The poll() based event framework for 389 is being revamped to use a new framework based on the project Nunc Stans. Nunc Stans is a thread pool based event framework wrapper. That is, it provides a layer on top of event frameworks like libevent, tevent, libev, etc., or directly on top of epoll() (if we didn't want to use an event framework). Nunc Stans has some features that are interesting to 389:
It provides thread safe access to the event framework, allowing the use of non-thread safe event frameworks.
It provides timed I/O events to facilitate idle timeouts.
It provides the ability to run event callbacks in a thread pool or in the main event loop thread.
It uses lock free data structures to reduce thread contention.