ruby-nio4r 2.3.1-1build1 (armhf binary) in ubuntu focal

 nio4r (New IO for Ruby) 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.