after(n) Tcl (7.5) 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
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after(n) Tcl (7.5) after(n)
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 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 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 bgerror mechanism is used
to report the error.
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 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
KEYWORDS
cancel, delay, idle callback, sleep, time
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