QWe are writing a screen saver that plays QuickTime movies. Our
WaitNextEvent loop and code is very basic. We have noticed that other
background applications don't get any time, even if we use
WaitNextEvent and make sure MoviesTask does not spend too
much time playing the movie. However, if we add code to track the
updateEvents with BeginUpdate and EndUpdate the
problem is gone. Why?
AQuickTime and other parts are sending update events to your application. If these update events are not handled, they are resent, resulting in no time yield to other applications.
By calling BeginUpdate/EndUpdate or otherwise taking care of the
update event inside your WaitNextEventLoop, you allow yielding to
other applications.
See Technote TB 37 Pending Update Perils, which discusses this situation.