Issue #21158 has been updated by luke-gru (Luke Gruber). Thank you for the report, I'm able to reproduce it. This is happening because if the proc doesn't match (`receive_if` fails), the basket value is changed from `reserved` to `ref` so it never goes back to sleep (`ractor_queue_empty_p` always return false and we don't get into the `ractor_sleep` function.) I'll take a closer look and try to get a patch out soon. ---------------------------------------- Bug #21158: Ractor using 'receive_if' sits in busy wait when there are skipped messages in the incoming queue https://bugs.ruby-lang.org/issues/21158#change-112154 * Author: NeilW (Neil Wilson) * Status: Open * ruby -v: ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [x86_64-linux] * Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- When using the conditional receive example from the Ractor documentation (either as a script, or within irb) <pre> r = Ractor.new do val = Ractor.receive_if{|msg| msg.is_a?(Array)} puts "Received successfully: #{val}" end r.send(1) r.send('test') </pre> ruby will sit in busy wait, pegging the processor at 100%, until it gets a message that matches the condition. Within irb it will often stop the REPL responding. The same problem occurs on ruby 3.02, 3.3.7 and 3.4.1 -- https://bugs.ruby-lang.org/