title: How to stop/cancel/suspend/resume tasks on GCD queue
body: <p>How to stop/cancel/suspend/resume tasks on GCD queue</p>
  
  <p>How does one stop background queue operations? I want to stop some screens in our app. And some screens it should be auto resume. So, how does one pass a queue in iOS?</p>
  
  <p>I mean when user have browsing the app time we run the background thread in dispatch_queue_t. But it never stops and resume in the code. So how does one suspend and resume a queue</p>