title: prevent multiple dispatch_queue_create from being created in viewDidLoad
body: <p>have a view that loads and a serial dispatch queue that is created, loads a ton of stuff in the background and works great.  Problem is when I navigate back and forth to that view a new queue is created again and then I have multiple things doing the exact same work.</p>
  
  <pre><code>- (void)viewDidLoad {
  
  dispatch_queue_t myQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0);
      dispatch_async(myQueue, ^{
          //function call to a helper outside the scope of this view 
      });
    }
  </code></pre>
  
  <p>How do I prevent this from happening?</p>
  
  <p>EDIT:
  creating my own queue was not necessary so I change my code - same problem still exists.</p>