nio4r provides an abstract, cross-platform stateful I/O selector API for Ruby.
I/O selectors are the heart of "reactor"-based event loops, and monitor multiple
I/O objects for various types of readiness, e.g. ready for reading or writing.

The most similar API provided by Ruby today is Kernel.select, however the select
API requires you to pass in arrays of all of the I/O objects you're interested
in every time. nio4r provides a more object-oriented API that lets you register
I/O objects with a selector then handle them when they're selected for various
types of events.

nio4r is modeled after the Java NIO API, but simplified for ease-of-use.

Its goals are:
- Expose high-level interfaces for stateful IO selectors
- Keep the API small to maximize both portability and performance across many
  different OSes and Ruby VMs
- Provide inherently thread-safe facilities for working with IO objects

WWW: https://github.com/socketry/nio4r