title: GCD vs custom queue
body: <p>I was wondering what is the difference in performance between these two. </p>
  
  <pre><code>dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
  
      // perform complex operation
  
      // dispatch back to main thread to update UI
  
  });
  
  
  
  dispatch_async(_myCustomConcurrentQueue, ^{
  
      // perform complex operation
  
      // dispatch back to main thread to update UI
  
  });
  </code></pre>
  
  <p>My assumption is the GCD is used across the os and other applications, and it will need to perform very quick background tasks, and be finished quick. And custom queues that are created are separate from GCD and they can run a different task, and will be added back to the pool once they are released. And so my assumption is that my customQueue performs better than GCD for a complex operation.</p>
  
  <p>What are your thoughts? Which performs better? Are they the same?</p>