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 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  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 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 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

       bgerror(3tcl), concat(3tcl), update(3tcl), vwait(3tcl)

KEYWORDS

       cancel, delay, idle callback, sleep, time

Tcl                                                    7.5                                           after(3tcl)