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man pages section 1: User Commands

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Updated: Wednesday, February 10, 2021
 
 

after (1t)

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?

Description

after(1t)                    Tcl Built-In Commands                   after(1t)



______________________________________________________________________________

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?
______________________________________________________________________________

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 com-
              mand 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 com-
              mand.  The command will be executed at global level (outside the
              context of any Tcl procedure).  If an error occurs while execut-
              ing 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  sepa-
              rators  (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 asso-
              ciated 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 appli-
       cation 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 (provid-
       ing 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


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+------------------+
       |ATTRIBUTE TYPE | ATTRIBUTE VALUE  |
       +---------------+------------------+
       |Availability   | runtime/tcl-8    |
       +---------------+------------------+
       |Stability      | Uncommitted      |
       +---------------+------------------+
SEE ALSO
       concat(n), interp(n), update(n), vwait(n)

KEYWORDS
       cancel, delay, idle callback, sleep, time



NOTES
       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source was downloaded from  http://prdownloads.sourceforge.net/tcl/tcl-
       core8.6.7-src.tar.gz

       Further information about this software can be found on the open source
       community website at https://www.tcl.tk/.



Tcl                                   7.5                            after(1t)