Returns the queue on which the currently executing block is running.
- iOS 4.0–6.0Deprecated
- macOS 10.6–10.9Deprecated
- tvOS 9.0–9.0Deprecated
- watchOS 2.0–2.0Deprecated
Returns the current queue.
This function is defined to never return
When called from outside of the context of a submitted block, this function returns the main queue if the call is executed from the main thread. If the call is made from any other thread, this function returns the default concurrent queue.