Run timer in background thread

ViewController.H

@property (nonatomic) UIBackgroundTaskIdentifier backgroundTask;

ViewController.M

self.backgroundTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{

        NSLog(@"Background handler called. Not running background taxsks anymore.");

        [[UIApplication sharedApplication] endBackgroundTask:self.backgroundTask];

        self.backgroundTask = UIBackgroundTaskInvalid;

    }];

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(countup)userInfo:nil repeats:YES];

        [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];

        [[NSRunLoop currentRunLoop] run];

    });

-(void)countup { 

  //Here i done another action run in main thread

 dispatch_async(dispatch_get_main_queue(), ^{  

               ViewController *Vc=[self.storyboard instantiateViewControllerWithIdentifier:@"view"];

                [self.navigationController pushViewController:Vc animated:YES];

            });

}