From ee79928441e7e291532b833455ebfee27d7cab5c Mon Sep 17 00:00:00 2001 From: Alexander Korotkov Date: Sun, 7 Apr 2024 00:32:35 +0300 Subject: Clarify what is protected by WaitLSNLock Not just WaitLSNState.waitersHeap, but also WaitLSNState.procInfos and updating of WaitLSNState.minWaitedLSN is protected by WaitLSNLock. There is one now documented exclusion on fast-path checking of WaitLSNProcInfo.inHeap flag. Discussion: https://postgr.es/m/202404030658.hhj3vfxeyhft%40alvherre.pgsql --- src/backend/commands/waitlsn.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) (limited to 'src/backend/commands/waitlsn.c') diff --git a/src/backend/commands/waitlsn.c b/src/backend/commands/waitlsn.c index a57b818a2d4..1a83c34e09f 100644 --- a/src/backend/commands/waitlsn.c +++ b/src/backend/commands/waitlsn.c @@ -109,13 +109,13 @@ addLSNWaiter(XLogRecPtr lsn) { WaitLSNProcInfo *procInfo = &waitLSN->procInfos[MyProcNumber]; + LWLockAcquire(WaitLSNLock, LW_EXCLUSIVE); + Assert(!procInfo->inHeap); procInfo->procnum = MyProcNumber; procInfo->waitLSN = lsn; - LWLockAcquire(WaitLSNLock, LW_EXCLUSIVE); - pairingheap_add(&waitLSN->waitersHeap, &procInfo->phNode); procInfo->inHeap = true; updateMinWaitedLSN(); @@ -203,6 +203,12 @@ WaitLSNSetLatches(XLogRecPtr currentLSN) void WaitLSNCleanup(void) { + /* + * We do a fast-path check of the 'inHeap' flag without the lock. This + * flag is set to true only by the process itself. So, it's only possible + * to get a false positive. But that will be eliminated by a recheck + * inside deleteLSNWaiter(). + */ if (waitLSN->procInfos[MyProcNumber].inHeap) deleteLSNWaiter(); } -- cgit v1.2.3