with_event_loop ~clock fn starts an Lwt event loop running and then executes fn (). When that finishes, the event loop is stopped.

run_eio fn allows running Eio code from within a Lwt function. It runs fn () in a new Eio fibre and returns a promise for the result. The new fibre is attached to the Lwt event loop's switch and will be cancelled if the function passed to with_event_loop returns.

notify () causes Lwt_engine.iter to return, indicating that the event loop should run the hooks and resume yielded threads. Ideally, you should call this when an Eio fibre wakes up a Lwt thread, e.g. by resolving a Lwt promise. In most cases however this isn't really needed, since Lwt_unix.yield is deprecated and Lwt.pause will call this automatically.