NAME

       update - Process pending events and idle callbacks

SYNOPSIS

       update ?idletasks?
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DESCRIPTION

       This  command is used to bring the application ``up to date'' by entering the event loop repeatedly until
       all pending events (including idle callbacks) have been processed.

       If the idletasks keyword is specified as an argument to the command, then no new  events  or  errors  are
       processed;   only idle callbacks are invoked.  This causes operations that are normally deferred, such as
       display updates and window layout calculations, to be performed immediately.

       The update idletasks command is useful in scripts where changes have been made to the application's state
       and  you  want  those changes to appear on the display immediately, rather than waiting for the script to
       complete.  Most display updates are performed as idle callbacks, so update idletasks will cause  them  to
       run.   However,  there  are  some  kinds of updates that only happen in response to events, such as those
       triggered by window size changes; these updates will not occur in update idletasks.

       The update command with no options  is  useful  in  scripts  where  you  are  performing  a  long-running
       computation  but  you  still want the application to respond to events such as user interactions;  if you
       occasionally call update then user input will be processed during the next call to update.

EXAMPLE

       Run computations for about a second and then finish:
              set x 1000
              set done 0
              after 1000 set done 1
              while {!$done} {
                  # A very silly example!
                  set x [expr {log($x) ** 2.8}]

                  # Test to see if our time-limit has been hit.  This would
                  # also give a chance for serving network sockets and, if
                  # the Tk package is loaded, updating a user interface.
                  update
              }

SEE ALSO

       after(3tcl), bgerror(3tcl)

KEYWORDS

       event, flush, handler, idle, update