotonic_time/0 can produce the same result.
Different runtime system instances will use different unspeci-
fied points in time as base for their Erlang monotonic clocks.
That is, it is pointless comparing monotonic times from differ-
ent runtime system instances. Different runtime system instances
can also place this unspecified point in time different relative
runtime system start. It can be placed in the future (time at
start is a negative value), the past (time at start is a posi-
tive value), or the runtime system start (time at start is
zero). The monotonic time at runtime system start can be
retrieved by calling erlang:system_info(start_time).
erlang:monotonic_time(Unit) -> integer()
Types:
Unit = time_unit()
Returns the current Erlang monotonic time converted into the
Unit passed as argument.
Same as calling erlang:convert_time_unit(erlang:mono-
tonic_time(), native, Unit), however optimized for commonly used
Units.
erlang:nif_error(Reason) -> no_return()
Types:
Reason = term()
Works exactly like error/1, but Dialyzer thinks that this BIF
will return an arbitrary term. When used in a stub function for
a NIF to generate an exception when the NIF library is not
loaded, Dialyzer does not generate false warnings.
erlang:nif_error(Reason, Args) -> no_return()
Types:
Reason = term()
Args = [term()]
Works exactly like error/2, but Dialyzer thinks that this BIF
will return an arbitrary term. When used in a stub function for
a NIF to generate an exception when the NIF library is not
loaded, Dialyzer does not generate false warnings.
node() -> Node
Types:
Node = node()
Returns the name of the local node. If the node is not alive,
nonode@nohost is returned instead.
Allowed in guard tests.
node(Arg) -> Node
Types:
Arg = pid() | port() | reference()
Node = node()
Returns the node where Arg originates. Arg can be a process
identifier, a reference, or a port. If Arg originates from the
local node and the local node is not alive, nonode@nohost is
returned.
Allowed in guard tests.
nodes() -> Nodes
Types:
Nodes = [node()]
Returns a list of all nodes connected to this node through nor-
mal connections (that is, hidden nodes are not listed). Same as
nodes(visible).
nodes(Arg) -> Nodes
Types:
Arg = NodeType | [NodeType]
NodeType = visible | hidden | connected | this | known
Nodes = [node()]
Returns a list of nodes according to the argument specified. The
returned result, when the argument is a list, is the list of
nodes satisfying the disjunction(s) of the list elements.
NodeTypes:
visible:
Nodes connected to this node through normal connections.
hidden:
Nodes connected to this node through hidden connections.
connected:
All nodes connected to this node.
this:
This node.
known:
Nodes that are known to this node. That is, connected nodes
and nodes referred to by process identifiers, port identi-
fiers, and references located on this node. The set of known
nodes is garbage collected. Notice that this garbage collec-
tion can be delayed. For more information, see erlang:sys-
tem_info(delayed_node_table_gc).
Some equalities: [node()] = nodes(this), nodes(connected) =
nodes([visible, hidden]), and nodes() = nodes(visible).
now() -> Timestamp
Types:
Timestamp = timestamp()
timestamp() =
{MegaSecs :: integer() >= 0,
Secs :: integer() >= 0,
MicroSecs :: integer() >= 0}
Warning:
This function is deprecated. Do not use it.
For more information, see section Time and Time Correction in
the User's Guide. Specifically, section Dos and Dont's
describes what to use instead of erlang:now/0.
Returns the tuple {MegaSecs, Secs, MicroSecs}, which is the
elapsed time since 00:00 GMT, January 1, 1970 (zero hour), if
provided by the underlying OS. Otherwise some other point in
time is chosen. It is also guaranteed that the following calls
to this BIF return continuously increasing values. Hence, the
return value from erlang:now/0 can be used to generate unique
time stamps. If it is called in a tight loop on a fast machine,
the time of the node can become skewed.
Can only be used to check the local time of day if the time-zone
information of the underlying OS is properly configured.
open_port(PortName, PortSettings) -> port()
Types:
PortName =
{spawn, Command :: string() | binary()} |
{spawn_driver, Command :: string() | binary()} |
{spawn_executable, FileName :: file:name_all()} |
{fd, In :: integer() >= 0, Out :: integer() >= 0}
PortSettings = [Opt]
Opt =
{packet, N :: 1 | 2 | 4} |
stream |
{line, L :: integer() >= 0} |
{cd, Dir :: string() | binary()} |
{env,
Env ::
[{Name :: os:env_var_name(),
Val :: os:env_var_value() | false}]} |
{args, [string() | binary()]} |
{arg0, string() | binary()} |
exit_status | use_stdio | nouse_stdio | stderr_to_stdout
|
in | out | binary | eof |
{parallelism, Boolean :: boolean()} |
hide |
{busy_limits_port,
{integer() >= 0, integer() >= 0} | disabled} |
{busy_limits_msgq,
{integer() >= 0, integer() >= 0} | disabled}
Returns a port identifier as the result of opening a new Erlang
port. A port can be seen as an external Erlang process.
The name of the executable as well as the arguments specifed in
cd, env, args, and arg0 are subject to Unicode filename transla-
tion if the system is running in Unicode filename mode. To avoid
translation or to force, for example UTF-8, supply the exe-
cutable and/or arguments as a binary in the correct encoding.
For details, see the module file(3), the function
file:native_name_encoding/0 in Kernel, and the Using Unicode in
Erlang User's Guide.
Note:
The characters in the name (if specified as a list) can only be
> 255 if the Erlang virtual machine is started in Unicode file-
name translation mode. Otherwise the name of the executable is
limited to the ISO Latin-1 character set.
PortNames:
{spawn, Command}:
Starts an external program. Command is the name of the
external program to be run. Command runs outside the Erlang
work space unless an Erlang driver with the name Command is
found. If found, that driver is started. A driver runs in
the Erlang work space, which means that it is linked with
the Erlang runtime system.
For external programs, PATH is searched (or an equivalent
method is used to find programs, depending on the OS). This
is done by invoking the shell on certain platforms. The
first space-separated token of the command is considered as
the name of the executable (or driver). This (among other
things) makes this option unsuitable for running programs
with spaces in filenames or directory names. If spaces in
executable filenames are desired, use {spawn_executable,
Command} instead.
{spawn_driver, Command}:
Works like {spawn, Command}, but demands the first (space-
separated) token of the command to be the name of a loaded
driver. If no driver with that name is loaded, a badarg
error is raised.
{spawn_executable, FileName}:
Works like {spawn, FileName}, but only runs external exe-
cutables. FileName in its whole is used as the name of the
executable, including any spaces. If arguments are to be
passed, the PortSettings args and arg0 can be used.
The shell is usually not invoked to start the program, it is
executed directly. PATH (or equivalent) is not searched. To
find a program in PATH to execute, use os:find_executable/1.
Only if a shell script or .bat file is executed, the appro-
priate command interpreter is invoked implicitly, but there
is still no command-argument expansion or implicit PATH
search.
If FileName cannot be run, an error exception is raised,
with the POSIX error code as the reason. The error reason
can differ between OSs. Typically the error enoent is raised
when an attempt is made to run a program that is not found
and eacces is raised when the specified file is not exe-
cutable.
{fd, In, Out}:
Allows an Erlang process to access any currently opened file
descriptors used by Erlang. The file descriptor In can be
used for standard input, and the file descriptor Out for
standard output. It is only used for various servers in the
Erlang OS (shell and user). Hence, its use is limited.
PortSettings is a list of settings for the port. The valid set-
tings are as follows:
{packet, N}:
Messages are preceded by their length, sent in N bytes, with
the most significant byte first. The valid values for N are
1, 2, and 4.
stream:
Output messages are sent without packet lengths. A user-
defined protocol must be used between the Erlang process and
the external object.
{line, L}:
Messages are delivered on a per line basis. Each line
(delimited by the OS-dependent newline sequence) is deliv-
ered in a single message. The message data format is {Flag,
Line}, where Flag is eol or noeol, and Line is the data
delivered (without the newline sequence).
L specifies the maximum line length in bytes. Lines longer
than this are delivered in more than one message, with Flag
set to noeol for all but the last message. If end of file is
encountered anywhere else than immediately following a new-
line sequence, the last line is also delivered with Flag set
to noeol. Otherwise lines are delivered with Flag set to
eol.
The {packet, N} and {line, L} settings are mutually exclu-
sive.
{cd, Dir}:
Only valid for {spawn, Command} and {spawn_executable, File-
Name}. The external program starts using Dir as its working
directory. Dir must be a string.
{env, Env}:
Types:
Name = os:env_var_name()
Val = os:env_var_value() | false
Env = [{Name, Val}]
Only valid for {spawn, Command}, and {spawn_executable,
FileName}. The environment of the started process is
extended using the environment specifications in Env.
Env is to be a list of tuples {Name, Val}, where Name is the
name of an environment variable, and Val is the value it is
to have in the spawned port process. Both Name and Val must
be strings. The one exception is Val being the atom false
(in analogy with os:getenv/1, which removes the environment
variable.
For information about encoding requirements, see documenta-
tion of the types for Name and Val.
{args, [ string() | binary() ]}:
Only valid for {spawn_executable, FileName} and specifies
arguments to the executable. Each argument is specified as a
separate string and (on Unix) eventually ends up as one ele-
ment each in the argument vector. On other platforms, a sim-
ilar behavior is mimicked.
The arguments are not expanded by the shell before they are
supplied to the executable. Most notably this means that
file wildcard expansion does not occur. To expand wildcards
for the arguments, use filelib:wildcard/1. Notice that even
if the program is a Unix shell script, meaning that the
shell ultimately is invoked, wildcard expansion does not
occur, and the script is provided with the untouched argu-
ments. On Windows, wildcard expansion is always up to the
program itself, therefore this is not an issue.
The executable name (also known as argv[0]) is not to be
specified in this list. The proper executable name is auto-
matically used as argv[0], where applicable.
If you explicitly want to set the program name in the argu-
ment vector, option arg0 can be used.
{arg0, string() | binary()}:
Only valid for {spawn_executable, FileName} and explicitly
specifies the program name argument when running an exe-
cutable. This can in some circumstances, on some OSs, be
desirable. How the program responds to this is highly sys-
tem-dependent and no specific effect is guaranteed.
exit_status:
Only valid for {spawn, Command}, where Command refers to an
external program, and for {spawn_executable, FileName}.
When the external process connected to the port exits, a
message of the form {Port,{exit_status,Status}} is sent to
the connected process, where Status is the exit status of
the external process. If the program aborts on Unix, the
same convention is used as the shells do (that is, 128+sig-
nal).
If option eof is specified also, the messages eof and
exit_status appear in an unspecified order.
If the port program closes its stdout without exiting,
option exit_status does not work.
use_stdio:
Only valid for {spawn, Command} and {spawn_executable, File-
Name}. It allows the standard input and output (file
descriptors 0 and 1) of the spawned (Unix) process for com-
munication with Erlang.
nouse_stdio:
The opposite of use_stdio. It uses file descriptors 3 and 4
for communication with Erlang.
stderr_to_stdout:
Affects ports to external programs. The executed program
gets its standard error file redirected to its standard out-
put file. stderr_to_stdout and nouse_stdio are mutually
exclusive.
overlapped_io:
Affects ports to external programs on Windows only. The
standard input and standard output handles of the port pro-
gram are, if this option is supplied, opened with flag
FILE_FLAG_OVERLAPPED, so that the port program can (and
must) do overlapped I/O on its standard handles. This is not
normally the case for simple port programs, but an option of
value for the experienced Windows programmer. On all other
platforms, this option is silently discarded.
in:
The port can only be used for input.
out:
The port can only be used for output.
binary:
All I/O from the port is binary data objects as opposed to
lists of bytes.
eof:
The port is not closed at the end of the file and does not
produce an exit signal. Instead, it remains open and a
{Port, eof} message is sent to the process holding the port.
hide:
When running on Windows, suppresses creation of a new con-
sole window when spawning the port program. (This option has
no effect on other platforms.)
{parallelism, Boolean}:
Sets scheduler hint for port parallelism. If set to true,
the virtual machine schedules port tasks; when doing so, it
improves parallelism in the system. If set to false, the
virtual machine tries to perform port tasks immediately,
improving latency at the expense of parallelism. The default
can be set at system startup by passing command-line argu-
ment +spp to erl(1).
{busy_limits_port, {Low, High} | disabled}:
Sets limits that will be used for controlling the busy state
of the port.
When the ports internal output queue size becomes larger
than or equal to High bytes, it enters the busy state. When
it becomes less than Low bytes it leaves the busy state.
When the port is in the busy state, processes sending com-
mands to it will be suspended until the port leaves the busy
state. Commands are in this context either Port ! {Owner,
{command, Data}} or port_command/[2,3].
The Low limit is automatically adjusted to the same as High
if it is set larger then High. Valid range of values for Low
and High is [1, (1 bsl (8*erlang:system_info(wordsize)))-2].
If the atom disabled is passed, the port will never enter
the busy state.
The defaults are Low = 4096 and High = 8192.
Note that this option is only valid when spawning an exe-
cutable (port program) by opening the spawn driver and when
opening the fd driver. This option will cause a failure with
a badarg exception when opening other drivers.
{busy_limits_msgq, {Low, High} | disabled}:
Sets limits that will be used for controlling the busy state
of the port message queue.
When the ports message queue size becomes larger than or
equal to High bytes it enters the busy state. When it
becomes less than Low bytes it leaves the busy state. When
the port message queue is in the busy state, processes send-
ing commands to it will be suspended until the port message
queue leaves the busy state. Commands are in this context
either Port ! {Owner, {command, Data}} or port_com-
mand/[2,3].
The Low limit is automatically adjusted to the same as High
if it is set larger then High. Valid range of values for Low
and High is [1, (1 bsl (8*erlang:system_info(wordsize)))-2].
If the atom disabled is passed, the port message queue will
never enter the busy state.
Note that if the driver statically has disabled the use of
this feature, a failure with a badarg exception will be
raised unless this option also is set to disable or not
passed at all.
The defaults are Low = 4096 and High = 8192 unless the
driver itself does modifications of these values.
Note that the driver might fail if it also adjust these lim-
its by itself and you have disabled this feature.
The spawn driver (used when spawning an executable) and the
fd driver do not disable this feature and do not adjust
these limits by themselves.
For more information see the documentation
erl_drv_busy_msgq_limits().
Default is stream for all port types and use_stdio for spawned
ports.
Failure: if the port cannot be opened, the exit reason is
badarg, system_limit, or the POSIX error code that most closely
describes the error, or einval if no POSIX code is appropriate:
badarg:
Bad input arguments to open_port.
system_limit:
All available ports in the Erlang emulator are in use.
enomem:
Not enough memory to create the port.
eagain:
No more available OS processes.
enametoolong:
Too long external command.
emfile:
No more available file descriptors (for the OS process that
the Erlang emulator runs in).
enfile:
Full file table (for the entire OS).
eacces:
Command specified in {spawn_executable, Command} does not
point out an executable file.
enoent:
FileName specified in {spawn_executable, FileName} does not
point out an existing file.
During use of a port opened using {spawn, Name}, {spawn_driver,
Name}, or {spawn_executable, Name}, errors arising when sending
messages to it are reported to the owning process using signals
of the form {'EXIT', Port, PosixCode}. For the possible values
of PosixCode, see file(3).
The maximum number of ports that can be open at the same time
can be configured by passing command-line flag +Q to erl(1).
erlang:phash(Term, Range) -> Hash
Types:
Term = term()
Range = Hash = integer() >= 1
Range = 1..2^32, Hash = 1..Range
Warning:
This function is deprecated as erlang:phash2/2 should be used
for new code. Note that erlang:phash(X,N) is not necessary equal
to erlang:phash2(X,N)
Portable hash function that gives the same hash for the same
Erlang term regardless of machine architecture and ERTS version
(the BIF was introduced in ERTS 4.9.1.1). The function returns a
hash value for Term within the range 1..Range. The maximum value
for Range is 2^32.
erlang:phash2(Term) -> Hash
erlang:phash2(Term, Range) -> Hash
Types:
Term = term()
Range = integer() >= 1
1..2^32
Hash = integer() >= 0
0..Range-1
Portable hash function that gives the same hash for the same
Erlang term regardless of machine architecture and ERTS version
(the BIF was introduced in ERTS 5.2). The function returns a
hash value for Term within the range 0..Range-1. The maximum
value for Range is 2^32. When without argument Range, a value in
the range 0..2^27-1 is returned.
This BIF is always to be used for hashing terms. It distributes
small integers better than phash/2, and it is faster for bignums
and binaries.
Notice that the range 0..Range-1 is different from the range of
phash/2, which is 1..Range.
pid_to_list(Pid) -> string()
Types:
Pid = pid()
Returns a string corresponding to the text representation of
Pid. Example:
> erlang:pid_to_list(self()).
"<0.85.0>"
Note:
The creation for the node is not included in the list represen-
tation of Pid. This means that processes in different incarna-
tions of a node with a specific name can get the same list rep-
resentation.
erlang:port_call(Port, Operation, Data) -> term()
Types:
Port = port() | atom()
Operation = integer()
Data = term()
Performs a synchronous call to a port. The meaning of Operation
and Data depends on the port, that is, on the port driver. Not
all port drivers support this feature.
Port is a port identifier, referring to a driver.
Operation is an integer, which is passed on to the driver.
Data is any Erlang term. This data is converted to binary term
format and sent to the port.
Returns a term from the driver. The meaning of the returned data
also depends on the port driver.
Failures:
badarg:
If Port is not an identifier of an open port, or the regis-
tered name of an open port. If the calling process was pre-
viously linked to the closed port, identified by Port, the
exit signal from the port is guaranteed to be delivered
before this badarg exception occurs.
badarg:
If Operation does not fit in a 32-bit integer.
badarg:
If the port driver does not support synchronous control
operations.
badarg:
If the port driver so decides for any reason (probably some-
thing wrong with Operation or Data).
Warning:
Do not call port_call with an unknown Port identifier and
expect badarg exception. Any undefined behavior is possible
(including node crash) depending on how the port driver inter-
prets the supplied arguments.
port_close(Port) -> true
Types:
Port = port() | atom()
Closes an open port. Roughly the same as Port ! {self(), close}
except for the error behavior (see below), being synchronous,
and that the port does not reply with {Port, closed}. Any
process can close a port with port_close/1, not only the port
owner (the connected process). If the calling process is linked
to the port identified by Port, the exit signal from the port is
guaranteed to be delivered before port_close/1 returns.
For comparison: Port ! {self(), close} only fails with badarg if
Port does not refer to a port or a process. If Port is a closed
port, nothing happens. If Port is an open port and the calling
process is the port owner, the port replies with {Port, closed}
when all buffers have been flushed and the port really closes.
If the calling process is not the port owner, the port owner
fails with badsig.
Notice that any process can close a port using Port ! {Por-
tOwner, close} as if it itself was the port owner, but the reply
always goes to the port owner.
As from Erlang/OTP R16, Port ! {PortOwner, close} is truly asyn-
chronous. Notice that this operation has always been documented
as an asynchronous operation, while the underlying implementa-
tion has been synchronous. port_close/1 is however still fully
synchronous because of its error behavior.
Failure: badarg if Port is not an identifier of an open port, or
the registered name of an open port. If the calling process was
previously linked to the closed port, identified by Port, the
exit signal from the port is guaranteed to be delivered before
this badarg exception occurs.
port_command(Port, Data) -> true
Types:
Port = port() | atom()
Data = iodata()
Sends data to a port. Same as Port ! {PortOwner, {command,
Data}} except for the error behavior and being synchronous (see
below). Any process can send data to a port with port_command/2,
not only the port owner (the connected process).
For comparison: Port ! {PortOwner, {command, Data}} only fails
with badarg if Port does not refer to a port or a process. If
Port is a closed port, the data message disappears without a
sound. If Port is open and the calling process is not the port
owner, the port owner fails with badsig. The port owner fails
with badsig also if Data is an invalid I/O list.
Notice that any process can send to a port using Port ! {Por-
tOwner, {command, Data}} as if it itself was the port owner.
If the port is busy, the calling process is suspended until the
port is not busy any more.
As from Erlang/OTP R16, Port ! {PortOwner, {command, Data}} is
truly asynchronous. Notice that this operation has always been
documented as an asynchronous operation, while the underlying
implementation has been synchronous. port_command/2 is however
still fully synchronous because of its error behavior.
Failures:
badarg:
If Port is not an identifier of an open port, or the regis-
tered name of an open port. If the calling process was pre-
viously linked to the closed port, identified by Port, the
exit signal from the port is guaranteed to be delivered
before this badarg exception occurs.
badarg:
If Data is an invalid I/O list.
Warning:
Do not send data to an unknown port. Any undefined behavior is
possible (including node crash) depending on how the port driver
interprets the data.
port_command(Port, Data, OptionList) -> boolean()
Types:
Port = port() | atom()
Data = iodata()
Option = force | nosuspend
OptionList = [Option]
Sends data to a port. port_command(Port, Data, []) equals
port_command(Port, Data).
If the port command is aborted, false is returned, otherwise
true.
If the port is busy, the calling process is suspended until the
port is not busy anymore.
Options:
force:
The calling process is not suspended if the port is busy,
instead the port command is forced through. The call fails
with a notsup exception if the driver of the port does not
support this. For more information, see driver flag
ERL_DRV_FLAG_SOFT_BUSY.
nosuspend:
The calling process is not suspended if the port is busy,
instead the port command is aborted and false is returned.
Note:
More options can be added in a future release.
Failures:
badarg:
If Port is not an identifier of an open port, or the regis-
tered name of an open port. If the calling process was pre-
viously linked to the closed port, identified by Port, the
exit signal from the port is guaranteed to be delivered
before this badarg exception occurs.
badarg:
If Data is an invalid I/O list.
badarg:
If OptionList is an invalid option list.
notsup:
If option force has been passed, but the driver of the port
does not allow forcing through a busy port.
Warning:
Do not send data to an unknown port. Any undefined behavior is
possible (including node crash) depending on how the port driver
interprets the data.
port_connect(Port, Pid) -> true
Types:
Port = port() | atom()
Pid = pid()
Sets the port owner (the connected port) to Pid. Roughly the
same as Port ! {Owner, {connect, Pid}} except for the following:
* The error behavior differs, see below.
* The port does not reply with {Port,connected}.
* port_connect/1 is synchronous, see below.
* The new port owner gets linked to the port.
The old port owner stays linked to the port and must call
unlink(Port) if this is not desired. Any process can set the
port owner to be any process with port_connect/2.
For comparison: Port ! {self(), {connect, Pid}} only fails with
badarg if Port does not refer to a port or a process. If Port is
a closed port, nothing happens. If Port is an open port and the
calling process is the port owner, the port replies with {Port,
connected} to the old port owner. Notice that the old port owner
is still linked to the port, while the new is not. If Port is an
open port and the calling process is not the port owner, the
port owner fails with badsig. The port owner fails with badsig
also if Pid is not an existing local process identifier.
Notice that any process can set the port owner using Port !
{PortOwner, {connect, Pid}} as if it itself was the port owner,
but the reply always goes to the port owner.
As from Erlang/OTP R16, Port ! {PortOwner, {connect, Pid}} is
truly asynchronous. Notice that this operation has always been
documented as an asynchronous operation, while the underlying
implementation has been synchronous. port_connect/2 is however
still fully synchronous because of its error behavior.
Failures:
badarg:
If Port is not an identifier of an open port, or the regis-
tered name of an open port. If the calling process was pre-
viously linked to the closed port, identified by Port, the
exit signal from the port is guaranteed to be delivered
before this badarg exception occurs.
badarg:
If the process identified by Pid is not an existing local
process.
port_control(Port, Operation, Data) -> iodata() | binary()
Types:
Port = port() | atom()
Operation = integer()
Data = iodata()
Performs a synchronous control operation on a port. The meaning
of Operation and Data depends on the port, that is, on the port
driver. Not all port drivers support this control feature.
Returns a list of integers in the range 0..255, or a binary,
depending on the port driver. The meaning of the returned data
also depends on the port driver.
Failures:
badarg:
If Port is not an open port or the registered name of an
open port.
badarg:
If Operation cannot fit in a 32-bit integer.
badarg:
If the port driver does not support synchronous control
operations.
badarg:
If the port driver so decides for any reason (probably
something wrong with Operation or Data).
Warning:
Do not call port_control/3 with an unknown Port identifier and
expect badarg exception. Any undefined behavior is possible
(including node crash) depending on how the port driver inter-
prets the supplied arguments.
erlang:port_info(Port) -> Result
Types:
Port = port() | atom()
ResultItem =
{registered_name, RegisteredName :: atom()} |
{id, Index :: integer() >= 0} |
{connected, Pid :: pid()} |
{links, Pids :: [pid()]} |
{name, String :: string()} |
{input, Bytes :: integer() >= 0} |
{output, Bytes :: integer() >= 0} |
{os_pid, OsPid :: integer() >= 0 | undefined}
Result = [ResultItem] | undefined
Returns a list containing tuples with information about Port, or
undefined if the port is not open. The order of the tuples is
undefined, and all the tuples are not mandatory. If the port is
closed and the calling process was previously linked to the
port, the exit signal from the port is guaranteed to be deliv-
ered before port_info/1 returns undefined.
The result contains information about the following Items:
* registered_name (if the port has a registered name)
* id
* connected
* links
* name
* input
* output
For more information about the different Items, see port_info/2.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: connected) ->
{connected, Pid} | undefined
Types:
Port = port() | atom()
Pid = pid()
Pid is the process identifier of the process connected to the
port.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: id) -> {id, Index} | undefined
Types:
Port = port() | atom()
Index = integer() >= 0
Index is the internal index of the port. This index can be used
to separate ports.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: input) ->
{input, Bytes} | undefined
Types:
Port = port() | atom()
Bytes = integer() >= 0
Bytes is the total number of bytes read from the port.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: links) -> {links, Pids} | undefined
Types:
Port = port() | atom()
Pids = [pid()]
Pids is a list of the process identifiers of the processes that
the port is linked to.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: locking) ->
{locking, Locking} | undefined
Types:
Port = port() | atom()
Locking = false | port_level | driver_level
Locking is one of the following:
* port_level (port-specific locking)
* driver_level (driver-specific locking)
Notice that these results are highly implementation-specific and
can change in a future release.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: memory) ->
{memory, Bytes} | undefined
Types:
Port = port() | atom()
Bytes = integer() >= 0
Bytes is the total number of bytes allocated for this port by
the runtime system. The port itself can have allocated memory
that is not included in Bytes.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: monitors) ->
{monitors, Monitors} | undefined
Types:
Port = port() | atom()
Monitors = [{process, pid()}]
Monitors represent processes monitored by this port.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: monitored_by) ->
{monitored_by, MonitoredBy} | undefined
Types:
Port = port() | atom()
MonitoredBy = [pid()]
Returns list of pids that are monitoring given port at the
moment.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: name) -> {name, Name} | undefined
Types:
Port = port() | atom()
Name = string()
Name is the command name set by open_port/2.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: os_pid) ->
{os_pid, OsPid} | undefined
Types:
Port = port() | atom()
OsPid = integer() >= 0 | undefined
OsPid is the process identifier (or equivalent) of an OS process
created with open_port({spawn | spawn_executable, Command},
Options). If the port is not the result of spawning an OS
process, the value is undefined.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: output) ->
{output, Bytes} | undefined
Types:
Port = port() | atom()
Bytes = integer() >= 0
Bytes is the total number of bytes written to the port from
Erlang processes using port_command/2, port_command/3, or Port !
{Owner, {command, Data}.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: parallelism) ->
{parallelism, Boolean} | undefined
Types:
Port = port() | atom()
Boolean = boolean()
Boolean corresponds to the port parallelism hint used by this
port. For more information, see option parallelism of
open_port/2.
erlang:port_info(Port, Item :: queue_size) ->
{queue_size, Bytes} | undefined
Types:
Port = port() | atom()
Bytes = integer() >= 0
Bytes is the total number of bytes queued by the port using the
ERTS driver queue implementation.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
erlang:port_info(Port, Item :: registered_name) ->
{registered_name, RegisteredName} |
[] | undefined
Types:
Port = port() | atom()
RegisteredName = atom()
RegisteredName is the registered name of the port. If the port
has no registered name, [] is returned.
If the port identified by Port is not open, undefined is
returned. If the port is closed and the calling process was pre-
viously linked to the port, the exit signal from the port is
guaranteed to be delivered before port_info/2 returns undefined.
Failure: badarg if Port is not a local port identifier, or an
atom.
port_to_list(Port) -> string()
Types:
Port = port()
Returns a string corresponding to the text representation of the
port identifier Port.
erlang:ports() -> [port()]
Returns a list of port identifiers corresponding to all the
ports existing on the local node.
Notice that an exiting port exists, but is not open.
pre_loaded() -> [module()]
Returns a list of Erlang modules that are preloaded in the run-
time system. Pre-loaded modules are Erlang modules that are
needed to bootstrap the system to load the first Erlang modules
from either disk or by using erl_boot_server.
erlang:process_display(Pid, Type) -> true
Types:
Pid = pid()
Type = backtrace
Writes information about the local process Pid on standard
error. The only allowed value for the atom Type is backtrace,
which shows the contents of the call stack, including informa-
tion about the call chain, with the current function printed
first. The format of the output is not further defined.
process_flag(Flag :: trap_exit, Boolean) -> OldBoolean
Types:
Boolean = OldBoolean = boolean()
When trap_exit is set to true, exit signals arriving to a
process are converted to {'EXIT', From, Reason} messages, which
can be received as ordinary messages. If trap_exit is set to
false, the process exits if it receives an exit signal other
than normal and the exit signal is propagated to its linked pro-
cesses. Application processes are normally not to trap exits.
Returns the old value of the flag.
See also exit/2.
process_flag(Flag :: error_handler, Module) -> OldModule
Types:
Module = OldModule = atom()
Used by a process to redefine the error handler for undefined
function calls and undefined registered processes. Inexperienced
users are not to use this flag, as code auto-loading depends on
the correct operation of the error handling module.
Returns the old value of the flag.
process_flag(Flag :: fullsweep_after, FullsweepAfter) ->
OldFullsweepAfter
Types:
FullsweepAfter = OldFullsweepAfter = integer() >= 0
Changes the maximum number of generational collections before
forcing a fullsweep for the calling process.
Returns the old value of the flag.
process_flag(Flag :: min_heap_size, MinHeapSize) -> OldMinHeapSize
Types:
MinHeapSize = OldMinHeapSize = integer() >= 0
Changes the minimum heap size for the calling process.
Returns the old value of the flag.
process_flag(Flag :: min_bin_vheap_size, MinBinVHeapSize) ->
OldMinBinVHeapSize
Types:
MinBinVHeapSize = OldMinBinVHeapSize = integer() >= 0
Changes the minimum binary virtual heap size for the calling
process.
Returns the old value of the flag.
process_flag(Flag :: max_heap_size, MaxHeapSize) -> OldMaxHeapSize
Types:
MaxHeapSize = OldMaxHeapSize = max_heap_size()
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
This flag sets the maximum heap size for the calling process. If
MaxHeapSize is an integer, the system default values for kill
and error_logger are used.
size:
The maximum size in words of the process. If set to zero,
the heap size limit is disabled. badarg is be thrown if the
value is smaller than min_heap_size. The size check is only
done when a garbage collection is triggered.
size is the entire heap of the process when garbage collec-
tion is triggered. This includes all generational heaps, the
process stack, any messages that are considered to be part
of the heap, and any extra memory that the garbage collector
needs during collection.
size is the same as can be retrieved using
erlang:process_info(Pid, total_heap_size), or by adding
heap_block_size, old_heap_block_size and mbuf_size from
erlang:process_info(Pid, garbage_collection_info).
kill:
When set to true, the runtime system sends an untrappable
exit signal with reason kill to the process if the maximum
heap size is reached. The garbage collection that triggered
the kill is not completed, instead the process exits as soon
as possible. When set to false, no exit signal is sent to
the process, instead it continues executing.
If kill is not defined in the map, the system default will
be used. The default system default is true. It can be
changed by either option +hmaxk in erl(1), or erlang:sys-
tem_flag(max_heap_size, MaxHeapSize).
error_logger:
When set to true, the runtime system logs an error event via
logger, containing details about the process when the maxi-
mum heap size is reached. One log event is sent each time
the limit is reached.
If error_logger is not defined in the map, the system
default is used. The default system default is true. It can
be changed by either the option +hmaxel int erl(1), or
erlang:system_flag(max_heap_size, MaxHeapSize).
The heap size of a process is quite hard to predict, especially
the amount of memory that is used during the garbage collection.
When contemplating using this option, it is recommended to first
run it in production with kill set to false and inspect the log
events to see what the normal peak sizes of the processes in the
system is and then tune the value accordingly.
process_flag(Flag :: message_queue_data, MQD) -> OldMQD
Types:
MQD = OldMQD = message_queue_data()
message_queue_data() = off_heap | on_heap
Determines how messages in the message queue are stored, as fol-
lows:
off_heap:
All messages in the message queue will be stored outside the
process heap. This implies that no messages in the message
queue will be part of a garbage collection of the process.
on_heap:
All messages in the message queue will eventually be placed
on the process heap. They can, however, be temporarily
stored off the heap. This is how messages have always been
stored up until ERTS 8.0.
The default value of the message_queue_data process flag is
determined by the command-line argument +hmqd in erl(1).
If the process may potentially accumulate a large number of mes-
sages in its queue it is recommended to set the flag value to
off_heap. This is due to the fact that the garbage collection of
a process that has a large number of messages stored on the heap
can become extremely expensive and the process can consume large
amounts of memory. The performance of the actual message passing
is, however, generally better when the flag value is on_heap.
Changing the flag value causes any existing messages to be
moved. The move operation is initiated, but not necessarily com-
pleted, by the time the function returns.
Returns the old value of the flag.
process_flag(Flag :: priority, Level) -> OldLevel
Types:
Level = OldLevel = priority_level()
priority_level() = low | normal | high | max
Sets the process priority. Level is an atom. Four priority lev-
els exist: low, normal, high, and max. Default is normal.
Note:
Priority level max is reserved for internal use in the Erlang
runtime system, and is not to be used by others.
Internally in each priority level, processes are scheduled in a
round robin fashion.
Execution of processes on priority normal and low are inter-
leaved. Processes on priority low are selected for execution
less frequently than processes on priority normal.
When runnable processes on priority high exist, no processes on
priority low or normal are selected for execution. Notice how-
ever that this does not mean that no processes on priority low
or normal can run when processes are running on priority high.
When using multiple schedulers, more processes can be running in
parallel than processes on priority high. That is, a low and a
high priority process can execute at the same time.
When runnable processes on priority max exist, no processes on
priority low, normal, or high are selected for execution. As
with priority high, processes on lower priorities can execute in
parallel with processes on priority max.
Scheduling is pre-emptive. Regardless of priority, a process is
pre-empted when it has consumed more than a certain number of
reductions since the last time it was selected for execution.
Note:
Do not depend on the scheduling to remain exactly as it is
today. Scheduling is likely to be changed in a future release to
use available processor cores better.
There is no automatic mechanism for avoiding priority inversion,
such as priority inheritance or priority ceilings. When using
priorities, take this into account and handle such scenarios by
yourself.
Making calls from a high priority process into code that you has
no control over can cause the high priority process to wait for
a process with lower priority. That is, effectively decreasing
the priority of the high priority process during the call. Even
if this is not the case with one version of the code that you
have no control over, it can be the case in a future version of
it. This can, for example, occur if a high priority process
triggers code loading, as the code server runs on priority nor-
mal.
Other priorities than normal are normally not needed. When other
priorities are used, use them with care, especially priority
high. A process on priority high is only to perform work for
short periods. Busy looping for long periods in a high priority
process causes most likely problems, as important OTP servers
run on priority normal.
Returns the old value of the flag.
process_flag(Flag :: save_calls, N) -> OldN
Types:
N = OldN = 0..10000
N must be an integer in the interval 0..10000. If N > 0, call
saving is made active for the process. This means that informa-
tion about the N most recent global function calls, BIF calls,
sends, and receives made by the process are saved in a list,
which can be retrieved with process_info(Pid, last_calls). A
global function call is one in which the module of the function
is explicitly mentioned. Only a fixed amount of information is
saved, as follows:
* A tuple {Module, Function, Arity} for function calls
* The atoms send, 'receive', and timeout for sends and
receives ('receive' when a message is received and timeout
when a receive times out)
If N = 0, call saving is disabled for the process, which is the
default. Whenever the size of the call saving list is set, its
contents are reset.
Returns the old value of the flag.
process_flag(Flag :: sensitive, Boolean) -> OldBoolean
Types:
Boolean = OldBoolean = boolean()
Sets or clears flag sensitive for the current process. When a
process has been marked as sensitive by calling
process_flag(sensitive, true), features in the runtime system
that can be used for examining the data or inner working of the
process are silently disabled.
Features that are disabled include (but are not limited to) the
following:
* Tracing. Trace flags can still be set for the process, but
no trace messages of any kind are generated. (If flag sensi-
tive is turned off, trace messages are again generated if
any trace flags are set.)
* Sequential tracing. The sequential trace token is propagated
as usual, but no sequential trace messages are generated.
process_info/1,2 cannot be used to read out the message queue or
the process dictionary (both are returned as empty lists).
Stack back-traces cannot be displayed for the process.
In crash dumps, the stack, messages, and the process dictionary
are omitted.
If {save_calls,N} has been set for the process, no function
calls are saved to the call saving list. (The call saving list
is not cleared. Also, send, receive, and time-out events are
still added to the list.)
Returns the old value of the flag.
process_flag(Pid, Flag, Value) -> OldValue
Types:
Pid = pid()
Flag = save_calls
Value = OldValue = integer() >= 0
Sets certain flags for the process Pid, in the same manner as
process_flag/2. Returns the old value of the flag. The valid
values for Flag are only a subset of those allowed in
process_flag/2, namely save_calls.
Failure: badarg if Pid is not a local process.
process_info(Pid) -> Info
Types:
Pid = pid()
Info = [InfoTuple] | undefined
InfoTuple = process_info_result_item()
process_info_result_item() =
{backtrace, Bin :: binary()} |
{binary,
BinInfo ::
[{integer() >= 0,
integer() >= 0,
integer() >= 0}]} |
{catchlevel, CatchLevel :: integer() >= 0} |
{current_function,
{Module :: module(), Function :: atom(), Arity :: arity()} |
undefined} |
{current_location,
{Module :: module(),
Function :: atom(),
Arity :: arity(),
Location ::
[{file, Filename :: string()} |
{line, Line :: integer() >= 1}]}} |
{current_stacktrace, Stack :: [stack_item()]} |
{dictionary, Dictionary :: [{Key :: term(), Value :: term()}]} |
{error_handler, Module :: module()} |
{garbage_collection, GCInfo :: [{atom(), integer() >= 0}]} |
{garbage_collection_info,
GCInfo :: [{atom(), integer() >= 0}]} |
{group_leader, GroupLeader :: pid()} |
{heap_size, Size :: integer() >= 0} |
{initial_call, mfa()} |
{links, PidsAndPorts :: [pid() | port()]} |
{last_calls, false | (Calls :: [mfa()])} |
{memory, Size :: integer() >= 0} |
{message_queue_len, MessageQueueLen :: integer() >= 0} |
{messages, MessageQueue :: [term()]} |
{min_heap_size, MinHeapSize :: integer() >= 0} |
{min_bin_vheap_size, MinBinVHeapSize :: integer() >= 0} |
{max_heap_size, MaxHeapSize :: max_heap_size()} |
{monitored_by,
MonitoredBy :: [pid() | port() | nif_resource()]} |
{monitors,
Monitors ::
[{process | port,
Pid ::
pid() |
port() |
{RegName :: atom(), Node :: node()}}]} |
{message_queue_data, MQD :: message_queue_data()} |
{priority, Level :: priority_level()} |
{reductions, Number :: integer() >= 0} |
{registered_name, [] | (Atom :: atom())} |
{sequential_trace_token,
[] | (SequentialTraceToken :: term())} |
{stack_size, Size :: integer() >= 0} |
{status,
Status ::
exiting | garbage_collecting | waiting | running |
runnable | suspended} |
{suspending,
SuspendeeList ::
[{Suspendee :: pid(),
ActiveSuspendCount :: integer() >= 0,
OutstandingSuspendCount :: integer() >= 0}]} |
{total_heap_size, Size :: integer() >= 0} |
{trace, InternalTraceFlags :: integer() >= 0} |
{trap_exit, Boolean :: boolean()}
priority_level() = low | normal | high | max
stack_item() =
{Module :: module(),
Function :: atom(),
Arity :: arity() | (Args :: [term()]),
Location ::
[{file, Filename :: string()} |
{line, Line :: integer() >= 1}]}
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
message_queue_data() = off_heap | on_heap
Returns a list containing InfoTuples with miscellaneous informa-
tion about the process identified by Pid, or undefined if the
process is not alive.
The order of the InfoTuples is undefined and all InfoTuples are
not mandatory. The InfoTuples part of the result can be changed
without prior notice.
The InfoTuples with the following items are part of the result:
* current_function
* initial_call
* status
* message_queue_len
* links
* dictionary
* trap_exit
* error_handler
* priority
* group_leader
* total_heap_size
* heap_size
* stack_size
* reductions
* garbage_collection
If the process identified by Pid has a registered name, also an
InfoTuple with item registered_name is included.
For information about specific InfoTuples, see process_info/2.
Warning:
This BIF is intended for debugging only. For all other purposes,
use process_info/2.
Failure: badarg if Pid is not a local process.
process_info(Pid, Item) -> InfoTuple | [] | undefined
process_info(Pid, ItemList) -> InfoTupleList | [] | undefined
Types:
Pid = pid()
ItemList = [Item]
Item = process_info_item()
InfoTupleList = [InfoTuple]
InfoTuple = process_info_result_item()
process_info_item() =
backtrace | binary | catchlevel | current_function |
current_location | current_stacktrace | dictionary |
error_handler | garbage_collection | garbage_collection_info |
group_leader | heap_size | initial_call | links | last_calls |
memory | message_queue_len | messages | min_heap_size |
min_bin_vheap_size | monitored_by | monitors |
message_queue_data | priority | reductions | registered_name |
sequential_trace_token | stack_size | status | suspending |
total_heap_size | trace | trap_exit
process_info_result_item() =
{backtrace, Bin :: binary()} |
{binary,
BinInfo ::
[{integer() >= 0,
integer() >= 0,
integer() >= 0}]} |
{catchlevel, CatchLevel :: integer() >= 0} |
{current_function,
{Module :: module(), Function :: atom(), Arity :: arity()} |
undefined} |
{current_location,
{Module :: module(),
Function :: atom(),
Arity :: arity(),
Location ::
[{file, Filename :: string()} |
{line, Line :: integer() >= 1}]}} |
{current_stacktrace, Stack :: [stack_item()]} |
{dictionary, Dictionary :: [{Key :: term(), Value :: term()}]} |
{error_handler, Module :: module()} |
{garbage_collection, GCInfo :: [{atom(), integer() >= 0}]} |
{garbage_collection_info,
GCInfo :: [{atom(), integer() >= 0}]} |
{group_leader, GroupLeader :: pid()} |
{heap_size, Size :: integer() >= 0} |
{initial_call, mfa()} |
{links, PidsAndPorts :: [pid() | port()]} |
{last_calls, false | (Calls :: [mfa()])} |
{memory, Size :: integer() >= 0} |
{message_queue_len, MessageQueueLen :: integer() >= 0} |
{messages, MessageQueue :: [term()]} |
{min_heap_size, MinHeapSize :: integer() >= 0} |
{min_bin_vheap_size, MinBinVHeapSize :: integer() >= 0} |
{max_heap_size, MaxHeapSize :: max_heap_size()} |
{monitored_by,
MonitoredBy :: [pid() | port() | nif_resource()]} |
{monitors,
Monitors ::
[{process | port,
Pid ::
pid() |
port() |
{RegName :: atom(), Node :: node()}}]} |
{message_queue_data, MQD :: message_queue_data()} |
{priority, Level :: priority_level()} |
{reductions, Number :: integer() >= 0} |
{registered_name, [] | (Atom :: atom())} |
{sequential_trace_token,
[] | (SequentialTraceToken :: term())} |
{stack_size, Size :: integer() >= 0} |
{status,
Status ::
exiting | garbage_collecting | waiting | running |
runnable | suspended} |
{suspending,
SuspendeeList ::
[{Suspendee :: pid(),
ActiveSuspendCount :: integer() >= 0,
OutstandingSuspendCount :: integer() >= 0}]} |
{total_heap_size, Size :: integer() >= 0} |
{trace, InternalTraceFlags :: integer() >= 0} |
{trap_exit, Boolean :: boolean()}
stack_item() =
{Module :: module(),
Function :: atom(),
Arity :: arity() | (Args :: [term()]),
Location ::
[{file, Filename :: string()} |
{line, Line :: integer() >= 1}]}
priority_level() = low | normal | high | max
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
message_queue_data() = off_heap | on_heap
Returns information about the process identified by Pid, as
specified by Item or ItemList. Returns undefined if the process
is not alive.
If the process is alive and a single Item is specified, the
returned value is the corresponding InfoTuple, unless Item =:=
registered_name and the process has no registered name. In this
case, [] is returned. This strange behavior is because of his-
torical reasons, and is kept for backward compatibility.
If ItemList is specified, the result is InfoTupleList. The Info-
Tuples in InfoTupleList are included with the corresponding
Items in the same order as the Items were included in ItemList.
Valid Items can be included multiple times in ItemList.
Getting process informations follows the signal ordering guaran-
tees described in the Processes Chapter in the Erlang Reference
Manual .
Note:
If registered_name is part of ItemList and the process has no
name registered, a {registered_name, []}, InfoTuple will be
included in the resulting InfoTupleList. This behavior is dif-
ferent when a single Item =:= registered_name is specified, and
when process_info/1 is used.
Valid InfoTuples with corresponding Items:
{backtrace, Bin}:
Binary Bin contains the same information as the output from
erlang:process_display(Pid, backtrace). Use binary_to_list/1
to obtain the string of characters from the binary.
{binary, BinInfo}:
BinInfo is a list containing miscellaneous information about
binaries on the heap of this process. This InfoTuple can be
changed or removed without prior notice. In the current
implementation BinInfo is a list of tuples. The tuples con-
tain; BinaryId, BinarySize, BinaryRefcCount.
Depending on the value of the message_queue_data process
flag the message queue may be stored on the heap.
{catchlevel, CatchLevel}:
CatchLevel is the number of currently active catches in this
process. This InfoTuple can be changed or removed without
prior notice.
{current_function, {Module, Function, Arity} | undefined}:
Module, Function, Arity is the current function call of the
process. The value undefined can be returned if the process
is currently executing native compiled code.
{current_location, {Module, Function, Arity, Location}}:
Module, Function, Arity is the current function call of the
process. Location is a list of two-tuples describing the
location in the source code.
{current_stacktrace, Stack}:
Returns the current call stack back-trace (stacktrace) of
the process. The stack has the same format as in the catch
part of a try. See The call-stack back trace (stacktrace).
The depth of the stacktrace is truncated according to the
backtrace_depth system flag setting.
{dictionary, Dictionary}:
Dictionary is the process dictionary.
{error_handler, Module}:
Module is the error handler module used by the process (for
undefined function calls, for example).
{garbage_collection, GCInfo}:
GCInfo is a list containing miscellaneous information about
garbage collection for this process. The content of GCInfo
can be changed without prior notice.
{garbage_collection_info, GCInfo}:
GCInfo is a list containing miscellaneous detailed informa-
tion about garbage collection for this process. The content
of GCInfo can be changed without prior notice. For details
about the meaning of each item, see gc_minor_start in
erlang:trace/3.
{group_leader, GroupLeader}:
GroupLeader is the group leader for the I/O of the process.
{heap_size, Size}:
Size is the size in words of the youngest heap generation of
the process. This generation includes the process stack.
This information is highly implementation-dependent, and can
change if the implementation changes.
{initial_call, {Module, Function, Arity}}:
Module, Function, Arity is the initial function call with
which the process was spawned.
{links, PidsAndPorts}:
PidsAndPorts is a list of process identifiers and port iden-
tifiers, with processes or ports to which the process has a
link.
{last_calls, false|Calls}:
The value is false if call saving is not active for the
process (see process_flag/3). If call saving is active, a
list is returned, in which the last element is the most
recent called.
{memory, Size}:
Size is the size in bytes of the process. This includes call
stack, heap, and internal structures.
{message_queue_len, MessageQueueLen}:
MessageQueueLen is the number of messages currently in the
message queue of the process. This is the length of the list
MessageQueue returned as the information item messages (see
below).
{messages, MessageQueue}:
MessageQueue is a list of the messages to the process, which
have not yet been processed.
{min_heap_size, MinHeapSize}:
MinHeapSize is the minimum heap size for the process.
{min_bin_vheap_size, MinBinVHeapSize}:
MinBinVHeapSize is the minimum binary virtual heap size for
the process.
{monitored_by, MonitoredBy}:
A list of identifiers for all the processes, ports and NIF
resources, that are monitoring the process.
{monitors, Monitors}:
A list of monitors (started by monitor/2) that are active
for the process. For a local process monitor or a remote
process monitor by a process identifier, the list consists
of:
{process, Pid}:
Process is monitored by pid.
{process, {RegName, Node}}:
Local or remote process is monitored by name.
{port, PortId}:
Local port is monitored by port id.
{port, {RegName, Node}}:
Local port is monitored by name. Please note, that remote
port monitors are not supported, so Node will always be
the local node name.
{message_queue_data, MQD}:
MQD is the current value of the message_queue_data process
flag, which can be either off_heap or on_heap. For more
information, see the documentation of process_flag(mes-
sage_queue_data, MQD).
{priority, Level}:
Level is the current priority level for the process. For
more information on priorities, see process_flag(priority,
Level).
{reductions, Number}:
Number is the number of reductions executed by the process.
{registered_name, Atom}:
Atom is the registered process name. If the process has no
registered name, this tuple is not present in the list.
{sequential_trace_token, [] | SequentialTraceToken}:
SequentialTraceToken is the sequential trace token for the
process. This InfoTuple can be changed or removed without
prior notice.
{stack_size, Size}:
Size is the stack size, in words, of the process.
{status, Status}:
Status is the status of the process and is one of the fol-
lowing:
* exiting
* garbage_collecting
* waiting (for a message)
* running
* runnable (ready to run, but another process is running)
* suspended (suspended on a "busy" port or by the BIF
erlang:suspend_process/1,2)
{suspending, SuspendeeList}:
SuspendeeList is a list of {Suspendee, ActiveSuspendCount,
OutstandingSuspendCount} tuples. Suspendee is the process
identifier of a process that has been, or is to be, sus-
pended by the process identified by Pid through the BIF
erlang:suspend_process/2 or erlang:suspend_process/1.
ActiveSuspendCount is the number of times Suspendee has been
suspended by Pid. OutstandingSuspendCount is the number of
not yet completed suspend requests sent by Pid, that is:
* If ActiveSuspendCount =/= 0, Suspendee is currently in the
suspended state.
* If OutstandingSuspendCount =/= 0, option asynchronous of
erlang:suspend_process/2 has been used and the suspendee
has not yet been suspended by Pid.
Notice that ActiveSuspendCount and OutstandingSuspendCount
are not the total suspend count on Suspendee, only the parts
contributed by Pid.
{total_heap_size, Size}:
Size is the total size, in words, of all heap fragments of
the process. This includes the process stack and any unre-
ceived messages that are considered to be part of the heap.
{trace, InternalTraceFlags}:
InternalTraceFlags is an integer representing the internal
trace flag for this process. This InfoTuple can be changed
or removed without prior notice.
{trap_exit, Boolean}:
Boolean is true if the process is trapping exits, otherwise
false.
Notice that not all implementations support all these Items.
Failures:
badarg:
If Pid is not a local process.
badarg:
If Item is an invalid item.
processes() -> [pid()]
Returns a list of process identifiers corresponding to all the
processes currently existing on the local node.
Notice that an exiting process exists, but is not alive. That
is, is_process_alive/1 returns false for an exiting process, but
its process identifier is part of the result returned from pro-
cesses/0.
Example:
> processes().
[<0.0.0>,<0.2.0>,<0.4.0>,<0.5.0>,<0.7.0>,<0.8.0>]
purge_module(Module) -> true
Types:
Module = atom()
Removes old code for Module. Before this BIF is used,
check_process_code/2 is to be called to check that no processes
execute old code in the module.
Warning:
This BIF is intended for the code server (see code(3)) and is
not to be used elsewhere.
Note:
As from ERTS 8.0 (Erlang/OTP 19), any lingering processes that
still execute the old code is killed by this function. In ear-
lier versions, such incorrect use could cause much more fatal
failures, like emulator crash.
Failure: badarg if there is no old code for Module.
put(Key, Val) -> term()
Types:
Key = Val = term()
Adds a new Key to the process dictionary, associated with the
value Val, and returns undefined. If Key exists, the old value
is deleted and replaced by Val, and the function returns the old
value. The average time complexity for the current implementa-
tion of this function is O(1) and the worst case time complexity
is O(N), where N is the number of items in the process dictio-
nary. Example:
> X = put(name, walrus), Y = put(name, carpenter),
Z = get(name),
{X, Y, Z}.
{undefined,walrus,carpenter}
Note:
The values stored when put is evaluated within the scope of a
catch are not retracted if a throw is evaluated, or if an error
occurs.
erlang:raise(Class, Reason, Stacktrace) -> badarg
Types:
Class = error | exit | throw
Reason = term()
Stacktrace = raise_stacktrace() | stacktrace()
raise_stacktrace() =
[{module(), atom(), arity() | [term()]} |
{function(), arity() | [term()]}]
Raises an exception of the specified class, reason, and call
stack backtrace (stacktrace).
Class is error, exit, or throw. So, if it were not for the
stacktrace, erlang:raise(Class, Reason, Stacktrace) is equiva-
lent to erlang:Class(Reason) (given that Class is a valid
class).
Reason can be any term.
Stacktrace is a list as provided in a try-catch clause.
try
...
catch Class:Reason:Stacktrace ->
...
end
That is, a list of four-tuples {Module, Function, Arity | Args,
ExtraInfo}, where Module and Function are atoms, and the third
element is an integer arity or an argument list. The stacktrace
can also contain {Fun, Args, ExtraInfo} tuples, where Fun is a
local fun and Args is an argument list.
Element ExtraInfo at the end is optional. Omitting it is equiva-
lent to specifying an empty list.
The stacktrace is used as the exception stacktrace for the call-
ing process; it is truncated to the current maximum stacktrace
depth.
As evaluating this function causes the process to terminate, it
has no return value unless the arguments are invalid, in which
case the function returns the error reason badarg. If you want
to be sure not to return, you can call error(erlang:raise(Class,
Reason, Stacktrace)) and hope to distinguish exceptions later.
See the reference manual about errors and error handling for
more information about exception classes and how to catch excep-
tions.
erlang:read_timer(TimerRef) -> Result
Types:
TimerRef = reference()
Time = integer() >= 0
Result = Time | false
Reads the state of a timer. The same as calling
erlang:read_timer(TimerRef, []).
erlang:read_timer(TimerRef, Options) -> Result | ok
Types:
TimerRef = reference()
Async = boolean()
Option = {async, Async}
Options = [Option]
Time = integer() >= 0
Result = Time | false
Reads the state of a timer that has been created by either
erlang:start_timer or erlang:send_after. TimerRef identifies the
timer, and was returned by the BIF that created the timer.
Options:
{async, Async}:
Asynchronous request for state information. Async defaults
to false, which causes the operation to be performed syn-
chronously. In this case, the Result is returned by
erlang:read_timer. When Async is true, erlang:read_timer
sends an asynchronous request for the state information to
the timer service that manages the timer, and then returns
ok. A message on the format {read_timer, TimerRef, Result}
is sent to the caller of erlang:read_timer when the opera-
tion has been processed.
More Options can be added in the future.
If Result is an integer, it represents the time in milliseconds
left until the timer expires.
If Result is false, a timer corresponding to TimerRef could not
be found. This because the timer had expired, or been canceled,
or because TimerRef never has corresponded to a timer. Even if
the timer has expired, it does not tell you whether or not the
time-out message has arrived at its destination yet.
Note:
The timer service that manages the timer can be co-located with
another scheduler than the scheduler that the calling process is
executing on. If so, communication with the timer service takes
much longer time than if it is located locally. If the calling
process is in a critical path, and can do other things while
waiting for the result of this operation, you want to use option
{async, true}. If using option {async, false}, the calling
process is blocked until the operation has been performed.
See also erlang:send_after/4, erlang:start_timer/4, and
erlang:cancel_timer/2.
ref_to_list(Ref) -> string()
Types:
Ref = reference()
Returns a string corresponding to the text representation of
Ref.
Warning:
This BIF is intended for debugging and is not to be used in
application programs.
register(RegName, PidOrPort) -> true
Types:
RegName = atom()
PidOrPort = port() | pid()
Registers the name RegName with a process identifier (pid) or a
port identifier in the name registry. RegName, which must be an
atom, can be used instead of the pid or port identifier in send
operator (RegName ! Message) and most other BIFs that take a pid
or port identifies as an argument. Example:
> register(db, Pid).
true
The registered name is considered a Directly Visible Erlang
Resource and is automatically unregistered when the process ter-
minates.
Failures:
badarg:
If PidOrPort is not an existing local process or port.
badarg:
If RegName is already in use.
badarg:
If the process or port is already registered (already has a
name).
badarg:
If RegName is the atom undefined.
registered() -> [RegName]
Types:
RegName = atom()
Returns a list of names that have been registered using regis-
ter/2, for example:
> registered().
[code_server, file_server, init, user, my_db]
erlang:resume_process(Suspendee) -> true
Types:
Suspendee = pid()
Decreases the suspend count on the process identified by Sus-
pendee. Suspendee is previously to have been suspended through
erlang:suspend_process/2 or erlang:suspend_process/1 by the
process calling erlang:resume_process(Suspendee). When the sus-
pend count on Suspendee reaches zero, Suspendee is resumed, that
is, its state is changed from suspended into the state it had
before it was suspended.
Warning:
This BIF is intended for debugging only.
Failures:
badarg:
If Suspendee is not a process identifier.
badarg:
If the process calling erlang:resume_process/1 had not pre-
viously increased the suspend count on the process identi-
fied by Suspendee.
badarg:
If the process identified by Suspendee is not alive.
round(Number) -> integer()
Types:
Number = number()
Returns an integer by rounding Number, for example:
round(42.1).
42
round(5.5).
6
round(-5.5).
-6
round(36028797018963969.0).
36028797018963968
In the last example, round(36028797018963969.0) evaluates to
36028797018963968. The reason for this is that the number
36028797018963969.0 cannot be represented exactly as a float
value. Instead, the float literal is represented as
36028797018963968.0, which is the closest number that can be
represented exactly as a float value. See Representation of
Floating Point Numbers for additional information.
Allowed in guard tests.
self() -> pid()
Returns the process identifier of the calling process, for exam-
ple:
> self().
<0.26.0>
Allowed in guard tests.
erlang:send(Dest, Msg) -> Msg
Types:
Dest = dst()
Msg = term()
dst() =
pid() |
reference() |
port() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}
Sends a message and returns Msg. This is the same as using the
send operator: Dest ! Msg.
Dest can be a remote or local process identifier, an alias, a
(local) port, a locally registered name, or a tuple {RegName,
Node} for a registered name at another node.
The function fails with a badarg run-time error if Dest is an
atom name, but this name is not registered. This is the only
case when send fails for an unreachable destination Dest (of
correct type).
erlang:send(Dest, Msg, Options) -> Res
Types:
Dest = dst()
Msg = term()
Options = [nosuspend | noconnect]
Res = ok | nosuspend | noconnect
dst() =
pid() |
reference() |
port() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}
Either sends a message and returns ok, or does not send the mes-
sage but returns something else (see below). Otherwise the same
as erlang:send/2. For more detailed explanation and warnings,
see erlang:send_nosuspend/2,3.
Options:
nosuspend:
If the sender would have to be suspended to do the send,
nosuspend is returned instead.
noconnect:
If the destination node would have to be auto-connected to
do the send, noconnect is returned instead.
Warning:
As with erlang:send_nosuspend/2,3: use with extreme care.
erlang:send_after(Time, Dest, Msg) -> TimerRef
Types:
Time = integer() >= 0
Dest = pid() | atom()
Msg = term()
TimerRef = reference()
Starts a timer. The same as calling erlang:send_after(Time,
Dest, Msg, []).
erlang:send_after(Time, Dest, Msg, Options) -> TimerRef
Types:
Time = integer()
Dest = pid() | atom()
Msg = term()
Options = [Option]
Abs = boolean()
Option = {abs, Abs}
TimerRef = reference()
Starts a timer. When the timer expires, the message Msg is sent
to the process identified by Dest. Apart from the format of the
time-out message, this function works exactly as
erlang:start_timer/4.
erlang:send_nosuspend(Dest, Msg) -> boolean()
Types:
Dest = dst()
Msg = term()
dst() =
pid() |
reference() |
port() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}
The same as erlang:send(Dest, Msg, [nosuspend]), but returns
true if the message was sent and false if the message was not
sent because the sender would have had to be suspended.
This function is intended for send operations to an unreliable
remote node without ever blocking the sending (Erlang) process.
If the connection to the remote node (usually not a real Erlang
node, but a node written in C or Java) is overloaded, this func-
tion does not send the message and returns false.
The same occurs if Dest refers to a local port that is busy. For
all other destinations (allowed for the ordinary send operator
'!'), this function sends the message and returns true.
This function is only to be used in rare circumstances where a
process communicates with Erlang nodes that can disappear with-
out any trace, causing the TCP buffers and the drivers queue to
be over-full before the node is shut down (because of tick time-
outs) by net_kernel. The normal reaction to take when this
occurs is some kind of premature shutdown of the other node.
Notice that ignoring the return value from this function would
result in an unreliable message passing, which is contradictory
to the Erlang programming model. The message is not sent if this
function returns false.
In many systems, transient states of overloaded queues are nor-
mal. Although this function returns false does not mean that the
other node is guaranteed to be non-responsive, it could be a
temporary overload. Also, a return value of true does only mean
that the message can be sent on the (TCP) channel without block-
ing; the message is not guaranteed to arrive at the remote node.
For a disconnected non-responsive node, the return value is true
(mimics the behavior of operator !). The expected behavior and
the actions to take when the function returns false are applica-
tion- and hardware-specific.
Warning:
Use with extreme care.
erlang:send_nosuspend(Dest, Msg, Options) -> boolean()
Types:
Dest = dst()
Msg = term()
Options = [noconnect]
dst() =
pid() |
reference() |
port() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}
The same as erlang:send(Dest, Msg, [nosuspend | Options]), but
with a Boolean return value.
This function behaves like erlang:send_nosuspend/2, but takes a
third parameter, a list of options. The only option is nocon-
nect, which makes the function return false if the remote node
is not currently reachable by the local node. The normal behav-
ior is to try to connect to the node, which can stall the
process during a short period. The use of option noconnect makes
it possible to be sure not to get the slightest delay when send-
ing to a remote process. This is especially useful when communi-
cating with nodes that expect to always be the connecting part
(that is, nodes written in C or Java).
Whenever the function returns false (either when a suspend would
occur or when noconnect was specified and the node was not
already connected), the message is guaranteed not to have been
sent.
Warning:
Use with extreme care.
erlang:set_cookie(Cookie) -> true
Types:
Cookie = atom()
Sets the magic cookie of the local node to the atom Cookie,
which is also the cookie for all nodes that have no explicit
cookie set with set_cookie/2 Cookie (see section Distributed
Erlang in the Erlang Reference Manual in System Documentation).
Failure: function_clause if the local node is not alive.
erlang:set_cookie(Node, Cookie) -> true
Types:
Node = node()
Cookie = atom()
Sets the magic cookie for Node to the atom Cookie. If Node is
the local node, the function sets the cookie of all other nodes
(that have no explicit cookie set with this function) to Cookie
(see section Distributed Erlang in the Erlang Reference Manual
in System Documentation).
Failure: function_clause if the local node is not alive.
setelement(Index, Tuple1, Value) -> Tuple2
Types:
Index = integer() >= 1
1..tuple_size(Tuple1
Tuple1 = Tuple2 = tuple()
Value = term()
Returns a tuple that is a copy of argument Tuple1 with the ele-
ment specified by integer argument Index (the first element is
the element with index 1) replaced by argument Value, for exam-
ple:
> setelement(2, {10, green, bottles}, red).
{10,red,bottles}
size(Item) -> integer() >= 0
Types:
Item = tuple() | binary()
Returns the number of elements in a tuple or the number of bytes
in a binary or bitstring, for example:
> size({morni, mulle, bwange}).
3
> size(<<11, 22, 33>>).
3
For bitstrings, the number of whole bytes is returned. That is,
if the number of bits in the bitstring is not divisible by 8,
the resulting number of bytes is rounded down.
Allowed in guard tests.
See also tuple_size/1, byte_size/1, and bit_size/1.
spawn(Fun) -> pid()
Types:
Fun = function()
Returns the process identifier of a new process started by the
application of Fun to the empty list []. Otherwise works like
spawn/3.
spawn(Node, Fun) -> pid()
Types:
Node = node()
Fun = function()
Returns the process identifier of a new process started by the
application of Fun to the empty list [] on Node. If Node does
not exist, a useless pid is returned. Otherwise works like
spawn/3.
spawn(Module, Function, Args) -> pid()
Types:
Module = module()
Function = atom()
Args = [term()]
Returns the process identifier of a new process started by the
application of Module:Function to Args.
error_handler:undefined_function(Module, Function, Args) is
evaluated by the new process if Module:Function/Arity does not
exist (where Arity is the length of Args). The error handler can
be redefined (see process_flag/2). If error_handler is unde-
fined, or the user has redefined the default error_handler and
its replacement is undefined, a failure with reason undef
occurs.
Example:
> spawn(speed, regulator, [high_speed, thin_cut]).
<0.13.1>
spawn(Node, Module, Function, Args) -> pid()
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Returns the process identifier (pid) of a new process started by
the application of Module:Function to Args on Node. If Node does
not exist, a useless pid is returned. Otherwise works like
spawn/3.
spawn_link(Fun) -> pid()
Types:
Fun = function()
Returns the process identifier of a new process started by the
application of Fun to the empty list []. A link is created
between the calling process and the new process, atomically.
Otherwise works like spawn/3.
spawn_link(Node, Fun) -> pid()
Types:
Node = node()
Fun = function()
Returns the process identifier (pid) of a new process started by
the application of Fun to the empty list [] on Node. A link is
created between the calling process and the new process, atomi-
cally. If Node does not exist, a useless pid is returned and an
exit signal with reason noconnection is sent to the calling
process. Otherwise works like spawn/3.
spawn_link(Module, Function, Args) -> pid()
Types:
Module = module()
Function = atom()
Args = [term()]
Returns the process identifier of a new process started by the
application of Module:Function to Args. A link is created
between the calling process and the new process, atomically.
Otherwise works like spawn/3.
spawn_link(Node, Module, Function, Args) -> pid()
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Returns the process identifier (pid) of a new process started by
the application of Module:Function to Args on Node. A link is
created between the calling process and the new process, atomi-
cally. If Node does not exist, a useless pid is returned and an
exit signal with reason noconnection is sent to the calling
process. Otherwise works like spawn/3.
spawn_monitor(Fun) -> {pid(), reference()}
Types:
Fun = function()
Returns the process identifier of a new process, started by the
application of Fun to the empty list [], and a reference for a
monitor created to the new process. Otherwise works like
spawn/3.
spawn_monitor(Node, Fun) -> {pid(), reference()}
Types:
Node = node()
Fun = function()
Returns the process identifier of a new process, started by the
application of Fun to the empty list [] on the node Node, and a
reference for a monitor created to the new process. Otherwise
works like spawn/3.
If the node identified by Node does not support distributed
spawn_monitor(), the call will fail with a notsup exception.
spawn_monitor(Module, Function, Args) -> {pid(), reference()}
Types:
Module = module()
Function = atom()
Args = [term()]
A new process is started by the application of Module:Function
to Args. The process is monitored at the same time. Returns the
process identifier and a reference for the monitor. Otherwise
works like spawn/3.
spawn_monitor(Node, Module, Function, Args) ->
{pid(), reference()}
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
A new process is started by the application of Module:Function
to Args on the node Node. The process is monitored at the same
time. Returns the process identifier and a reference for the
monitor. Otherwise works like spawn/3.
If the node identified by Node does not support distributed
spawn_monitor(), the call will fail with a notsup exception.
spawn_opt(Fun, Options) -> pid() | {pid(), reference()}
Types:
Fun = function()
Options = [spawn_opt_option()]
priority_level() = low | normal | high | max
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
message_queue_data() = off_heap | on_heap
spawn_opt_option() =
link | monitor |
{monitor, MonitorOpts :: [monitor_option()]} |
{priority, Level :: priority_level()} |
{fullsweep_after, Number :: integer() >= 0} |
{min_heap_size, Size :: integer() >= 0} |
{min_bin_vheap_size, VSize :: integer() >= 0} |
{max_heap_size, Size :: max_heap_size()} |
{message_queue_data, MQD :: message_queue_data()}
Returns the process identifier (pid) of a new process started by
the application of Fun to the empty list []. Otherwise works
like spawn_opt/4.
If option monitor is specified, the newly created process is
monitored, and both the pid and reference for the monitor are
returned.
spawn_opt(Node, Fun, Options) -> pid() | {pid(), reference()}
Types:
Node = node()
Fun = function()
Options =
[monitor | {monitor, [monitor_option()]} | link | Oth-
erOption]
OtherOption = term()
Returns the process identifier (pid) of a new process started by
the application of Fun to the empty list [] on Node. If Node
does not exist, a useless pid is returned. Otherwise works like
spawn_opt/4.
Valid options depends on what options are supported by the node
identified by Node. A description of valid Options for the local
node of current OTP version can be found in the documentation of
spawn_opt/4.
spawn_opt(Module, Function, Args, Options) ->
Pid | {Pid, MonitorRef}
Types:
Module = module()
Function = atom()
Args = [term()]
Options = [spawn_opt_option()]
Pid = pid()
MonitorRef = reference()
priority_level() = low | normal | high | max
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
message_queue_data() = off_heap | on_heap
spawn_opt_option() =
link | monitor |
{monitor, MonitorOpts :: [monitor_option()]} |
{priority, Level :: priority_level()} |
{fullsweep_after, Number :: integer() >= 0} |
{min_heap_size, Size :: integer() >= 0} |
{min_bin_vheap_size, VSize :: integer() >= 0} |
{max_heap_size, Size :: max_heap_size()} |
{message_queue_data, MQD :: message_queue_data()}
Works as spawn/3, except that an extra option list is specified
when creating the process.
If option monitor is specified, the newly created process is
monitored, and both the pid and reference for the monitor are
returned.
Options:
link:
Sets a link to the parent process (like spawn_link/3 does).
monitor:
Monitors the new process (like monitor(process, Pid) does).
A {Pid, MonitorRef} tuple will be returned instead of just a
Pid.
{monitor, MonitorOpts}:
Monitors the new process with options (like monitor(process,
Pid, MonitorOpts) does). A {Pid, MonitorRef} tuple will be
returned instead of just a Pid.
{priority, Level}:
Sets the priority of the new process. Equivalent to execut-
ing process_flag(priority, Level) in the start function of
the new process, except that the priority is set before the
process is selected for execution for the first time. For
more information on priorities, see process_flag(priority,
Level).
{fullsweep_after, Number}:
Useful only for performance tuning. Do not use this option
unless you know that there is problem with execution times
or memory consumption, and ensure that the option improves
matters.
The Erlang runtime system uses a generational garbage col-
lection scheme, using an "old heap" for data that has sur-
vived at least one garbage collection. When there is no more
room on the old heap, a fullsweep garbage collection is
done.
Option fullsweep_after makes it possible to specify the max-
imum number of generational collections before forcing a
fullsweep, even if there is room on the old heap. Setting
the number to zero disables the general collection algo-
rithm, that is, all live data is copied at every garbage
collection.
A few cases when it can be useful to change fullsweep_after:
* If binaries that are no longer used are to be thrown away
as soon as possible. (Set Number to zero.)
* A process that mostly have short-lived data is fullsweeped
seldom or never, that is, the old heap contains mostly
garbage. To ensure a fullsweep occasionally, set Number to
a suitable value, such as 10 or 20.
* In embedded systems with a limited amount of RAM and no
virtual memory, you might want to preserve memory by set-
ting Number to zero. (The value can be set globally, see
erlang:system_flag/2.)
{min_heap_size, Size}:
Useful only for performance tuning. Do not use this option
unless you know that there is problem with execution times
or memory consumption, and ensure that the option improves
matters.
Gives a minimum heap size, in words. Setting this value
higher than the system default can speed up some processes
because less garbage collection is done. However, setting a
too high value can waste memory and slow down the system
because of worse data locality. Therefore, use this option
only for fine-tuning an application and to measure the exe-
cution time with various Size values.
{min_bin_vheap_size, VSize}:
Useful only for performance tuning. Do not use this option
unless you know that there is problem with execution times
or memory consumption, and ensure that the option improves
matters.
Gives a minimum binary virtual heap size, in words. Setting
this value higher than the system default can speed up some
processes because less garbage collection is done. However,
setting a too high value can waste memory. Therefore, use
this option only for fine-tuning an application and to mea-
sure the execution time with various VSize values.
{max_heap_size, Size}:
Sets the max_heap_size process flag. The default
max_heap_size is determined by command-line argument +hmax
in erl(1). For more information, see the documentation of
process_flag(max_heap_size, Size).
{message_queue_data, MQD}:
Sets the value of the message_queue_data process flag. MQD
can be either off_heap or on_heap. The default value of the
message_queue_data process flag is determined by the com-
mand-line argument +hmqd in erl(1). For more information,
see the documentation of process_flag(message_queue_data,
MQD).
spawn_opt(Node, Module, Function, Args, Options) ->
pid() | {pid(), reference()}
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Options =
[monitor | {monitor, [monitor_option()]} | link | Oth-
erOption]
OtherOption = term()
Returns the process identifier (pid) of a new process started by
the application of Module:Function to Args on Node. If Node does
not exist, a useless pid is returned. Otherwise works like
spawn_opt/4.
Valid options depends on what options are supported by the node
identified by Node. A description of valid Options for the local
node of current OTP version can be found in the documentation of
spawn_opt/4.
spawn_request(Fun) -> ReqId
Types:
Fun = function()
ReqId = reference()
The same as the call spawn_request(node(),Fun,[]). That is, a
spawn request on the local node with no options.
spawn_request(Fun, Options) -> ReqId
Types:
Fun = function()
Option =
{reply_tag, ReplyTag} | {reply, Reply} |
spawn_opt_option()
ReplyTag = term()
Reply = yes | no | error_only | success_only
Options = [Option]
ReqId = reference()
The same as the call spawn_request(node(),Fun,Options). That is,
a spawn request on the local node.
spawn_request(Node, Fun) -> ReqId
Types:
Node = node()
Fun = function()
ReqId = reference()
The same as the call spawn_request(Node,Fun,[]). That is, a
spawn request with no options.
spawn_request(Node, Fun, Options) -> ReqId
Types:
Node = node()
Fun = function()
Options = [Option]
Option =
monitor |
{monitor, [monitor_option()]} |
link |
{reply_tag, ReplyTag} |
{reply, Reply} |
OtherOption
ReplyTag = term()
Reply = yes | no | error_only | success_only
OtherOption = term()
ReqId = reference()
The same as spawn_request(Node,erlang,apply,[Fun,[]],Options).
That is, a spawn request using the fun Fun of arity zero as
entry point.
This function will fail with a badarg exception if:
* Node is not an atom.
* Fun is not a fun of arity zero.
* Options is not a proper list of terms.
spawn_request(Module, Function, Args) -> ReqId
Types:
Module = module()
Function = atom()
Args = [term()]
ReqId = reference()
The same as the call spawn_request(node(),Module,Func-
tion,Args,[]). That is, a spawn request on the local node with
no options.
spawn_request(Node, Module, Function, Args) -> ReqId
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
ReqId = reference()
The same as the call spawn_request(Node,Module,Func-
tion,Args,[]). That is, a spawn request with no options.
spawn_request(Module, Function, Args, Options) -> ReqId
Types:
Module = module()
Function = atom()
Args = [term()]
Option =
{reply_tag, ReplyTag} | {reply, Reply} |
spawn_opt_option()
ReplyTag = term()
Reply = yes | no | error_only | success_only
Options = [Option]
ReqId = reference()
The same as the call spawn_request(node(),Module,Func-
tion,Args,Options). That is, a spawn request on the local node.
spawn_request(Node, Module, Function, Args, Options) -> ReqId
Types:
Node = node()
Module = module()
Function = atom()
Args = [term()]
Options = [Option]
Option =
monitor |
{monitor, [monitor_option()]} |
link |
{reply_tag, ReplyTag} |
{reply, Reply} |
OtherOption
ReplyTag = term()
Reply = yes | no | error_only | success_only
OtherOption = term()
ReqId = reference()
Asynchronously send a spawn request. Returns a request identi-
fier ReqId.
If the spawn operation succeeds, a new process is created on the
node identified by Node. When a spawn operation succeeds, the
caller will by default be sent a message on the form {ReplyTag,
ReqId, ok, Pid} where Pid is the process identifier of the newly
created process. Such a message is referred to as a success mes-
sage below in the text. ReplyTag is by default the atom
spawn_reply unless modified by the {reply_tag, ReplyTag} option.
The new process is started by the application of Module:Function
to Args.
The spawn operation fails either if creation of a new process
failed or if the spawn operation was interrupted by a connection
failure. When a spawn operation fails, the caller will by
default be sent a message on the form {ReplyTag, ReqId, error,
Reason} where Reason is the error reason. Such a message is
referred to as an error message below in the text. Currently
the following spawn error Reasons are defined, but other reasons
can appear at any time without prior notice:
badopt:
An invalid Option was passed as argument. Note that differ-
ent runtime systems may support different options.
notsup:
The node identified by Node does not support spawn opera-
tions issued by spawn_request().
noconnection:
Failure to set up a connection to the node identified by
Node or the connection to that node was lost during the
spawn operation. In the case the connection was lost, a
process may or may not have been created.
system_limit:
Could not create a new process due to that some system limit
was reached. Typically the process table was full.
Valid Options:
monitor:
In the absence of spawn operation failures, atomically sets
up a monitor to the newly created process. That is, as if
the calling process had called monitor(process, Pid) where
Pid is the process identifier of the newly created process.
The ReqId returned by spawn_request() is also used as moni-
tor reference as if it was returned from monitor(process,
Pid).
The monitor will not be activated for the calling process
until the spawn operation has succeeded. The monitor can not
be demonitored before the operation has succeeded. A 'DOWN'
message for the corresponding monitor is guaranteed not to
be delivered before a success message that corresponds to
the spawn operation. If the spawn operation fails, no 'DOWN'
message will be delivered.
If the connection between the nodes involved in the spawn
operation is lost during the spawn operation, the spawn
operation will fail with an error reason of noconnection. A
new process may or may not have been created.
{monitor, MonitorOpts}:
In the absence of spawn operation failures, atomically sets
up a monitor to the newly created process. That is, as if
the calling process had called monitor(process, Pid, Moni-
torOpts) where Pid is the process identifier of the newly
created process. See the monitor option above for more
information.
Note that the monitor will not be activated for the calling
process until the spawn operation has succeeded. For exam-
ple, in the case that an alias is created using the monitor
option, the alias will not be active until the monitor is
activated.
link:
In absence of spawn operation failures, atomically sets up a
link between the calling process and the newly created
process. That is, as if the calling process had called
link(Pid) where Pid is the process identifier of the newly
created process.
The link will not be activated for the calling process until
the spawn operation has succeeded. The link can not be
removed before the operation has succeeded. An exit signal
due to the link is guaranteed not to be delivered before a
success message that corresponds to the spawn operation. If
the spawn operation fails, no exit signal due to the link
will be delivered to the caller of spawn_request().
If the connection between the nodes involved in the spawn
operation is lost during the spawn operation, the spawn
operation will fail with an error reason of noconnection. A
new process may or may not have been created. If it has been
created, it will be delivered an exit signal with an exit
reason of noconnection.
{reply, Reply}:
Valid Reply values:
yes:
A spawn reply message will be sent to the caller regard-
less of whether the operation succeeds or not. If the call
to spawn_request() returns without raising an exception
and the reply option is set to yes, the caller is guaran-
teed to be delivered either a success message or an error
message . The reply option is by default set to yes.
no:
No spawn reply message will be sent to the caller when the
spawn operation completes. This regardless of whether the
operation succeeds or not.
error_only:
No spawn reply message will be sent to the caller if the
spawn operation succeeds, but an error message will be
sent to the caller if the operation fails.
success_only:
No spawn reply message will be sent to the caller if the
spawn operation fails, but a success message will be sent
to the caller if the operation succeeds.
{reply_tag, ReplyTag}:
Sets the reply tag to ReplyTag in the reply message. That
is, in the success or error message that is sent to the
caller due to the spawn operation. The default reply tag is
the atom spawn_reply.
OtherOption:
Other valid options depends on what options are supported by
the node identified by Node. A description of other valid
Options for the local node of current OTP version can be
found in the documentation of spawn_opt/4.
This function will fail with a badarg exception if:
* Node is not an atom.
* Module is not an atom.
* Function is not an atom.
* Args is not a proper list of terms.
* Options is not a proper list of terms.
Note that not all individual Options are checked when the spawn
request is sent. Some Options can only be checked on reception
of the request. Therefore an invalid option does not cause a
badarg exception, but will cause the spawn operation to fail
with an error reason of badopt.
A spawn request can be abandoned by calling spawn_request_aban-
don/1.
spawn_request_abandon(ReqId :: reference()) -> boolean()
Abandon a previously issued spawn request. ReqId corresponds to
a request identifier previously returned by spawn_request() in a
call from current process. That is, only the process that has
made the request can abandon the request.
A spawn request can only be successfully abandoned until the
spawn request has completed. When a spawn request has been suc-
cessfully abandoned, the caller will not be effected by future
direct effects of the spawn request itself. For example, it will
not receive a spawn reply message. The request is however not
withdrawn, so a new process may or may not be created due to the
request. If a new process is created after the spawn request was
abandoned, no monitors nor links will be set up to the caller of
spawn_request_abandon/1 due to the spawn request. If the spawn
request included the link option, the process created due to
this request will be sent an exit signal from its parent with
the exit reason abandoned when it is detected that the spawn
operation has succeeded.
Note:
A process created due to a spawn request that has been abandoned
may communicate with its parent as any other process. It is only
the direct effects on the parent of the actual spawn request,
that will be canceled by abandoning a spawn request.
Return values:
true:
The spawn request was successfully abandoned.
false:
No spawn request was abandoned. The ReqId request identifier
did not correspond to an outstanding spawn request issued by
the calling process. The reason for this is either:
* ReqId corresponds to a spawn request previoulsy made by
the calling process. The spawn operation has completed and
a spawn reply has already been delivered to the calling
process unless the spawn reply was disabled in the
request.
* ReqId does not correspond to a spawn request that has been
made by the calling process.
This function fail with a badarg exception if ReqId is not a
reference.
split_binary(Bin, Pos) -> {binary(), binary()}
Types:
Bin = binary()
Pos = integer() >= 0
0..byte_size(Bin)
Returns a tuple containing the binaries that are the result of
splitting Bin into two parts at position Pos. This is not a
destructive operation. After the operation, there are three
binaries altogether. Example:
> B = list_to_binary("0123456789").
<<"0123456789">>
> byte_size(B).
10
> {B1, B2} = split_binary(B,3).
{<<"012">>,<<"3456789">>}
> byte_size(B1).
3
> byte_size(B2).
7
erlang:start_timer(Time, Dest, Msg) -> TimerRef
Types:
Time = integer() >= 0
Dest = pid() | atom()
Msg = term()
TimerRef = reference()
Starts a timer. The same as calling erlang:start_timer(Time,
Dest, Msg, []).
erlang:start_timer(Time, Dest, Msg, Options) -> TimerRef
Types:
Time = integer()
Dest = pid() | atom()
Msg = term()
Options = [Option]
Abs = boolean()
Option = {abs, Abs}
TimerRef = reference()
Starts a timer. When the timer expires, the message {timeout,
TimerRef, Msg} is sent to the process identified by Dest.
Options:
{abs, false}:
This is the default. It means the Time value is interpreted
as a time in milliseconds relative current Erlang monotonic
time.
{abs, true}:
Absolute Time value. The Time value is interpreted as an
absolute Erlang monotonic time in milliseconds.
More Options can be added in the future.
The absolute point in time, the timer is set to expire on, must
be in the interval [ erlang:convert_time_unit(erlang:sys-
tem_info(start_time), native, millisecond), erlang:con-
vert_time_unit(erlang:system_info(end_time), native, millisec-
ond) ]. If a relative time is specified, the Time value is not
allowed to be negative.
If Dest is a pid(), it must be a pid() of a process created on
the current runtime system instance. This process has either
terminated or not. If Dest is an atom(), it is interpreted as
the name of a locally registered process. The process referred
to by the name is looked up at the time of timer expiration. No
error is returned if the name does not refer to a process.
If Dest is a pid(), the timer is automatically canceled if the
process referred to by the pid() is not alive, or if the process
exits. This feature was introduced in ERTS 5.4.11. Notice that
timers are not automatically canceled when Dest is an atom().
See also erlang:send_after/4, erlang:cancel_timer/2, and
erlang:read_timer/2.
Failure: badarg if the arguments do not satisfy the requirements
specified here.
statistics(Item :: active_tasks) -> [ActiveTasks]
Types:
ActiveTasks = integer() >= 0
Returns the same as statistics(active_tasks_all) with the excep-
tion that no information about the dirty IO run queue and its
associated schedulers is part of the result. That is, only tasks
that are expected to be CPU bound are part of the result.
statistics(Item :: active_tasks_all) -> [ActiveTasks]
Types:
ActiveTasks = integer() >= 0
Returns a list where each element represents the amount of
active processes and ports on each run queue and its associated
schedulers. That is, the number of processes and ports that are
ready to run, or are currently running. Values for normal run
queues and their associated schedulers are located first in the
resulting list. The first element corresponds to scheduler num-
ber 1 and so on. If support for dirty schedulers exist, an ele-
ment with the value for the dirty CPU run queue and its associ-
ated dirty CPU schedulers follow and then as last element the
value for the the dirty IO run queue and its associated dirty IO
schedulers follow. The information is not gathered atomically.
That is, the result is not necessarily a consistent snapshot of
the state, but instead quite efficiently gathered.
Note:
Each normal scheduler has one run queue that it manages. If
dirty schedulers schedulers are supported, all dirty CPU sched-
ulers share one run queue, and all dirty IO schedulers share one
run queue. That is, we have multiple normal run queues, one
dirty CPU run queue and one dirty IO run queue. Work can not
migrate between the different types of run queues. Only work in
normal run queues can migrate to other normal run queues. This
has to be taken into account when evaluating the result.
See also statistics(total_active_tasks), statis-
tics(run_queue_lengths), statistics(run_queue_lengths_all), sta-
tistics(total_run_queue_lengths), and statis-
tics(total_run_queue_lengths_all).
statistics(Item :: context_switches) -> {ContextSwitches, 0}
Types:
ContextSwitches = integer() >= 0
Returns the total number of context switches since the system
started.
statistics(Item :: exact_reductions) ->
{Total_Exact_Reductions,
Exact_Reductions_Since_Last_Call}
Types:
Total_Exact_Reductions = Exact_Reductions_Since_Last_Call =
integer() >= 0
Returns the number of exact reductions.
Note:
statistics(exact_reductions) is a more expensive operation than
statistics(reductions).
statistics(Item :: garbage_collection) ->
{Number_of_GCs, Words_Reclaimed, 0}
Types:
Number_of_GCs = Words_Reclaimed = integer() >= 0
Returns information about garbage collection, for example:
> statistics(garbage_collection).
{85,23961,0}
This information can be invalid for some implementations.
statistics(Item :: io) -> {{input, Input}, {output, Output}}
Types:
Input = Output = integer() >= 0
Returns Input, which is the total number of bytes received
through ports, and Output, which is the total number of bytes
output to ports.
statistics(Item :: microstate_accounting) ->
[MSAcc_Thread] | undefined
Types:
MSAcc_Thread =
#{type := MSAcc_Thread_Type,
id := MSAcc_Thread_Id,
counters := MSAcc_Counters}
MSAcc_Thread_Type =
async | aux | dirty_io_scheduler | dirty_cpu_scheduler |
poll | scheduler
MSAcc_Thread_Id = integer() >= 0
MSAcc_Counters = #{MSAcc_Thread_State => integer() >= 0}
MSAcc_Thread_State =
alloc | aux | bif | busy_wait | check_io | emulator | ets
|
gc | gc_fullsweep | nif | other | port | send | sleep |
timers
Microstate accounting can be used to measure how much time the
Erlang runtime system spends doing various tasks. It is designed
to be as lightweight as possible, but some overhead exists when
this is enabled. Microstate accounting is meant to be a profil-
ing tool to help finding performance bottlenecks. To
start/stop/reset microstate accounting, use system flag
microstate_accounting.
statistics(microstate_accounting) returns a list of maps repre-
senting some of the OS threads within ERTS. Each map contains
type and id fields that can be used to identify what thread it
is, and also a counters field that contains data about how much
time has been spent in the various states.
Example:
> erlang:statistics(microstate_accounting).
[#{counters => #{aux => 1899182914,
check_io => 2605863602,
emulator => 45731880463,
gc => 1512206910,
other => 5421338456,
port => 221631,
sleep => 5150294100},
id => 1,
type => scheduler}|...]
The time unit is the same as returned by os:perf_counter/0. So,
to convert it to milliseconds, you can do something like this:
lists:map(
fun(#{ counters := Cnt } = M) ->
MsCnt = maps:map(fun(_K, PerfCount) ->
erlang:convert_time_unit(PerfCount, perf_counter, 1000)
end, Cnt),
M#{ counters := MsCnt }
end, erlang:statistics(microstate_accounting)).
Notice that these values are not guaranteed to be the exact time
spent in each state. This is because of various optimisation
done to keep the overhead as small as possible.
MSAcc_Thread_Types:
scheduler:
The main execution threads that do most of the work. See erl
+S for more details.
dirty_cpu_scheduler:
The threads for long running cpu intensive work. See erl
+SDcpu for more details.
dirty_io_scheduler:
The threads for long running I/O work. See erl +SDio for
more details.
async:
Async threads are used by various linked-in drivers (mainly
the file drivers) do offload non-CPU intensive work. See erl
+A for more details.
aux:
Takes care of any work that is not specifically assigned to
a scheduler.
poll:
Does the IO polling for the emulator. See erl +IOt for more
details.
The following MSAcc_Thread_States are available. All states are
exclusive, meaning that a thread cannot be in two states at
once. So, if you add the numbers of all counters in a thread,
you get the total runtime for that thread.
aux:
Time spent handling auxiliary jobs.
check_io:
Time spent checking for new I/O events.
emulator:
Time spent executing Erlang processes.
gc:
Time spent doing garbage collection. When extra states are
enabled this is the time spent doing non-fullsweep garbage
collections.
other:
Time spent doing unaccounted things.
port:
Time spent executing ports.
sleep:
Time spent sleeping.
More fine-grained MSAcc_Thread_States can be added through con-
figure (such as ./configure --with-microstate-accounting=extra).
Enabling these states causes performance degradation when
microstate accounting is turned off and increases the overhead
when it is turned on.
alloc:
Time spent managing memory. Without extra states this time
is spread out over all other states.
bif:
Time spent in BIFs. Without extra states this time is part
of the emulator state.
busy_wait:
Time spent busy waiting. This is also the state where a
scheduler no longer reports that it is active when using
statistics(scheduler_wall_time). So, if you add all other
states but this and sleep, and then divide that by all time
in the thread, you should get something very similar to the
scheduler_wall_time fraction. Without extra states this time
is part of the other state.
ets:
Time spent executing ETS BIFs. Without extra states this
time is part of the emulator state.
gc_full:
Time spent doing fullsweep garbage collection. Without extra
states this time is part of the gc state.
nif:
Time spent in NIFs. Without extra states this time is part
of the emulator state.
send:
Time spent sending messages (processes only). Without extra
states this time is part of the emulator state.
timers:
Time spent managing timers. Without extra states this time
is part of the other state.
The utility module msacc(3) can be used to more easily analyse
these statistics.
Returns undefined if system flag microstate_accounting is turned
off.
The list of thread information is unsorted and can appear in
different order between calls.
Note:
The threads and states are subject to change without any prior
notice.
statistics(Item :: reductions) ->
{Total_Reductions, Reductions_Since_Last_Call}
Types:
Total_Reductions = Reductions_Since_Last_Call = integer() >=
0
Returns information about reductions, for example:
> statistics(reductions).
{2046,11}
Note:
As from ERTS 5.5 (Erlang/OTP R11B), this value does not include
reductions performed in current time slices of currently sched-
uled processes. If an exact value is wanted, use statis-
tics(exact_reductions).
statistics(Item :: run_queue) -> integer() >= 0
Returns the total length of all normal and dirty CPU run queues.
That is, queued work that is expected to be CPU bound. The
information is gathered atomically. That is, the result is a
consistent snapshot of the state, but this operation is much
more expensive compared to statistics(total_run_queue_lengths),
especially when a large amount of schedulers is used.
statistics(Item :: run_queue_lengths) -> [RunQueueLength]
Types:
RunQueueLength = integer() >= 0
Returns the same as statistics(run_queue_lengths_all) with the
exception that no information about the dirty IO run queue is
part of the result. That is, only run queues with work that is
expected to be CPU bound is part of the result.
statistics(Item :: run_queue_lengths_all) -> [RunQueueLength]
Types:
RunQueueLength = integer() >= 0
Returns a list where each element represents the amount of pro-
cesses and ports ready to run for each run queue. Values for
normal run queues are located first in the resulting list. The
first element corresponds to the normal run queue of scheduler
number 1 and so on. If support for dirty schedulers exist, val-
ues for the dirty CPU run queue and the dirty IO run queue fol-
low (in that order) at the end. The information is not gathered
atomically. That is, the result is not necessarily a consistent
snapshot of the state, but instead quite efficiently gathered.
Note:
Each normal scheduler has one run queue that it manages. If
dirty schedulers schedulers are supported, all dirty CPU sched-
ulers share one run queue, and all dirty IO schedulers share one
run queue. That is, we have multiple normal run queues, one
dirty CPU run queue and one dirty IO run queue. Work can not
migrate between the different types of run queues. Only work in
normal run queues can migrate to other normal run queues. This
has to be taken into account when evaluating the result.
See also statistics(run_queue_lengths), statis-
tics(total_run_queue_lengths_all), statis-
tics(total_run_queue_lengths), statistics(active_tasks), statis-
tics(active_tasks_all), and statistics(total_active_tasks), sta-
tistics(total_active_tasks_all).
statistics(Item :: runtime) ->
{Total_Run_Time, Time_Since_Last_Call}
Types:
Total_Run_Time = Time_Since_Last_Call = integer() >= 0
Returns information about runtime, in milliseconds.
This is the sum of the runtime for all threads in the Erlang
runtime system and can therefore be greater than the wall clock
time.
Warning:
This value might wrap due to limitations in the underlying func-
tionality provided by the operating system that is used.
Example:
> statistics(runtime).
{1690,1620}
statistics(Item :: scheduler_wall_time) ->
[{SchedulerId, ActiveTime, TotalTime}] | undefined
Types:
SchedulerId = integer() >= 1
ActiveTime = TotalTime = integer() >= 0
Returns information describing how much time normal and dirty
CPU schedulers in the system have been busy. This value is nor-
mally a better indicator of how much load an Erlang node is
under instead of looking at the CPU utilization privided by
tools such as top or sysstat. This is because sched-
uler_wall_time also includes time where the scheduler is waiting
for some other reasource (such as an internal mutex) to be
available but does not use the CPU. In order to better under-
stand what a scheduler is busy doing you can use microstate
accounting.
The definition of a busy scheduler is when it is not idle and
not busy waiting for new work, that is:
* Executing process code
* Executing linked-in driver or NIF code
* Executing BIFs, or any other runtime handling
* Garbage collecting
* Handling any other memory management
Notice that a scheduler can also be busy even if the OS has
scheduled out the scheduler thread.
Note:
It is recommended to use the module scheduler instead of this
function directly as it provides an easier way to get the infor-
mation that you usually want.
If enabled this function returns a list of tuples with {Schedu-
lerId, ActiveTime, TotalTime}, where SchedulerId is an integer
ID of the scheduler, ActiveTime is the duration the scheduler
has been busy, and TotalTime is the total time duration since
scheduler_wall_time activation for the specific scheduler. The
time unit returned is undefined and can be subject to change
between releases, OSs, and system restarts. scheduler_wall_time
is only to be used to calculate relative values for scheduler
utilization. The ActiveTime can never exceed TotalTime. The list
of scheduler information is unsorted and can appear in different
order between calls.
The disabled this function returns undefined.
The activation time can differ significantly between schedulers.
Currently dirty schedulers are activated at system start while
normal schedulers are activated some time after the sched-
uler_wall_time functionality is enabled.
Only information about schedulers that are expected to handle
CPU bound work is included in the return values from this func-
tion. If you also want information about dirty I/O schedulers,
use statistics(scheduler_wall_time_all) instead.
Normal schedulers will have scheduler identifiers in the range 1
=< SchedulerId =< erlang:system_info(schedulers). Dirty CPU
schedulers will have scheduler identifiers in the range
erlang:system_info(schedulers) < SchedulerId =< erlang:sys-
tem_info(schedulers) + erlang:system_info(dirty_cpu_schedulers).
Note:
The different types of schedulers handle specific types of jobs.
Every job is assigned to a specific scheduler type. Jobs can
migrate between different schedulers of the same type, but never
between schedulers of different types. This fact has to be taken
under consideration when evaluating the result returned.
You can use scheduler_wall_time to calculate scheduler utiliza-
tion. First you take a sample of the values returned by
erlang:statistics(scheduler_wall_time).
> erlang:system_flag(scheduler_wall_time, true).
false
> Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.
ok
Some time later the user takes another snapshot and calculates
scheduler utilization per scheduler, for example:
> Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.
ok
> lists:map(fun({{I, A0, T0}, {I, A1, T1}}) -> {I, (A1 - A0)/(T1 - T0)} end, lists:zip(Ts0,Ts1)).
[{1,0.9743474730177548},
{2,0.9744843782751444},
{3,0.9995902361669045},
{4,0.9738012596572161},
{5,0.9717956667018103},
{6,0.9739235846420741},
{7,0.973237033077876},
{8,0.9741297293248656}]
Using the same snapshots to calculate a total scheduler utiliza-
tion:
> {A, T} = lists:foldl(fun({{_, A0, T0}, {_, A1, T1}}, {Ai,Ti}) -> {Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)), TotalSchedulerUtilization = A/T.
0.9769136803764825
Total scheduler utilization will equal 1.0 when all schedulers
have been active all the time between the two measurements.
Another (probably more) useful value is to calculate total
scheduler utilization weighted against maximum amount of avail-
able CPU time:
> WeightedSchedulerUtilization = (TotalSchedulerUtilization * (erlang:system_info(schedulers) + erlang:system_info(dirty_cpu_schedulers))) / erlang:system_info(logical_processors_available).
0.9769136803764825
This weighted scheduler utilization will reach 1.0 when sched-
ulers are active the same amount of time as maximum available
CPU time. If more schedulers exist than available logical pro-
cessors, this value may be greater than 1.0.
As of ERTS version 9.0, the Erlang runtime system will as
default have more schedulers than logical processors. This due
to the dirty schedulers.
Note:
scheduler_wall_time is by default disabled. To enable it, use
erlang:system_flag(scheduler_wall_time, true).
statistics(Item :: scheduler_wall_time_all) ->
[{SchedulerId, ActiveTime, TotalTime}] | undefined
Types:
SchedulerId = integer() >= 1
ActiveTime = TotalTime = integer() >= 0
The same as statistics(scheduler_wall_time), except that it also
include information about all dirty I/O schedulers.
Dirty IO schedulers will have scheduler identifiers in the range
erlang:system_info(schedulers) + erlang:sys-
tem_info(dirty_cpu_schedulers) < SchedulerId =< erlang:sys-
tem_info(schedulers) + erlang:system_info(dirty_cpu_schedulers)
+ erlang:system_info(dirty_io_schedulers).
Note:
Note that work executing on dirty I/O schedulers are expected to
mainly wait for I/O. That is, when you get high scheduler uti-
lization on dirty I/O schedulers, CPU utilization is not
expected to be high due to this work.
statistics(Item :: total_active_tasks) -> ActiveTasks
Types:
ActiveTasks = integer() >= 0
The same as calling lists:sum(statistics(active_tasks)), but
more efficient.
statistics(Item :: total_active_tasks_all) -> ActiveTasks
Types:
ActiveTasks = integer() >= 0
The same as calling lists:sum(statistics(active_tasks_all)), but
more efficient.
statistics(Item :: total_run_queue_lengths) ->
TotalRunQueueLengths
Types:
TotalRunQueueLengths = integer() >= 0
The same as calling lists:sum(statistics(run_queue_lengths)),
but more efficient.
statistics(Item :: total_run_queue_lengths_all) ->
TotalRunQueueLengths
Types:
TotalRunQueueLengths = integer() >= 0
The same as calling lists:sum(statis-
tics(run_queue_lengths_all)), but more efficient.
statistics(Item :: wall_clock) ->
{Total_Wallclock_Time,
Wallclock_Time_Since_Last_Call}
Types:
Total_Wallclock_Time = Wallclock_Time_Since_Last_Call = inte-
ger() >= 0
Returns information about wall clock. wall_clock can be used in
the same manner as runtime, except that real time is measured as
opposed to runtime or CPU time.
erlang:suspend_process(Suspendee) -> true
Types:
Suspendee = pid()
Suspends the process identified by Suspendee. The same as call-
ing erlang:suspend_process(Suspendee, []).
Warning:
This BIF is intended for debugging only.
erlang:suspend_process(Suspendee, OptList) -> boolean()
Types:
Suspendee = pid()
OptList = [Opt]
Opt = unless_suspending | asynchronous | {asynchronous,
term()}
Increases the suspend count on the process identified by Sus-
pendee and puts it in the suspended state if it is not already
in that state. A suspended process is not scheduled for execu-
tion until the process has been resumed.
A process can be suspended by multiple processes and can be sus-
pended multiple times by a single process. A suspended process
does not leave the suspended state until its suspend count
reaches zero. The suspend count of Suspendee is decreased when
erlang:resume_process(Suspendee) is called by the same process
that called erlang:suspend_process(Suspendee). All increased
suspend counts on other processes acquired by a process are
automatically decreased when the process terminates.
Options (Opts):
asynchronous:
A suspend request is sent to the process identified by Sus-
pendee. Suspendee eventually suspends unless it is resumed
before it could suspend. The caller of erlang:sus-
pend_process/2 returns immediately, regardless of whether
Suspendee has suspended yet or not. The point in time when
Suspendee suspends cannot be deduced from other events in
the system. It is only guaranteed that Suspendee eventually
suspends (unless it is resumed). If no asynchronous options
has been passed, the caller of erlang:suspend_process/2 is
blocked until Suspendee has suspended.
{asynchronous, ReplyTag}:
A suspend request is sent to the process identified by Sus-
pendee. When the suspend request has been processed, a reply
message is sent to the caller of this function. The reply is
on the form {ReplyTag, State} where State is either:
exited:
Suspendee has exited.
suspended:
Suspendee is now suspended.
not_suspended:
Suspendee is not suspended. This can only happen when the
process that issued this request, have called
resume_process(Suspendee) before getting the reply.
Appart from the reply message, the {asynchronous, ReplyTag}
option behaves exactly the same as the asynchronous option
without reply tag.
unless_suspending:
The process identified by Suspendee is suspended unless the
calling process already is suspending Suspendee. If
unless_suspending is combined with option asynchronous, a
suspend request is sent unless the calling process already
is suspending Suspendee or if a suspend request already has
been sent and is in transit. If the calling process already
is suspending Suspendee, or if combined with option asyn-
chronous and a send request already is in transit, false is
returned and the suspend count on Suspendee remains
unchanged.
If the suspend count on the process identified by Suspendee is
increased, true is returned, otherwise false.
Warning:
This BIF is intended for debugging only.
Warning:
You can easily create deadlocks if processes suspends each other
(directly or in circles). In ERTS versions prior to ERTS version
10.0, the runtime system prevented such deadlocks, but this pre-
vention has now been removed due to performance reasons.
Failures:
badarg:
If Suspendee is not a process identifier.
badarg:
If the process identified by Suspendee is the same process
as the process calling erlang:suspend_process/2.
badarg:
If the process identified by Suspendee is not alive.
badarg:
If the process identified by Suspendee resides on another
node.
badarg:
If OptList is not a proper list of valid Opts.
system_limit:
If the process identified by Suspendee has been suspended
more times by the calling process than can be represented by
the currently used internal data structures. The system
limit is greater than 2,000,000,000 suspends and will never
be lower.
erlang:system_flag(Flag :: backtrace_depth, Depth) -> OldDepth
Types:
Depth = OldDepth = integer() >= 0
Sets the maximum depth of call stack back-traces in the exit
reason element of 'EXIT' tuples. The flag also limits the stack-
trace depth returned by process_info item current_stacktrace.
Returns the old value of the flag.
erlang:system_flag(Flag :: cpu_topology, CpuTopology) ->
OldCpuTopology
Types:
CpuTopology = OldCpuTopology = cpu_topology()
cpu_topology() = [LevelEntry :: level_entry()] | undefined
level_entry() =
{LevelTag :: level_tag(), SubLevel :: sub_level()} |
{LevelTag :: level_tag(),
InfoList :: info_list(),
SubLevel :: sub_level()}
level_tag() = core | node | processor | thread
sub_level() =
[LevelEntry :: level_entry()] |
(LogicalCpuId :: {logical, integer() >= 0})
info_list() = []
Warning:
This argument is deprecated. Instead of using this argument, use
command-line argument +sct in erl(1).
When this argument is removed, a final CPU topology to use is
determined at emulator boot time.
Sets the user-defined CpuTopology. The user-defined CPU topology
overrides any automatically detected CPU topology. By passing
undefined as CpuTopology, the system reverts to the CPU topology
automatically detected. The returned value equals the value
returned from erlang:system_info(cpu_topology) before the change
was made.
Returns the old value of the flag.
The CPU topology is used when binding schedulers to logical pro-
cessors. If schedulers are already bound when the CPU topology
is changed, the schedulers are sent a request to rebind accord-
ing to the new CPU topology.
The user-defined CPU topology can also be set by passing com-
mand-line argument +sct to erl(1).
For information on type CpuTopology and more, see erlang:sys-
tem_info(cpu_topology) as well as command-line flags +sct and
+sbt in erl(1).
erlang:system_flag(Flag :: dirty_cpu_schedulers_online,
DirtyCPUSchedulersOnline) ->
OldDirtyCPUSchedulersOnline
Types:
DirtyCPUSchedulersOnline = OldDirtyCPUSchedulersOnline =
integer() >= 1
Sets the number of dirty CPU schedulers online. Range is 1 <=
DirtyCPUSchedulersOnline <= N, where N is the smallest of the
return values of erlang:system_info(dirty_cpu_schedulers) and
erlang:system_info(schedulers_online).
Returns the old value of the flag.
The number of dirty CPU schedulers online can change if the num-
ber of schedulers online changes. For example, if 12 schedulers
and 6 dirty CPU schedulers are online, and system_flag/2 is used
to set the number of schedulers online to 6, then the number of
dirty CPU schedulers online is automatically decreased by half
as well, down to 3. Similarly, the number of dirty CPU sched-
ulers online increases proportionally to increases in the number
of schedulers online.
For more information, see erlang:system_info(dirty_cpu_sched-
ulers) and erlang:system_info(dirty_cpu_schedulers_online).
erlang:system_flag(Flag :: erts_alloc, Value :: {Alloc, F, V}) ->
ok | notsup
Types:
Alloc = F = atom()
V = integer()
Sets system flags for erts_alloc(3). Alloc is the allocator to
affect, for example binary_alloc. F is the flag to change and V
is the new value.
Only a subset of all erts_alloc flags can be changed at run
time. This subset is currently only the flag sbct.
Returns ok if the flag was set or notsup if not supported by
erts_alloc.
erlang:system_flag(Flag :: fullsweep_after, Number) -> OldNumber
Types:
Number = OldNumber = integer() >= 0
Sets system flag fullsweep_after. Number is a non-negative inte-
ger indicating how many times generational garbage collections
can be done without forcing a fullsweep collection. The value
applies to new processes, while processes already running are
not affected.
Returns the old value of the flag.
In low-memory systems (especially without virtual memory), set-
ting the value to 0 can help to conserve memory.
This value can also be set through (OS) environment variable
ERL_FULLSWEEP_AFTER.
erlang:system_flag(Flag :: microstate_accounting, Action) ->
OldState
Types:
Action = true | false | reset
OldState = true | false
Turns on/off microstate accounting measurements. When passing
reset, all counters are reset to 0.
For more information see statistics(microstate_accounting).
erlang:system_flag(Flag :: min_heap_size, MinHeapSize) ->
OldMinHeapSize
Types:
MinHeapSize = OldMinHeapSize = integer() >= 0
Sets the default minimum heap size for processes. The size is
specified in words. The new min_heap_size effects only processes
spawned after the change of min_heap_size has been made.
min_heap_size can be set for individual processes by using
spawn_opt/4 or process_flag/2.
Returns the old value of the flag.
erlang:system_flag(Flag :: min_bin_vheap_size, MinBinVHeapSize) ->
OldMinBinVHeapSize
Types:
MinBinVHeapSize = OldMinBinVHeapSize = integer() >= 0
Sets the default minimum binary virtual heap size for processes.
The size is specified in words. The new min_bin_vhheap_size
effects only processes spawned after the change of
min_bin_vheap_size has been made. min_bin_vheap_size can be set
for individual processes by using spawn_opt/2,3,4 or
process_flag/2.
Returns the old value of the flag.
erlang:system_flag(Flag :: max_heap_size, MaxHeapSize) ->
OldMaxHeapSize
Types:
MaxHeapSize = OldMaxHeapSize = max_heap_size()
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
Sets the default maximum heap size settings for processes. The
size is specified in words. The new max_heap_size effects only
processes spawned efter the change has been made. max_heap_size
can be set for individual processes using spawn_opt/2,3,4 or
process_flag/2.
Returns the old value of the flag.
erlang:system_flag(Flag :: multi_scheduling, BlockState) ->
OldBlockState
Types:
BlockState = block | unblock | block_normal | unblock_normal
OldBlockState = blocked | disabled | enabled
If multi-scheduling is enabled, more than one scheduler thread
is used by the emulator. Multi-scheduling can be blocked in two
different ways. Either all schedulers but one is blocked, or all
normal schedulers but one is blocked. When only normal sched-
ulers are blocked, dirty schedulers are free to continue to
schedule processes.
If BlockState =:= block, multi-scheduling is blocked. That is,
one and only one scheduler thread will execute. If BlockState
=:= unblock and no one else blocks multi-scheduling, and this
process has blocked only once, multi-scheduling is unblocked.
If BlockState =:= block_normal, normal multi-scheduling is
blocked. That is, only one normal scheduler thread will execute,
but multiple dirty schedulers can execute. If BlockState =:=
unblock_normal and no one else blocks normal multi-scheduling,
and this process has blocked only once, normal multi-scheduling
is unblocked.
One process can block multi-scheduling and normal multi-schedul-
ing multiple times. If a process has blocked multiple times, it
must unblock exactly as many times as it has blocked before it
has released its multi-scheduling block. If a process that has
blocked multi-scheduling or normal multi-scheduling exits, it
automatically releases its blocking of multi-scheduling and nor-
mal multi-scheduling.
The return values are disabled, blocked, blocked_normal, or
enabled. The returned value describes the state just after the
call to erlang:system_flag(multi_scheduling, BlockState) has
been made. For information about the return values, see
erlang:system_info(multi_scheduling).
Note:
Blocking of multi-scheduling and normal multi-scheduling is nor-
mally not needed. If you feel that you need to use these fea-
tures, consider it a few more times again. Blocking multi-sched-
uling is only to be used as a last resort, as it is most likely
a very inefficient way to solve the problem.
See also erlang:system_info(multi_scheduling), erlang:sys-
tem_info(normal_multi_scheduling_blockers), erlang:sys-
tem_info(multi_scheduling_blockers), and erlang:sys-
tem_info(schedulers).
erlang:system_flag(Flag :: outstanding_system_requests_limit,
NewLimit) ->
OldLimit
Types:
NewLimit = OldLimit = 1..134217727
Sets a limit on the amount of outstanding requests made by a
system process orchestrating system wide changes. Currently
there are two such processes:
The Code Purger:
The code purger orchestrates checking of references to old
code before old code is removed from the system.
The Literal Area Collector:
The literal area collector orchestrates copying of refer-
ences from old literal areas before removal of such areas
from the system.
Each of these processes are allowed to have as many outstanding
requests as this limit is set to. By default this limit is set
to twice the amount of schedulers on the system. This will
ensure that schedulers will have enough work scheduled to per-
form these operations as quickly as possible at the same time as
other work will be interleaved with this work. Currently used
limit can be checked by calling erlang:system_info(outstand-
ing_system_requests_limit).
This limit can also be set by passing the command line argument
+zosrl <Limit> to erl.
erlang:system_flag(Flag :: scheduler_bind_type, How) ->
OldBindType
Types:
How = scheduler_bind_type() | default_bind
OldBindType = scheduler_bind_type()
scheduler_bind_type() =
no_node_processor_spread | no_node_thread_spread | no_spread |
processor_spread | spread | thread_spread |
thread_no_node_processor_spread | unbound
Warning:
This argument is deprecated. Instead of using this argument, use
command-line argument +sbt in erl(1). When this argument is
removed, a final scheduler bind type to use is determined at
emulator boot time.
Controls if and how schedulers are bound to logical processors.
When erlang:system_flag(scheduler_bind_type, How) is called, an
asynchronous signal is sent to all schedulers online, causing
them to try to bind or unbind as requested.
Note:
If a scheduler fails to bind, this is often silently ignored, as
it is not always possible to verify valid logical processor
identifiers. If an error is reported, an error event is logged.
To verify that the schedulers have bound as requested, call
erlang:system_info(scheduler_bindings).
Schedulers can be bound on newer Linux, Solaris, FreeBSD, and
Windows systems, but more systems will be supported in future
releases.
In order for the runtime system to be able to bind schedulers,
the CPU topology must be known. If the runtime system fails to
detect the CPU topology automatically, it can be defined. For
more information on how to define the CPU topology, see command-
line flag +sct in erl(1).
The runtime system does by default not bind schedulers to logi-
cal processors.
Note:
If the Erlang runtime system is the only OS process binding
threads to logical processors, this improves the performance of
the runtime system. However, if other OS processes (for example,
another Erlang runtime system) also bind threads to logical pro-
cessors, there can be a performance penalty instead. Sometimes
this performance penalty can be severe. If so, it is recommended
to not bind the schedulers.
Schedulers can be bound in different ways. Argument How deter-
mines how schedulers are bound and can be any of the following:
unbound:
Same as command-line argument +sbt u in erl(1).
no_spread:
Same as command-line argument +sbt ns in erl(1).
thread_spread:
Same as command-line argument +sbt ts in erl(1).
processor_spread:
Same as command-line argument +sbt ps in erl(1).
spread:
Same as command-line argument +sbt s in erl(1).
no_node_thread_spread:
Same as command-line argument +sbt nnts in erl(1).
no_node_processor_spread:
Same as command-line argument +sbt nnps in erl(1).
thread_no_node_processor_spread:
Same as command-line argument +sbt tnnps in erl(1).
default_bind:
Same as command-line argument +sbt db in erl(1).
The returned value equals How before flag scheduler_bind_type
was changed.
Failures:
notsup:
If binding of schedulers is not supported.
badarg:
If How is not one of the documented alternatives.
badarg:
If CPU topology information is unavailable.
The scheduler bind type can also be set by passing command-line
argument +sbt to erl(1).
For more information, see erlang:system_info(sched-
uler_bind_type), erlang:system_info(scheduler_bindings), as well
as command-line flags +sbt and +sct in erl(1).
erlang:system_flag(Flag :: scheduler_wall_time, Boolean) ->
OldBoolean
Types:
Boolean = OldBoolean = boolean()
Turns on or off scheduler wall time measurements.
For more information, see statistics(scheduler_wall_time).
erlang:system_flag(Flag :: schedulers_online, SchedulersOnline) ->
OldSchedulersOnline
Types:
SchedulersOnline = OldSchedulersOnline = integer() >= 1
Sets the number of schedulers online. Range is 1 <= Scheduler-
sOnline <= erlang:system_info(schedulers).
Returns the old value of the flag.
If the emulator was built with support for dirty schedulers,
changing the number of schedulers online can also change the
number of dirty CPU schedulers online. For example, if 12 sched-
ulers and 6 dirty CPU schedulers are online, and system_flag/2
is used to set the number of schedulers online to 6, then the
number of dirty CPU schedulers online is automatically decreased
by half as well, down to 3. Similarly, the number of dirty CPU
schedulers online increases proportionally to increases in the
number of schedulers online.
For more information, see erlang:system_info(schedulers) and
erlang:system_info(schedulers_online).
erlang:system_flag(Flag :: system_logger, Logger) -> PrevLogger
Types:
Logger = PrevLogger = logger | undefined | pid()
Sets the process that will receive the logging messages gener-
ated by ERTS. If set to undefined, all logging messages gener-
ated by ERTS will be dropped. The messages will be in the for-
mat:
{log,Level,Format,ArgList,Metadata} where
Level = atom(),
Format = string(),
ArgList = list(term()),
Metadata = #{ pid => pid(),
group_leader => pid(),
time := logger:timestamp(),
error_logger := #{ emulator := true, tag := atom() }
If the system_logger process dies, this flag will be reset to
logger.
The default is the process named logger.
Returns the old value of the flag.
Note:
This function is designed to be used by the KERNEL logger. Be
careful if you change it to something else as log messages may
be lost. If you want to intercept emulator log messages, do it
by adding a specialized handler to the KERNEL logger.
erlang:system_flag(Flag :: trace_control_word, TCW) -> OldTCW
Types:
TCW = OldTCW = integer() >= 0
Sets the value of the node trace control word to TCW, which is
to be an unsigned integer. For more information, see function
set_tcw in section "Match Specifications in Erlang" in the
User's Guide.
Returns the old value of the flag.
erlang:system_flag(Flag :: time_offset, Value :: finalize) ->
OldState
Types:
OldState = preliminary | final | volatile
Finalizes the time offset when single time warp mode is used. If
another time warp mode is used, the time offset state is left
unchanged.
Returns the old state identifier, that is:
* If preliminary is returned, finalization was performed and
the time offset is now final.
* If final is returned, the time offset was already in the
final state. This either because another erlang:sys-
tem_flag(time_offset, finalize) call or because no time warp
mode is used.
* If volatile is returned, the time offset cannot be finalized
because multi-time warp mode is used.
erlang:system_info(Item :: update_cpu_info) -> changed | unchanged
Returns information about the current system. The documentation
of this function is broken into the following sections in order
to make it easier to navigate.
Memory Allocation:
allocated_areas, allocator, alloc_util_allocators, alloca-
tor_sizes
CPU Topology:
cpu_topology, logical_processors, update_cpu_info
Process Information:
fullsweep_after, garbage_collection, heap_sizes, heap_type,
max_heap_size, message_queue_data, min_heap_size,
min_bin_vheap_size, procs
System Limits:
atom_count, atom_limit, ets_count, ets_limit, port_count,
port_limit, process_count, process_limit
System Time:
end_time, os_monotonic_time_source, os_system_time_source,
start_time, time_correction, time_offset, time_warp_mode,
tolerant_timeofday
Scheduler Information:
dirty_cpu_schedulers, dirty_cpu_schedulers_online,
dirty_io_schedulers, multi_scheduling, multi_schedul-
ing_blockers, normal_multi_scheduling_blockers, sched-
uler_bind_type, scheduler_bindings, scheduler_id, sched-
ulers, smp_support, threads, thread_pool_size
Distribution Information:
creation, delayed_node_table_gc, dist, dist_buf_busy_limit,
dist_ctrl
System Information:
c_compiler_used, check_io, compat_rel, debug_compiled,
driver_version, dynamic_trace, dynamic_trace_probes,
emu_flavor, emu_type, info, kernel_poll, loaded, machine,
modified_timing_level, nif_version, otp_release, outstand-
ing_system_requests_limit, port_parallelism, system_archi-
tecture, system_logger, system_version, trace_control_word,
version, wordsize
erlang:system_info(Item :: allocated_areas) -> [tuple()]
erlang:system_info(Item :: allocator) ->
{Allocator, Version, Features, Settings}
erlang:system_info(Item :: {allocator, Alloc}) -> [term()]
erlang:system_info(Item :: alloc_util_allocators) -> [Alloc]
erlang:system_info(Item :: {allocator_sizes, Alloc}) -> [term()]
Types:
Allocator = undefined | glibc
Version = [integer() >= 0]
Features = [atom()]
Settings =
[{Subsystem :: atom(),
[{Parameter :: atom(), Value :: term()}]}]
Alloc = atom()
Returns various information about the memory allocators of the
current system (emulator) as specified by Item:
allocated_areas:
Returns a list of tuples with information about miscella-
neous allocated memory areas.
Each tuple contains an atom describing the type of memory as
first element and the amount of allocated memory in bytes as
second element. When information about allocated and used
memory is present, also a third element is present, contain-
ing the amount of used memory in bytes.
erlang:system_info(allocated_areas) is intended for debug-
ging, and the content is highly implementation-dependent.
The content of the results therefore changes when needed
without prior notice.
Notice that the sum of these values is not the total amount
of memory allocated by the emulator. Some values are part of
other values, and some memory areas are not part of the
result. For information about the total amount of memory
allocated by the emulator, see erlang:memory/0,1.
allocator:
Returns {Allocator, Version, Features, Settings, where:
* Allocator corresponds to the malloc() implementation used.
If Allocator equals undefined, the malloc() implementation
used cannot be identified. glibc can be identified.
* Version is a list of integers (but not a string) repre-
senting the version of the malloc() implementation used.
* Features is a list of atoms representing the allocation
features used.
* Settings is a list of subsystems, their configurable
parameters, and used values. Settings can differ between
different combinations of platforms, allocators, and allo-
cation features. Memory sizes are given in bytes.
See also "System Flags Effecting erts_alloc" in
erts_alloc(3).
{allocator, Alloc}:
Returns information about the specified allocator. As from
ERTS 5.6.1, the return value is a list of {instance, Instan-
ceNo, InstanceInfo} tuples, where InstanceInfo contains
information about a specific instance of the allocator. If
Alloc is not a recognized allocator, undefined is returned.
If Alloc is disabled, false is returned.
Notice that the information returned is highly implementa-
tion-dependent and can be changed or removed at any time
without prior notice. It was initially intended as a tool
when developing new allocators, but as it can be of interest
for others it has been briefly documented.
The recognized allocators are listed in erts_alloc(3).
Information about super carriers can be obtained from ERTS
8.0 with {allocator, erts_mmap} or from ERTS 5.10.4; the
returned list when calling with {allocator, mseg_alloc} also
includes an {erts_mmap, _} tuple as one element in the list.
After reading the erts_alloc(3) documentation, the returned
information more or less speaks for itself, but it can be
worth explaining some things. Call counts are presented by
two values, the first value is giga calls, and the second
value is calls. mbcs and sbcs denote multi-block carriers,
and single-block carriers, respectively. Sizes are presented
in bytes. When a size is not presented, it is the amount of
something. Sizes and amounts are often presented by three
values:
* The first is the current value.
* The second is the maximum value since the last call to
erlang:system_info({allocator, Alloc}).
* The third is the maximum value since the emulator was
started.
If only one value is present, it is the current value.
fix_alloc memory block types are presented by two values.
The first value is the memory pool size and the second value
is the used memory size.
alloc_util_allocators:
Returns a list of the names of all allocators using the ERTS
internal alloc_util framework as atoms. For more informa-
tion, see section The alloc_util framework in erts_alloc(3).
{allocator_sizes, Alloc}:
Returns various size information for the specified alloca-
tor. The information returned is a subset of the information
returned by erlang:system_info({allocator, Alloc}).
erlang:system_info(Item :: cpu_topology) -> CpuTopology
erlang:system_info(Item ::
{cpu_topology, defined | detected | used}) ->
CpuTopology
erlang:system_info(Item ::
logical_processors |
logical_processors_available |
logical_processors_online) ->
unknown | integer() >= 1
erlang:system_info(Item :: trace_control_word) ->
integer() >= 0
Types:
cpu_topology() = [LevelEntry :: level_entry()] | undefined
All LevelEntrys of a list must contain the same LevelTag,
except on the top level where both node and processor-
LevelTags can coexist.
level_entry() =
{LevelTag :: level_tag(), SubLevel :: sub_level()} |
{LevelTag :: level_tag(),
InfoList :: info_list(),
SubLevel :: sub_level()}
{LevelTag, SubLevel} == {LevelTag, [], SubLevel}
level_tag() = core | node | processor | thread
More LevelTags can be introduced in a future release.
sub_level() =
[LevelEntry :: level_entry()] |
(LogicalCpuId :: {logical, integer() >= 0})
info_list() = []
The info_list() can be extended in a future release.
Returns various information about the CPU topology of the cur-
rent system (emulator) as specified by Item:
cpu_topology:
Returns the CpuTopology currently used by the emulator. The
CPU topology is used when binding schedulers to logical pro-
cessors. The CPU topology used is the user-defined CPU
topology, if such exists, otherwise the automatically
detected CPU topology, if such exists. If no CPU topology
exists, undefined is returned.
node refers to Non-Uniform Memory Access (NUMA) nodes.
thread refers to hardware threads (for example, Intel hyper-
threads).
A level in term CpuTopology can be omitted if only one entry
exists and InfoList is empty.
thread can only be a sublevel to core. core can be a sub-
level to processor or node. processor can be on the top
level or a sublevel to node. node can be on the top level or
a sublevel to processor. That is, NUMA nodes can be proces-
sor internal or processor external. A CPU topology can con-
sist of a mix of processor internal and external NUMA nodes,
as long as each logical CPU belongs to one NUMA node. Cache
hierarchy is not part of the CpuTopology type, but will be
in a future release. Other things can also make it into the
CPU topology in a future release. So, expect the CpuTopology
type to change.
{cpu_topology, defined}:
Returns the user-defined CpuTopology. For more information,
see command-line flag +sct in erl(1) and argument cpu_topol-
ogy.
{cpu_topology, detected}:
Returns the automatically detected CpuTopologyy. The emula-
tor detects the CPU topology on some newer Linux, Solaris,
FreeBSD, and Windows systems. On Windows system with more
than 32 logical processors, the CPU topology is not
detected.
For more information, see argument cpu_topology.
{cpu_topology, used}:
Returns CpuTopology used by the emulator. For more informa-
tion, see argument cpu_topology.
logical_processors:
Returns the detected number of logical processors configured
in the system. The return value is either an integer, or the
atom unknown if the emulator cannot detect the configured
logical processors.
logical_processors_available:
Returns the detected number of logical processors available
to the Erlang runtime system. The return value is either an
integer, or the atom unknown if the emulator cannot detect
the available logical processors. The number of available
logical processors is less than or equal to the number of
logical processors online.
logical_processors_online:
Returns the detected number of logical processors online on
the system. The return value is either an integer, or the
atom unknown if the emulator cannot detect logical proces-
sors online. The number of logical processors online is less
than or equal to the number of logical processors config-
ured.
cpu_quota:
Returns the detected CPU quota the emulator is limited by.
The return value is an integer saying how many processors'
worth of runtime we get (between 1 and the number of logical
processors), or the atom unknown if the emulator cannot
detect a quota.
update_cpu_info:
The runtime system rereads the CPU information available and
updates its internally stored information about the detected
CPU topology and the number of logical processors config-
ured, online, available, and cpu quota.
If the CPU information has changed since the last time it
was read, the atom changed is returned, otherwise the atom
unchanged. If the CPU information has changed, you probably
want to adjust the number of schedulers online. You typi-
cally want to have as many schedulers online as logical pro-
cessors available.
erlang:system_info(Item :: fullsweep_after) ->
{fullsweep_after, integer() >= 0}
erlang:system_info(Item :: garbage_collection) ->
[{atom(), integer()}]
erlang:system_info(Item :: heap_sizes) -> [integer() >= 0]
erlang:system_info(Item :: heap_type) -> private
erlang:system_info(Item :: max_heap_size) ->
{max_heap_size,
MaxHeapSize :: max_heap_size()}
erlang:system_info(Item :: message_queue_data) ->
message_queue_data()
erlang:system_info(Item :: min_heap_size) ->
{min_heap_size,
MinHeapSize :: integer() >= 1}
erlang:system_info(Item :: min_bin_vheap_size) ->
{min_bin_vheap_size,
MinBinVHeapSize :: integer() >= 1}
erlang:system_info(Item :: process_limit) -> integer() >= 1
Types:
message_queue_data() = off_heap | on_heap
max_heap_size() =
integer() >= 0 |
#{size => integer() >= 0,
kill => boolean(),
error_logger => boolean()}
Returns information about the default process heap settings:
fullsweep_after:
Returns {fullsweep_after, integer() >= 0}, which is the
fullsweep_after garbage collection setting used by default.
For more information, see garbage_collection described
below.
garbage_collection:
Returns a list describing the default garbage collection
settings. A process spawned on the local node by a spawn or
spawn_link uses these garbage collection settings. The
default settings can be changed by using erlang:sys-
tem_flag/2. spawn_opt/2,3,4 can spawn a process that does
not use the default settings.
heap_sizes:
Returns a list of integers representing valid heap sizes in
words. All Erlang heaps are sized from sizes in this list.
heap_type:
Returns the heap type used by the current emulator. One heap
type exists:
private:
Each process has a heap reserved for its use and no ref-
erences between heaps of different processes are allowed.
Messages passed between processes are copied between
heaps.
max_heap_size:
Returns {max_heap_size, MaxHeapSize}, where MaxHeapSize is
the current system-wide maximum heap size settings for
spawned processes. This setting can be set using the com-
mand-line flags +hmax, +hmaxk and +hmaxel in erl(1). It can
also be changed at runtime using erlang:sys-
tem_flag(max_heap_size, MaxHeapSize). For more details about
the max_heap_size process flag, see
process_flag(max_heap_size, MaxHeapSize).
message_queue_data:
Returns the default value of the message_queue_data process
flag, which can be either off_heap or on_heap. The default
value is set by the command-line argument +hmqd in erl(1).
For more information, see the documentation of
process_flag(message_queue_data, MQD).
min_heap_size:
Returns {min_heap_size, MinHeapSize}, where MinHeapSize is
the current system-wide minimum heap size for spawned pro-
cesses.
min_bin_vheap_size:
Returns {min_bin_vheap_size, MinBinVHeapSize}, where MinBin-
VHeapSize is the current system-wide minimum binary virtual
heap size for spawned processes.
procs:
Returns a binary containing a string of process and port
information formatted as in Erlang crash dumps. For more
information, see section How to interpret the Erlang crash
dumps in the User's Guide.
erlang:system_info(Item :: atom_count) -> integer() >= 1
erlang:system_info(Item :: atom_limit) -> integer() >= 1
erlang:system_info(Item :: ets_count) -> integer() >= 1
erlang:system_info(Item :: ets_limit) -> integer() >= 1
erlang:system_info(Item :: port_parallelism) -> boolean()
erlang:system_info(Item :: port_count) -> integer() >= 0
erlang:system_info(Item :: port_limit) -> integer() >= 1
erlang:system_info(Item :: process_count) -> integer() >= 1
Returns information about the current system (emulator) limits
as specified by Item:
atom_count:
Returns the number of atoms currently existing at the local
node. The value is given as an integer.
atom_limit:
Returns the maximum number of atoms allowed. This limit can
be increased at startup by passing command-line flag +t to
erl(1).
ets_count:
Returns the number of ETS tables currently existing at the
local node.
ets_limit:
Returns the limit for number of ETS tables. This limit is
partially obsolete and number of tables are only limited by
available memory.
port_count:
Returns the number of ports currently existing at the local
node. The value is given as an integer. This is the same
value as returned by length(erlang:ports()), but more effi-
cient.
port_limit:
Returns the maximum number of simultaneously existing ports
at the local node as an integer. This limit can be config-
ured at startup by using command-line flag +Q in erl(1).
process_count:
Returns the number of processes currently existing at the
local node. The value is given as an integer. This is the
same value as returned by length(processes()), but more
efficient.
process_limit:
Returns the maximum number of simultaneously existing pro-
cesses at the local node. The value is given as an integer.
This limit can be configured at startup by using command-
line flag +P in erl(1).
erlang:system_info(Item :: end_time) -> integer() >= 0
erlang:system_info(Item :: os_monotonic_time_source) ->
[{atom(), term()}]
erlang:system_info(Item :: os_system_time_source) ->
[{atom(), term()}]
erlang:system_info(Item :: smp_support) -> boolean()
erlang:system_info(Item :: thread_pool_size) -> integer() >= 0
erlang:system_info(Item :: time_correction) -> true | false
erlang:system_info(Item :: time_offset) ->
preliminary | final | volatile
erlang:system_info(Item :: time_warp_mode) ->
no_time_warp | single_time_warp |
multi_time_warp
Returns information about the current system (emulator) time as
specified by Item:
end_time:
The last Erlang monotonic time in native time unit that can
be represented internally in the current Erlang runtime sys-
tem instance. The time between the start time and the end
time is at least a quarter of a millennium.
os_monotonic_time_source:
Returns a list containing information about the source of OS
monotonic time that is used by the runtime system.
If [] is returned, no OS monotonic time is available. The
list contains two-tuples with Keys as first element, and
Values as second element. The order of these tuples is unde-
fined. The following tuples can be part of the list, but
more tuples can be introduced in the future:
{function, Function}:
Function is the name of the function used. This tuple
always exists if OS monotonic time is available to the
runtime system.
{clock_id, ClockId}:
This tuple only exists if Function can be used with dif-
ferent clocks. ClockId corresponds to the clock identifier
used when calling Function.
{resolution, OsMonotonicTimeResolution}:
Highest possible resolution of current OS monotonic time
source as parts per second. If no resolution information
can be retrieved from the OS, OsMonotonicTimeResolution is
set to the resolution of the time unit of Functions return
value. That is, the actual resolution can be lower than
OsMonotonicTimeResolution. Notice that the resolution does
not say anything about the accuracy or whether the pre-
cision aligns with the resolution. You do, however, know
that the precision is not better than OsMonotonicTimeReso-
lution.
{extended, Extended}:
Extended equals yes if the range of time values has been
extended; otherwise Extended equals no. The range must be
extended if Function returns values that wrap fast. This
typically is the case when the return value is a 32-bit
value.
{parallel, Parallel}:
Parallel equals yes if Function is called in parallel from
multiple threads. If it is not called in parallel, because
calls must be serialized, Parallel equals no.
{time, OsMonotonicTime}:
OsMonotonicTime equals current OS monotonic time in native
time unit.
os_system_time_source:
Returns a list containing information about the source of OS
system time that is used by the runtime system.
The list contains two-tuples with Keys as first element, and
Values as second element. The order of these tuples is unde-
fined. The following tuples can be part of the list, but
more tuples can be introduced in the future:
{function, Function}:
Function is the name of the funcion used.
{clock_id, ClockId}:
Exists only if Function can be used with different clocks.
ClockId corresponds to the clock identifier used when
calling Function.
{resolution, OsSystemTimeResolution}:
Highest possible resolution of current OS system time
source as parts per second. If no resolution information
can be retrieved from the OS, OsSystemTimeResolution is
set to the resolution of the time unit of Functions return
value. That is, the actual resolution can be lower than
OsSystemTimeResolution. Notice that the resolution does
not say anything about the accuracy or whether the pre-
cision do align with the resolution. You do, however, know
that the precision is not better than OsSystemTimeResolu-
tion.
{parallel, Parallel}:
Parallel equals yes if Function is called in parallel from
multiple threads. If it is not called in parallel, because
calls needs to be serialized, Parallel equals no.
{time, OsSystemTime}:
OsSystemTime equals current OS system time in native time
unit.
start_time:
The Erlang monotonic time in native time unit at the time
when current Erlang runtime system instance started.
See also erlang:system_info(end_time).
time_correction:
Returns a boolean value indicating whether time correction
is enabled or not.
time_offset:
Returns the state of the time offset:
preliminary:
The time offset is preliminary, and will be changed and
finalized later. The preliminary time offset is used dur-
ing the preliminary phase of the single time warp mode.
final:
The time offset is final. This either because no time
warp mode is used, or because the time offset have been
finalized when single time warp mode is used.
volatile:
The time offset is volatile. That is, it can change at any
time. This is because multi-time warp mode is used.
time_warp_mode:
Returns a value identifying the time warp mode that is
used:
no_time_warp:
The no time warp mode is used.
single_time_warp:
The single time warp mode is used.
multi_time_warp:
The multi-time warp mode is used.
tolerant_timeofday:
Returns whether a pre ERTS 7.0 backwards compatible compen-
sation for sudden changes of system time is enabled or dis-
abled. Such compensation is enabled when the time offset is
final, and time correction is enabled.
erlang:system_info(Item :: dirty_cpu_schedulers) ->
integer() >= 0
erlang:system_info(Item :: dirty_cpu_schedulers_online) ->
integer() >= 0
erlang:system_info(Item :: dirty_io_schedulers) ->
integer() >= 0
erlang:system_info(Item :: multi_scheduling) ->
disabled | blocked | blocked_normal |
enabled
erlang:system_info(Item :: multi_scheduling_blockers) ->
[Pid :: pid()]
erlang:system_info(Item :: normal_multi_scheduling_blockers) ->
[Pid :: pid()]
erlang:system_info(Item :: procs) -> binary()
erlang:system_info(Item :: scheduler_bind_type) ->
spread | processor_spread | thread_spread |
thread_no_node_processor_spread |
no_node_processor_spread |
no_node_thread_spread | no_spread | unbound
erlang:system_info(Item :: scheduler_bindings) -> tuple()
erlang:system_info(Item :: scheduler_id) ->
SchedulerId :: integer() >= 1
erlang:system_info(Item :: schedulers | schedulers_online) ->
integer() >= 1
erlang:system_info(Item :: system_version) -> string()
erlang:system_info(Item :: threads) -> boolean()
Returns information about schedulers, scheduling and threads in
the current system as specified by Item:
dirty_cpu_schedulers:
Returns the number of dirty CPU scheduler threads used by
the emulator. Dirty CPU schedulers execute CPU-bound native
functions, such as NIFs, linked-in driver code, and BIFs
that cannot be managed cleanly by the normal emulator sched-
ulers.
The number of dirty CPU scheduler threads is determined at
emulator boot time and cannot be changed after that. How-
ever, the number of dirty CPU scheduler threads online can
be changed at any time. The number of dirty CPU schedulers
can be set at startup by passing command-line flag +SDcpu or
+SDPcpu in erl(1).
See also erlang:system_flag(dirty_cpu_schedulers_online,
DirtyCPUSchedulersOnline), erlang:sys-
tem_info(dirty_cpu_schedulers_online), erlang:sys-
tem_info(dirty_io_schedulers), erlang:system_info(sched-
ulers), erlang:system_info(schedulers_online), and
erlang:system_flag(schedulers_online, SchedulersOnline).
dirty_cpu_schedulers_online:
Returns the number of dirty CPU schedulers online. The
return value satisfies 1 <= DirtyCPUSchedulersOnline <= N,
where N is the smallest of the return values of erlang:sys-
tem_info(dirty_cpu_schedulers) and erlang:system_info(sched-
ulers_online).
The number of dirty CPU schedulers online can be set at
startup by passing command-line flag +SDcpu in erl(1).
For more information, see erlang:sys-
tem_info(dirty_cpu_schedulers), erlang:sys-
tem_info(dirty_io_schedulers), erlang:system_info(sched-
ulers_online), and erlang:system_flag(dirty_cpu_sched-
ulers_online, DirtyCPUSchedulersOnline).
dirty_io_schedulers:
Returns the number of dirty I/O schedulers as an integer.
Dirty I/O schedulers execute I/O-bound native functions,
such as NIFs and linked-in driver code, which cannot be man-
aged cleanly by the normal emulator schedulers.
This value can be set at startup by passing command-line
argument +SDio in erl(1).
For more information, see erlang:sys-
tem_info(dirty_cpu_schedulers), erlang:sys-
tem_info(dirty_cpu_schedulers_online), and erlang:sys-
tem_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOn-
line).
multi_scheduling:
Returns one of the following:
disabled:
The emulator has been started with only one scheduler
thread.
blocked:
The emulator has more than one scheduler thread, but all
scheduler threads except one are blocked. That is, only
one scheduler thread schedules Erlang processes and exe-
cutes Erlang code.
blocked_normal:
The emulator has more than one scheduler thread, but all
normal scheduler threads except one are blocked. Notice
that dirty schedulers are not blocked, and can schedule
Erlang processes and execute native code.
enabled:
The emulator has more than one scheduler thread, and no
scheduler threads are blocked. That is, all available
scheduler threads schedule Erlang processes and execute
Erlang code.
See also erlang:system_flag(multi_scheduling, BlockState),
erlang:system_info(multi_scheduling_blockers), erlang:sys-
tem_info(normal_multi_scheduling_blockers), and erlang:sys-
tem_info(schedulers).
multi_scheduling_blockers:
Returns a list of Pids when multi-scheduling is blocked,
otherwise the empty list is returned. The Pids in the list
represent all the processes currently blocking multi-sched-
uling. A Pid occurs only once in the list, even if the cor-
responding process has blocked multiple times.
See also erlang:system_flag(multi_scheduling, BlockState),
erlang:system_info(multi_scheduling), erlang:sys-
tem_info(normal_multi_scheduling_blockers), and erlang:sys-
tem_info(schedulers).
normal_multi_scheduling_blockers:
Returns a list of Pids when normal multi-scheduling is
blocked (that is, all normal schedulers but one is blocked),
otherwise the empty list is returned. The Pids in the list
represent all the processes currently blocking normal multi-
scheduling. A Pid occurs only once in the list, even if the
corresponding process has blocked multiple times.
See also erlang:system_flag(multi_scheduling, BlockState),
erlang:system_info(multi_scheduling), erlang:sys-
tem_info(multi_scheduling_blockers), and erlang:sys-
tem_info(schedulers).
scheduler_bind_type:
Returns information about how the user has requested sched-
ulers to be bound or not bound.
Notice that although a user has requested schedulers to be
bound, they can silently have failed to bind. To inspect the
scheduler bindings, call erlang:system_info(scheduler_bind-
ings).
For more information, see command-line argument +sbt in
erl(1) and erlang:system_info(scheduler_bindings).
scheduler_bindings:
Returns information about the currently used scheduler bind-
ings.
A tuple of a size equal to erlang:system_info(schedulers) is
returned. The tuple elements are integers or the atom
unbound. Logical processor identifiers are represented as
integers. The Nth element of the tuple equals the current
binding for the scheduler with the scheduler identifier
equal to N. For example, if the schedulers are bound, ele-
ment(erlang:system_info(scheduler_id), erlang:sys-
tem_info(scheduler_bindings)) returns the identifier of the
logical processor that the calling process is executing on.
Notice that only schedulers online can be bound to logical
processors.
For more information, see command-line argument +sbt in
erl(1) and erlang:system_info(schedulers_online).
scheduler_id:
Returns the scheduler ID (SchedulerId) of the scheduler
thread that the calling process is executing on. SchedulerId
is a positive integer, where 1 <= SchedulerId <= erlang:sys-
tem_info(schedulers).
See also erlang:system_info(schedulers).
schedulers:
Returns the number of scheduler threads used by the emula-
tor. Scheduler threads online schedules Erlang processes and
Erlang ports, and execute Erlang code and Erlang linked-in
driver code.
The number of scheduler threads is determined at emulator
boot time and cannot be changed later. However, the number
of schedulers online can be changed at any time.
See also erlang:system_flag(schedulers_online, SchedulersOn-
line), erlang:system_info(schedulers_online), erlang:sys-
tem_info(scheduler_id), erlang:system_flag(multi_scheduling,
BlockState), erlang:system_info(multi_scheduling),
erlang:system_info(normal_multi_scheduling_blockers) and
erlang:system_info(multi_scheduling_blockers).
schedulers_online:
Returns the number of schedulers online. The scheduler iden-
tifiers of schedulers online satisfy the relationship 1 <=
SchedulerId <= erlang:system_info(schedulers_online).
For more information, see erlang:system_info(schedulers) and
erlang:system_flag(schedulers_online, SchedulersOnline).
smp_support:
Returns true.
threads:
Returns true.
thread_pool_size:
Returns the number of async threads in the async thread pool
used for asynchronous driver calls
(erl_driver:driver_async()). The value is given as an inte-
ger.
erlang:system_info(Item :: creation) -> integer()
erlang:system_info(Item :: delayed_node_table_gc) ->
infinity | integer() >= 0
erlang:system_info(Item :: dist) -> binary()
erlang:system_info(Item :: dist_buf_busy_limit) ->
integer() >= 0
erlang:system_info(Item :: dist_ctrl) ->
{Node :: node(),
ControllingEntity :: port() | pid()}
Returns information about Erlang Distribution in the current
system as specified by Item:
creation:
Returns the creation of the local node as an integer. The
creation is changed when a node is restarted. The creation
of a node is stored in process identifiers, port identi-
fiers, and references. This makes it (to some extent) possi-
ble to distinguish between identifiers from different incar-
nations of a node. The valid creations are integers in the
range 1..3, but this will probably change in a future
release. If the node is not alive, 0 is returned.
delayed_node_table_gc:
Returns the amount of time in seconds garbage collection of
an entry in a node table is delayed. This limit can be set
on startup by passing command-line flag +zdntgc to erl(1).
For more information, see the documentation of the command-
line flag.
dist:
Returns a binary containing a string of distribution infor-
mation formatted as in Erlang crash dumps. For more informa-
tion, see section How to interpret the Erlang crash dumps
in the User's Guide.
dist_buf_busy_limit:
Returns the value of the distribution buffer busy limit in
bytes. This limit can be set at startup by passing command-
line flag +zdbbl to erl(1).
dist_ctrl:
Returns a list of tuples {Node, ControllingEntity}, one
entry for each connected remote node. Node is the node name
and ControllingEntity is the port or process identifier
responsible for the communication to that node. More specif-
ically, ControllingEntity for nodes connected through TCP/IP
(the normal case) is the socket used in communication with
the specific node.
erlang:system_info(Item :: c_compiler_used) -> {atom(), term()}
erlang:system_info(Item :: check_io) -> [term()]
erlang:system_info(Item :: compat_rel) -> integer()
erlang:system_info(Item :: debug_compiled) -> boolean()
erlang:system_info(Item :: driver_version) -> string()
erlang:system_info(Item :: dynamic_trace) ->
none | dtrace | systemtap
erlang:system_info(Item :: dynamic_trace_probes) -> boolean()
erlang:system_info(Item :: emu_flavor) -> emu | jit
erlang:system_info(Item :: emu_type) ->
opt | debug | gcov | valgrind | gprof |
lcnt | frmptr
erlang:system_info(Item :: info) -> binary()
erlang:system_info(Item :: kernel_poll) -> boolean()
erlang:system_info(Item :: loaded) -> binary()
erlang:system_info(Item :: machine) -> string()
erlang:system_info(Item :: modified_timing_level) ->
integer() | undefined
erlang:system_info(Item :: nif_version) -> string()
erlang:system_info(Item :: otp_release) -> string()
erlang:system_info(Item :: outstanding_system_requests_limit) ->
1..134217727
erlang:system_info(Item :: port_parallelism) -> boolean()
erlang:system_info(Item :: system_architecture) -> string()
erlang:system_info(Item :: system_logger) ->
logger | undefined | pid()
erlang:system_info(Item :: system_version) -> string()
erlang:system_info(Item :: trace_control_word) ->
integer() >= 0
erlang:system_info(Item :: version) -> string()
erlang:system_info(Item ::
wordsize |
{wordsize, internal} |
{wordsize, external}) ->
4 | 8
Returns various information about the current system (emulator)
as specified by Item:
build_type:
Deprecated, use emu_type instead
c_compiler_used:
Returns a two-tuple describing the C compiler used when com-
piling the runtime system. The first element is an atom
describing the name of the compiler, or undefined if
unknown. The second element is a term describing the version
of the compiler, or undefined if unknown.
check_io:
Returns a list containing miscellaneous information about
the emulators internal I/O checking. Notice that the content
of the returned list can vary between platforms and over
time. It is only guaranteed that a list is returned.
compat_rel:
Returns the compatibility mode of the local node as an inte-
ger. The integer returned represents the Erlang/OTP release
that the current emulator has been set to be backward com-
patible with. The compatibility mode can be configured at
startup by using command-line flag +R in erl(1).
debug_compiled:
Returns true if the emulator has been debug-compiled, other-
wise false.
driver_version:
Returns a string containing the Erlang driver version used
by the runtime system. It has the form "<major ver>.<minor
ver>".
dynamic_trace:
Returns an atom describing the dynamic trace framework com-
piled into the virtual machine. It can be dtrace, systemtap,
or none. For a commercial or standard build, it is always
none. The other return values indicate a custom configura-
tion (for example, ./configure --with-dynamic-trace=dtrace).
For more information about dynamic tracing, see dyntrace(3)
manual page and the README.dtrace/README.systemtap files in
the Erlang source code top directory.
dynamic_trace_probes:
Returns a boolean() indicating if dynamic trace probes
(dtrace or systemtap) are built into the emulator. This can
only be true if the virtual machine was built for dynamic
tracing (that is, system_info(dynamic_trace) returns dtrace
or systemtap).
emu_flavor:
Returns an atom describing the flavor of the runtime system.
This will be either emu or jit. Possible return values can
be added or removed at any time without prior notice.
emu_type:
Returns an atom describing the build type of the runtime
system. This is normally the atom opt for optimized. Other
possible return values are debug, gcov, valgrind, gprof, and
lcnt. Possible return values can be added or removed at any
time without prior notice.
info:
Returns a binary containing a string of miscellaneous system
information formatted as in Erlang crash dumps. For more
information, see section How to interpret the Erlang crash
dumps in the User's Guide.
kernel_poll:
Returns true if the emulator uses some kind of kernel-poll
implementation, otherwise false.
loaded:
Returns a binary containing a string of loaded module infor-
mation formatted as in Erlang crash dumps. For more informa-
tion, see section How to interpret the Erlang crash dumps in
the User's Guide.
machine:
Returns a string containing the Erlang machine name.
modified_timing_level:
Returns the modified timing-level (an integer) if modified
timing is enabled, otherwise undefined. For more information
about modified timing, see command-line flag +T in erl(1)
nif_version:
Returns a string containing the version of the Erlang NIF
interface used by the runtime system. It is on the form
"<major ver>.<minor ver>".
otp_release:
Returns a string containing the OTP release number of the
OTP release that the currently executing ERTS application is
part of.
As from Erlang/OTP 17, the OTP release number corresponds to
the major OTP version number. No erlang:system_info() argu-
ment gives the exact OTP version. This is because the exact
OTP version in the general case is difficult to determine.
For more information, see the description of versions in
System principles in System Documentation.
outstanding_system_requests_limit:
Returns the limit on the amount of outstanding requests made
by a system process orchestrating system wide changes. See
erlang:system_flag(outstanding_system_requests_limit, Limit)
for more information.
port_parallelism:
Returns the default port parallelism scheduling hint used.
For more information, see command-line argument +spp in
erl(1).
system_architecture:
Returns a string containing the processor and OS architec-
ture the emulator is built for.
system_logger:
Returns the current system_logger as set by erlang:sys-
tem_flag(system_logger, _).
system_version:
Returns a string containing version number and some impor-
tant properties, such as the number of schedulers.
trace_control_word:
Returns the value of the node trace control word. For more
information, see function get_tcw in section Match Specifi-
cations in Erlang in the User's Guide.
version:
Returns a string containing the version number of the emula-
tor.
wordsize:
Same as {wordsize, internal}.
{wordsize, internal}:
Returns the size of Erlang term words in bytes as an inte-
ger, that is, 4 is returned on a 32-bit architecture, and 8
is returned on a 64-bit architecture.
{wordsize, external}:
Returns the true word size of the emulator, that is, the
size of a pointer. The value is given in bytes as an inte-
ger. On a pure 32-bit architecture, 4 is returned. On a
64-bit architecture, 8 is returned.
erlang:system_monitor() -> MonSettings
Types:
MonSettings = undefined | {MonitorPid, Options}
MonitorPid = pid()
Options = [system_monitor_option()]
system_monitor_option() =
busy_port | busy_dist_port |
{long_gc, integer() >= 0} |
{long_schedule, integer() >= 0} |
{large_heap, integer() >= 0}
Returns the current system monitoring settings set by
erlang:system_monitor/2 as {MonitorPid, Options}, or undefined
if no settings exist. The order of the options can be different
from the one that was set.
erlang:system_monitor(Arg) -> MonSettings
Types:
Arg = MonSettings = undefined | {MonitorPid, Options}
MonitorPid = pid()
Options = [system_monitor_option()]
system_monitor_option() =
busy_port | busy_dist_port |
{long_gc, integer() >= 0} |
{long_schedule, integer() >= 0} |
{large_heap, integer() >= 0}
When called with argument undefined, all system performance mon-
itoring settings are cleared.
Calling the function with {MonitorPid, Options} as argument is
the same as calling erlang:system_monitor(MonitorPid, Options).
Returns the previous system monitor settings just like
erlang:system_monitor/0.
erlang:system_monitor(MonitorPid, Options) -> MonSettings
Types:
MonitorPid = pid()
Options = [system_monitor_option()]
MonSettings = undefined | {OldMonitorPid, OldOptions}
OldMonitorPid = pid()
OldOptions = [system_monitor_option()]
system_monitor_option() =
busy_port | busy_dist_port |
{long_gc, integer() >= 0} |
{long_schedule, integer() >= 0} |
{large_heap, integer() >= 0}
Sets the system performance monitoring options. MonitorPid is a
local process identifier (pid) receiving system monitor mes-
sages. The second argument is a list of monitoring options:
{long_gc, Time}:
If a garbage collection in the system takes at least Time
wall clock milliseconds, a message {monitor, GcPid, long_gc,
Info} is sent to MonitorPid. GcPid is the pid that was
garbage collected. Info is a list of two-element tuples
describing the result of the garbage collection.
One of the tuples is {timeout, GcTime}, where GcTime is the
time for the garbage collection in milliseconds. The other
tuples are tagged with heap_size, heap_block_size,
stack_size, mbuf_size, old_heap_size, and
old_heap_block_size. These tuples are explained in the
description of trace message gc_minor_start (see
erlang:trace/3). New tuples can be added, and the order of
the tuples in the Info list can be changed at any time with-
out prior notice.
{long_schedule, Time}:
If a process or port in the system runs uninterrupted for at
least Time wall clock milliseconds, a message {monitor,
PidOrPort, long_schedule, Info} is sent to MonitorPid.
PidOrPort is the process or port that was running. Info is a
list of two-element tuples describing the event.
If a pid(), the tuples {timeout, Millis}, {in, Location},
and {out, Location} are present, where Location is either an
MFA ({Module, Function, Arity}) describing the function
where the process was scheduled in/out, or the atom unde-
fined.
If a port(), the tuples {timeout, Millis} and {port_op,Op}
are present. Op is one of proc_sig, timeout, input, output,
event, or dist_cmd, depending on which driver callback was
executing.
proc_sig is an internal operation and is never to appear,
while the others represent the corresponding driver call-
backs timeout, ready_input, ready_output, event, and outputv
(when the port is used by distribution). Value Millis in
tuple timeout informs about the uninterrupted execution time
of the process or port, which always is equal to or higher
than the Time value supplied when starting the trace. New
tuples can be added to the Info list in a future release.
The order of the tuples in the list can be changed at any
time without prior notice.
This can be used to detect problems with NIFs or drivers
that take too long to execute. 1 ms is considered a good
maximum time for a driver callback or a NIF. However, a
time-sharing system is usually to consider everything < 100
ms as "possible" and fairly "normal". However, longer sched-
ule times can indicate swapping or a misbehaving NIF/driver.
Misbehaving NIFs and drivers can cause bad resource utiliza-
tion and bad overall system performance.
{large_heap, Size}:
If a garbage collection in the system results in the allo-
cated size of a heap being at least Size words, a message
{monitor, GcPid, large_heap, Info} is sent to MonitorPid.
GcPid and Info are the same as for long_gc earlier, except
that the tuple tagged with timeout is not present.
The monitor message is sent if the sum of the sizes of all
memory blocks allocated for all heap generations after a
garbage collection is equal to or higher than Size.
When a process is killed by max_heap_size, it is killed
before the garbage collection is complete and thus no large
heap message is sent.
busy_port:
If a process in the system gets suspended because it sends
to a busy port, a message {monitor, SusPid, busy_port, Port}
is sent to MonitorPid. SusPid is the pid that got suspended
when sending to Port.
busy_dist_port:
If a process in the system gets suspended because it sends
to a process on a remote node whose inter-node communication
was handled by a busy port, a message {monitor, SusPid,
busy_dist_port, Port} is sent to MonitorPid. SusPid is the
pid that got suspended when sending through the inter-node
communication port Port.
Returns the previous system monitor settings just like
erlang:system_monitor/0.
The arguments to system_monitor/2 specifies how all system moni-
toring on the node should be done, not how it should be changed.
This means only one process at a time (MonitorPid) can be the
receiver of system monitor messages. Also, the way to clear a
specific monitor option is to not include it in the list
Options. All system monitoring will, however, be cleared if the
process identified by MonitorPid terminates.
There are no special option values (like zero) to clear an
option. Some of the options have a unspecified minimum value.
Lower values will be adjusted to the minimum value. For example,
it is currently not possible to monitor all garbage collections
with {long_gc, 0}.
Note:
If a monitoring process gets so large that it itself starts to
cause system monitor messages when garbage collecting, the mes-
sages enlarge the process message queue and probably make the
problem worse.
Keep the monitoring process neat and do not set the system moni-
tor limits too tight.
Failures:
badarg:
If MonitorPid does not exist.
badarg:
If MonitorPid is not a local process.
erlang:system_profile() -> ProfilerSettings
Types:
ProfilerSettings = undefined | {ProfilerPid, Options}
ProfilerPid = pid() | port()
Options = [system_profile_option()]
system_profile_option() =
exclusive | runnable_ports | runnable_procs | scheduler |
timestamp | monotonic_timestamp | strict_monotonic_timestamp
Returns the current system profiling settings set by erlang:sys-
tem_profile/2 as {ProfilerPid, Options}, or undefined if there
are no settings. The order of the options can be different from
the one that was set.
erlang:system_profile(ProfilerPid, Options) -> ProfilerSettings
Types:
ProfilerPid = pid() | port() | undefined
Options = [system_profile_option()]
ProfilerSettings =
undefined | {pid() | port(), [system_profile_option()]}
system_profile_option() =
exclusive | runnable_ports | runnable_procs | scheduler |
timestamp | monotonic_timestamp | strict_monotonic_timestamp
Sets system profiler options. ProfilerPid is a local process
identifier (pid) or port receiving profiling messages. The
receiver is excluded from all profiling. The second argument is
a list of profiling options:
exclusive:
If a synchronous call to a port from a process is done, the
calling process is considered not runnable during the call
runtime to the port. The calling process is notified as
inactive, and later active when the port callback returns.
monotonic_timestamp:
Time stamps in profile messages use Erlang monotonic time.
The time stamp (Ts) has the same format and value as pro-
duced by erlang:monotonic_time(nanosecond).
runnable_procs:
If a process is put into or removed from the run queue, a
message, {profile, Pid, State, Mfa, Ts}, is sent to Profil-
erPid. Running processes that are reinserted into the run
queue after having been pre-empted do not trigger this mes-
sage.
runnable_ports:
If a port is put into or removed from the run queue, a mes-
sage, {profile, Port, State, 0, Ts}, is sent to ProfilerPid.
scheduler:
If a scheduler is put to sleep or awoken, a message, {pro-
file, scheduler, Id, State, NoScheds, Ts}, is sent to Pro-
filerPid.
strict_monotonic_timestamp:
Time stamps in profile messages consist of Erlang monotonic
time and a monotonically increasing integer. The time stamp
(Ts) has the same format and value as produced by
{erlang:monotonic_time(nanosecond), erlang:unique_inte-
ger([monotonic])}.
timestamp:
Time stamps in profile messages include a time stamp (Ts)
that has the same form as returned by erlang:now(). This is
also the default if no time stamp flag is specified. If
cpu_timestamp has been enabled through erlang:trace/3, this
also effects the time stamp produced in profiling messages
when flag timestamp is enabled.
Note:
erlang:system_profile behavior can change in a future release.
erlang:system_time() -> integer()
Returns current Erlang system time in native time unit.
Calling erlang:system_time() is equivalent to erlang:mono-
tonic_time() + erlang:time_offset().
Note:
This time is not a monotonically increasing time in the general
case. For more information, see the documentation of time warp
modes in the User's Guide.
erlang:system_time(Unit) -> integer()
Types:
Unit = time_unit()
Returns current Erlang system time converted into the Unit
passed as argument.
Calling erlang:system_time(Unit) is equivalent to erlang:con-
vert_time_unit(erlang:system_time(), native, Unit).
Note:
This time is not a monotonically increasing time in the general
case. For more information, see the documentation of time warp
modes in the User's Guide.
term_to_binary(Term) -> ext_binary()
Types:
Term = term()
Returns a binary data object that is the result of encoding Term
according to the Erlang external term format.
This can be used for various purposes, for example, writing a
term to a file in an efficient way, or sending an Erlang term to
some type of communications channel not supported by distributed
Erlang.
> Bin = term_to_binary(hello).
<<131,100,0,5,104,101,108,108,111>>
> hello = binary_to_term(Bin).
hello
See also binary_to_term/1.
Note:
There is no guarantee that this function will return the same
encoded representation for the same term.
term_to_binary(Term, Options) -> ext_binary()
Types:
Term = term()
Options =
[compressed |
{compressed, Level :: 0..9} |
deterministic |
{minor_version, Version :: 0..2}]
Returns a binary data object that is the result of encoding Term
according to the Erlang external term format.
If option compressed is provided, the external term format is
compressed. The compressed format is automatically recognized by
binary_to_term/1 as from Erlang/OTP R7B.
A compression level can be specified by giving option {com-
pressed, Level}. Level is an integer with range 0..9, where:
* 0 - No compression is done (it is the same as giving no com-
pressed option).
* 1 - Takes least time but may not compress as well as the
higher levels.
* 6 - Default level when option compressed is provided.
* 9 - Takes most time and tries to produce a smaller result.
Notice "tries" in the preceding sentence; depending on the
input term, level 9 compression either does or does not pro-
duce a smaller result than level 1 compression.
Option {minor_version, Version} can be used to control some
encoding details. This option was introduced in Erlang/OTP
R11B-4. The valid values for Version are:
0:
Floats are encoded using a textual representation. This
option is useful to ensure that releases before Erlang/OTP
R11B-4 can decode resulting binary.
This version encode atoms that can be represented by a
latin1 string using latin1 encoding while only atoms that
cannot be represented by latin1 are encoded using utf8.
1:
This is as of Erlang/OTP 17.0 the default. It forces any
floats in the term to be encoded in a more space-efficient
and exact way (namely in the 64-bit IEEE format, rather than
converted to a textual representation). As from Erlang/OTP
R11B-4, binary_to_term/1 can decode this representation.
This version encode atoms that can be represented by a
latin1 string using latin1 encoding while only atoms that
cannot be represented by latin1 are encoded using utf8.
2:
Drops usage of the latin1 atom encoding and unconditionally
use utf8 encoding for all atoms. Erlang/OTP systems as of
R16B can decode this representation.
Note:
In Erlang/OTP 26, the default minor_version is planned to
change from 1 to 2. See Upcoming Potential Incompatibilities
.
Option deterministic (introduced in OTP 24.1) can be used to
ensure that within the same major release of Erlang/OTP, the
same encoded representation is returned for the same term. There
is still no guarantee that the encoded representation remains
the same between major releases of Erlang/OTP.
See also binary_to_term/1.
term_to_iovec(Term) -> ext_iovec()
Types:
Term = term()
Returns the encoding of Term according to the Erlang external
term format as ext_iovec().
This function produce the same encoding as term_to_binary/1, but
with another return type. The call
iolist_to_binary(term_to_iovec(Term)) will produce exactly the
same result as the call term_to_binary(Term).
term_to_iovec() is a pure optimization of the functionality
term_to_binary() provide. term_to_iovec() can for example refer
directly to off heap binaries instead of copying the binary data
into the result.
See also term_to_binary/1.
term_to_iovec(Term, Options) -> ext_iovec()
Types:
Term = term()
Options =
[compressed |
{compressed, Level :: 0..9} |
deterministic |
{minor_version, Version :: 0..2}]
Returns the encoding of Term according to the Erlang external
term format as ext_iovec().
This function produce the same encoding as term_to_binary/2, but
with another return type. The call
iolist_to_binary(term_to_iovec(Term, Opts)) will produce exactly
the same result as term_to_binary(Term, Opts).
Currently recognised options are all options recognised by
term_to_binary/2.
term_to_iovec() is a pure optimization of the functionality
term_to_binary() provide. term_to_iovec() can for example refer
directly to off heap binaries instead of copying the binary data
into the result.
See also term_to_binary/2.
throw(Any) -> no_return()
Types:
Any = term()
Raises an exception of class throw. Intended to be used to do
non-local returns from functions.
If evaluated within a catch expression, the catch expression
returns value Any. Example:
> catch throw({hello, there}).
{hello,there}
If evaluated within a try-block of a try expression, the value
Any can be caught within the catch block. Example:
try
throw({my_exception, "Something happened"})
catch
throw:{my_exception, Desc} ->
io:format(standard_error, "Error: ~s~n", [Desc])
end
Failure: nocatch if not caught by an exception handler.
See the guide about errors and error handling for additional
information.
time() -> Time
Types:
Time = calendar:time()
Returns the current time as {Hour, Minute, Second}.
The time zone and Daylight Saving Time correction depend on the
underlying OS. The return value is based on the OS System Time.
Example:
> time().
{9,42,44}
erlang:time_offset() -> integer()
Returns the current time offset between Erlang monotonic time
and Erlang system time in native time unit. Current time offset
added to an Erlang monotonic time gives corresponding Erlang
system time.
The time offset may or may not change during operation depending
on the time warp mode used.
Note:
A change in time offset can be observed at slightly different
points in time by different processes.
If the runtime system is in multi-time warp mode, the time off-
set is changed when the runtime system detects that the OS sys-
tem time has changed. The runtime system will, however, not
detect this immediately when it occurs. A task checking the time
offset is scheduled to execute at least once a minute; so, under
normal operation this is to be detected within a minute, but
during heavy load it can take longer time.
erlang:time_offset(Unit) -> integer()
Types:
Unit = time_unit()
Returns the current time offset between Erlang monotonic time
and Erlang system time converted into the Unit passed as argu-
ment.
Same as calling erlang:convert_time_unit(erlang:time_offset(),
native, Unit) however optimized for commonly used Units.
erlang:timestamp() -> Timestamp
Types:
Timestamp = timestamp()
timestamp() =
{MegaSecs :: integer() >= 0,
Secs :: integer() >= 0,
MicroSecs :: integer() >= 0}
Returns current Erlang system time on the format {MegaSecs,
Secs, MicroSecs}. This format is the same as os:timestamp/0 and
the deprecated erlang:now/0 use. The reason for the existence of
erlang:timestamp() is purely to simplify use for existing code
that assumes this time stamp format. Current Erlang system time
can more efficiently be retrieved in the time unit of your
choice using erlang:system_time/1.
The erlang:timestamp() BIF is equivalent to:
timestamp() ->
ErlangSystemTime = erlang:system_time(microsecond),
MegaSecs = ErlangSystemTime div 1000_000_000_000,
Secs = ErlangSystemTime div 1000_000 - MegaSecs*1000_000,
MicroSecs = ErlangSystemTime rem 1000_000,
{MegaSecs, Secs, MicroSecs}.
It, however, uses a native implementation that does not build
garbage on the heap and with slightly better performance.
Note:
This time is not a monotonically increasing time in the general
case. For more information, see the documentation of time warp
modes in the User's Guide.
tl(List) -> term()
Types:
List = nonempty_maybe_improper_list()
Returns the tail of List, that is, the list minus the first ele-
ment, for example:
> tl([geesties, guilies, beasties]).
[guilies, beasties]
> tl([geesties]).
[]
> tl([geesties, guilies, beasties | improper_end]).
[guilies, beasties | improper_end]
> tl([geesties | improper_end]).
improper_end
Allowed in guard tests.
Failure: badarg if List is the empty list [].
erlang:trace(PidPortSpec, How, FlagList) -> integer()
Types:
PidPortSpec =
pid() |
port() |
all | processes | ports | existing | existing_processes |
existing_ports | new | new_processes | new_ports
How = boolean()
FlagList = [trace_flag()]
trace_flag() =
all | send | 'receive' | procs | ports | call | arity |
return_to | silent | running | exiting | running_procs |
running_ports | garbage_collection | timestamp |
cpu_timestamp | monotonic_timestamp |
strict_monotonic_timestamp | set_on_spawn |
set_on_first_spawn | set_on_link | set_on_first_link |
{tracer, pid() | port()} |
{tracer, module(), term()}
Turns on (if How == true) or off (if How == false) the trace
flags in FlagList for the process or processes represented by
PidPortSpec.
PidPortSpec is either a process identifier (pid) for a local
process, a port identifier, or one of the following atoms:
all:
All currently existing processes and ports and all that will
be created in the future.
processes:
All currently existing processes and all that will be cre-
ated in the future.
ports:
All currently existing ports and all that will be created in
the future.
existing:
All currently existing processes and ports.
existing_processes:
All currently existing processes.
existing_ports:
All currently existing ports.
new:
All processes and ports that will be created in the future.
new_processes:
All processes that will be created in the future.
new_ports:
All ports that will be created in the future.
FlagList can contain any number of the following flags (the
"message tags" refers to the list of trace messages):
all:
Sets all trace flags except tracer and cpu_timestamp, which
are in their nature different than the others.
send:
Traces sending of messages.
Message tags: send and send_to_non_existing_process.
'receive':
Traces receiving of messages.
Message tags: 'receive'.
call:
Traces certain function calls. Specify which function calls
to trace by calling erlang:trace_pattern/3.
Message tags: call and return_from.
silent:
Used with the call trace flag. The call, return_from, and
return_to trace messages are inhibited if this flag is set,
but they are executed as normal if there are match specifi-
cations.
Silent mode is inhibited by executing erlang:trace(_, false,
[silent|_]), or by a match specification executing the func-
tion {silent, false}.
The silent trace flag facilitates setting up a trace on many
or even all processes in the system. The trace can then be
activated and deactivated using the match specification
function {silent,Bool}, giving a high degree of control of
which functions with which arguments that trigger the trace.
Message tags: call, return_from, and return_to. Or rather,
the absence of.
return_to:
Used with the call trace flag. Traces the return from a
traced function back to its caller. Only works for functions
traced with option local to erlang:trace_pattern/3.
The semantics is that a trace message is sent when a call
traced function returns, that is, when a chain of tail
recursive calls ends. Only one trace message is sent per
chain of tail recursive calls, so the properties of tail
recursiveness for function calls are kept while tracing with
this flag. Using call and return_to trace together makes it
possible to know exactly in which function a process exe-
cutes at any time.
To get trace messages containing return values from func-
tions, use the {return_trace} match specification action
instead.
Message tags: return_to.
procs:
Traces process-related events.
Message tags: spawn, spawned, exit, register, unregister,
link, unlink, getting_linked, and getting_unlinked.
ports:
Traces port-related events.
Message tags: open, closed, register, unregister, get-
ting_linked, and getting_unlinked.
running:
Traces scheduling of processes.
Message tags: in and out.
exiting:
Traces scheduling of exiting processes.
Message tags: in_exiting, out_exiting, and out_exited.
running_procs:
Traces scheduling of processes just like running. However,
this option also includes schedule events when the process
executes within the context of a port without being sched-
uled out itself.
Message tags: in and out.
running_ports:
Traces scheduling of ports.
Message tags: in and out.
garbage_collection:
Traces garbage collections of processes.
Message tags: gc_minor_start, gc_max_heap_size, and
gc_minor_end.
timestamp:
Includes a time stamp in all trace messages. The time stamp
(Ts) has the same form as returned by erlang:now().
cpu_timestamp:
A global trace flag for the Erlang node that makes all trace
time stamps using flag timestamp to be in CPU time, not wall
clock time. That is, cpu_timestamp is not be used if mono-
tonic_timestamp or strict_monotonic_timestamp is enabled.
Only allowed with PidPortSpec==all. If the host machine OS
does not support high-resolution CPU time measurements,
trace/3 exits with badarg. Notice that most OS do not syn-
chronize this value across cores, so be prepared that time
can seem to go backwards when using this option.
monotonic_timestamp:
Includes an Erlang monotonic time time stamp in all trace
messages. The time stamp (Ts) has the same format and value
as produced by erlang:monotonic_time(nanosecond). This flag
overrides flag cpu_timestamp.
strict_monotonic_timestamp:
Includes an time stamp consisting of Erlang monotonic time
and a monotonically increasing integer in all trace mes-
sages. The time stamp (Ts) has the same format and value as
produced by { erlang:monotonic_time(nanosecond),
erlang:unique_integer([monotonic])}. This flag overrides
flag cpu_timestamp.
arity:
Used with the call trace flag. {M, F, Arity} is specified
instead of {M, F, Args} in call trace messages.
set_on_spawn:
Makes any process created by a traced process inherit its
trace flags, including flag set_on_spawn.
set_on_first_spawn:
Makes the first process created by a traced process inherit
its trace flags, excluding flag set_on_first_spawn.
set_on_link:
Makes any process linked by a traced process inherit its
trace flags, including flag set_on_link.
set_on_first_link:
Makes the first process linked to by a traced process
inherit its trace flags, excluding flag set_on_first_link.
{tracer, Tracer}:
Specifies where to send the trace messages. Tracer must be
the process identifier of a local process or the port iden-
tifier of a local port.
{tracer, TracerModule, TracerState}:
Specifies that a tracer module is to be called instead of
sending a trace message. The tracer module can then ignore
or change the trace message. For more details on how to
write a tracer module, see erl_tracer(3).
If no tracer is specified, the calling process receives all the
trace messages.
The effect of combining set_on_first_link with set_on_link is
the same as set_on_first_link alone. Likewise for set_on_spawn
and set_on_first_spawn.
The tracing process receives the trace messages described in the
following list. Pid is the process identifier of the traced
process in which the traced event has occurred. The third tuple
element is the message tag.
If flag timestamp, strict_monotonic_timestamp, or mono-
tonic_timestamp is specified, the first tuple element is
trace_ts instead, and the time stamp is added as an extra ele-
ment last in the message tuple. If multiple time stamp flags are
passed, timestamp has precedence over strict_monotonic_time-
stamp, which in turn has precedence over monotonic_timestamp.
All time stamp flags are remembered, so if two are passed and
the one with highest precedence later is disabled, the other one
becomes active.
If a match specification (applicable only for call, send and
'receive' tracing) contains a {message} action function with a
non-boolean value, that value is added as an extra element to
the message tuple either in the last position or before the
timestamp (if it is present).
Trace messages:
{trace, PidPort, send, Msg, To}:
When PidPort sends message Msg to process To.
{trace, PidPort, send_to_non_existing_process, Msg, To}:
When PidPort sends message Msg to the non-existing process
To.
{trace, PidPort, 'receive', Msg}:
When PidPort receives message Msg. If Msg is set to time-
out, a receive statement can have timed out, or the process
received a message with the payload timeout.
{trace, Pid, call, {M, F, Args}}:
When Pid calls a traced function. The return values of calls
are never supplied, only the call and its arguments.
Trace flag arity can be used to change the contents of this
message, so that Arity is specified instead of Args.
{trace, Pid, return_to, {M, F, Arity}}:
When Pid returns to the specified function. This trace mes-
sage is sent if both the flags call and return_to are set,
and the function is set to be traced on local function
calls. The message is only sent when returning from a chain
of tail recursive function calls, where at least one call
generated a call trace message (that is, the functions match
specification matched, and {message, false} was not an
action).
{trace, Pid, return_from, {M, F, Arity}, ReturnValue}:
When Pid returns from the specified function. This trace
message is sent if flag call is set, and the function has a
match specification with a return_trace or exception_trace
action.
{trace, Pid, exception_from, {M, F, Arity}, {Class, Value}}:
When Pid exits from the specified function because of an
exception. This trace message is sent if flag call is set,
and the function has a match specification with an excep-
tion_trace action.
{trace, Pid, spawn, Pid2, {M, F, Args}}:
When Pid spawns a new process Pid2 with the specified func-
tion call as entry point.
Args is supposed to be the argument list, but can be any
term if the spawn is erroneous.
{trace, Pid, spawned, Pid2, {M, F, Args}}:
When Pid is spawned by process Pid2 with the specified func-
tion call as entry point.
Args is supposed to be the argument list, but can be any
term if the spawn is erroneous.
{trace, Pid, exit, Reason}:
When Pid exits with reason Reason.
{trace, PidPort, register, RegName}:
When PidPort gets the name RegName registered.
{trace, PidPort, unregister, RegName}:
When PidPort gets the name RegName unregistered. This is
done automatically when a registered process or port exits.
{trace, Pid, link, Pid2}:
When Pid links to a process Pid2.
{trace, Pid, unlink, Pid2}:
When Pid removes the link from a process Pid2.
{trace, PidPort, getting_linked, Pid2}:
When PidPort gets linked to a process Pid2.
{trace, PidPort, getting_unlinked, Pid2}:
When PidPort gets unlinked from a process Pid2.
{trace, Port, open, Pid, Driver}:
When Pid opens a new port Port with the running Driver.
Driver is the name of the driver as an atom.
{trace, Port, closed, Reason}:
When Port closes with Reason.
{trace, Pid, in | in_exiting, {M, F, Arity} | 0}:
When Pid is scheduled to run. The process runs in function
{M, F, Arity}. On some rare occasions, the current function
cannot be determined, then the last element is 0.
{trace, Pid, out | out_exiting | out_exited, {M, F, Arity} |
0}:
When Pid is scheduled out. The process was running in func-
tion {M, F, Arity}. On some rare occasions, the current
function cannot be determined, then the last element is 0.
{trace, Port, in, Command | 0}:
When Port is scheduled to run. Command is the first thing
the port will execute, it can however run several commands
before being scheduled out. On some rare occasions, the cur-
rent function cannot be determined, then the last element is
0.
The possible commands are call, close, command, connect,
control, flush, info, link, open, and unlink.
{trace, Port, out, Command | 0}:
When Port is scheduled out. The last command run was Com-
mand. On some rare occasions, the current function cannot be
determined, then the last element is 0. Command can contain
the same commands as in
{trace, Pid, gc_minor_start, Info}:
Sent when a young garbage collection is about to be started.
Info is a list of two-element tuples, where the first ele-
ment is a key, and the second is the value. Do not depend on
any order of the tuples. The following keys are defined:
heap_size:
The size of the used part of the heap.
heap_block_size:
The size of the memory block used for storing the heap and
the stack.
old_heap_size:
The size of the used part of the old heap.
old_heap_block_size:
The size of the memory block used for storing the old
heap.
stack_size:
The size of the stack.
recent_size:
The size of the data that survived the previous garbage
collection.
mbuf_size:
The combined size of message buffers associated with the
process.
bin_vheap_size:
The total size of unique off-heap binaries referenced from
the process heap.
bin_vheap_block_size:
The total size of binaries allowed in the virtual heap in
the process before doing a garbage collection.
bin_old_vheap_size:
The total size of unique off-heap binaries referenced from
the process old heap.
bin_old_vheap_block_size:
The total size of binaries allowed in the virtual old heap
in the process before doing a garbage collection.
wordsize:
For the gc_minor_start event it is the size of the need
that triggered the GC. For the corresponding gc_minor_end
event it is the size of reclaimed memory = start heap_size
- end heap_size.
All sizes are in words.
{trace, Pid, gc_max_heap_size, Info}:
Sent when the max_heap_size is reached during garbage col-
lection. Info contains the same kind of list as in message
gc_start, but the sizes reflect the sizes that triggered
max_heap_size to be reached.
{trace, Pid, gc_minor_end, Info}:
Sent when young garbage collection is finished. Info con-
tains the same kind of list as in message gc_minor_start,
but the sizes reflect the new sizes after garbage collec-
tion.
{trace, Pid, gc_major_start, Info}:
Sent when fullsweep garbage collection is about to be
started. Info contains the same kind of list as in message
gc_minor_start.
{trace, Pid, gc_major_end, Info}:
Sent when fullsweep garbage collection is finished. Info
contains the same kind of list as in message gc_minor_start,
but the sizes reflect the new sizes after a fullsweep
garbage collection.
If the tracing process/port dies or the tracer module returns
remove, the flags are silently removed.
Each process can only be traced by one tracer. Therefore,
attempts to trace an already traced process fail.
Returns a number indicating the number of processes that matched
PidPortSpec. If PidPortSpec is a process identifier, the return
value is 1. If PidPortSpec is all or existing, the return value
is the number of processes running. If PidPortSpec is new, the
return value is 0.
Failure: badarg if the specified arguments are not supported.
For example, cpu_timestamp is not supported on all platforms.
erlang:trace_delivered(Tracee) -> Ref
Types:
Tracee = pid() | all
Ref = reference()
The delivery of trace messages (generated by erlang:trace/3,
seq_trace(3), or erlang:system_profile/2) is dislocated on the
time-line compared to other events in the system. If you know
that Tracee has passed some specific point in its execution, and
you want to know when at least all trace messages corresponding
to events up to this point have reached the tracer, use
erlang:trace_delivered(Tracee).
When it is guaranteed that all trace messages are delivered to
the tracer up to the point that Tracee reached at the time of
the call to erlang:trace_delivered(Tracee), then a {trace_deliv-
ered, Tracee, Ref} message is sent to the caller of
erlang:trace_delivered(Tracee) .
Notice that message trace_delivered does not imply that trace
messages have been delivered. Instead it implies that all trace
messages that are to be delivered have been delivered. It is not
an error if Tracee is not, and has not been traced by someone,
but if this is the case, no trace messages have been delivered
when the trace_delivered message arrives.
Notice that Tracee must refer to a process currently or previ-
ously existing on the same node as the caller of
erlang:trace_delivered(Tracee) resides on. The special Tracee
atom all denotes all processes that currently are traced in the
node.
When used together with a Tracer Module, any message sent in
the trace callback is guaranteed to have reached its recipient
before the trace_delivered message is sent.
Example: Process A is Tracee, port B is tracer, and process C is
the port owner of B. C wants to close B when A exits. To ensure
that the trace is not truncated, C can call erlang:trace_deliv-
ered(A) when A exits, and wait for message {trace_delivered, A,
Ref} before closing B.
Failure: badarg if Tracee does not refer to a process (dead or
alive) on the same node as the caller of erlang:trace_deliv-
ered(Tracee) resides on.
erlang:trace_info(PidPortFuncEvent, Item) -> Res
Types:
PidPortFuncEvent =
pid() |
port() |
new | new_processes | new_ports |
{Module, Function, Arity} |
on_load | send | 'receive'
Module = module()
Function = atom()
Arity = arity()
Item =
flags | tracer | traced | match_spec | meta |
meta_match_spec | call_count | call_time | all
Res = trace_info_return()
trace_info_return() =
undefined |
{flags, [trace_info_flag()]} |
{tracer, pid() | port() | []} |
{tracer, module(), term()} |
trace_info_item_result() |
{all, [trace_info_item_result()] | false | undefined}
trace_info_item_result() =
{traced, global | local | false | undefined} |
{match_spec, trace_match_spec() | false | undefined} |
{meta, pid() | port() | false | undefined | []} |
{meta, module(), term()} |
{meta_match_spec, trace_match_spec() | false | undefined} |
{call_count, integer() >= 0 | boolean() | undefined} |
{call_time,
[{pid(),
integer() >= 0,
integer() >= 0,
integer() >= 0}] |
boolean() |
undefined}
trace_info_flag() =
send | 'receive' | set_on_spawn | call | return_to | procs |
set_on_first_spawn | set_on_link | running |
garbage_collection | timestamp | monotonic_timestamp |
strict_monotonic_timestamp | arity
trace_match_spec() =
[{[term()] | '_' | match_variable(), [term()], [term()]}]
match_variable() = atom()
Approximation of '$1' | '$2' | '$3' | ...
Returns trace information about a port, process, function, or
event.
To get information about a port or process, PidPortFuncEvent is
to be a process identifier (pid), port identifier, or one of the
atoms new, new_processes, or new_ports. The atom new or new_pro-
cesses means that the default trace state for processes to be
created is returned. The atom new_ports means that the default
trace state for ports to be created is returned.
Valid Items for ports and processes:
flags:
Returns a list of atoms indicating what kind of traces is
enabled for the process. The list is empty if no traces are
enabled, and one or more of the followings atoms if traces
are enabled: send, 'receive', set_on_spawn, call, return_to,
procs, ports, set_on_first_spawn, set_on_link, running, run-
ning_procs, running_ports, silent, exiting, monotonic_time-
stamp, strict_monotonic_timestamp, garbage_collection, time-
stamp, and arity. The order is arbitrary.
tracer:
Returns the identifier for process, port, or a tuple con-
taining the tracer module and tracer state tracing this
process. If this process is not traced, the return value is
[].
To get information about a function, PidPortFuncEvent is to be
the three-element tuple {Module, Function, Arity} or the atom
on_load. No wildcards are allowed. Returns undefined if the
function does not exist, or false if the function is not traced.
If PidPortFuncEvent is on_load, the information returned refers
to the default value for code that will be loaded.
Valid Items for functions:
traced:
Returns global if this function is traced on global function
calls, local if this function is traced on local function
calls (that is, local and global function calls), and false
if local or global function calls are not traced.
match_spec:
Returns the match specification for this function, if it has
one. If the function is locally or globally traced but has
no match specification defined, the returned value is [].
meta:
Returns the meta-trace tracer process, port, or trace module
for this function, if it has one. If the function is not
meta-traced, the returned value is false. If the function is
meta-traced but has once detected that the tracer process is
invalid, the returned value is [].
meta_match_spec:
Returns the meta-trace match specification for this func-
tion, if it has one. If the function is meta-traced but has
no match specification defined, the returned value is [].
call_count:
Returns the call count value for this function or true for
the pseudo function on_load if call count tracing is active.
Otherwise false is returned.
See also erlang:trace_pattern/3.
call_time:
Returns the call time values for this function or true for
the pseudo function on_load if call time tracing is active.
Otherwise false is returned. The call time values returned,
[{Pid, Count, S, Us}], is a list of each process that exe-
cuted the function and its specific counters.
See also erlang:trace_pattern/3.
all:
Returns a list containing the {Item, Value} tuples for all
other items, or returns false if no tracing is active for
this function.
To get information about an event, PidPortFuncEvent is to be one
of the atoms send or 'receive'.
One valid Item for events exists:
match_spec:
Returns the match specification for this event, if it has
one, or true if no match specification has been set.
The return value is {Item, Value}, where Value is the requested
information as described earlier. If a pid for a dead process
was specified, or the name of a non-existing function, Value is
undefined.
erlang:trace_pattern(MFA, MatchSpec) -> integer() >= 0
Types:
MFA = trace_pattern_mfa() | send | 'receive'
MatchSpec =
(MatchSpecList :: trace_match_spec()) |
boolean() |
restart | pause
trace_pattern_mfa() = {atom(), atom(), arity() | '_'} | on_load
trace_match_spec() =
[{[term()] | '_' | match_variable(), [term()], [term()]}]
match_variable() = atom()
Approximation of '$1' | '$2' | '$3' | ...
The same as erlang:trace_pattern(Event, MatchSpec, []), retained
for backward compatibility.
erlang:trace_pattern(MFA :: send, MatchSpec, FlagList :: []) ->
integer() >= 0
Types:
MatchSpec = (MatchSpecList :: trace_match_spec()) | boolean()
trace_match_spec() =
[{[term()] | '_' | match_variable(), [term()], [term()]}]
match_variable() = atom()
Approximation of '$1' | '$2' | '$3' | ...
Sets trace pattern for message sending. Must be combined with
erlang:trace/3 to set the send trace flag for one or more pro-
cesses. By default all messages sent from send traced processes
are traced. To limit traced send events based on the message
content, the sender and/or the receiver, use erlang:trace_pat-
tern/3.
Argument MatchSpec can take the following forms:
MatchSpecList:
A list of match specifications. The matching is done on the
list [Receiver, Msg]. Receiver is the process or port iden-
tity of the receiver and Msg is the message term. The pid of
the sending process can be accessed with the guard function
self/0. An empty list is the same as true. For more informa-
tion, see section Match Specifications in Erlang in the
User's Guide.
true:
Enables tracing for all sent messages (from send traced pro-
cesses). Any match specification is removed. This is the
default.
false:
Disables tracing for all sent messages. Any match specifica-
tion is removed.
Argument FlagList must be [] for send tracing.
The return value is always 1.
Examples:
Only trace messages to a specific process Pid:
> erlang:trace_pattern(send, [{[Pid, '_'],[],[]}], []).
1
Only trace messages matching {reply, _}:
> erlang:trace_pattern(send, [{['_', {reply,'_'}],[],[]}], []).
1
Only trace messages sent to the sender itself:
> erlang:trace_pattern(send, [{['$1', '_'],[{'=:=','$1',{self}}],[]}], []).
1
Only trace messages sent to other nodes:
> erlang:trace_pattern(send, [{['$1', '_'],[{'=/=',{node,'$1'},{node}}],[]}], []).
1
Note:
A match specification for send trace can use all guard and body
functions except caller.
Fails by raising an error exception with an error reason of:
badarg:
If an argument is invalid.
system_limit:
If a match specification passed as argument has excessive
nesting which causes scheduler stack exhaustion for the
scheduler that the calling process is executing on. Sched-
uler stack size can be configured when starting the runtime
system.
erlang:trace_pattern(MFA :: 'receive', MatchSpec, FlagList :: []) ->
integer() >= 0
Types:
MatchSpec = (MatchSpecList :: trace_match_spec()) | boolean()
trace_match_spec() =
[{[term()] | '_' | match_variable(), [term()], [term()]}]
match_variable() = atom()
Approximation of '$1' | '$2' | '$3' | ...
Sets trace pattern for message receiving. Must be combined with
erlang:trace/3 to set the 'receive' trace flag for one or more
processes. By default all messages received by 'receive' traced
processes are traced. To limit traced receive events based on
the message content, the sender and/or the receiver, use
erlang:trace_pattern/3.
Argument MatchSpec can take the following forms:
MatchSpecList:
A list of match specifications. The matching is done on the
list [Node, Sender, Msg]. Node is the node name of the
sender. Sender is the process or port identity of the
sender, or the atom undefined if the sender is not known
(which can be the case for remote senders). Msg is the mes-
sage term. The pid of the receiving process can be accessed
with the guard function self/0. An empty list is the same as
true. For more information, see section Match Specifica-
tions in Erlang in the User's Guide.
true:
Enables tracing for all received messages (to 'receive'
traced processes). Any match specification is removed. This
is the default.
false:
Disables tracing for all received messages. Any match speci-
fication is removed.
Argument FlagList must be [] for receive tracing.
The return value is always 1.
Examples:
Only trace messages from a specific process Pid:
> erlang:trace_pattern('receive', [{['_',Pid, '_'],[],[]}], []).
1
Only trace messages matching {reply, _}:
> erlang:trace_pattern('receive', [{['_','_', {reply,'_'}],[],[]}], []).
1
Only trace messages from other nodes:
> erlang:trace_pattern('receive', [{['$1', '_', '_'],[{'=/=','$1',{node}}],[]}], []).
1
Note:
A match specification for 'receive' trace can use all guard and
body functions except caller, is_seq_trace, get_seq_token,
set_seq_token, enable_trace, disable_trace, trace, silent, and
process_dump.
Fails by raising an error exception with an error reason of:
badarg:
If an argument is invalid.
system_limit:
If a match specification passed as argument has excessive
nesting which causes scheduler stack exhaustion for the
scheduler that the calling process is executing on. Sched-
uler stack size can be configured when starting the runtime
system.
erlang:trace_pattern(MFA, MatchSpec, FlagList) ->
integer() >= 0
Types:
MFA = trace_pattern_mfa()
MatchSpec =
(MatchSpecList :: trace_match_spec()) |
boolean() |
restart | pause
FlagList = [trace_pattern_flag()]
trace_pattern_mfa() = {atom(), atom(), arity() | '_'} | on_load
trace_match_spec() =
[{[term()] | '_' | match_variable(), [term()], [term()]}]
trace_pattern_flag() =
global | local | meta |
{meta, Pid :: pid()} |
{meta, TracerModule :: module(), TracerState :: term()} |
call_count | call_time
match_variable() = atom()
Approximation of '$1' | '$2' | '$3' | ...
Enables or disables call tracing for one or more functions. Must
be combined with erlang:trace/3 to set the call trace flag for
one or more processes.
Conceptually, call tracing works as follows. Inside the Erlang
virtual machine, a set of processes and a set of functions are
to be traced. If a traced process calls a traced function, the
trace action is taken. Otherwise, nothing happens.
To add or remove one or more processes to the set of traced pro-
cesses, use erlang:trace/3.
To add or remove functions to the set of traced functions, use
erlang:trace_pattern/3.
The BIF erlang:trace_pattern/3 can also add match specifications
to a function. A match specification comprises a pattern that
the function arguments must match, a guard expression that must
evaluate to true, and an action to be performed. The default
action is to send a trace message. If the pattern does not match
or the guard fails, the action is not executed.
Argument MFA is to be a tuple, such as {Module, Function,
Arity}, or the atom on_load (described below). It can be the
module, function, and arity for a function (or a BIF in any mod-
ule). The atom '_' can be used as a wildcard in any of the fol-
lowing ways:
{Module,Function,'_'}:
All functions of any arity named Function in module Module.
{Module,'_','_'}:
All functions in module Module.
{'_','_','_'}:
All functions in all loaded modules.
Other combinations, such as {Module,'_',Arity}, are not allowed.
Local functions match wildcards only if option local is in
FlagList.
If argument MFA is the atom on_load, the match specification and
flag list are used on all modules that are newly loaded.
Argument MatchSpec can take the following forms:
false:
Disables tracing for the matching functions. Any match spec-
ification is removed.
true:
Enables tracing for the matching functions. Any match speci-
fication is removed.
MatchSpecList:
A list of match specifications. An empty list is equivalent
to true. For a description of match specifications, see sec-
tion Match Specifications in Erlang in the User's Guide.
restart:
For the FlagList options call_count and call_time: restarts
the existing counters. The behavior is undefined for other
FlagList options.
pause:
For the FlagList options call_count and call_time: pauses
the existing counters. The behavior is undefined for other
FlagList options.
Parameter FlagList is a list of options. The following are the
valid options:
global:
Turns on or off call tracing for global function calls (that
is, calls specifying the module explicitly). Only exported
functions match and only global calls generate trace mes-
sages. This is the default.
local:
Turns on or off call tracing for all types of function
calls. Trace messages are sent whenever any of the specified
functions are called, regardless of how they are called. If
flag return_to is set for the process, a return_to message
is also sent when this function returns to its caller.
meta | {meta, Pid} | {meta, TracerModule, TracerState}:
Turns on or off meta-tracing for all types of function
calls. Trace messages are sent to the tracer whenever any of
the specified functions are called. If no tracer is speci-
fied, self() is used as a default tracer process.
Meta-tracing traces all processes and does not care about
the process trace flags set by erlang:trace/3, the trace
flags are instead fixed to [call, timestamp].
The match specification function {return_trace} works with
meta-trace and sends its trace message to the same tracer.
call_count:
Starts (MatchSpec == true) or stops (MatchSpec == false)
call count tracing for all types of function calls. For
every function, a counter is incremented when the function
is called, in any process. No process trace flags need to be
activated.
If call count tracing is started while already running, the
count is restarted from zero. To pause running counters, use
MatchSpec == pause. Paused and running counters can be
restarted from zero with MatchSpec == restart.
To read the counter value, use erlang:trace_info/2.
call_time:
Starts (MatchSpec == true) or stops (MatchSpec == false)
call time tracing for all types of function calls. For every
function, a counter is incremented when the function is
called. Time spent in the function is accumulated in two
other counters, seconds and microseconds. The counters are
stored for each call traced process.
If call time tracing is started while already running, the
count and time restart from zero. To pause running counters,
use MatchSpec == pause. Paused and running counters can be
restarted from zero with MatchSpec == restart.
To read the counter value, use erlang:trace_info/2.
The options global and local are mutually exclusive, and global
is the default (if no options are specified). The options
call_count and meta perform a kind of local tracing, and cannot
be combined with global. A function can be globally or locally
traced. If global tracing is specified for a set of functions,
then local, meta, call time, and call count tracing for the
matching set of local functions is disabled, and conversely.
When disabling trace, the option must match the type of trace
set on the function. That is, local tracing must be disabled
with option local and global tracing with option global (or no
option), and so on.
Part of a match specification list cannot be changed directly.
If a function has a match specification, it can be replaced with
a new one. To change an existing match specification, use the
BIF erlang:trace_info/2 to retrieve the existing match specifi-
cation.
Returns the number of functions matching argument MFA. This is
zero if none matched.
Fails by raising an error exception with an error reason of:
badarg:
If an argument is invalid.
system_limit:
If a match specification passed as argument has excessive
nesting which causes scheduler stack exhaustion for the
scheduler that the calling process is executing on. Sched-
uler stack size can be configured when starting the runtime
system.
trunc(Number) -> integer()
Types:
Number = number()
Truncates the decimals of Number, for example:
> trunc(5.7).
5
> trunc(-5.7).
-5
> trunc(5).
5
> trunc(36028797018963969.0).
36028797018963968
In the last example, trunc(36028797018963969.0) evaluates to
36028797018963968. The reason for this is that the number
36028797018963969.0 cannot be represented exactly as a float
value. Instead, the float literal is represented as
36028797018963968.0, which is the closest number that can be
represented exactly as a float value. See Representation of
Floating Point Numbers for additional information.
Allowed in guard tests.
tuple_size(Tuple) -> integer() >= 0
Types:
Tuple = tuple()
Returns an integer that is the number of elements in Tuple, for
example:
> tuple_size({morni, mulle, bwange}).
3
Allowed in guard tests.
tuple_to_list(Tuple) -> [term()]
Types:
Tuple = tuple()
Returns a list corresponding to Tuple. Tuple can contain any
Erlang terms. Example:
> tuple_to_list({share, {'Ericsson_B', 163}}).
[share,{'Ericsson_B',163}]
unalias(Alias) -> boolean()
Types:
Alias = reference()
Deactivate the alias Alias previously created by the calling
process. An alias can for example be created via alias/0, or
monitor/3. unalias/1 will always deactivate the alias regardless
of options used when creating the alias.
Returns true if Alias was a currently active alias for current
processes; otherwise, false.
For more information on process aliases see the Process Aliases
section of the Erlang Reference Manual .
erlang:unique_integer() -> integer()
Generates and returns an integer unique on current runtime sys-
tem instance. The same as calling erlang:unique_integer([]).
erlang:unique_integer(ModifierList) -> integer()
Types:
ModifierList = [Modifier]
Modifier = positive | monotonic
Generates and returns an integer unique on current runtime sys-
tem instance. The integer is unique in the sense that this BIF,
using the same set of modifiers, does not return the same inte-
ger more than once on the current runtime system instance. Each
integer value can of course be constructed by other means.
By default, when [] is passed as ModifierList, both negative and
positive integers can be returned. This to use the range of
integers that do not need heap memory allocation as much as pos-
sible. By default the returned integers are also only guaranteed
to be unique, that is, any returned integer can be smaller or
larger than previously returned integers.
Modifiers:
positive:
Returns only positive integers.
Notice that by passing the positive modifier you will get
heap allocated integers (bignums) quicker.
monotonic:
Returns strictly monotonically increasing integers corre-
sponding to creation time. That is, the integer returned is
always larger than previously returned integers on the cur-
rent runtime system instance.
These values can be used to determine order between events
on the runtime system instance. That is, if both X =
erlang:unique_integer([monotonic]) and Y =
erlang:unique_integer([monotonic]) are executed by different
processes (or the same process) on the same runtime system
instance and X < Y, we know that X was created before Y.
Warning:
Strictly monotonically increasing values are inherently quite
expensive to generate and scales poorly. This is because the
values need to be synchronized between CPU cores. That is, do
not pass the monotonic modifier unless you really need
strictly monotonically increasing values.
All valid Modifiers can be combined. Repeated (valid) Modifiers
in the ModifierList are ignored.
Note:
The set of integers returned by erlang:unique_integer/1 using
different sets of Modifiers will overlap. For example, by call-
ing unique_integer([monotonic]), and unique_integer([positive,
monotonic]) repeatedly, you will eventually see some integers
that are returned by both calls.
Failures:
badarg:
if ModifierList is not a proper list.
badarg:
if Modifier is not a valid modifier.
erlang:universaltime() -> DateTime
Types:
DateTime = calendar:datetime()
Returns the current date and time according to Universal Time
Coordinated (UTC) in the form {{Year, Month, Day}, {Hour,
Minute, Second}} if supported by the underlying OS. Otherwise
erlang:universaltime() is equivalent to erlang:localtime(). The
return value is based on the OS System Time. Example:
> erlang:universaltime().
{{1996,11,6},{14,18,43}}
erlang:universaltime_to_localtime(Universaltime) -> Localtime
Types:
Localtime = Universaltime = calendar:datetime()
Converts Universal Time Coordinated (UTC) date and time to local
date and time in the form {{Year, Month, Day}, {Hour, Minute,
Second}} if supported by the underlying OS. Otherwise no conver-
sion is done, and Universaltime is returned. Example:
> erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}).
{{1996,11,7},{15,18,43}}
Failure: badarg if Universaltime denotes an invalid date and
time.
unlink(Id) -> true
Types:
Id = pid() | port()
Removes a link between the calling process and another process
or a port identified by Id. We will from here on call the iden-
tified process or port unlinkee.
A link can be set up using the link/1 BIF. For more information
on links and exit signals due to links, see the Processes chap-
ter in the Erlang Reference Manual :
* Links
* Sending Exit Signals
* Receiving Exit Signals
Once unlink(Id) has returned, it is guaranteed that the link
between the caller and the unlinkee has no effect on the caller
in the future (unless the link is setup again). Note that if the
caller is trapping exits, an {'EXIT', Id, ExitReason} message
due to the link may have been placed in the message queue of the
caller before the unlink(Id) call completed. Also note that the
{'EXIT', Id, ExitReason} message may be the result of the link,
but may also be the result of the unlikee sending the caller an
exit signal by calling the exit/2 BIF. Therefore, it may or may
not be appropriate to clean up the message queue after a call to
unlink(Id) as follows, when trapping exits:
unlink(Id),
receive
{'EXIT', Id, _} ->
true
after 0 ->
true
end
The link removal is performed asynchronously. If such a link
does not exist, nothing is done. A detailed description of the
link protocol can be found in the Distribution Protocol chapter
of the ERTS User's Guide .
Failure: badarg if Id does not identify a process or a node
local port.
unregister(RegName) -> true
Types:
RegName = atom()
Removes the registered name RegName associated with a process
identifier or a port identifier from the name registry. For
example:
> unregister(db).
true
Keep in mind that you can still receive signals associated with
the registered name after it has been unregistered as the sender
may have looked up the name before sending to it.
Users are advised not to unregister system processes.
Failure: badarg if RegName is not a registered name.
whereis(RegName) -> pid() | port() | undefined
Types:
RegName = atom()
Returns the process identifier or port identifier with the reg-
istered name RegName from the name registry. Returns undefined
if the name is not registered. Example:
> whereis(db).
<0.43.0>
erlang:yield() -> true
Tries to give other processes with the same or higher priority
(if any) a chance to execute before returning. There is no guar-
antee that any other process runs between the invocation and
return of erlang:yield/0.
See the documentation for receive-after expressions for how to
make the current process sleep for a specific number of mil-
liseconds.
Warning:
There is seldom or never any need to use this BIF. Using this
BIF without a thorough grasp of how the scheduler works can
cause performance degradation. The current implementation of
this function puts the current process last in the current
scheduler's queue for processes of the same priority as the cur-
rent process.
Ericsson AB erts 12.2 erlang(3)