update(3Tk)

NAME
     update - Process pending events and/or when-idle handlers

SYNOPSIS
     update ?idletasks?


DESCRIPTION
     This command is used to bring the entire application world ``up to
     date.''  It flushes all pending output to the display,  waits for the
     server to process that output and return errors or events, handles all
     pending events of any sort (including when-idle handlers), and repeats
     this set of operations until there are no pending events, no pending
     when-idle handlers, no pending output to the server, and no operations
     still outstanding at the server.

     If the idletasks keyword is specified as an argument to the command, then
     no new events or errors are processed;  only when-idle idlers 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 handlers, 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 user interactions;  if you occasionally call update then
     user input will be processed during the next call to update.


KEYWORDS
     event, flush, handler, idle, update