Brandon got Discourse running a year ago:
https://twitter.com/brandonfish/status/1486755128577253376
https://twitter.com/brandonfish/status/1519726230936993792
One issue IIRC was some gems rely on Hash being thread-safe, which we have a general solution for but is not merged/integrated yet in TruffleRuby. OTOH it’s very rarely correct to just use Hash concurrently, it often results in hiding concurrency bugs in harder-to-find ways. So it’s arguably better to just fix the gems relying on that, but that takes time.
We need to benchmark performance, and for that to be meaningful/representative we should benchmark multi-threaded. That needs A way to mark C extensions as thread-safe, so they can be executed in parallel · Issue #2136 · truffleruby/truffleruby · GitHub