diff options
Diffstat (limited to 'src/backend/storage/lmgr/lwlock.c')
| -rw-r--r-- | src/backend/storage/lmgr/lwlock.c | 11 |
1 files changed, 8 insertions, 3 deletions
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c index ffa865eb28a..315a78cda92 100644 --- a/src/backend/storage/lmgr/lwlock.c +++ b/src/backend/storage/lmgr/lwlock.c @@ -1556,9 +1556,10 @@ LWLockConflictsWithVar(LWLock *lock, pg_atomic_uint64 *valptr, uint64 oldval, /* * Test first to see if it the slot is free right now. * - * XXX: the caller uses a spinlock before this, so we don't need a memory - * barrier here as far as the current usage is concerned. But that might - * not be safe in general. + * XXX: the unique caller of this routine, WaitXLogInsertionsToFinish() + * via LWLockWaitForVar(), uses an implied barrier with a spinlock before + * this, so we don't need a memory barrier here as far as the current + * usage is concerned. But that might not be safe in general. */ mustwait = (pg_atomic_read_u32(&lock->state) & LW_VAL_EXCLUSIVE) != 0; @@ -1601,6 +1602,10 @@ LWLockConflictsWithVar(LWLock *lock, pg_atomic_uint64 *valptr, uint64 oldval, * * Note: this function ignores shared lock holders; if the lock is held * in shared mode, returns 'true'. + * + * Be aware that LWLockConflictsWithVar() does not include a memory barrier, + * hence the caller of this function may want to rely on an explicit barrier or + * an implied barrier via spinlock or LWLock to avoid memory ordering issues. */ bool LWLockWaitForVar(LWLock *lock, pg_atomic_uint64 *valptr, uint64 oldval, |