For details on the differences between the two types of queue, see Lion’s answer. Both approaches will work. However, NSOperation is mostly needed when more advanced scheduling (including dependencies, canceling, etc.) is required. So in this case, a simple DispatchQueue.main.async { /* do work */ } will be just fine. That would be equivalent to … Read more
NSOperation* classes are the higher level api. They hide GCD’s lower level api from you so that you can concentrate on getting the task done. The rule of thumb is: Use the api of the highest level first and then degrade based on what you need to accomplish. The advantage of this approach is that … Read more
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
Your intuition here is correct. If issuing many requests, having an NSOperationQueue with maxConcurrentOperationCount of 4 or 5 can be very useful. In the absence of that, if you issue many requests (say, 50 large images), you can suffer timeout problems when working on a slow network connection (e.g. some cellular connections). Operation queues have … 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