cancel()
Asynchronously cancels the dispatch source, preventing any further invocation of its event handler block.
Declaration
func cancel()Discussion
Cancellation prevents any further invocation of the event handler block for the dispatch source, but does not interrupt any work that is already in progress. If a cancellation handler was set before cancellation, it is sub mitted to the target queue once any in-progress event handler work is finished. Once the cancellation handler is submitted, it is safe to close the source’s handle (file descriptor or mach port). It is invalid to close a file descriptor or deallocate a mach port that is currently being tracked by a dispatch source object before the cancellation handler is invoked.