Yes, Grad Centeral Dispatch may seems big and complex. But if you need to put some work into background, its pretty easy, all you have to do is:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
// do your job here
});
Simple, isn’t it? In case you want to put more CPU cycles into your background process, you can change priority to DISPATCH_QUEUE_PRIORITY_DEFAULT or even DISPATCH_QUEUE_PRIORITY_HIGH. You can use also DISPATCH_QUEUE_PRIORITY_BACKGROUND but this one will cause your code to run at very end, when all higher priorities are done.