gcd.m

gistfile1.m

dispatch_queue_t myQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
    
dispatch_async(myQueue, ^{
     [self performSelectorOnMainThread:@selector(someActionToUpdate:) withObject:an_object waitUntilDone:YES];
});

-(void)someActionToUpdate:(id)an_object {
    // an_object can be any kind of type
}