Alternatives to dispatch_get_current_queue() for c

Question

I have a method that accepts a block and a completion block. The first block should run in the background, while the completion block should run in whatever queue the method was called.

For the latter I always used dispatch_get_current_queue(), but it seems like it's deprecated in iOS 6 or higher. What should I use instead?

Answer 1

This is a me too answer. So I will talk about our use case.

We have a services layer and the UI layer (among other layers). The services layer runs tasks in the background. (Data manipulation tasks, CoreData tasks, Network calls etc). The service layer has a couple operation queues to satisfy the needs of the UI layer.

The UI layer relies on the services layer to do its work and then run a success completion block. This block can have UIKit code in it. A simple use case is to get all messages from the server and reload the collection view.

Here we guarantee that the blocks that are passed into the services layer are dispatched on the queue on which the service was invoked on. Since dispatch_get_current_queue is a deprecated method, we use the NSOperationQueue.currentQueue to get the caller's current queue. Important note on this property.

Calling this method from outside the context of a running operation typically results in nil being returned.

Since we always invoke our services on a known queue (Our custom queues and Main queue) this works well for us. We do have cases where serviceA can call serviceB which can call serviceC. Since we control where the first service call is being made from, we know the rest of the services will follow the same rules.

So NSOperationQueue.currentQueue will always return one of our Queues or the MainQueue.