Pause NSOperation

Question

I have NSOperationQueue with some NSOperations in it (NSInvocationOperations, in particular). This operations do some calculations and change states of UI elements accordingly (of course, via performSelectorOnMainThread:...), often with use of animations.

My UI has UINavigationViewController and some buttons for navigation to another views. So user can leave current view, while calculations / animations are still in progress. And what I need is to stop this somehow until user comes back to current view.

The only solution I found is to create some thread-safe boolean flag - and to check it in all threads (something like: while !flag sleep_for_some_time;). Is there something better?

Answer 1

The question is a bit vague, so it's hard to say without knowing all of the code in play. With that said, I may approach the problem by:

Option 1. In your subclass of NSOperation, add your own atomic KVO property "isPaused". Within the operation itself, observe that property and handle accordingly if it ever changes.

Option 2. Are you ever suspending the Operation Queue itself? If so, consider observing that property from within your operations, and each one independently can take action if that value changes.

Option 3. Cancel all operations in the queue, and if the view appears again, just restart with new operations.

Overall, though, there is no magic bullet for pausing operations already in progress. You'll have to bake your own solution. The damage shouldn't be too bad though.