Home/ Questions/Q 7092005
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-28T08:15:31+00:00

When I cancel an NSOperation (when user presses a button) cancel method is called

  • 0

When I cancel an NSOperation (when user presses a button) cancel method is called from the main thread, but evidently the operation is running in another thread.
So, to avoid race conditions when I change _isExecuting and _isFinished, I think cancel (or at least its logic) should be called from the same thread that the NSOperation. Apart from that, when user cancels it, several files are deleted and it takes time. Because cancel is called from main thread, all the app becomes unresponsive for a while, which is ugly.

How can I execute cancel code in the same thread that the current NSOperation?

I tried this in cancel (similar to what I saw in ASIHTTPRequest):

if (_operationThread) {
    [self performSelector:@selector(cancelOnRequestThread) onThread:_operationThread withObject:nil waitUntilDone:NO];
} else {
    [self cancelOnRequestThread];
}

And _operationThread is setted in start method using:
_operationThread=[NSThread currentThread];

But it doesn’t work.

Any idea or suggestion?

Note: I use concurrent operations, so I use start instead of main.

Thanks a lot for help.
Ricardo.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    It’s fine to call cancel on an NSOperation from the main thread. The cancel method is thread-safe.

    That shouldn’t cause any blocking on your main thread because the cancel method itself shouldn’t be doing any work. If you have overridden the cancel method of your operation to delete files, etc then that is the wrong approach. You shouldn’t override the cancel method, instead just check the isCancelled method at regular points within the operation’s main method (e.g. inside any tight loops) and then return from main early if isCancelled returns YES, which will then cancel the operation on the same thread as the rest of the execution.

    If that’s how you’ve implemented it already and you’re still having performance issues, is it possible that your operation is not really running on a background thread at all? For example if you’ve added it to the queue returned by [NSOperationQueue mainQueue] then that’s actually running on the main application thread.

    • 0