summaryrefslogtreecommitdiffstats
path: root/src/backend/storage
diff options
context:
space:
mode:
Diffstat (limited to 'src/backend/storage')
-rw-r--r--src/backend/storage/ipc/procarray.c3
-rw-r--r--src/backend/storage/lmgr/lwlock.c53
-rw-r--r--src/backend/storage/lmgr/proc.c4
3 files changed, 33 insertions, 27 deletions
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 4655d8c..3c4da3c 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2220,8 +2220,7 @@ GetSnapshotDataReuse(Snapshot snapshot)
* but since PGPROC has only a limited cache area for subxact XIDs, full
* information may not be available. If we find any overflowed subxid arrays,
* we have to mark the snapshot's subxid data as overflowed, and extra work
- * *may* need to be done to determine what's running (see XidInMVCCSnapshot()
- * in heapam_visibility.c).
+ * *may* need to be done to determine what's running (see XidInMVCCSnapshot()).
*
* We also update the following backend-global variables:
* TransactionXmin: the oldest xmin of any snapshot in use in the
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 3bb4486..ea34ee7 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -988,6 +988,15 @@ LWLockWakeup(LWLock *lock)
}
/*
+ * Signal that the process isn't on the wait list anymore. This allows
+ * LWLockDequeueSelf() to remove itself of the waitlist with a
+ * proclist_delete(), rather than having to check if it has been
+ * removed from the list.
+ */
+ Assert(waiter->lwWaiting == LW_WS_WAITING);
+ waiter->lwWaiting = LW_WS_PENDING_WAKEUP;
+
+ /*
* Once we've woken up an exclusive lock, there's no point in waking
* up anybody else.
*/
@@ -1044,7 +1053,7 @@ LWLockWakeup(LWLock *lock)
* another lock.
*/
pg_write_barrier();
- waiter->lwWaiting = false;
+ waiter->lwWaiting = LW_WS_NOT_WAITING;
PGSemaphoreUnlock(waiter->sem);
}
}
@@ -1065,7 +1074,7 @@ LWLockQueueSelf(LWLock *lock, LWLockMode mode)
if (MyProc == NULL)
elog(PANIC, "cannot wait without a PGPROC structure");
- if (MyProc->lwWaiting)
+ if (MyProc->lwWaiting != LW_WS_NOT_WAITING)
elog(PANIC, "queueing for lock while waiting on another one");
LWLockWaitListLock(lock);
@@ -1073,7 +1082,7 @@ LWLockQueueSelf(LWLock *lock, LWLockMode mode)
/* setting the flag is protected by the spinlock */
pg_atomic_fetch_or_u32(&lock->state, LW_FLAG_HAS_WAITERS);
- MyProc->lwWaiting = true;
+ MyProc->lwWaiting = LW_WS_WAITING;
MyProc->lwWaitMode = mode;
/* LW_WAIT_UNTIL_FREE waiters are always at the front of the queue */
@@ -1100,8 +1109,7 @@ LWLockQueueSelf(LWLock *lock, LWLockMode mode)
static void
LWLockDequeueSelf(LWLock *lock)
{
- bool found = false;
- proclist_mutable_iter iter;
+ bool on_waitlist;
#ifdef LWLOCK_STATS
lwlock_stats *lwstats;
@@ -1114,18 +1122,13 @@ LWLockDequeueSelf(LWLock *lock)
LWLockWaitListLock(lock);
/*
- * Can't just remove ourselves from the list, but we need to iterate over
- * all entries as somebody else could have dequeued us.
+ * Remove ourselves from the waitlist, unless we've already been
+ * removed. The removal happens with the wait list lock held, so there's
+ * no race in this check.
*/
- proclist_foreach_modify(iter, &lock->waiters, lwWaitLink)
- {
- if (iter.cur == MyProc->pgprocno)
- {
- found = true;
- proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
- break;
- }
- }
+ on_waitlist = MyProc->lwWaiting == LW_WS_WAITING;
+ if (on_waitlist)
+ proclist_delete(&lock->waiters, MyProc->pgprocno, lwWaitLink);
if (proclist_is_empty(&lock->waiters) &&
(pg_atomic_read_u32(&lock->state) & LW_FLAG_HAS_WAITERS) != 0)
@@ -1137,8 +1140,8 @@ LWLockDequeueSelf(LWLock *lock)
LWLockWaitListUnlock(lock);
/* clear waiting state again, nice for debugging */
- if (found)
- MyProc->lwWaiting = false;
+ if (on_waitlist)
+ MyProc->lwWaiting = LW_WS_NOT_WAITING;
else
{
int extraWaits = 0;
@@ -1162,7 +1165,7 @@ LWLockDequeueSelf(LWLock *lock)
for (;;)
{
PGSemaphoreLock(MyProc->sem);
- if (!MyProc->lwWaiting)
+ if (MyProc->lwWaiting == LW_WS_NOT_WAITING)
break;
extraWaits++;
}
@@ -1313,7 +1316,7 @@ LWLockAcquire(LWLock *lock, LWLockMode mode)
for (;;)
{
PGSemaphoreLock(proc->sem);
- if (!proc->lwWaiting)
+ if (proc->lwWaiting == LW_WS_NOT_WAITING)
break;
extraWaits++;
}
@@ -1478,7 +1481,7 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
for (;;)
{
PGSemaphoreLock(proc->sem);
- if (!proc->lwWaiting)
+ if (proc->lwWaiting == LW_WS_NOT_WAITING)
break;
extraWaits++;
}
@@ -1694,7 +1697,7 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
for (;;)
{
PGSemaphoreLock(proc->sem);
- if (!proc->lwWaiting)
+ if (proc->lwWaiting == LW_WS_NOT_WAITING)
break;
extraWaits++;
}
@@ -1772,6 +1775,10 @@ LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 val)
proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
proclist_push_tail(&wakeup, iter.cur, lwWaitLink);
+
+ /* see LWLockWakeup() */
+ Assert(waiter->lwWaiting == LW_WS_WAITING);
+ waiter->lwWaiting = LW_WS_PENDING_WAKEUP;
}
/* We are done updating shared state of the lock itself. */
@@ -1787,7 +1794,7 @@ LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 val)
proclist_delete(&wakeup, iter.cur, lwWaitLink);
/* check comment in LWLockWakeup() about this barrier */
pg_write_barrier();
- waiter->lwWaiting = false;
+ waiter->lwWaiting = LW_WS_NOT_WAITING;
PGSemaphoreUnlock(waiter->sem);
}
}
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index 1b514f4..c60707b 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -397,7 +397,7 @@ InitProcess(void)
/* NB -- autovac launcher intentionally does not set IS_AUTOVACUUM */
if (IsAutoVacuumWorkerProcess())
MyProc->statusFlags |= PROC_IS_AUTOVACUUM;
- MyProc->lwWaiting = false;
+ MyProc->lwWaiting = LW_WS_NOT_WAITING;
MyProc->lwWaitMode = 0;
MyProc->waitLock = NULL;
MyProc->waitProcLock = NULL;
@@ -579,7 +579,7 @@ InitAuxiliaryProcess(void)
MyProc->isBackgroundWorker = IsBackgroundWorker;
MyProc->delayChkptFlags = 0;
MyProc->statusFlags = 0;
- MyProc->lwWaiting = false;
+ MyProc->lwWaiting = LW_WS_NOT_WAITING;
MyProc->lwWaitMode = 0;
MyProc->waitLock = NULL;
MyProc->waitProcLock = NULL;
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-04 02:17:51 +0000