Volume 6A: Motif Programming Manual

Getting back to CheckForInterrupt(), if the user presses the Stop in the dialog, the event is processed and the

stop() callback routine is invoked. This routine simply sets the global variable stopped to True. By the time that

CheckForInterrupt() is ready to return, stopped has been set, so the function returns True. If the

WorkingDialog does not have a Stop button, the callback routine is not installed, so stopped is never set to True.

After the get_busy() routine finishes processing, it calls TimeoutCursors() again to unlock the application.

When on is set to False, the routine uses XCheckMaskEvent() to look in the event queue for button and

keyboard events. In this case, the events are thrown away, since the input is no longer useful. The routine also

destroys the WorkingDialog. In one sense, TimeoutCursors() implements a kind of modality, similar to that

discussed in Section #smodaldlg. However, modality alone cannot provide the functionality necessary to handle

long−running tasks.

22.2.4 Updating the Display

As discussed earlier, XmUpdateDisplay() checks the event queue for all Expose events and processes them

immediately. However, there are some circumstances under which the routine does not work as you might expect. For

example, let's say that your application creates and posts a dialog that contains a DrawingArea widget. You call

XSync() and XmUpdateDisplay() to make sure that the dialog is on the screen and fully exposed. After you call

XClearWindow() to make sure the window is clear, ...