Async (Ruby)

Async Ruby adds new concurrency features to the language; you can think of it as “threads with none of the downsides”. It’s been in the making for a couple of years, and with Ruby 3.0, it’s finally ready for prime time. - Bruno Sutic / HN

why async/await seems to have taken over the world?

In single threaded scripting languages, it has arisen as a way to allow overlapping computation with communication without having to introduce multi threading and dealing with the fact that memory management and existing code in the language aren’t thread-safe.
when you require 1 thread per 1 connection, you have trouble getting to thousands of active connections and people want to scale way beyond that. (C10k problem)
- The alternative is lightweight/green threads and actors.
- Those are all some form of coroutines.
- The thing with await is that it can be retrofitted onto existing languages and runtimes with relatively little effort.

Ruby

Ruby 3.0 implements a “fiber scheduler” feature that enables “colorless Async”.

Async Ruby is much more performant than threads. There are less context switches, enabled by the event reactor. The performance benefits are visible in simple scenarios like making a thousand HTTP requests.
Async is more scalable, can handle millions concurrent tasks (like HTTP connections). There can only be a couple thousand threads at the same time.

I regret adding threads. —Matz