The manual page for XtAppMainLoop says that it's just a simple loop that
calls
XEvent event;
XtAppNextEvent(app, &event);
XtDispatchEvent(&event);
... until XtAppGetExitFlag() returns true.
And looking at the code in libXt-1.0.9/src/Event.c seems to show that to
be the case.
But: XtAppNextEvent() doesn't return until there's an actual XEvent to
be handled; it handles Xt-internal events (inputs, timers, signals)
itself, but doesn't return (because of course, those aren't XEvents).
Which means that the exit flag doesn't get a chance to break the loop
until/unless there's an actual XEvent.
If you're not using a Display at all in your app, you lose: timers or
input sources can't signal the main loop to exit using this mechanism.
A workaround -- and what I would suggest XtAppMainLoop be fixed to do
instead -- is code that looks more like this:
for (;;) {
XtAppProcessEvent(app, XtIMAll);
if (XtAppGetExitFlag(app))
break;
}
XtAppProcessEvent() returns when *any* event has been dispatched, not
just ones that involve a Display. For the source tree, it would look
something like this:
void XtAppMainLoop(XtAppContext app) {
LOCK_APP(app);
do {
XtAppProcessEvent(app, XtIMAll);
} while (! app->exit_flag);
UNLOCK_APP(app);
}
I guess I'm the only one who uses Xt this way?
Thanks,
/jordan
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