gistfile1.m

    // Replace
    [self.gameTimer invalidate];
    self.gameTimer = nil;
    // With
    dispatch_async(dispatch_get_main_queue(), ^{
        [self.gameTimer invalidate];
        self.gameTimer = nil;
    });
    
    
    
    // Replace
    self.startTime = [NSDate timeIntervalSinceReferenceDate];
    self.gameTimer = [NSTimer scheduledTimerWithTimeInterval:0.005
                                                      target:self
                                                    selector:@selector(gameTimerFired)
                                                    userInfo:nil
                                                    repeats:YES];
    // With                                                 
    dispatch_async(dispatch_get_main_queue(), ^{
        self.startTime = [NSDate timeIntervalSinceReferenceDate];
        self.gameTimer = [NSTimer scheduledTimerWithTimeInterval:0.005
                                                          target:self
                                                        selector:@selector(gameTimerFired)
                                                        userInfo:nil
                                                        repeats:YES];
    });