Question 

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        while(!weakSelf.isAnotherThreadCompleted && [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]])
            ;
         [weakSelf doSomething];

    });

Is it correct to put async thread to wait another thread in this way?

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Solution

You're going to stall the global queue corresponding to DISPATCH_QUEUE_PRIORITY_DEFAULT. If you dispatch something else to this queue, it won't execute until you're done waiting.

In addition, I don't think a run loop will exist in the thread corresponding to this dispatch queue, so you're going to create one by calling - currentRunLoop and since no source will be attached to it, it will return immediately with the value NO (or, there will be a random run loop, and the behavior will be completely unpredictable).

Why don't you just call a block at the end of your working thread? Or use only one mechanism (GCD, NSOperation, threads, run loops) and the synchronization that goes with it, instead of mixing them?

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