Gets the value for the key associated with the specified dispatch queue.
- iOS 5.0+
- macOS 10.7+
- UIKit for Mac 13.0+Beta
- tvOS 9.0+
- watchOS 2.0+
The queue containing the desired context data. This parameter must not be
The key that identifies the associated context data. Keys are only compared as pointers and are never dereferenced. Thus, you can use a pointer to a static variable for a specific subsystem or any other value that allows you to identify the value uniquely. Specifying a pointer to a string constant is not recommended.
The context data associated with
NULL if no context was found.
You can use this method to get the context data associated with a specific dispatch queue. Blocks executing on a queue can use the
dispatch function to retrieve the context associated with that specific queue instead.