In what cases would you prefer to use NSOperationQueue over GCD?
From my limited experience of these two, I take it that with NSOperationQueue you basically have control over how many concurrent operations there are.
With GCD you can't do this, since you are using a queue. Except you can somehow simulate this with a multi core processor, although still I think there's no way to control it.
NSOperationQueue is built on GCD as of iOS 4. Use the simplest API for the task at hand.Measure if it's a performance problem and then reevaluate if needed.dispatch_async is lower level, usually C-type stuff (but not limited to), and is good for one-shot and sequential type deals. NSOperationQueues are higher level, Objective-C stuff, and are good if you are adding a lot of operations at various points in your code, and/or need to manage concurrency, priorities and dependencies.
I assume by NSPriorityQueue you mean NSOperationQueue? The main reasons to use NSOperationQueue over GCD are if you need its additional features:
- Older OS support
- KVO on operation properties
- Dependencies
- Queue width limiting (although you can do this fairly easily in GCD with dispatch_semaphore_t)
Otherwise, unless you're working with an API that takes an NSOperationQueue, GCD is probably a better bet
Being at higher level,I found NSOperationQueue more elegant to manage tasks/operations instead of handling them at lower level using GCD.
来源：https://stackoverflow.com/questions/8033465/nsoperationqueue-vs-gcd