Add spin-wait hint to BlockingMpscQueue producer-side busy loops#4831
Merged
Conversation
zymap
approved these changes
Jul 14, 2026
merlimat
added a commit
that referenced
this pull request
Jul 14, 2026
(cherry picked from commit f1d7cc1)
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Motivation
BlockingMpscQueue.put()and the timedoffer()busy-spin onrelaxedOffer()in a bare loop, with no pause hint. When the queue fills up under back-pressure (e.g. the journal queue withenableBusyWait=true), every blocked producer thread pins a core spinning at full speed — competing for CPU with the very consumer thread that needs to run to drain the queue.The consumer side (
take()/poll()) already idles throughWAIT_STRATEGY.idle(), which uses theThread.onSpinWait()intrinsic (viaBusyWait.onSpinWait()). The producer side was missing the same treatment.Changes
Apply the same wait strategy in the
put()andoffer(timeout)spin loops. The producers still busy-spin (by design for this queue), but with the spin-wait hint that reduces power/pipeline contention and lets the sibling hyperthread — often the consumer — make progress.Verified with
BlockingMpscQueueTest(4/4 pass) and module checkstyle.