Multithreading and Grand Central Dispatch on iOS (most simple example)

gcd_example.m

-(void) viewDidLoad {
    [super viewDidLoad];  
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
      //Here your non-main thread.
      NSLog (@"Hi, I'm new thread");
      dispatch_async(dispatch_get_main_queue(), ^{
        //Here you returns to main thread.
        NSLog (@"Hi, I'm main thread");
      });
  });
}