title: Dispatching on correct queue dispatch_get_specific
body: <p>I'm looking at other's code and found this:</p>
  
  <pre><code>//Obj-C
  if (dispatch_get_specific(moduleQueueTag))
      block();
  else
      dispatch_sync(moduleQueue, block);
  </code></pre>
  
  <p>I'm trying to do the same thing in Swift. Is it required to do this:</p>
  
  <pre><code>    if dispatch_get_specific(moduleQueueTag) != nil {
          block()
      } else {
          dispatch_async(moduleQueue) {
              block()
          }
      }
  </code></pre>
  
  <p>or is it okay just to do this:</p>
  
  <pre><code>        dispatch_async(moduleQueue) {
              block()
          }
  </code></pre>