invokeOnCompletion

Register a handle to be invoked when this EnqueuedJob completes, either successfully or by cancellation/error. If handle is already registered, Disposable.noOp is returned.

If the job has already completed, handle is invoked immediately and Disposable.noOp is returned.

If the job completed by cancellation, handle will be invoked with a CancellationException argument to indicate as such.

handle should NOT throw exception. In the event that it does, it will be delegated to the closest UncaughtException.Handler. If handle is being invoked immediately (job completed), exceptions will be delegated to UncaughtException.Handler.THROW. handle should be non-blocking, fast, and thread-safe.

There is no guarantee on the execution context for which handle is invoked from.