Beispiel #1
0
/*
 * LWLockAcquire - acquire a lightweight lock in the specified mode
 *
 * If the lock is not available, sleep until it is.
 *
 * Side effect: cancel/die interrupts are held off until lock release.
 */
void
LWLockAcquire(LWLockId lockid, LWLockMode mode)
{
	volatile LWLock *lock = &(LWLockArray[lockid].lock);
#if LWLOCK_LOCK_PARTS > 1
	volatile LWLockPart *part = LWLOCK_PART(lock, lockid, MyBackendId);
#endif
	PGPROC	   *proc = MyProc;
	bool		retry = false;
	int			extraWaits = 0;

	PRINT_LWDEBUG("LWLockAcquire", lockid, lock);

#ifdef LWLOCK_STATS
	/* Set up local count state first time through in a given process */
	if (counts_for_pid != MyProcPid)
	{
		int		   *LWLockCounter = (int *) ((char *) LWLockArray - 2 * sizeof(int));
		int			numLocks = LWLockCounter[1];

		sh_acquire_counts = calloc(numLocks, sizeof(int));
		ex_acquire_counts = calloc(numLocks, sizeof(int));
		block_counts = calloc(numLocks, sizeof(int));
		counts_for_pid = MyProcPid;
		on_shmem_exit(print_lwlock_stats, 0);
	}
	/* Count lock acquisition attempts */
	if (mode == LW_EXCLUSIVE)
		ex_acquire_counts[lockid]++;
	else
		sh_acquire_counts[lockid]++;
#endif   /* LWLOCK_STATS */

	/*
	 * We can't wait if we haven't got a PGPROC.  This should only occur
	 * during bootstrap or shared memory initialization.  Put an Assert here
	 * to catch unsafe coding practices.
	 */
	Assert(!(proc == NULL && IsUnderPostmaster));

	/* Ensure we will have room to remember the lock */
	if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
		elog(ERROR, "too many LWLocks taken");
		
	/*
	 * Lock out cancel/die interrupts until we exit the code section protected
	 * by the LWLock.  This ensures that interrupts will not interfere with
	 * manipulations of data structures in shared memory.
	 */
	HOLD_INTERRUPTS();

	/*
	 * Loop here to try to acquire lock after each time we are signaled by
	 * LWLockRelease.
	 *
	 * NOTE: it might seem better to have LWLockRelease actually grant us the
	 * lock, rather than retrying and possibly having to go back to sleep. But
	 * in practice that is no good because it means a process swap for every
	 * lock acquisition when two or more processes are contending for the same
	 * lock.  Since LWLocks are normally used to protect not-very-long
	 * sections of computation, a process needs to be able to acquire and
	 * release the same lock many times during a single CPU time slice, even
	 * in the presence of contention.  The efficiency of being able to do that
	 * outweighs the inefficiency of sometimes wasting a process dispatch
	 * cycle because the lock is not free when a released waiter finally gets
	 * to run.	See pgsql-hackers archives for 29-Dec-01.
	 */
	for (;;)
	{
		bool		mustwait;
		
		if (mode == LW_SHARED)
		{
#ifdef		LWLOCK_PART_SHARED_OPS_ATOMIC
			/* Increment shared counter partition. If there's no contention,
			 * this is sufficient to take the lock
			 */
			LWLOCK_PART_SHARED_POSTINC_ATOMIC(lock, lockid, part, MyBackendId);
			LWLOCK_PART_SHARED_FENCE();
			
			/* A concurrent exclusive locking attempt does the following
			 * three steps
			 *   1) Acquire mutex
			 *   2) Check shared counter partitions for readers.
			 *   3a) If found add proc to wait queue, block, restart at (1)
			 *   3b) If not found, set exclusive flag, continue with (4)
			 *   4) Enter protected section
			 * The fence after the atomic add above ensures that no further
			 * such attempt can proceed to (3b) or beyond. There may be
			 * pre-existing exclusive locking attempts at step (3b) or beyond,
			 * but we can recognize those by either the mutex being taken, or
			 * the exclusive flag being set. Conversely, if we see neither, we
			 * may proceed and enter the protected section.
			 *
			 * FIXME: This doesn't work if slock_t is a struct or doesn't
			 * use 0 for state "unlocked".
			 */

			if ((lock->mutex == 0) && (lock->exclusive == 0)) {
				/* If retrying, allow LWLockRelease to release waiters again.
				 * Usually this happens after we acquired the mutex, but if
				 * we skip that, we still need to set releaseOK.
				 *
				 * Acquiring the mutex here is not really an option - if many
				 * reader are awoken simultaneously by an exclusive unlock,
				 * that would be a source of considerable contention.
				 *
				 * Fotunately, this is safe even without the mutex. First,
				 * there actually cannot be any non-fast path unlocking
				 * attempt in progress, because we'd then either still see
				 * the exclusive flag set or the mutex being taken. And
				 * even if there was, and such an attempt cleared the flag
				 * immediately after we set it, it'd also wake up some waiter
				 * who'd then re-set the flag.
				 *
				 * The only reason to do this here, and not directly
				 * after returning from PGSemaphoreLock(), is that it seems
				 * benefical to make SpinLockAcquire() the first thing to
				 * touch the lock if possible, in case we acquire the spin
				 * lock at all. That way, the cache line doesn't go through
				 * a possible shared state, but instead directly to exclusive.
				 * On Opterons at least, there seems to be a difference, c.f.
				 * the comment above tas() for x86_64 in s_lock.h
				 */
				if (retry && !lock->releaseOK)
					lock->releaseOK = true;
					
				goto lock_acquired;
			}
				
			/* At this point, we don't know if the concurrent exclusive locker
			 * has proceeded to (3b) or blocked. We must take the mutex and
			 * re-check
			 */
#endif /* LWLOCK_PART_SHARED_OPS_ATOMIC */
			
			/* Acquire mutex.  Time spent holding mutex should be short! */
			SpinLockAcquire(&lock->mutex);
			
			if (lock->exclusive == 0)
			{
#ifdef LWLOCK_PART_SHARED_OPS_ATOMIC
				/* Already incremented the shared counter partition above */
#else
				lock->shared++;
#endif
				mustwait = false;
			}
			else
			{
#ifdef LWLOCK_PART_SHARED_OPS_ATOMIC
				/* Must undo shared counter partition increment. Note that
				 * we *need* to do that while holding the mutex. Otherwise,
				 * the exclusive lock could be released and attempted to be
				 * re-acquired before we undo the increment. That attempt
				 * would then block, even though there'd be no lock holder
				 * left
				 */
				LWLOCK_PART_SHARED_POSTDEC_ATOMIC(lock, lockid, part, MyBackendId);
#endif
				mustwait = true;
			}
		}
		else
		{
			/* Step (1). Acquire mutex. Time spent holding mutex should be
			 *                          short!
			 */
			SpinLockAcquire(&lock->mutex);
			
			if (lock->exclusive == 0)
			{
				/* Step (2). Check for shared lockers. This surely happens
				 * after (1), otherwise SpinLockAcquire() is broken. Lock
				 * acquire semantics demand that no load must be re-ordered
				 * from after a lock acquisition to before, for obvious
				 * reasons.
				 */

				LWLOCK_IS_SHARED(mustwait, lock, lockid);
				
				if (!mustwait) {
					/* Step (3a). Set exclusive flag. This surely happens
					 * after (2) because it depends on the result of (2),
					 * no matter how much reordering is going on here.
					 */
					lock->exclusive++;
				}
			}
			else
				mustwait = true;
		}
		
		/* If retrying, allow LWLockRelease to release waiters again.
		 * This is also separately done in the LW_SHARED early exit case
		 * above, and in contrast to there we don't hold the mutex there.
		 * See the comment there for why this is safe
		 */
		if (retry)
			lock->releaseOK = true;
		
		if (!mustwait)
			break;				/* got the lock */
			
		/*
		 * Step (3b). Add myself to wait queue.
		 *
		 * If we don't have a PGPROC structure, there's no way to wait. This
		 * should never occur, since MyProc should only be null during shared
		 * memory initialization.
		 */
		if (proc == NULL)
			elog(PANIC, "cannot wait without a PGPROC structure");

		proc->lwWaiting = true;
		proc->lwExclusive = (mode == LW_EXCLUSIVE);
		proc->lwWaitLink = NULL;
		if (lock->head == NULL)
			lock->head = proc;
		else
			lock->tail->lwWaitLink = proc;
		lock->tail = proc;

		/* Can release the mutex now */
		SpinLockRelease(&lock->mutex);

		/*
		 * Wait until awakened.
		 *
		 * Since we share the process wait semaphore with the regular lock
		 * manager and ProcWaitForSignal, and we may need to acquire an LWLock
		 * while one of those is pending, it is possible that we get awakened
		 * for a reason other than being signaled by LWLockRelease. If so,
		 * loop back and wait again.  Once we've gotten the LWLock,
		 * re-increment the sema by the number of additional signals received,
		 * so that the lock manager or signal manager will see the received
		 * signal when it next waits.
		 */
		LOG_LWDEBUG("LWLockAcquire", lockid, "waiting");

#ifdef LWLOCK_STATS
		block_counts[lockid]++;
#endif

		TRACE_POSTGRESQL_LWLOCK_WAIT_START(lockid, mode);

		for (;;)
		{
			/* "false" means cannot accept cancel/die interrupt here. */
			PGSemaphoreLock(&proc->sem, false);
			if (!proc->lwWaiting)
				break;
			extraWaits++;
		}

		TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(lockid, mode);

		LOG_LWDEBUG("LWLockAcquire", lockid, "awakened");

		/* Now loop back and try to acquire lock again. */
		retry = true;
	}

	/* We are done updating shared state of the lock itself. */
	SpinLockRelease(&lock->mutex);
	
	/* Step 4. Enter protected section. This surely happens after (3),
	 * this time because lock release semantics demand that no store
	 * must be moved from before a lock release to after the release,
	 * again for obvious reasons
	 */

#ifdef LWLOCK_PART_SHARED_OPS_ATOMIC
lock_acquired:
#endif

	TRACE_POSTGRESQL_LWLOCK_ACQUIRE(lockid, mode);

	/* Add lock to list of locks held by this backend */
	held_lwlocks[num_held_lwlocks] = lockid;
	held_lwlocks_mode[num_held_lwlocks] = mode;
	++num_held_lwlocks;

	/*
	 * Fix the process wait semaphore's count for any absorbed wakeups.
	 */
	while (extraWaits-- > 0)
		PGSemaphoreUnlock(&proc->sem);
}
Beispiel #2
0
/*
 * LWLockWaitForVar - Wait until lock is free, or a variable is updated.
 *
 * If the lock is held and *valptr equals oldval, waits until the lock is
 * either freed, or the lock holder updates *valptr by calling
 * LWLockUpdateVar.  If the lock is free on exit (immediately or after
 * waiting), returns true.  If the lock is still held, but *valptr no longer
 * matches oldval, returns false and sets *newval to the current value in
 * *valptr.
 *
 * It's possible that the lock holder releases the lock, but another backend
 * acquires it again before we get a chance to observe that the lock was
 * momentarily released.  We wouldn't need to wait for the new lock holder,
 * but we cannot distinguish that case, so we will have to wait.
 *
 * Note: this function ignores shared lock holders; if the lock is held
 * in shared mode, returns 'true'.
 */
bool
LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
{
	PGPROC	   *proc = MyProc;
	int			extraWaits = 0;
	bool		result = false;
#ifdef LWLOCK_STATS
	lwlock_stats *lwstats;
#endif

	PRINT_LWDEBUG("LWLockWaitForVar", lock);

#ifdef LWLOCK_STATS
	lwstats = get_lwlock_stats_entry(lock);
#endif   /* LWLOCK_STATS */

	/*
	 * Quick 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.
	 */
	if (lock->exclusive == 0)
		return true;

	/*
	 * Lock out cancel/die interrupts while we sleep on the lock.  There is no
	 * cleanup mechanism to remove us from the wait queue if we got
	 * interrupted.
	 */
	HOLD_INTERRUPTS();

	/*
	 * Loop here to check the lock's status after each time we are signaled.
	 */
	for (;;)
	{
		bool		mustwait;
		uint64		value;

		/* Acquire mutex.  Time spent holding mutex should be short! */
#ifdef LWLOCK_STATS
		lwstats->spin_delay_count += SpinLockAcquire(&lock->mutex);
#else
		SpinLockAcquire(&lock->mutex);
#endif

		/* Is the lock now free, and if not, does the value match? */
		if (lock->exclusive == 0)
		{
			result = true;
			mustwait = false;
		}
		else
		{
			value = *valptr;
			if (value != oldval)
			{
				result = false;
				mustwait = false;
				*newval = value;
			}
			else
				mustwait = true;
		}

		if (!mustwait)
			break;				/* the lock was free or value didn't match */

		/*
		 * Add myself to wait queue.
		 */
		proc->lwWaiting = true;
		proc->lwWaitMode = LW_WAIT_UNTIL_FREE;
		/* waiters are added to the front of the queue */
		proc->lwWaitLink = lock->head;
		if (lock->head == NULL)
			lock->tail = proc;
		lock->head = proc;

		/*
		 * Set releaseOK, to make sure we get woken up as soon as the lock is
		 * released.
		 */
		lock->releaseOK = true;

		/* Can release the mutex now */
		SpinLockRelease(&lock->mutex);

		/*
		 * Wait until awakened.
		 *
		 * Since we share the process wait semaphore with the regular lock
		 * manager and ProcWaitForSignal, and we may need to acquire an LWLock
		 * while one of those is pending, it is possible that we get awakened
		 * for a reason other than being signaled by LWLockRelease. If so,
		 * loop back and wait again.  Once we've gotten the LWLock,
		 * re-increment the sema by the number of additional signals received,
		 * so that the lock manager or signal manager will see the received
		 * signal when it next waits.
		 */
		LOG_LWDEBUG("LWLockWaitForVar", T_NAME(lock), T_ID(lock), "waiting");

#ifdef LWLOCK_STATS
		lwstats->block_count++;
#endif

		TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), T_ID(lock),
										   LW_EXCLUSIVE);

		for (;;)
		{
			/* "false" means cannot accept cancel/die interrupt here. */
			PGSemaphoreLock(&proc->sem, false);
			if (!proc->lwWaiting)
				break;
			extraWaits++;
		}

		TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), T_ID(lock),
										  LW_EXCLUSIVE);

		LOG_LWDEBUG("LWLockWaitForVar", T_NAME(lock), T_ID(lock), "awakened");

		/* Now loop back and check the status of the lock again. */
	}

	/* We are done updating shared state of the lock itself. */
	SpinLockRelease(&lock->mutex);

	TRACE_POSTGRESQL_LWLOCK_ACQUIRE(T_NAME(lock), T_ID(lock), LW_EXCLUSIVE);

	/*
	 * Fix the process wait semaphore's count for any absorbed wakeups.
	 */
	while (extraWaits-- > 0)
		PGSemaphoreUnlock(&proc->sem);

	/*
	 * Now okay to allow cancel/die interrupts.
	 */
	RESUME_INTERRUPTS();

	return result;
}
Beispiel #3
0
/*
 * LWLockAcquire - acquire a lightweight lock in the specified mode
 *
 * If the lock is not available, sleep until it is.
 *
 * Side effect: cancel/die interrupts are held off until lock release.
 */
void
LWLockAcquire(LWLockId lockid, LWLockMode mode)
{
	volatile LWLock *lock = &(LWLockArray[lockid].lock);
	PGPROC	   *proc = MyProc;
	bool		retry = false;
	int			extraWaits = 0;

	PRINT_LWDEBUG("LWLockAcquire", lockid, lock);

#ifdef LWLOCK_STATS
	/* Set up local count state first time through in a given process */
	if (counts_for_pid != MyProcPid)
	{
		int		   *LWLockCounter = (int *) ((char *) LWLockArray - 2 * sizeof(int));
		int			numLocks = LWLockCounter[1];

		sh_acquire_counts = calloc(numLocks, sizeof(int));
		ex_acquire_counts = calloc(numLocks, sizeof(int));
		block_counts = calloc(numLocks, sizeof(int));
		counts_for_pid = MyProcPid;
		on_shmem_exit(print_lwlock_stats, 0);
	}
	/* Count lock acquisition attempts */
	if (mode == LW_EXCLUSIVE)
		ex_acquire_counts[lockid]++;
	else
		sh_acquire_counts[lockid]++;
#endif   /* LWLOCK_STATS */

	/*
	 * We can't wait if we haven't got a PGPROC.  This should only occur
	 * during bootstrap or shared memory initialization.  Put an Assert here
	 * to catch unsafe coding practices.
	 */
	Assert(!(proc == NULL && IsUnderPostmaster));

	/* Ensure we will have room to remember the lock */
	if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
		elog(ERROR, "too many LWLocks taken");

	/*
	 * Lock out cancel/die interrupts until we exit the code section protected
	 * by the LWLock.  This ensures that interrupts will not interfere with
	 * manipulations of data structures in shared memory.
	 */
	HOLD_INTERRUPTS();

	/*
	 * Loop here to try to acquire lock after each time we are signaled by
	 * LWLockRelease.
	 *
	 * NOTE: it might seem better to have LWLockRelease actually grant us the
	 * lock, rather than retrying and possibly having to go back to sleep. But
	 * in practice that is no good because it means a process swap for every
	 * lock acquisition when two or more processes are contending for the same
	 * lock.  Since LWLocks are normally used to protect not-very-long
	 * sections of computation, a process needs to be able to acquire and
	 * release the same lock many times during a single CPU time slice, even
	 * in the presence of contention.  The efficiency of being able to do that
	 * outweighs the inefficiency of sometimes wasting a process dispatch
	 * cycle because the lock is not free when a released waiter finally gets
	 * to run.	See pgsql-hackers archives for 29-Dec-01.
	 */
	for (;;)
	{
		bool		mustwait;

		/* Acquire mutex.  Time spent holding mutex should be short! */
		SpinLockAcquire(&lock->mutex);

		/* If retrying, allow LWLockRelease to release waiters again */
		if (retry)
			lock->releaseOK = true;

		/* If I can get the lock, do so quickly. */
		if (mode == LW_EXCLUSIVE)
		{
			if (lock->exclusive == 0 && lock->shared == 0)
			{
				lock->exclusive++;
				mustwait = false;
			}
			else
				mustwait = true;
		}
		else
		{
			if (lock->exclusive == 0)
			{
				lock->shared++;
				mustwait = false;
			}
			else
				mustwait = true;
		}

		if (!mustwait)
			break;				/* got the lock */

		/*
		 * Add myself to wait queue.
		 *
		 * If we don't have a PGPROC structure, there's no way to wait. This
		 * should never occur, since MyProc should only be null during shared
		 * memory initialization.
		 */
		if (proc == NULL)
			elog(PANIC, "cannot wait without a PGPROC structure");

		proc->lwWaiting = true;
		proc->lwExclusive = (mode == LW_EXCLUSIVE);
		proc->lwWaitLink = NULL;
		if (lock->head == NULL)
			lock->head = proc;
		else
			lock->tail->lwWaitLink = proc;
		lock->tail = proc;

		/* Can release the mutex now */
		SpinLockRelease(&lock->mutex);

		/*
		 * Wait until awakened.
		 *
		 * Since we share the process wait semaphore with the regular lock
		 * manager and ProcWaitForSignal, and we may need to acquire an LWLock
		 * while one of those is pending, it is possible that we get awakened
		 * for a reason other than being signaled by LWLockRelease. If so,
		 * loop back and wait again.  Once we've gotten the LWLock,
		 * re-increment the sema by the number of additional signals received,
		 * so that the lock manager or signal manager will see the received
		 * signal when it next waits.
		 */
		LOG_LWDEBUG("LWLockAcquire", lockid, "waiting");

#ifdef LWLOCK_STATS
		block_counts[lockid]++;
#endif

		TRACE_POSTGRESQL_LWLOCK_WAIT_START(lockid, mode);

		for (;;)
		{
			/* "false" means cannot accept cancel/die interrupt here. */
			PGSemaphoreLock(&proc->sem, false);
			if (!proc->lwWaiting)
				break;
			extraWaits++;
		}

		TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(lockid, mode);

		LOG_LWDEBUG("LWLockAcquire", lockid, "awakened");

		/* Now loop back and try to acquire lock again. */
		retry = true;
	}

	/* We are done updating shared state of the lock itself. */
	SpinLockRelease(&lock->mutex);

	TRACE_POSTGRESQL_LWLOCK_ACQUIRE(lockid, mode);

	/* Add lock to list of locks held by this backend */
	held_lwlocks[num_held_lwlocks++] = lockid;

	/*
	 * Fix the process wait semaphore's count for any absorbed wakeups.
	 */
	while (extraWaits-- > 0)
		PGSemaphoreUnlock(&proc->sem);
}
Beispiel #4
0
/*
 * LWLockAcquireOrWait - Acquire lock, or wait until it's free
 *
 * The semantics of this function are a bit funky.  If the lock is currently
 * free, it is acquired in the given mode, and the function returns true.  If
 * the lock isn't immediately free, the function waits until it is released
 * and returns false, but does not acquire the lock.
 *
 * This is currently used for WALWriteLock: when a backend flushes the WAL,
 * holding WALWriteLock, it can flush the commit records of many other
 * backends as a side-effect.  Those other backends need to wait until the
 * flush finishes, but don't need to acquire the lock anymore.  They can just
 * wake up, observe that their records have already been flushed, and return.
 */
bool
LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
{
	PGPROC	   *proc = MyProc;
	bool		mustwait;
	int			extraWaits = 0;
#ifdef LWLOCK_STATS
	lwlock_stats *lwstats;
#endif

	PRINT_LWDEBUG("LWLockAcquireOrWait", lock);

#ifdef LWLOCK_STATS
	lwstats = get_lwlock_stats_entry(lock);
#endif

	/* Ensure we will have room to remember the lock */
	if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
		elog(ERROR, "too many LWLocks taken");

	/*
	 * Lock out cancel/die interrupts until we exit the code section protected
	 * by the LWLock.  This ensures that interrupts will not interfere with
	 * manipulations of data structures in shared memory.
	 */
	HOLD_INTERRUPTS();

	/* Acquire mutex.  Time spent holding mutex should be short! */
	SpinLockAcquire(&lock->mutex);

	/* If I can get the lock, do so quickly. */
	if (mode == LW_EXCLUSIVE)
	{
		if (lock->exclusive == 0 && lock->shared == 0)
		{
			lock->exclusive++;
			mustwait = false;
		}
		else
			mustwait = true;
	}
	else
	{
		if (lock->exclusive == 0)
		{
			lock->shared++;
			mustwait = false;
		}
		else
			mustwait = true;
	}

	if (mustwait)
	{
		/*
		 * Add myself to wait queue.
		 *
		 * If we don't have a PGPROC structure, there's no way to wait.  This
		 * should never occur, since MyProc should only be null during shared
		 * memory initialization.
		 */
		if (proc == NULL)
			elog(PANIC, "cannot wait without a PGPROC structure");

		proc->lwWaiting = true;
		proc->lwWaitMode = LW_WAIT_UNTIL_FREE;
		proc->lwWaitLink = NULL;
		if (lock->head == NULL)
			lock->head = proc;
		else
			lock->tail->lwWaitLink = proc;
		lock->tail = proc;

		/* Can release the mutex now */
		SpinLockRelease(&lock->mutex);

		/*
		 * Wait until awakened.  Like in LWLockAcquire, be prepared for bogus
		 * wakups, because we share the semaphore with ProcWaitForSignal.
		 */
		LOG_LWDEBUG("LWLockAcquireOrWait", T_NAME(lock), T_ID(lock),
					"waiting");

#ifdef LWLOCK_STATS
		lwstats->block_count++;
#endif

		TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), T_ID(lock), mode);

		for (;;)
		{
			/* "false" means cannot accept cancel/die interrupt here. */
			PGSemaphoreLock(&proc->sem, false);
			if (!proc->lwWaiting)
				break;
			extraWaits++;
		}

		TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), T_ID(lock), mode);

		LOG_LWDEBUG("LWLockAcquireOrWait", T_NAME(lock), T_ID(lock),
					"awakened");
	}
	else
	{
		/* We are done updating shared state of the lock itself. */
		SpinLockRelease(&lock->mutex);
	}

	/*
	 * Fix the process wait semaphore's count for any absorbed wakeups.
	 */
	while (extraWaits-- > 0)
		PGSemaphoreUnlock(&proc->sem);

	if (mustwait)
	{
		/* Failed to get lock, so release interrupt holdoff */
		RESUME_INTERRUPTS();
		LOG_LWDEBUG("LWLockAcquireOrWait", T_NAME(lock), T_ID(lock), "failed");
		TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT_FAIL(T_NAME(lock), T_ID(lock),
													 mode);
	}
	else
	{
		/* Add lock to list of locks held by this backend */
		held_lwlocks[num_held_lwlocks++] = lock;
		TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT(T_NAME(lock), T_ID(lock),
												mode);
	}

	return !mustwait;
}