title: NSInvocationOperation Yield equivalent
body: <p>I'm porting an Android app I made to iOS. Android has a <code>Yield()</code> function to move the thread from running to the back(?) of the thread queue. This is useful so that this thread doesn't hog up too much CPU and make everything else sluggish. It works well in my Android app.</p>
  
  <p>I'm using <code>NSInvocationOperation</code> objects to implement my threads. How do I add functionality similar to Android's (POSIX's) <code>Yield()</code>?</p>