IPhone : Managing thread loop in objective-c

I take a look to the GCD, and coming from c++, it comes natural to write code in this way:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

   while(YES) {
     if(<condition>) {
       /* here I need to call a delegate */
     }
     sleep(1);
   }

});

Is this the right way to do a loop in a objective-c thread?

Trying to understand, I was looking inside Reachability framework that I suppose launch a background thread to continuously check connection status, but I can't understand how do the "loop".