Longstanding bug in ... XtAppMainLoop?

[Jordan Hayes]

> when do application do not have a display ?

Xt is also a powerful general purpose environment for event-driven 
programming.  Input events, timers, now signals ... all handled pretty 
well.  Originally the big drawback was that XtAppMainLoop would *never* 
return, but this ExitFlag stuff appears to be an attempt to allow it.  I 
also think it should return when there's no chance of ever getting 
another event: if there's no display, no input sources are defined, no 
signals are being watched, and no timers are set.  Someday I'll see if I 
can come up with a patch for that, but in the mean time changing the 
main loop would be a good thing.

Here's some code that shows the problem:

#include <X11/Intrinsic.h>

static void _Tick(XtPointer baton, XtIntervalId* id) {
    static int count = 0;

    printf("%d beep!\n", ++count);

    XtAppContext app = (XtAppContext)baton;
    if (3 == count)
        XtAppSetExitFlag(app);
    else
        XtAppAddTimeOut(app, 3000, _Tick, app);
}

int main(int argc, char** argv) {
    XtToolkitInitialize();
    XtAppContext app = XtCreateApplicationContext();
    XtAppAddTimeOut(app, 3000, _Tick, app);

#ifdef    SHOWBUG
    XtAppMainLoop(app);
#else
    for (;;) {
        XtAppProcessEvent(app, XtIMAll);
        if (XtAppGetExitFlag(app))
            break;
    }
#endif

    return 0;
}

I wrote this paper nearly 20 years ago about it :-)

http://bitway.com/jordan/papers/USENIX/AppDev.html

/jordan