问题
I have a 'concurrent' NSOperation, and during it's work it uses some controller classes that internally use GCD. When these controller classes return with their completion block, the completion block is on another thread.
I know I could store the current thread in the operation start method and run performSelectorOnThread:, but ideally I would like to wrap the completion in a GCD block and dispatch onto the same thread as the operation started on. Is this even possible with GCD, as I can only specify a queue to dispatch to.
What's the best way to bring this work back onto the same thread that the operation started on? Apart from what I already suggested... unless this is the best way.
回答1:
When the operation is completed the UI update or any other related things has to be done on main thread. The following link might be useful to you about CGD.
http://www.raywenderlich.com/4295/multithreading-and-grand-central-dispatch-on-ios-for-beginners-tutorial
回答2:
I don't think this is really possible/advisable. Since iOS 4 onwards, NSOperation is using GCD , and as GCD is managing my threads - I don't think I should be keeping references to them.
I did find some util methods for executing blocks of code on a particular thread. See Practical Blocks by Mike Ash or this article doing similar thing.
As my goal was to keep my core data calls on the same thread, instead I opted to upgrade my code to use parent/child managed object contexts with NSPrivateQueueConcurrencyType, and then used performBlock: on the managed object context to ensure all my call backs on the separate threads got executed correctly by core data.
来源：https://stackoverflow.com/questions/16164879/nsoperation-using-gcd-ensure-all-on-the-same-thread