after(3tcl)						       Tcl Built-In Commands						       after(3tcl)

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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 background error will be reported by  the  com-
	      mand  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 can-
	      cel 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  can-
	      cel.   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
	      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.

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 (providing 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(3tcl), interp(3tcl), update(3tcl), vwait(3tcl)

KEYWORDS

       cancel, delay, idle callback, sleep, time

Tcl									7.5							       after(3tcl)