proc.c

关系型数据库 Postgresql 6.5.2

 * to acquire it, we sleep.
 *
 * ASSUME: that no one will fiddle with the queue until after
 *		we release the spin lock.
 *
 * NOTES: The process queue is now a priority queue for locking.
 */
int
ProcSleep(PROC_QUEUE *waitQueue,/* lock->waitProcs */
		  LOCKMETHODCTL *lockctl,
		  int token,			/* lockmode */
		  LOCK *lock)
{
	int			i;
	SPINLOCK	spinlock = lockctl->masterLock;
	PROC	   *proc;
	int			myMask = (1 << token);
	int			waitMask = lock->waitMask;
	int			aheadHolders[MAX_LOCKMODES];
	bool		selfConflict = (lockctl->conflictTab[token] & myMask),
				prevSame = false;
	bool		deadlock_checked = false;
	struct itimerval timeval,
				dummy;

	MyProc->token = token;
	MyProc->waitLock = lock;

	proc = (PROC *) MAKE_PTR(waitQueue->links.prev);

	/* if we don't conflict with any waiter - be first in queue */
	if (!(lockctl->conflictTab[token] & waitMask))
		goto ins;

	for (i = 1; i < MAX_LOCKMODES; i++)
		aheadHolders[i] = lock->activeHolders[i];
	(aheadHolders[token])++;

	for (i = 0; i < waitQueue->size; i++)
	{
		/* am I waiting for him ? */
		if (lockctl->conflictTab[token] & proc->holdLock)
		{
			/* is he waiting for me ? */
			if (lockctl->conflictTab[proc->token] & MyProc->holdLock)
			{
				MyProc->errType = STATUS_ERROR;
				elog(NOTICE, DeadLockMessage);
				goto rt;
			}
			/* being waiting for him - go past */
		}
		/* if he waits for me */
		else if (lockctl->conflictTab[proc->token] & MyProc->holdLock)
			break;
		/* if conflicting locks requested */
		else if (lockctl->conflictTab[proc->token] & myMask)
		{

			/*
			 * If I request non self-conflicting lock and there are others
			 * requesting the same lock just before me - stay here.
			 */
			if (!selfConflict && prevSame)
				break;
		}

		/*
		 * Last attempt to don't move any more: if we don't conflict with
		 * rest waiters in queue.
		 */
		else if (!(lockctl->conflictTab[token] & waitMask))
			break;

		prevSame = (proc->token == token);
		(aheadHolders[proc->token])++;
		if (aheadHolders[proc->token] == lock->holders[proc->token])
			waitMask &= ~(1 << proc->token);
		proc = (PROC *) MAKE_PTR(proc->links.prev);
	}

ins:;
	/* -------------------
	 * assume that these two operations are atomic (because
	 * of the spinlock).
	 * -------------------
	 */
	SHMQueueInsertTL(&(proc->links), &(MyProc->links));
	waitQueue->size++;

	lock->waitMask |= myMask;
	SpinRelease(spinlock);

	/* --------------
	 * We set this so we can wake up periodically and check for a deadlock.
	 * If a deadlock is detected, the handler releases the processes
	 * semaphore and aborts the current transaction.
	 *
	 * Need to zero out struct to set the interval and the micro seconds fields
	 * to 0.
	 * --------------
	 */
	MemSet(&timeval, 0, sizeof(struct itimerval));
	timeval.it_value.tv_sec = \
		(DeadlockCheckTimer ? DeadlockCheckTimer : DEADLOCK_CHECK_TIMER);

	do
	{
		MyProc->errType = NO_ERROR;		/* reset flag after deadlock check */

		if (!deadlock_checked)
			if (setitimer(ITIMER_REAL, &timeval, &dummy))
				elog(FATAL, "ProcSleep: Unable to set timer for process wakeup");
		deadlock_checked = true;

		/* --------------
		 * if someone wakes us between SpinRelease and IpcSemaphoreLock,
		 * IpcSemaphoreLock will not block.  The wakeup is "saved" by
		 * the semaphore implementation.
		 * --------------
		 */
		IpcSemaphoreLock(MyProc->sem.semId, MyProc->sem.semNum,
						 IpcExclusiveLock);
	} while (MyProc->errType == STATUS_NOT_FOUND);		/* sleep after deadlock
														 * check */

	/* ---------------
	 * We were awoken before a timeout - now disable the timer
	 * ---------------
	 */
	timeval.it_value.tv_sec = 0;
	if (setitimer(ITIMER_REAL, &timeval, &dummy))
		elog(FATAL, "ProcSleep: Unable to diable timer for process wakeup");

	/* ----------------
	 * We were assumed to be in a critical section when we went
	 * to sleep.
	 * ----------------
	 */
	SpinAcquire(spinlock);

rt:;

#ifdef LOCK_MGR_DEBUG
	/* Just to get meaningful debug messages from DumpLocks() */
	MyProc->waitLock = (LOCK *) NULL;
#endif

	return MyProc->errType;
}


/*
 * ProcWakeup -- wake up a process by releasing its private semaphore.
 *
 *	 remove the process from the wait queue and set its links invalid.
 *	 RETURN: the next process in the wait queue.
 */
PROC *
ProcWakeup(PROC *proc, int errType)
{
	PROC	   *retProc;

	/* assume that spinlock has been acquired */

	if (proc->links.prev == INVALID_OFFSET ||
		proc->links.next == INVALID_OFFSET)
		return (PROC *) NULL;

	retProc = (PROC *) MAKE_PTR(proc->links.prev);

	/* you have to update waitLock->waitProcs.size yourself */
	SHMQueueDelete(&(proc->links));
	SHMQueueElemInit(&(proc->links));

	proc->errType = errType;

	IpcSemaphoreUnlock(proc->sem.semId, proc->sem.semNum, IpcExclusiveLock);

	return retProc;
}

/*
 * ProcLockWakeup -- routine for waking up processes when a lock is
 *		released.
 */
int
ProcLockWakeup(PROC_QUEUE *queue, LOCKMETHOD lockmethod, LOCK *lock)
{
	PROC	   *proc;
	int			count = 0;
	int			trace_flag;
	int			last_locktype = 0;
	int			queue_size = queue->size;

	Assert(queue->size >= 0);

	if (!queue->size)
		return STATUS_NOT_FOUND;

	proc = (PROC *) MAKE_PTR(queue->links.prev);
	while ((queue_size--) && (proc))
	{

		/*
		 * This proc will conflict as the previous one did, don't even
		 * try.
		 */
		if (proc->token == last_locktype)
			continue;

		/*
		 * Does this proc conflict with locks held by others ?
		 */
		if (LockResolveConflicts(lockmethod,
								 lock,
								 proc->token,
								 proc->xid,
								 (XIDLookupEnt *) NULL) != STATUS_OK)
		{
			if (count != 0)
				break;
			last_locktype = proc->token;
			continue;
		}

		/*
		 * there was a waiting process, grant it the lock before waking it
		 * up.	This will prevent another process from seizing the lock
		 * between the time we release the lock master (spinlock) and the
		 * time that the awoken process begins executing again.
		 */
		GrantLock(lock, proc->token);

		/*
		 * ProcWakeup removes proc from the lock waiting process queue and
		 * returns the next proc in chain.
		 */

		count++;
		queue->size--;
		proc = ProcWakeup(proc, NO_ERROR);
	}

	Assert(queue->size >= 0);

	if (count)
		return STATUS_OK;
	else
	{
		/* Something is still blocking us.	May have deadlocked. */
		trace_flag = (lock->tag.lockmethod == USER_LOCKMETHOD) ? \
			TRACE_USERLOCKS : TRACE_LOCKS;
		TPRINTF(trace_flag,
				"ProcLockWakeup: lock(%x) can't wake up any process",
				MAKE_OFFSET(lock));
#ifdef DEADLOCK_DEBUG
		if (pg_options[trace_flag] >= 2)
			DumpAllLocks();
#endif
		return STATUS_NOT_FOUND;
	}
}

void
ProcAddLock(SHM_QUEUE *elem)
{
	SHMQueueInsertTL(&MyProc->lockQueue, elem);
}

/* --------------------
 * We only get to this routine if we got SIGALRM after DEADLOCK_CHECK_TIMER
 * while waiting for a lock to be released by some other process.  If we have
 * a real deadlock, we must also indicate that I'm no longer waiting
 * on a lock so that other processes don't try to wake me up and screw
 * up my semaphore.
 * --------------------
 */
static void
HandleDeadLock(int sig)
{
	LOCK	   *mywaitlock;

	LockLockTable();

	/* ---------------------
	 * Check to see if we've been awoken by anyone in the interim.
	 *
	 * If we have we can return and resume our transaction -- happy day.
	 * Before we are awoken the process releasing the lock grants it to
	 * us so we know that we don't have to wait anymore.
	 *
	 * Damn these names are LONG! -mer
	 * ---------------------
	 */
	if (IpcSemaphoreGetCount(MyProc->sem.semId, MyProc->sem.semNum) ==
		IpcSemaphoreDefaultStartValue)
	{
		UnlockLockTable();
		return;
	}

	/*
	 * you would think this would be unnecessary, but...
	 *
	 * this also means we've been removed already.  in some ports (e.g.,
	 * sparc and aix) the semop(2) implementation is such that we can
	 * actually end up in this handler after someone has removed us from
	 * the queue and bopped the semaphore *but the test above fails to
	 * detect the semaphore update* (presumably something weird having to
	 * do with the order in which the semaphore wakeup signal and SIGALRM
	 * get handled).
	 */
	if (MyProc->links.prev == INVALID_OFFSET ||
		MyProc->links.next == INVALID_OFFSET)
	{
		UnlockLockTable();
		return;
	}

#ifdef DEADLOCK_DEBUG
	DumpAllLocks();
#endif

	MyProc->errType = STATUS_NOT_FOUND;
	if (!DeadLockCheck(MyProc, MyProc->waitLock))
	{
		UnlockLockTable();
		return;
	}

	mywaitlock = MyProc->waitLock;

	/* ------------------------
	 * Get this process off the lock's wait queue
	 * ------------------------
	 */
	Assert(mywaitlock->waitProcs.size > 0);
	--mywaitlock->waitProcs.size;
	SHMQueueDelete(&(MyProc->links));
	SHMQueueElemInit(&(MyProc->links));

	/* ------------------
	 * Unlock my semaphore so that the count is right for next time.
	 * I was awoken by a signal, not by someone unlocking my semaphore.
	 * ------------------
	 */
	IpcSemaphoreUnlock(MyProc->sem.semId, MyProc->sem.semNum,
					   IpcExclusiveLock);

	/* -------------
	 * Set MyProc->errType to STATUS_ERROR so that we abort after
	 * returning from this handler.
	 * -------------
	 */
	MyProc->errType = STATUS_ERROR;

	/*
	 * if this doesn't follow the IpcSemaphoreUnlock then we get lock
	 * table corruption ("LockReplace: xid table corrupted") due to race
	 * conditions.	i don't claim to understand this...
	 */
	UnlockLockTable();

	elog(NOTICE, DeadLockMessage);
	return;
}

void
ProcReleaseSpins(PROC *proc)
{
	int			i;

	if (!proc)
		proc = MyProc;

	if (!proc)
		return;
	for (i = 0; i < (int) MAX_SPINS; i++)
	{
		if (proc->sLocks[i])
		{
			Assert(proc->sLocks[i] == 1);
			SpinRelease(i);
		}
	}
}

/*****************************************************************************
 *
 *****************************************************************************/

/*
 * ProcGetNewSemKeyAndNum -
 *	  scan the free semaphore bitmap and allocate a single semaphore from
 *	  a semaphore set. (If the semaphore set doesn't exist yet,
 *	  IpcSemaphoreCreate will create it. Otherwise, we use the existing
 *	  semaphore set.)
 */
static void
ProcGetNewSemKeyAndNum(IPCKey *key, int *semNum)
{
	int			i;
	int32	   *freeSemMap = ProcGlobal->freeSemMap;
	int32		fullmask = (1 << (PROC_NSEMS_PER_SET + 1)) - 1;

	/*
	 * we hold ProcStructLock when entering this routine. We scan through
	 * the bitmap to look for a free semaphore.
	 */

	for (i = 0; i < MAX_PROC_SEMS / PROC_NSEMS_PER_SET; i++)
	{
		int			mask = 1;
		int			j;

		if (freeSemMap[i] == fullmask)
			continue;			/* this set is fully allocated */

		for (j = 0; j < PROC_NSEMS_PER_SET; j++)
		{
			if ((freeSemMap[i] & mask) == 0)
			{

				/*
				 * a free semaphore found. Mark it as allocated. Also set
				 * the bit indicating whole set is allocated.
				 */
				freeSemMap[i] |= mask + (1 << PROC_NSEMS_PER_SET);

				*key = ProcGlobal->currKey + i;
				*semNum = j;
				return;
			}
			mask <<= 1;
		}
	}

	/* if we reach here, all the semaphores are in use. */
	elog(ERROR, "InitProc: cannot allocate a free semaphore");
}

/*
 * ProcFreeSem -
 *	  free up our semaphore in the semaphore set.
 */
static void
ProcFreeSem(IpcSemaphoreKey semKey, int semNum)
{
	int			mask;
	int			i;
	int32	   *freeSemMap = ProcGlobal->freeSemMap;

	i = semKey - ProcGlobal->currKey;
	mask = ~(1 << semNum);
	freeSemMap[i] &= mask;

	/*
	 * Formerly we'd release a semaphore set if it was now completely
	 * unused, but now we keep the semaphores to ensure we won't run out
	 * when starting new backends --- cf. InitProcGlobal.  Note that the
	 * PROC_NSEMS_PER_SET+1'st bit of the freeSemMap entry remains set to
	 * indicate it is still allocated; ProcFreeAllSemaphores() needs that.
	 */
}

/*
 * ProcFreeAllSemaphores -
 *	  called at shmem_exit time, ie when exiting the postmaster or
 *	  destroying shared state for a failed set of backends.
 *	  Free up all the semaphores allocated to the lmgrs of the backends.
 */
static void
ProcFreeAllSemaphores()
{
	int			i;
	int32	   *freeSemMap = ProcGlobal->freeSemMap;

	for (i = 0; i < MAX_PROC_SEMS / PROC_NSEMS_PER_SET; i++)
	{
		if (freeSemMap[i] != 0)
			IpcSemaphoreKill(ProcGlobal->currKey + i);
	}
}