lock.c

postgresql8.3.4源码,开源数据库

/*
 * GrantLock -- update the lock and proclock data structures to show
 *		the lock request has been granted.
 *
 * NOTE: if proc was blocked, it also needs to be removed from the wait list
 * and have its waitLock/waitProcLock fields cleared.  That's not done here.
 *
 * NOTE: the lock grant also has to be recorded in the associated LOCALLOCK
 * table entry; but since we may be awaking some other process, we can't do
 * that here; it's done by GrantLockLocal, instead.
 */
void
GrantLock(LOCK *lock, PROCLOCK *proclock, LOCKMODE lockmode)
{
	lock->nGranted++;
	lock->granted[lockmode]++;
	lock->grantMask |= LOCKBIT_ON(lockmode);
	if (lock->granted[lockmode] == lock->requested[lockmode])
		lock->waitMask &= LOCKBIT_OFF(lockmode);
	proclock->holdMask |= LOCKBIT_ON(lockmode);
	LOCK_PRINT("GrantLock", lock, lockmode);
	Assert((lock->nGranted > 0) && (lock->granted[lockmode] > 0));
	Assert(lock->nGranted <= lock->nRequested);
}

/*
 * UnGrantLock -- opposite of GrantLock.
 *
 * Updates the lock and proclock data structures to show that the lock
 * is no longer held nor requested by the current holder.
 *
 * Returns true if there were any waiters waiting on the lock that
 * should now be woken up with ProcLockWakeup.
 */
static bool
UnGrantLock(LOCK *lock, LOCKMODE lockmode,
			PROCLOCK *proclock, LockMethod lockMethodTable)
{
	bool		wakeupNeeded = false;

	Assert((lock->nRequested > 0) && (lock->requested[lockmode] > 0));
	Assert((lock->nGranted > 0) && (lock->granted[lockmode] > 0));
	Assert(lock->nGranted <= lock->nRequested);

	/*
	 * fix the general lock stats
	 */
	lock->nRequested--;
	lock->requested[lockmode]--;
	lock->nGranted--;
	lock->granted[lockmode]--;

	if (lock->granted[lockmode] == 0)
	{
		/* change the conflict mask.  No more of this lock type. */
		lock->grantMask &= LOCKBIT_OFF(lockmode);
	}

	LOCK_PRINT("UnGrantLock: updated", lock, lockmode);

	/*
	 * We need only run ProcLockWakeup if the released lock conflicts with at
	 * least one of the lock types requested by waiter(s).	Otherwise whatever
	 * conflict made them wait must still exist.  NOTE: before MVCC, we could
	 * skip wakeup if lock->granted[lockmode] was still positive. But that's
	 * not true anymore, because the remaining granted locks might belong to
	 * some waiter, who could now be awakened because he doesn't conflict with
	 * his own locks.
	 */
	if (lockMethodTable->conflictTab[lockmode] & lock->waitMask)
		wakeupNeeded = true;

	/*
	 * Now fix the per-proclock state.
	 */
	proclock->holdMask &= LOCKBIT_OFF(lockmode);
	PROCLOCK_PRINT("UnGrantLock: updated", proclock);

	return wakeupNeeded;
}

/*
 * CleanUpLock -- clean up after releasing a lock.	We garbage-collect the
 * proclock and lock objects if possible, and call ProcLockWakeup if there
 * are remaining requests and the caller says it's OK.  (Normally, this
 * should be called after UnGrantLock, and wakeupNeeded is the result from
 * UnGrantLock.)
 *
 * The appropriate partition lock must be held at entry, and will be
 * held at exit.
 */
static void
CleanUpLock(LOCK *lock, PROCLOCK *proclock,
			LockMethod lockMethodTable, uint32 hashcode,
			bool wakeupNeeded)
{
	/*
	 * If this was my last hold on this lock, delete my entry in the proclock
	 * table.
	 */
	if (proclock->holdMask == 0)
	{
		uint32		proclock_hashcode;

		PROCLOCK_PRINT("CleanUpLock: deleting", proclock);
		SHMQueueDelete(&proclock->lockLink);
		SHMQueueDelete(&proclock->procLink);
		proclock_hashcode = ProcLockHashCode(&proclock->tag, hashcode);
		if (!hash_search_with_hash_value(LockMethodProcLockHash,
										 (void *) &(proclock->tag),
										 proclock_hashcode,
										 HASH_REMOVE,
										 NULL))
			elog(PANIC, "proclock table corrupted");
	}

	if (lock->nRequested == 0)
	{
		/*
		 * The caller just released the last lock, so garbage-collect the lock
		 * object.
		 */
		LOCK_PRINT("CleanUpLock: deleting", lock, 0);
		Assert(SHMQueueEmpty(&(lock->procLocks)));
		if (!hash_search_with_hash_value(LockMethodLockHash,
										 (void *) &(lock->tag),
										 hashcode,
										 HASH_REMOVE,
										 NULL))
			elog(PANIC, "lock table corrupted");
	}
	else if (wakeupNeeded)
	{
		/* There are waiters on this lock, so wake them up. */
		ProcLockWakeup(lockMethodTable, lock);
	}
}

/*
 * GrantLockLocal -- update the locallock data structures to show
 *		the lock request has been granted.
 *
 * We expect that LockAcquire made sure there is room to add a new
 * ResourceOwner entry.
 */
static void
GrantLockLocal(LOCALLOCK *locallock, ResourceOwner owner)
{
	LOCALLOCKOWNER *lockOwners = locallock->lockOwners;
	int			i;

	Assert(locallock->numLockOwners < locallock->maxLockOwners);
	/* Count the total */
	locallock->nLocks++;
	/* Count the per-owner lock */
	for (i = 0; i < locallock->numLockOwners; i++)
	{
		if (lockOwners[i].owner == owner)
		{
			lockOwners[i].nLocks++;
			return;
		}
	}
	lockOwners[i].owner = owner;
	lockOwners[i].nLocks = 1;
	locallock->numLockOwners++;
}

/*
 * GrantAwaitedLock -- call GrantLockLocal for the lock we are doing
 *		WaitOnLock on.
 *
 * proc.c needs this for the case where we are booted off the lock by
 * timeout, but discover that someone granted us the lock anyway.
 *
 * We could just export GrantLockLocal, but that would require including
 * resowner.h in lock.h, which creates circularity.
 */
void
GrantAwaitedLock(void)
{
	GrantLockLocal(awaitedLock, awaitedOwner);
}

/*
 * WaitOnLock -- wait to acquire a lock
 *
 * Caller must have set MyProc->heldLocks to reflect locks already held
 * on the lockable object by this process.
 *
 * The appropriate partition lock must be held at entry.
 */
static void
WaitOnLock(LOCALLOCK *locallock, ResourceOwner owner)
{
	LOCKMETHODID lockmethodid = LOCALLOCK_LOCKMETHOD(*locallock);
	LockMethod	lockMethodTable = LockMethods[lockmethodid];
	char	   * volatile new_status = NULL;

	LOCK_PRINT("WaitOnLock: sleeping on lock",
			   locallock->lock, locallock->tag.mode);

	/* Report change to waiting status */
	if (update_process_title)
	{
		const char *old_status;
		int			len;

		old_status = get_ps_display(&len);
		new_status = (char *) palloc(len + 8 + 1);
		memcpy(new_status, old_status, len);
		strcpy(new_status + len, " waiting");
		set_ps_display(new_status, false);
		new_status[len] = '\0'; /* truncate off " waiting" */
	}
	pgstat_report_waiting(true);

	awaitedLock = locallock;
	awaitedOwner = owner;

	/*
	 * NOTE: Think not to put any shared-state cleanup after the call to
	 * ProcSleep, in either the normal or failure path.  The lock state must
	 * be fully set by the lock grantor, or by CheckDeadLock if we give up
	 * waiting for the lock.  This is necessary because of the possibility
	 * that a cancel/die interrupt will interrupt ProcSleep after someone else
	 * grants us the lock, but before we've noticed it. Hence, after granting,
	 * the locktable state must fully reflect the fact that we own the lock;
	 * we can't do additional work on return.
	 *
	 * We can and do use a PG_TRY block to try to clean up after failure,
	 * but this still has a major limitation: elog(FATAL) can occur while
	 * waiting (eg, a "die" interrupt), and then control won't come back here.
	 * So all cleanup of essential state should happen in LockWaitCancel,
	 * not here.  We can use PG_TRY to clear the "waiting" status flags,
	 * since doing that is unimportant if the process exits.
	 */
	PG_TRY();
	{
		if (ProcSleep(locallock, lockMethodTable) != STATUS_OK)
		{
			/*
			 * We failed as a result of a deadlock, see CheckDeadLock().
			 * Quit now.
			 */
			awaitedLock = NULL;
			LOCK_PRINT("WaitOnLock: aborting on lock",
					   locallock->lock, locallock->tag.mode);
			LWLockRelease(LockHashPartitionLock(locallock->hashcode));

			/*
			 * Now that we aren't holding the partition lock, we can give an
			 * error report including details about the detected deadlock.
			 */
			DeadLockReport();
			/* not reached */
		}
	}
	PG_CATCH();
	{
		/* In this path, awaitedLock remains set until LockWaitCancel */

		/* Report change to non-waiting status */
		pgstat_report_waiting(false);
		if (update_process_title)
		{
			set_ps_display(new_status, false);
			pfree(new_status);
		}

		/* and propagate the error */
		PG_RE_THROW();
	}
	PG_END_TRY();

	awaitedLock = NULL;

	/* Report change to non-waiting status */
	pgstat_report_waiting(false);
	if (update_process_title)
	{
		set_ps_display(new_status, false);
		pfree(new_status);
	}

	LOCK_PRINT("WaitOnLock: wakeup on lock",
			   locallock->lock, locallock->tag.mode);
}

/*
 * Remove a proc from the wait-queue it is on (caller must know it is on one).
 * This is only used when the proc has failed to get the lock, so we set its
 * waitStatus to STATUS_ERROR.
 *
 * Appropriate partition lock must be held by caller.  Also, caller is
 * responsible for signaling the proc if needed.
 *
 * NB: this does not clean up any locallock object that may exist for the lock.
 */
void
RemoveFromWaitQueue(PGPROC *proc, uint32 hashcode)
{
	LOCK	   *waitLock = proc->waitLock;
	PROCLOCK   *proclock = proc->waitProcLock;
	LOCKMODE	lockmode = proc->waitLockMode;
	LOCKMETHODID lockmethodid = LOCK_LOCKMETHOD(*waitLock);

	/* Make sure proc is waiting */
	Assert(proc->waitStatus == STATUS_WAITING);
	Assert(proc->links.next != INVALID_OFFSET);
	Assert(waitLock);
	Assert(waitLock->waitProcs.size > 0);
	Assert(0 < lockmethodid && lockmethodid < lengthof(LockMethods));

	/* Remove proc from lock's wait queue */
	SHMQueueDelete(&(proc->links));
	waitLock->waitProcs.size--;

	/* Undo increments of request counts by waiting process */
	Assert(waitLock->nRequested > 0);
	Assert(waitLock->nRequested > proc->waitLock->nGranted);
	waitLock->nRequested--;
	Assert(waitLock->requested[lockmode] > 0);
	waitLock->requested[lockmode]--;
	/* don't forget to clear waitMask bit if appropriate */
	if (waitLock->granted[lockmode] == waitLock->requested[lockmode])
		waitLock->waitMask &= LOCKBIT_OFF(lockmode);

	/* Clean up the proc's own state, and pass it the ok/fail signal */
	proc->waitLock = NULL;
	proc->waitProcLock = NULL;
	proc->waitStatus = STATUS_ERROR;

	/*
	 * Delete the proclock immediately if it represents no already-held locks.
	 * (This must happen now because if the owner of the lock decides to
	 * release it, and the requested/granted counts then go to zero,
	 * LockRelease expects there to be no remaining proclocks.) Then see if
	 * any other waiters for the lock can be woken up now.
	 */
	CleanUpLock(waitLock, proclock,
				LockMethods[lockmethodid], hashcode,
				true);
}

/*
 * LockRelease -- look up 'locktag' and release one 'lockmode' lock on it.
 *		Release a session lock if 'sessionLock' is true, else release a
 *		regular transaction lock.
 *
 * Side Effects: find any waiting processes that are now wakable,
 *		grant them their requested locks and awaken them.
 *		(We have to grant the lock here to avoid a race between
 *		the waking process and any new process to
 *		come along and request the lock.)
 */
bool
LockRelease(const LOCKTAG *locktag, LOCKMODE lockmode, bool sessionLock)
{
	LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid;
	LockMethod	lockMethodTable;
	LOCALLOCKTAG localtag;
	LOCALLOCK  *locallock;
	LOCK	   *lock;
	PROCLOCK   *proclock;
	LWLockId	partitionLock;
	bool		wakeupNeeded;

	if (lockmethodid <= 0 || lockmethodid >= lengthof(LockMethods))
		elog(ERROR, "unrecognized lock method: %d", lockmethodid);
	lockMethodTable = LockMethods[lockmethodid];
	if (lockmode <= 0 || lockmode > lockMethodTable->numLockModes)
		elog(ERROR, "unrecognized lock mode: %d", lockmode);

#ifdef LOCK_DEBUG
	if (LOCK_DEBUG_ENABLED(locktag))
		elog(LOG, "LockRelease: lock [%u,%u] %s",
			 locktag->locktag_field1, locktag->locktag_field2,
			 lockMethodTable->lockModeNames[lockmode]);
#endif

	/*
	 * Find the LOCALLOCK entry for this lock and lockmode
	 */
	MemSet(&localtag, 0, sizeof(localtag));		/* must clear padding */
	localtag.lock = *locktag;
	localtag.mode = lockmode;

	locallock = (LOCALLOCK *) hash_search(LockMethodLocalHash,
										  (void *) &localtag,
										  HASH_FIND, NULL);

	/*
	 * let the caller print its own error message, too. Do not ereport(ERROR).
	 */
	if (!locallock || locallock->nLocks <= 0)
	{
		elog(WARNING, "you don't own a lock of type %s",
			 lockMethodTable->lockModeNames[lockmode]);
		return FALSE;
	}

	/*
	 * Decrease the count for the resource owner.
	 */
	{
		LOCALLOCKOWNER *lockOwners = locallock->lockOwners;
		ResourceOwner owner;
		int			i;

		/* Session locks are never transactional, else check table */
		if (!sessionLock && lockMethodTable->transactional)
			owner = CurrentResourceOwner;
		else
			owner = NULL;

		for (i = locallock->numLockOwners - 1; i >= 0; i--)
		{
			if (lockOwners[i].owner == owner)
			{
				Assert(lockOwners[i].nLocks > 0);
				if (--lockOwners[i].nLocks == 0)
				{
					/* compact out unused slot */
					locallock->numLockOwners--;
					if (i < locallock->numLockOwners)
						lockOwners[i] = lockOwners[locallock->numLockOwners];
				}
				break;
			}
		}
		if (i < 0)
		{
			/* don't release a lock belonging to another owner */
			elog(WARNING, "you don't own a lock of type %s",
				 lockMethodTable->lockModeNames[lockmode]);
			return FALSE;
		}
	}

	/*
	 * Decrease the total local count.	If we're still holding the lock, we're
	 * done.
	 */
	locallock->nLocks--;

	if (locallock->nLocks > 0)
		return TRUE;

	/*
	 * Otherwise we've got to mess with the shared lock table.
	 */
	partitionLock = LockHashPartitionLock(locallock->hashcode);