CFRunLoopSourceSignal doesn't work

Question

I'm debugging Qt5.3.1 on Mac, because my program freezes sometimes (intermittent ). I discovered that it is because the QTimer can't work properly.

In Qt code, they use the following two lines to trigger function activateTimersSourceCallback

CFRunLoopSourceSignal(d->activateTimersSourceRef);
CFRunLoopWakeUp(mainRunLoop());

void QCocoaEventDispatcherPrivate::activateTimersSourceCallback(void *info)
{
    static int counter = 0;
    NSLog(@"finished activeteTimersSourceCallback %d", counter++);
}

but sometimes, these two lines doesn't work, activateTimersSourceCallback won't get called.

I googled, but I couldn't find any solution? is this a known OS bug?

the initialization details:

// keep our sources running when modal loops are running
CFRunLoopAddCommonMode(mainRunLoop(), (CFStringRef) NSModalPanelRunLoopMode);

CFRunLoopSourceContext context;
bzero(&context, sizeof(CFRunLoopSourceContext));
context.info = d;
context.equal = runLoopSourceEqualCallback;

// source used to activate timers
context.perform = QCocoaEventDispatcherPrivate::activateTimersSourceCallback;
d->activateTimersSourceRef = CFRunLoopSourceCreate(kCFAllocatorDefault, 0, &context);
Q_ASSERT(d->activateTimersSourceRef);
CFRunLoopAddSource(mainRunLoop(), d->activateTimersSourceRef, kCFRunLoopCommonModes);

Answer 1

Such behavior very likely can occur when UI event loop is overloaded with events or some business logic takes too long time. You should to check your business logic and move it to separate thread or run asynchronous.