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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  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.

       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 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 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
       concat(n), interp(n), update(n), vwait(n)

KEYWORDS
       cancel, delay, idle callback, sleep, time

Tcl				      7.5			      after(n)
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