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after(n)                     Tcl Built-In Commands                    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 mil-
              liseconds 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
              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 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 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 com-
              mand 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  han-
              dler 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.

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


KEYWORDS
       cancel, delay, idle callback, sleep, time



Tcl                                   7.5                             after(n)