simple function for running UI Updates (or anything) on main thread for Cocoa. Can be useful if you have a callback you are not sure it always runs on main thread.

onMainQueue.mm

void onMainQueue(void(^block)(void)) {
    if ([NSThread isMainThread])
        block();
    else
        dispatch_sync(dispatch_get_main_queue(), block);
}

//usage example:
- (void)callbackThatIDontKnowWhichThreadIsItRunningOn {
    onMainQueue(^{
        [UIView beginAnimations:nil context:nil];
        self.alpha = 0;
        [UIView commitAnimations];
    });
}