- NAME
- after — Execute a command after a time delay
- SYNOPSIS
- DESCRIPTION
- after ms
- after ms ?script script script ...?
- after cancel id
- after cancel script script ...
- after idle script ?script script ...?
- after info ?id?
- EXAMPLES
- SEE ALSO
- KEYWORDS
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?
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.
A negative number is treated as 0.
The command 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 command.
The command will be executed at global level (outside the context
of any Tcl procedure).
If an error occurs while executing 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.
A ms value of 0 (or negative) queues the event immediately with
priority over other event types (if not installed withn an event proc,
which will wait for next round of events).
- 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
separators (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 associated
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 application 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.
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
(providing 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
concat, interp, update, vwait
cancel, delay, idle callback, sleep, time
Copyright © 1990-1994 The Regents of the University of California.
Copyright © 1994-1996 Sun Microsystems, Inc.