From: "ioquatix (Samuel Williams) via ruby-core" Date: 2023-06-12T02:18:55+00:00 Subject: [ruby-core:113877] [Ruby master Feature#19717] `ConditionVariable#signal` is not fair when the wakeup is consistently spurious. Issue #19717 has been updated by ioquatix (Samuel Williams). > the thread which was waiting the longest will actually be the one woken To me, this is the correct behaviour and what I try to implement in Async. If there is a spurious wakeup, you don't loose your position in the queue. ---------------------------------------- Feature #19717: `ConditionVariable#signal` is not fair when the wakeup is consistently spurious. https://bugs.ruby-lang.org/issues/19717#change-103527 * Author: ioquatix (Samuel Williams) * Status: Open * Priority: Normal ---------------------------------------- For background, see this issue . 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: . 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/ ______________________________________________ ruby-core mailing list -- ruby-core@ml.ruby-lang.org To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org ruby-core info -- https://ml.ruby-lang.org/mailman3/postorius/lists/ruby-core.ml.ruby-lang.org/