I haven't touched Ruby in a while, but are there any common multithreaded use cases? It seemed like the direction was to go multi-process for web workloads (E.g. with Unicorn).
I outline some of the key improvements in this talk:
I converted the streaming and Autopark clients in the Tesla API gem from EM to Async and has been great: https://github.com/timdorr/tesla-api/blob/master/lib/tesla_a...
No more globals, which makes it much safer to use inside of threaded job runners like Sidekiq.
"Nobody is using Ruby for multithreading" is both cause and effect.
That's why I'm not terribly optimistic about projects like this (or the proposed Swift 6). That's not how these things work. Can you imagine a language which features good concurrency support today (like Erlang or Clojure) having been launched without it, and then announcing 5 (or 25) years later "We're going to address concurrency now"?
Even if the background process is I/O intensive (which is supposed to be most of the time waiting, therefore freeing the CPU for the foreground process), it doesn't mean it won't end up still blocking (I've experienced this with filesystem operations).