Returns a Boolean value that indicates whether the run loop is waiting for an event.
- iOS 2.0+
- macOS 10.0+
- tvOS 9.0+
- watchOS 2.0+
- Core Foundation
The run loop to examine.
rl has no events to process and is blocking, waiting for a source or timer to become ready to fire;
rl either is not running or is currently processing a source, timer, or observer.
This function is useful only to test the state of another thread’s run loop. When called with the current thread’s run loop, this function always returns