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 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 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