update - Process pending events and idle callbacks

       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 updateidletasks 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 updateidletasks 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 updateidletasks.

       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.

       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
              }

       asynchronous I/O, event, flush, handler, idle, update

Tcl                                                    7.5                                          update(3tcl)

       update - Process pending events and idle callbacks

after(3tcl), interp(3tcl)

update ?idletasks?
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