iOS : Multithread block + UI

multithread_blocks

dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // Add code here to do background processing
    //
    //
    dispatch_async( dispatch_get_main_queue(), ^{
        // Add code here to update the UI/send notifications based on the
        // results of the background processing
    });
});