after - Execute a command after a time delay
after ms after ms ?script script script ...? after cancel id after cancel script script script ... after idle ?script script script ...? after info ?id?
after(1t) Tcl Built-In Commands after(1t)
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NAME
after - Execute a command after a time delay
SYNOPSIS
after ms
after ms ?script script script ...?
after cancel id
after cancel script script script ...
after idle ?script script script ...?
after info ?id?
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DESCRIPTION
This command is used to delay execution of the program or to execute a
command in background sometime in the future. It has several forms,
depending on the first argument to the command:
after ms
Ms must be an integer giving a time in milliseconds. The com-
mand sleeps for ms milliseconds and then returns. While the
command is sleeping the application does not respond to events.
after ms ?script script script ...?
In this form the command returns immediately, but it arranges
for a Tcl command to be executed ms milliseconds later as an
event handler. The command will be executed exactly once, at
the given time. The delayed command is formed by concatenating
all the script arguments in the same fashion as the concat com-
mand. The command will be executed at global level (outside the
context of any Tcl procedure). If an error occurs while execut-
ing the delayed command then the background error will be
reported by the command registered with interp bgerror. The
after command returns an identifier that can be used to cancel
the delayed command using after cancel.
after cancel id
Cancels the execution of a delayed command that was previously
scheduled. Id indicates which command should be canceled; it
must have been the return value from a previous after command.
If the command given by id has already been executed then the
after cancel command has no effect.
after cancel script script ...
This command also cancels the execution of a delayed command.
The script arguments are concatenated together with space sepa-
rators (just as in the concat command). If there is a pending
command that matches the string, it is canceled and will never
be executed; if no such command is currently pending then the
after cancel command has no effect.
after idle script ?script script ...?
Concatenates the script arguments together with space separators
(just as in the concat command), and arranges for the resulting
script to be evaluated later as an idle callback. The script
will be run exactly once, the next time the event loop is
entered and there are no events to process. The command returns
an identifier that can be used to cancel the delayed command
using after cancel. If an error occurs while executing the
script then the background error will be reported by the command
registered with interp bgerror.
after info ?id?
This command returns information about existing event handlers.
If no id argument is supplied, the command returns a list of the
identifiers for all existing event handlers created by the after
command for this interpreter. If id is supplied, it specifies
an existing handler; id must have been the return value from
some previous call to after and it must not have triggered yet
or been canceled. In this case the command returns a list with
two elements. The first element of the list is the script asso-
ciated with id, and the second element is either idle or timer
to indicate what kind of event handler it is.
The after ms and after idle forms of the command assume that the appli-
cation is event driven: the delayed commands will not be executed
unless the application enters the event loop. In applications that are
not normally event-driven, such as tclsh, the event loop can be entered
with the vwait and update commands.
EXAMPLES
This defines a command to make Tcl do nothing at all for N seconds:
proc sleep {N} {
after [expr {int($N * 1000)}]
}
This arranges for the command wake_up to be run in eight hours (provid-
ing the event loop is active at that time):
after [expr {1000 * 60 * 60 * 8}] wake_up
The following command can be used to do long-running calculations (as
represented here by ::my_calc::one_step, which is assumed to return a
boolean indicating whether another step should be performed) in a step-
by-step fashion, though the calculation itself needs to be arranged so
it can work step-wise. This technique is extra careful to ensure that
the event loop is not starved by the rescheduling of processing steps
(arranging for the next step to be done using an already-triggered
timer event only when the event queue has been drained) and is useful
when you want to ensure that a Tk GUI remains responsive during a slow
task.
proc doOneStep {} {
if {[::my_calc::one_step]} {
after idle [list after 0 doOneStep]
}
}
doOneStep
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | runtime/tcl-8 |
+---------------+------------------+
|Stability | Uncommitted |
+---------------+------------------+
SEE ALSO
concat(n), interp(n), update(n), vwait(n)
KEYWORDS
cancel, delay, idle callback, sleep, time
NOTES
Source code for open source software components in Oracle Solaris can
be found at https://www.oracle.com/downloads/opensource/solaris-source-
code-downloads.html.
This software was built from source available at
https://github.com/oracle/solaris-userland. The original community
source was downloaded from http://prdownloads.sourceforge.net/tcl/tcl-
core8.6.7-src.tar.gz.
Further information about this software can be found on the open source
community website at https://www.tcl.tk/.
Tcl 7.5 after(1t)