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.  A negative number  is  treated  as  0.   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  command registered with interp bgerror.  The after command returns an
              identifier that can be used to cancel the delayed command using after cancel.  A ms value of 0 (or
              negative)  queues  the  event  immediately  with priority over other event types (if not installed
              withn an event proc, which will wait for next round of events).

       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 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 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