Cancels the specified dispatch block asynchronously.
- iOS 8.0+
- macOS 10.10+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 2.0+
Cancellation causes any future execution of the dispatch block to return immediately, but does not affect any execution of the block object that is already in progress.
Release of any resources associated with the block object is delayed until execution of the block object is next attempted (or any execution already in progress completes).