proc.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

	/* And awaken it */
	PGSemaphoreUnlock(&proc->sem);

	return retProc;
}

/*
 * ProcLockWakeup -- routine for waking up processes when a lock is
 *		released (or a prior waiter is aborted).  Scan all waiters
 *		for lock, waken any that are no longer blocked.
 */
void
ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock)
{
	PROC_QUEUE *waitQueue = &(lock->waitProcs);
	int			queue_size = waitQueue->size;
	PGPROC	   *proc;
	LOCKMASK	aheadRequests = 0;

	Assert(queue_size >= 0);

	if (queue_size == 0)
		return;

	proc = (PGPROC *) MAKE_PTR(waitQueue->links.next);

	while (queue_size-- > 0)
	{
		LOCKMODE	lockmode = proc->waitLockMode;

		/*
		 * Waken if (a) doesn't conflict with requests of earlier waiters, and
		 * (b) doesn't conflict with already-held locks.
		 */
		if ((lockMethodTable->conflictTab[lockmode] & aheadRequests) == 0 &&
			LockCheckConflicts(lockMethodTable,
							   lockmode,
							   lock,
							   proc->waitProcLock,
							   proc) == STATUS_OK)
		{
			/* OK to waken */
			GrantLock(lock, proc->waitProcLock, lockmode);
			proc = ProcWakeup(proc, STATUS_OK);

			/*
			 * ProcWakeup removes proc from the lock's waiting process queue
			 * and returns the next proc in chain; don't use proc's next-link,
			 * because it's been cleared.
			 */
		}
		else
		{
			/*
			 * Cannot wake this guy. Remember his request for later checks.
			 */
			aheadRequests |= LOCKBIT_ON(lockmode);
			proc = (PGPROC *) MAKE_PTR(proc->links.next);
		}
	}

	Assert(waitQueue->size >= 0);
}

/* --------------------
 * We only get to this routine if we got SIGALRM after DeadlockTimeout
 * while waiting for a lock to be released by some other process.  Look
 * to see if there's a deadlock; if not, just return and continue waiting.
 * If we have a real deadlock, remove ourselves from the lock's wait queue
 * and signal an error to ProcSleep.
 * --------------------
 */
static void
CheckDeadLock(void)
{
	/*
	 * Acquire locktable lock.	Note that the deadlock check interrupt had
	 * better not be enabled anywhere that this process itself holds the
	 * locktable lock, else this will wait forever.  Also note that
	 * LWLockAcquire creates a critical section, so that this routine cannot
	 * be interrupted by cancel/die interrupts.
	 */
	LWLockAcquire(LockMgrLock, LW_EXCLUSIVE);

	/*
	 * 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.
	 *
	 * We check by looking to see if we've been unlinked from the wait queue.
	 * This is quicker than checking our semaphore's state, since no kernel
	 * call is needed, and it is safe because we hold the locktable lock.
	 */
	if (MyProc->links.prev == INVALID_OFFSET ||
		MyProc->links.next == INVALID_OFFSET)
	{
		LWLockRelease(LockMgrLock);
		return;
	}

#ifdef LOCK_DEBUG
	if (Debug_deadlocks)
		DumpAllLocks();
#endif

	if (!DeadLockCheck(MyProc))
	{
		/* No deadlock, so keep waiting */
		LWLockRelease(LockMgrLock);
		return;
	}

	/*
	 * Oops.  We have a deadlock.
	 *
	 * Get this process out of wait state.
	 */
	RemoveFromWaitQueue(MyProc);

	/*
	 * Set MyProc->waitStatus to STATUS_ERROR so that ProcSleep will report an
	 * error after we return from the signal handler.
	 */
	MyProc->waitStatus = STATUS_ERROR;

	/*
	 * Unlock my semaphore so that the interrupted ProcSleep() call can
	 * finish.
	 */
	PGSemaphoreUnlock(&MyProc->sem);

	/*
	 * We're done here.  Transaction abort caused by the error that ProcSleep
	 * will raise will cause any other locks we hold to be released, thus
	 * allowing other processes to wake up; we don't need to do that here.
	 * NOTE: an exception is that releasing locks we hold doesn't consider the
	 * possibility of waiters that were blocked behind us on the lock we just
	 * failed to get, and might now be wakable because we're not in front of
	 * them anymore.  However, RemoveFromWaitQueue took care of waking up any
	 * such processes.
	 */
	LWLockRelease(LockMgrLock);
}


/*
 * ProcWaitForSignal - wait for a signal from another backend.
 *
 * This can share the semaphore normally used for waiting for locks,
 * since a backend could never be waiting for a lock and a signal at
 * the same time.  As with locks, it's OK if the signal arrives just
 * before we actually reach the waiting state.
 */
void
ProcWaitForSignal(void)
{
	PGSemaphoreLock(&MyProc->sem, true);
}

/*
 * ProcCancelWaitForSignal - clean up an aborted wait for signal
 *
 * We need this in case the signal arrived after we aborted waiting,
 * or if it arrived but we never reached ProcWaitForSignal() at all.
 * Caller should call this after resetting the signal request status.
 */
void
ProcCancelWaitForSignal(void)
{
	PGSemaphoreReset(&MyProc->sem);
}

/*
 * ProcSendSignal - send a signal to a backend identified by PID
 */
void
ProcSendSignal(int pid)
{
	PGPROC	   *proc = BackendPidGetProc(pid);

	if (proc != NULL)
		PGSemaphoreUnlock(&proc->sem);
}


/*****************************************************************************
 * SIGALRM interrupt support
 *
 * Maybe these should be in pqsignal.c?
 *****************************************************************************/

/*
 * Enable the SIGALRM interrupt to fire after the specified delay
 *
 * Delay is given in milliseconds.	Caller should be sure a SIGALRM
 * signal handler is installed before this is called.
 *
 * This code properly handles nesting of deadlock timeout alarms within
 * statement timeout alarms.
 *
 * Returns TRUE if okay, FALSE on failure.
 */
bool
enable_sig_alarm(int delayms, bool is_statement_timeout)
{
	struct timeval fin_time;

#ifndef __BEOS__
	struct itimerval timeval;
#else
	bigtime_t	time_interval;
#endif

	/* Compute target timeout time if we will need it */
	if (is_statement_timeout || statement_timeout_active)
	{
		gettimeofday(&fin_time, NULL);
		fin_time.tv_sec += delayms / 1000;
		fin_time.tv_usec += (delayms % 1000) * 1000;
		if (fin_time.tv_usec >= 1000000)
		{
			fin_time.tv_sec++;
			fin_time.tv_usec -= 1000000;
		}
	}

	if (is_statement_timeout)
	{
		/* Begin statement-level timeout */
		Assert(!deadlock_timeout_active);
		statement_fin_time = fin_time;
		statement_timeout_active = true;
		cancel_from_timeout = false;
	}
	else if (statement_timeout_active)
	{
		/*
		 * Begin deadlock timeout with statement-level timeout active
		 *
		 * Here, we want to interrupt at the closer of the two timeout times.
		 * If fin_time >= statement_fin_time then we need not touch the
		 * existing timer setting; else set up to interrupt at the deadlock
		 * timeout time.
		 *
		 * NOTE: in this case it is possible that this routine will be
		 * interrupted by the previously-set timer alarm.  This is okay
		 * because the signal handler will do only what it should do according
		 * to the state variables.	The deadlock checker may get run earlier
		 * than normal, but that does no harm.
		 */
		deadlock_timeout_active = true;
		if (fin_time.tv_sec > statement_fin_time.tv_sec ||
			(fin_time.tv_sec == statement_fin_time.tv_sec &&
			 fin_time.tv_usec >= statement_fin_time.tv_usec))
			return true;
	}
	else
	{
		/* Begin deadlock timeout with no statement-level timeout */
		deadlock_timeout_active = true;
	}

	/* If we reach here, okay to set the timer interrupt */
#ifndef __BEOS__
	MemSet(&timeval, 0, sizeof(struct itimerval));
	timeval.it_value.tv_sec = delayms / 1000;
	timeval.it_value.tv_usec = (delayms % 1000) * 1000;
	if (setitimer(ITIMER_REAL, &timeval, NULL))
		return false;
#else
	/* BeOS doesn't have setitimer, but has set_alarm */
	time_interval = delayms * 1000;		/* usecs */
	if (set_alarm(time_interval, B_ONE_SHOT_RELATIVE_ALARM) < 0)
		return false;
#endif
	return true;
}

/*
 * Cancel the SIGALRM timer, either for a deadlock timeout or a statement
 * timeout.  If a deadlock timeout is canceled, any active statement timeout
 * remains in force.
 *
 * Returns TRUE if okay, FALSE on failure.
 */
bool
disable_sig_alarm(bool is_statement_timeout)
{
	/*
	 * Always disable the interrupt if it is active; this avoids being
	 * interrupted by the signal handler and thereby possibly getting
	 * confused.
	 *
	 * We will re-enable the interrupt if necessary in CheckStatementTimeout.
	 */
	if (statement_timeout_active || deadlock_timeout_active)
	{
#ifndef __BEOS__
		struct itimerval timeval;

		MemSet(&timeval, 0, sizeof(struct itimerval));
		if (setitimer(ITIMER_REAL, &timeval, NULL))
		{
			statement_timeout_active = false;
			cancel_from_timeout = false;
			deadlock_timeout_active = false;
			return false;
		}
#else
		/* BeOS doesn't have setitimer, but has set_alarm */
		if (set_alarm(B_INFINITE_TIMEOUT, B_PERIODIC_ALARM) < 0)
		{
			statement_timeout_active = false;
			cancel_from_timeout = false;
			deadlock_timeout_active = false;
			return false;
		}
#endif
	}

	/* Always cancel deadlock timeout, in case this is error cleanup */
	deadlock_timeout_active = false;

	/* Cancel or reschedule statement timeout */
	if (is_statement_timeout)
	{
		statement_timeout_active = false;
		cancel_from_timeout = false;
	}
	else if (statement_timeout_active)
	{
		if (!CheckStatementTimeout())
			return false;
	}
	return true;
}


/*
 * Check for statement timeout.  If the timeout time has come,
 * trigger a query-cancel interrupt; if not, reschedule the SIGALRM
 * interrupt to occur at the right time.
 *
 * Returns true if okay, false if failed to set the interrupt.
 */
static bool
CheckStatementTimeout(void)
{
	struct timeval now;

	if (!statement_timeout_active)
		return true;			/* do nothing if not active */

	gettimeofday(&now, NULL);

	if (now.tv_sec > statement_fin_time.tv_sec ||
		(now.tv_sec == statement_fin_time.tv_sec &&
		 now.tv_usec >= statement_fin_time.tv_usec))
	{
		/* Time to die */
		statement_timeout_active = false;
		cancel_from_timeout = true;
		kill(MyProcPid, SIGINT);
	}
	else
	{
		/* Not time yet, so (re)schedule the interrupt */
#ifndef __BEOS__
		struct itimerval timeval;

		MemSet(&timeval, 0, sizeof(struct itimerval));
		timeval.it_value.tv_sec = statement_fin_time.tv_sec - now.tv_sec;
		timeval.it_value.tv_usec = statement_fin_time.tv_usec - now.tv_usec;
		if (timeval.it_value.tv_usec < 0)
		{
			timeval.it_value.tv_sec--;
			timeval.it_value.tv_usec += 1000000;
		}
		if (setitimer(ITIMER_REAL, &timeval, NULL))
			return false;
#else
		/* BeOS doesn't have setitimer, but has set_alarm */
		bigtime_t	time_interval;

		time_interval =
			(statement_fin_time.tv_sec - now.tv_sec) * 1000000 +
			(statement_fin_time.tv_usec - now.tv_usec);
		if (set_alarm(time_interval, B_ONE_SHOT_RELATIVE_ALARM) < 0)
			return false;
#endif
	}

	return true;
}


/*
 * Signal handler for SIGALRM
 *
 * Process deadlock check and/or statement timeout check, as needed.
 * To avoid various edge cases, we must be careful to do nothing
 * when there is nothing to be done.  We also need to be able to
 * reschedule the timer interrupt if called before end of statement.
 */
void
handle_sig_alarm(SIGNAL_ARGS)
{
	int			save_errno = errno;

	if (deadlock_timeout_active)
	{
		deadlock_timeout_active = false;
		CheckDeadLock();
	}

	if (statement_timeout_active)
		(void) CheckStatementTimeout();

	errno = save_errno;
}