How can I Pause a NSOperation in a NSOperationQueue?

Question

I need to pause a running NSOperation which was inserted in an NSOperationQueue. Currently I am canceling all operations and restarting them. But this would lead to some kind of duplication in terms of process done. I tried with setSuspended flag of NSOperationQueue. But it's not suspending the operation. Is there any way out?

Solution 1

see this: Link

And here from the apple docs:

Suspending and Resuming Queues If you want to issue a temporary halt to the execution of operations, you can suspend the corresponding operation queue using the setSuspended: method.

Suspending a queue does not cause already executing operations to pause in the middle of their tasks. It simply prevents new operations from being scheduled for execution. You might suspend a queue in response to a user request to pause any ongoing work, because the expectation is that the user might eventually want to resume that work.

Solution 2

I've not tried this, but I would probably start here:

• add a isPaused flag to your NSOperation subclass
• implement a copy/move method for the operation's data
• if paused, setCancelled: (watch for this change in -main)
• create a new operation moving the state from paused operation to new operation
• adjust priority to reorder operation order in queue, if you like
• add the clone to the queue
• return from -main if in -main

note that this will just suspend it. if you really want to pause and explicitly resume, you would manually 'new operation` when you want to resume.

now, if you are observing or have special completions, then you will have a few other problems. for simple cases, it seems this approach would seem to work fine.