after(n) Tcl Built-In Commands after(n)_________________________________________________________________NAMEafter - Execute a command after a time delay
SYNOPSISafter ms
after ms ?script script script ...?
after cancel id
after cancel script script script ...
after idle ?script script script ...?
after info ?id?
_________________________________________________________________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 millisec-
onds. 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 com-
mand will be executed exactly once, at the given
time. The delayed command is formed by concatenat-
ing 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 com-
mand given by id has already been executed then the
after cancel command has no effect.
Tcl 7.5 1
after(n) Tcl Built-In Commands after(n)after cancel script script ...
This command also cancels the execution of a
delayed command. The script arguments are concate-
nated 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 evalu-
ated 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 com-
mand 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 can-
celled. 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 com-
mands 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
Tcl 7.5 2
