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after(n)		     Tcl Built-In Commands		      after(n)

______________________________________________________________________________

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?
_________________________________________________________________

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 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 concatenated together with space	 sepa-
	      rators  (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 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

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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