Release the Notifier in your “stop” event case in the top loop; that will cause an error in the “wait on notification" in the bottom loop, causing it to shutdown (since the error is wired to the stop of the loop).
That was the use case of the original post; to start and stop listening on FIFO for incoming data. I use secondary loops like this for things I have to wait on, such as a TCP connection. If instead you want a second loop to execute commands from the primary loop, then you are better off using a queue. But you can still use the destruction of the queue in the primary loop to trigger shutdown of the secondary.