app - Application resource file.
Please see following description for synopsis
app(5) Files app(5)
NAME
app - Application resource file.
DESCRIPTION
The application resource file specifies the resources an application
uses, and how the application is started. There must always be one
application resource file called Application.app for each application
Application in the system.
The file is read by the application controller when an application is
loaded/started. It is also used by the functions in systools, for exam-
ple when generating start scripts.
FILE SYNTAX
The application resource file is to be called Application.app, where
Application is the application name. The file is to be located in
directory ebin for the application.
The file must contain a single Erlang term, which is called an applica-
tion specification:
{application, Application,
[{description, Description},
{id, Id},
{vsn, Vsn},
{modules, Modules},
{maxP, MaxP},
{maxT, MaxT},
{registered, Names},
{included_applications, Apps},
{optional_applications, Apps},
{applications, Apps},
{env, Env},
{mod, Start},
{start_phases, Phases},
{runtime_dependencies, RTDeps}]}.
Value Default
----- -------
Application atom() -
Description string() ""
Id string() ""
Vsn string() ""
Modules [Module] []
MaxP int() infinity
MaxT int() infinity
Names [Name] []
Apps [App] []
Env [{Par,Val}] []
Start {Module,StartArgs} []
Phases [{Phase,PhaseArgs}] undefined
RTDeps [ApplicationVersion] []
Module = Name = App = Par = Phase = atom()
Val = StartArgs = PhaseArgs = term()
ApplicationVersion = string()
Application:
Application name.
For the application controller, all keys are optional. The respective
default values are used for any omitted keys.
The functions in systools require more information. If they are used,
the following keys are mandatory:
* description
* vsn
* modules
* registered
* applications
The other keys are ignored by systools.
description:
A one-line description of the application.
id:
Product identification, or similar.
vsn:
Version of the application.
modules:
All modules introduced by this application. systools uses this list
when generating start scripts and tar files. A module can only be
defined in one application.
maxP:
Deprecated - is ignored
Maximum number of processes allowed in the application.
maxT:
Maximum time, in milliseconds, that the application is allowed to
run. After the specified time, the application terminates automati-
cally.
registered:
All names of registered processes started in this application. sys-
tools uses this list to detect name clashes between different
applications.
included_applications:
All applications included by this application. When this applica-
tion is started, all included applications are loaded automati-
cally, but not started, by the application controller. It is
assumed that the top-most supervisor of the included application is
started by a supervisor of this application.
applications:
All applications that must be started before this application. If
an application is also listed in optional_applications, then the
application is not required to exist (but if it exists, it is also
guaranteed to be started before this one).
systools uses this list to generate correct start scripts. Defaults
to the empty list, but notice that all applications have dependen-
cies to (at least) Kernel and STDLIB.
optional_applications:
A list of applications that are optional. Note if you want an
optional dependency to be automatically started before the current
application whenever it is available, it must be listed on both
applications and optional_applications.
env:
Configuration parameters used by the application. The value of a
configuration parameter is retrieved by calling applica-
tion:get_env/1,2. The values in the application resource file can
be overridden by values in a configuration file (see config(4)) or
by command-line flags (see erts:erl(1)).
mod:
Specifies the application callback module and a start argument, see
application(3).
Key mod is necessary for an application implemented as a supervi-
sion tree, otherwise the application controller does not know how
to start it. mod can be omitted for applications without processes,
typically code libraries, for example, STDLIB.
start_phases:
A list of start phases and corresponding start arguments for the
application. If this key is present, the application master, in
addition to the usual call to Module:start/2, also calls Mod-
ule:start_phase(Phase,Type,PhaseArgs) for each start phase defined
by key start_phases. Only after this extended start procedure,
application:start(Application) returns.
Start phases can be used to synchronize startup of an application
and its included applications. In this case, key mod must be speci-
fied as follows:
{mod, {application_starter,[Module,StartArgs]}}
The application master then calls Module:start/2 for the primary
application, followed by calls to Module:start_phase/3 for each
start phase (as defined for the primary application), both for the
primary application and for each of its included applications, for
which the start phase is defined.
This implies that for an included application, the set of start
phases must be a subset of the set of phases defined for the pri-
mary application. For more information, see OTP Design Principles.
runtime_dependencies:
A list of application versions that the application depends on. An
example of such an application version is "kernel-3.0". Application
versions specified as runtime dependencies are minimum require-
ments. That is, a larger application version than the one specified
in the dependency satisfies the requirement. For information about
how to compare application versions, see section Versions in the
System Principles User's Guide.
Notice that the application version specifies a source code ver-
sion. One more, indirect, requirement is that the installed binary
application of the specified version is built so that it is compat-
ible with the rest of the system.
Some dependencies can only be required in specific runtime scenar-
ios. When such optional dependencies exist, these are specified and
documented in the corresponding "App" documentation of the specific
application.
Warning:
The runtime_dependencies key was introduced in OTP 17.0. The type of
its value might be subject to changes during the OTP 17 release.
Warning:
All runtime dependencies specified in OTP applications during the OTP
17 release may not be completely correct. This is actively being
worked on. Declared runtime dependencies in OTP applications are
expected to be correct in OTP 18.
SEE ALSO
application(3), systools(3)
Ericsson AB kernel 8.2 app(5)