How to stop current NSOperation?

Question

I'm using NSOperationQueue, and NSOperation for running some function on background click. But I want to be able, when user clicks some button, stop that Operation.

How can I do it?

Something like, [currentoperation stop];
Cancel - won't work me. I want to stop immediately.

Thanks

Answer 1

You should be calling the -cancel method, and the operation itself has to support being cancelled by monitoring the isCancelled property/keypath and safely stopping when its value becomes YES. If the NSOperation is your own, you will probably have to create a custom subclass to implement this functionality. You cannot (safely) force an arbitrary operation to immediately stop. It has to support being cancelled.

Answer 2

You can't stop immediately by using anything Apple provides with NSOperation. You can use -[cancel] as other people have suggested here, but the current operation will still run until completion. One way of getting close to use -[isCancelled] inside of your operation and sprinkle that throughout the code (especially in long running loops). Something like:

- (void)main {
    // do a little work
    if ([self isCancelled]) { return; }

    // do a little more work
    if ([self isCancelled]) { return; }
}

This way you'll get things stopped relatively soon.

If you're looking to really force the thread to stop, you may need to look into signal handling. There's a threaded example here. Sending a custom signal to a specific thread, you may be able to then terminate that thread in some way. This will be a lot more work, though, and is probably much more trouble than it's worth.

Answer 3

you use cancel, and test whether self (the NSOperation) has been cancelled during execution.