From aee0f0645919d3e7b46fcea9a55f8747b635bf7e Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Mon, 5 Jan 2026 20:40:38 -0500 Subject: [PATCH v9 04/10] lwlock: Invert meaning of LW_FLAG_RELEASE_OK Instead of setting a flag whenever a lock release is supposed to wake up waiters - the majority of the time - set a flag whenever wakeups are inhibited. The motivation for this that in an upcoming commit, buffer content locks are implemented separately from lwlocks, and for buffer content locks it is useful to be able to reset all buffer flags when a buffer invalidated, alternatively we would have to set the release-ok flag when making a buffer valid. It seems good to keep the implementation of lwlocks and buffer content locks as similar as reasonably possible. Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- src/backend/storage/lmgr/lwlock.c | 42 +++++++++++++++---------------- 1 file changed, 20 insertions(+), 22 deletions(-) diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c index 6a9f86d5025..148309cc186 100644 --- a/src/backend/storage/lmgr/lwlock.c +++ b/src/backend/storage/lmgr/lwlock.c @@ -92,7 +92,7 @@ #define LW_FLAG_HAS_WAITERS ((uint32) 1 << 31) -#define LW_FLAG_RELEASE_OK ((uint32) 1 << 30) +#define LW_FLAG_WAKE_IN_PROGRESS ((uint32) 1 << 30) #define LW_FLAG_LOCKED ((uint32) 1 << 29) #define LW_FLAG_BITS 3 #define LW_FLAG_MASK (((1<nwaiters), - (state & LW_FLAG_RELEASE_OK) != 0))); + (state & LW_FLAG_WAKE_IN_PROGRESS) != 0))); } } @@ -700,7 +700,7 @@ LWLockInitialize(LWLock *lock, int tranche_id) /* verify the tranche_id is valid */ (void) GetLWTrancheName(tranche_id); - pg_atomic_init_u32(&lock->state, LW_FLAG_RELEASE_OK); + pg_atomic_init_u32(&lock->state, 0); #ifdef LOCK_DEBUG pg_atomic_init_u32(&lock->nwaiters, 0); #endif @@ -929,15 +929,13 @@ LWLockWaitListUnlock(LWLock *lock) static void LWLockWakeup(LWLock *lock) { - bool new_release_ok; + bool new_release_in_progress = false; bool wokeup_somebody = false; proclist_head wakeup; proclist_mutable_iter iter; proclist_init(&wakeup); - new_release_ok = true; - /* lock wait list while collecting backends to wake up */ LWLockWaitListLock(lock); @@ -958,7 +956,7 @@ LWLockWakeup(LWLock *lock) * that are just waiting for the lock to become free don't retry * automatically. */ - new_release_ok = false; + new_release_in_progress = true; /* * Don't wakeup (further) exclusive locks. @@ -997,10 +995,10 @@ LWLockWakeup(LWLock *lock) /* compute desired flags */ - if (new_release_ok) - desired_state |= LW_FLAG_RELEASE_OK; + if (new_release_in_progress) + desired_state |= LW_FLAG_WAKE_IN_PROGRESS; else - desired_state &= ~LW_FLAG_RELEASE_OK; + desired_state &= ~LW_FLAG_WAKE_IN_PROGRESS; if (proclist_is_empty(&lock->waiters)) desired_state &= ~LW_FLAG_HAS_WAITERS; @@ -1131,10 +1129,10 @@ LWLockDequeueSelf(LWLock *lock) */ /* - * Reset RELEASE_OK flag if somebody woke us before we removed - * ourselves - they'll have set it to false. + * Clear LW_FLAG_WAKE_IN_PROGRESS if somebody woke us before we + * removed ourselves - they'll have set it. */ - pg_atomic_fetch_or_u32(&lock->state, LW_FLAG_RELEASE_OK); + pg_atomic_fetch_and_u32(&lock->state, ~LW_FLAG_WAKE_IN_PROGRESS); /* * Now wait for the scheduled wakeup, otherwise our ->lwWaiting would @@ -1301,7 +1299,7 @@ LWLockAcquire(LWLock *lock, LWLockMode mode) } /* Retrying, allow LWLockRelease to release waiters again. */ - pg_atomic_fetch_or_u32(&lock->state, LW_FLAG_RELEASE_OK); + pg_atomic_fetch_and_u32(&lock->state, ~LW_FLAG_WAKE_IN_PROGRESS); #ifdef LOCK_DEBUG { @@ -1636,10 +1634,10 @@ LWLockWaitForVar(LWLock *lock, pg_atomic_uint64 *valptr, uint64 oldval, LWLockQueueSelf(lock, LW_WAIT_UNTIL_FREE); /* - * Set RELEASE_OK flag, to make sure we get woken up as soon as the - * lock is released. + * Clear LW_FLAG_WAKE_IN_PROGRESS flag, to make sure we get woken up + * as soon as the lock is released. */ - pg_atomic_fetch_or_u32(&lock->state, LW_FLAG_RELEASE_OK); + pg_atomic_fetch_and_u32(&lock->state, ~LW_FLAG_WAKE_IN_PROGRESS); /* * We're now guaranteed to be woken up if necessary. Recheck the lock @@ -1852,11 +1850,11 @@ LWLockReleaseInternal(LWLock *lock, LWLockMode mode) TRACE_POSTGRESQL_LWLOCK_RELEASE(T_NAME(lock)); /* - * We're still waiting for backends to get scheduled, don't wake them up - * again. + * Check if we're still waiting for backends to get scheduled, if so, + * don't wake them up again. */ - if ((oldstate & (LW_FLAG_HAS_WAITERS | LW_FLAG_RELEASE_OK)) == - (LW_FLAG_HAS_WAITERS | LW_FLAG_RELEASE_OK) && + if ((oldstate & LW_FLAG_HAS_WAITERS) && + !(oldstate & LW_FLAG_WAKE_IN_PROGRESS) && (oldstate & LW_LOCK_MASK) == 0) check_waiters = true; else -- 2.48.1.76.g4e746b1a31.dirty