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| author | Alexander Korotkov <akorotkov@postgresql.org> | 2024-04-07 00:32:35 +0300 |
|---|---|---|
| committer | Alexander Korotkov <akorotkov@postgresql.org> | 2024-04-07 00:49:53 +0300 |
| commit | ee79928441e7e291532b833455ebfee27d7cab5c (patch) | |
| tree | bc8115da4fbef2a910f5f45531b21c9095b716bb /src/backend/commands/waitlsn.c | |
| parent | 25f42429e2ff2acca35c9154fc2e36b75c79227a (diff) | |
| download | postgresql-ee79928441e7e291532b833455ebfee27d7cab5c.tar.gz postgresql-ee79928441e7e291532b833455ebfee27d7cab5c.zip | |
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
Diffstat (limited to 'src/backend/commands/waitlsn.c')
| -rw-r--r-- | src/backend/commands/waitlsn.c | 10 |
1 files changed, 8 insertions, 2 deletions
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(); } |