Doh. Dear future googlers: of course operation is nil when copied by the block, but it doesn’t have to be copied. It can be qualified with __block like so: //THIS MIGHT LEAK! See the update below. __block NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{ while( ! [operation isCancelled]){ //do something… } }]; UPDATE: Upon further meditation, it … Read more
Okay, so as I understand it, you have two questions: Do you need the performSelectorOnMainThread: segment that appears in comments in your code? What does that code do? Why is the _isCancelled flag is not modified when you call cancelAllOperations on the NSOperationQueue that contains this operation? Let’s deal with these in order. I’m going … Read more
My question is whether the database write operation occur in main thread or in a background thread? If you create an NSOperationQueue from scratch as in: NSOperationQueue *myQueue = [[NSOperationQueue alloc] init]; It will be in a background thread: Operation queues usually provide the threads used to run their operations. In OS X v10.6 and … Read more
GCD is a low-level C-based API that enables very simple use of a task-based concurrency model. NSOperation and NSOperationQueue are Objective-C classes that do a similar thing. NSOperation was introduced first, but as of 10.5 and iOS 2, NSOperationQueue and friends are internally implemented using GCD. In general, you should use the highest level of … Read more