after(n) Tcl Built-In Commands after(n)
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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 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 bgerror mechanism is used to report the error. 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 con-catenated concatenated
catenated together with space separators (just as in the concat command). If there is a pend-ing pending
ing command that matches the string, it is cancelled 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 com-mand), command),
mand), 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 bgerror
mechanism is used to report the error.
after info ?id?
This command returns information about existing event handlers. If no id argument is sup-plied, supplied,
plied, 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 han-dler; handler;
dler; id must have been the return value from some previous call to after and it must not have
triggered yet or been cancelled. 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.
SEE ALSO
bgerror(n), concat(n), update(n), vwait(n)
KEYWORDS
cancel, delay, idle callback, sleep, time
Tcl 7.5 after(n)
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