Add spin-wait hint to BlockingMpscQueue producer-side busy loops#4831
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merlimat wants to merge 1 commit into
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Add spin-wait hint to BlockingMpscQueue producer-side busy loops#4831merlimat wants to merge 1 commit into
merlimat wants to merge 1 commit into
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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.