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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 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 con-catenated concatenated
              catenated together with space separators (just as in the concat command).  If there is a pend-ing pending
              ing  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  com-mand), command),
              mand),  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 sup-plied, supplied,
              plied, 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 han-dler; handler;
              dler; 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(n), interp(n), update(n), vwait(n)


KEYWORDS
       cancel, delay, idle callback, sleep, time



Tcl                                                  7.5                                            after(n)