Issue #19717 has been updated by kjtsanaktsidis (KJ Tsanaktsidis). I finished spiking out a bit of a POC of how this kind of handoff could work - https://github.com/ruby/ruby/pull/7977 I'm sure it is chock-a-block full of other fun bugs, but it seems to make your reproduction script work; it runs to completion in 10 seconds now instead of crashing after ~500ms. WDYT? Is this an approach that's worth pursuing? ---------------------------------------- Feature #19717: `ConditionVariable#signal` is not fair when the wakeup is consistently spurious. https://bugs.ruby-lang.org/issues/19717#change-103678 * Author: ioquatix (Samuel Williams) * Status: Open * Priority: Normal ---------------------------------------- For background, see this issue <https://github.com/socketry/async/issues/99>. It looks like `ConditionVariable#signal` is not fair, if the calling thread immediately reacquires the resource. I've given a detailed reproduction here as it's non-trivial: <https://github.com/ioquatix/ruby-condition-variable-timeout>. Because the spurious wakeup occurs, the thread is pushed to the back of the waitq, which means any other waiting thread will acquire the resource, and that thread will perpetually be at the back of the queue. I believe the solution is to change `ConditionVarialbe#signal` should only remove the thread from the waitq if it's possible to acquire the lock. Otherwise it should be left in place, so that the order is retained, this should result in fair scheduling. -- https://bugs.ruby-lang.org/