title: Queue of NSOperations and handling application exit
body: <p>I'm about to create a series of <code>NSOperation</code>s and run them in a queue.</p>
  
  <p>They will all be sequential and run one at a time.</p>
  
  <p>These operations will fetch data from the web and create and save core data managed objects.</p>
  
  <p>How do I handle the situation where the application exits? As the operations run in detached threads, how can I make the main thread wait until the current operation is "safe" to quit?  There are situations where I'm happy for the threads (operations) to exit before they are complete as on further app launches the job will continue and pick up where it left off.</p>
  
  <p>Many thanks,</p>
  
  <p>Mike</p>