title: Is a memory warning received on the main thread in iOS?
body: <p>I have seen some unusual behavior when my app responds to memory warnings - data getting out of sync primarily. </p>
  
  <p>If my app receives a memory warning, will the warning pass control to the main thread?  </p>
  
  <p>If not, I assume I must do some data protection if the memory warning will free data that might be in use on the main thread. </p>