1 /*-------------------------------------------------------------------------
4 * routines to manage per-process shared memory data structure
6 * Portions Copyright (c) 1996-2000, PostgreSQL, Inc
7 * Portions Copyright (c) 1994, Regents of the University of California
11 * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.74 2000/05/31 00:28:30 petere Exp $
13 *-------------------------------------------------------------------------
16 * Each postgres backend gets one of these. We'll use it to
17 * clean up after the process should the process suddenly die.
21 * ProcSleep(), ProcWakeup(), ProcWakeupNext(),
22 * ProcQueueAlloc() -- create a shm queue for sleeping processes
23 * ProcQueueInit() -- create a queue without allocing memory
25 * Locking and waiting for buffers can cause the backend to be
26 * put to sleep. Whoever releases the lock, etc. wakes the
27 * process up again (and gives it an error code so it knows
28 * whether it was awoken on an error condition).
32 * ProcReleaseLocks -- frees the locks associated with this process,
33 * ProcKill -- destroys the shared memory state (and locks)
34 * associated with the process.
36 * 5/15/91 -- removed the buffer pool based lock chain in favor
37 * of a shared memory lock chain. The write-protection is
38 * more expensive if the lock chain is in the buffer pool.
39 * The only reason I kept the lock chain in the buffer pool
40 * in the first place was to allow the lock table to grow larger
41 * than available shared memory and that isn't going to work
42 * without a lot of unimplemented support anyway.
44 * 4/7/95 -- instead of allocating a set of 1 semaphore per process, we
45 * allocate a semaphore from a set of PROC_NSEMS_PER_SET semaphores
46 * shared among backends (we keep a few sets of semaphores around).
47 * This is so that we can support more backends. (system-wide semaphore
48 * sets run out pretty fast.) -ay 4/95
50 * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.74 2000/05/31 00:28:30 petere Exp $
55 #include <sys/types.h>
57 #if defined(solaris_sparc) || defined(__CYGWIN__)
63 #include "miscadmin.h"
66 /* In Ultrix and QNX, sem.h must be included after ipc.h */
69 #include "storage/lock.h"
70 #include "storage/proc.h"
72 void HandleDeadLock(SIGNAL_ARGS);
73 static void ProcFreeAllSemaphores(void);
74 static bool GetOffWaitqueue(PROC *);
76 int DeadlockTimeout = 1000;
78 /* --------------------
79 * Spin lock for manipulating the shared process data structure:
80 * ProcGlobal.... Adding an extra spin lock seemed like the smallest
81 * hack to get around reading and updating this structure in shared
82 * memory. -mer 17 July 1991
83 * --------------------
85 SPINLOCK ProcStructLock;
87 static PROC_HDR *ProcGlobal = NULL;
91 static void ProcKill(int exitStatus, int pid);
92 static void ProcGetNewSemKeyAndNum(IPCKey *key, int *semNum);
93 static void ProcFreeSem(IpcSemaphoreKey semKey, int semNum);
95 static char *DeadLockMessage = "Deadlock detected -- See the lock(l) manual page for a possible cause.";
99 * initializes the global process table. We put it here so that
100 * the postmaster can do this initialization. (ProcFreeAllSemaphores needs
101 * to read this table on exiting the postmaster. If we have the first
102 * backend do this, starting up and killing the postmaster without
103 * starting any backends will be a problem.)
105 * We also allocate all the per-process semaphores we will need to support
106 * the requested number of backends. We used to allocate semaphores
107 * only when backends were actually started up, but that is bad because
108 * it lets Postgres fail under load --- a lot of Unix systems are
109 * (mis)configured with small limits on the number of semaphores, and
110 * running out when trying to start another backend is a common failure.
111 * So, now we grab enough semaphores to support the desired max number
112 * of backends immediately at initialization --- if the sysadmin has set
113 * MaxBackends higher than his kernel will support, he'll find out sooner
117 InitProcGlobal(IPCKey key, int maxBackends)
121 /* attach to the free list */
122 ProcGlobal = (PROC_HDR *)
123 ShmemInitStruct("Proc Header", (unsigned) sizeof(PROC_HDR), &found);
125 /* --------------------
126 * We're the first - initialize.
127 * XXX if found should ever be true, it is a sign of impending doom ...
128 * ought to complain if so?
129 * --------------------
135 ProcGlobal->freeProcs = INVALID_OFFSET;
136 ProcGlobal->currKey = IPCGetProcessSemaphoreInitKey(key);
137 for (i = 0; i < MAX_PROC_SEMS / PROC_NSEMS_PER_SET; i++)
138 ProcGlobal->freeSemMap[i] = 0;
141 * Arrange to delete semas on exit --- set this up now so that we
142 * will clean up if pre-allocation fails...
144 on_shmem_exit(ProcFreeAllSemaphores, NULL);
147 * Pre-create the semaphores for the first maxBackends processes,
148 * unless we are running as a standalone backend.
150 if (key != PrivateIPCKey)
153 i < (maxBackends + PROC_NSEMS_PER_SET - 1) / PROC_NSEMS_PER_SET;
156 IPCKey semKey = ProcGlobal->currKey + i;
159 semId = IpcSemaphoreCreate(semKey,
162 IpcSemaphoreDefaultStartValue,
165 elog(FATAL, "InitProcGlobal: IpcSemaphoreCreate failed");
166 /* mark this sema set allocated */
167 ProcGlobal->freeSemMap[i] = (1 << PROC_NSEMS_PER_SET);
173 /* ------------------------
174 * InitProc -- create a per-process data structure for this process
175 * used by the lock manager on semaphore queues.
176 * ------------------------
179 InitProcess(IPCKey key)
182 unsigned long location,
185 SpinAcquire(ProcStructLock);
187 /* attach to the free list */
188 ProcGlobal = (PROC_HDR *)
189 ShmemInitStruct("Proc Header", (unsigned) sizeof(PROC_HDR), &found);
192 /* this should not happen. InitProcGlobal() is called before this. */
193 elog(STOP, "InitProcess: Proc Header uninitialized");
198 SpinRelease(ProcStructLock);
199 elog(ERROR, "ProcInit: you already exist");
203 /* try to get a proc from the free list first */
205 myOffset = ProcGlobal->freeProcs;
207 if (myOffset != INVALID_OFFSET)
209 MyProc = (PROC *) MAKE_PTR(myOffset);
210 ProcGlobal->freeProcs = MyProc->links.next;
216 * have to allocate one. We can't use the normal shmem index
217 * table mechanism because the proc structure is stored by PID
218 * instead of by a global name (need to look it up by PID when we
219 * cleanup dead processes).
222 MyProc = (PROC *) ShmemAlloc((unsigned) sizeof(PROC));
225 SpinRelease(ProcStructLock);
226 elog(FATAL, "cannot create new proc: out of memory");
229 /* this cannot be initialized until after the buffer pool */
230 SHMQueueInit(&(MyProc->lockQueue));
234 * zero out the spin lock counts and set the sLocks field for
235 * ProcStructLock to 1 as we have acquired this spinlock above but
236 * didn't record it since we didn't have MyProc until now.
238 MemSet(MyProc->sLocks, 0, sizeof(MyProc->sLocks));
239 MyProc->sLocks[ProcStructLock] = 1;
242 if (IsUnderPostmaster)
249 ProcGetNewSemKeyAndNum(&semKey, &semNum);
252 * Note: because of the pre-allocation done in InitProcGlobal,
253 * this call should always attach to an existing semaphore. It
254 * will (try to) create a new group of semaphores only if the
255 * postmaster tries to start more backends than it said it would.
257 semId = IpcSemaphoreCreate(semKey,
260 IpcSemaphoreDefaultStartValue,
264 * we might be reusing a semaphore that belongs to a dead backend.
265 * So be careful and reinitialize its value here.
267 semun.val = IpcSemaphoreDefaultStartValue;
268 semctl(semId, semNum, SETVAL, semun);
270 IpcSemaphoreLock(semId, semNum, IpcExclusiveLock);
271 MyProc->sem.semId = semId;
272 MyProc->sem.semNum = semNum;
273 MyProc->sem.semKey = semKey;
276 MyProc->sem.semId = -1;
278 /* ----------------------
280 * ----------------------
282 SpinRelease(ProcStructLock);
284 MyProc->pid = MyProcPid;
285 MyProc->databaseId = MyDatabaseId;
286 MyProc->xid = InvalidTransactionId;
287 MyProc->xmin = InvalidTransactionId;
290 * Start keeping spin lock stats from here on. Any botch before
291 * this initialization is forever botched
294 MemSet(MyProc->sLocks, 0, MAX_SPINS * sizeof(*MyProc->sLocks));
296 /* -------------------------
297 * Install ourselves in the shmem index table. The name to
298 * use is determined by the OS-assigned process id. That
299 * allows the cleanup process to find us after any untimely
301 * -------------------------
303 location = MAKE_OFFSET(MyProc);
304 if ((!ShmemPIDLookup(MyProcPid, &location)) || (location != MAKE_OFFSET(MyProc)))
305 elog(STOP, "InitProc: ShmemPID table broken");
307 MyProc->errType = NO_ERROR;
308 SHMQueueElemInit(&(MyProc->links));
310 on_shmem_exit(ProcKill, (caddr_t) MyProcPid);
313 /* -----------------------
314 * get off the wait queue
315 * -----------------------
318 GetOffWaitqueue(PROC *proc)
320 bool getoffed = false;
323 if (proc->links.next != INVALID_OFFSET)
325 int lockmode = proc->token;
327 Assert(proc->waitLock->waitProcs.size > 0);
328 SHMQueueDelete(&(proc->links));
329 --proc->waitLock->waitProcs.size;
330 Assert(proc->waitLock->nHolding > 0);
331 Assert(proc->waitLock->nHolding > proc->waitLock->nActive);
332 --proc->waitLock->nHolding;
333 Assert(proc->waitLock->holders[lockmode] > 0);
334 --proc->waitLock->holders[lockmode];
335 if (proc->waitLock->activeHolders[lockmode] ==
336 proc->waitLock->holders[lockmode])
337 proc->waitLock->waitMask &= ~(1 << lockmode);
340 SHMQueueElemInit(&(proc->links));
347 * ProcReleaseLocks() -- release all locks associated with this process
355 LockReleaseAll(1, &MyProc->lockQueue);
356 GetOffWaitqueue(MyProc);
361 * used by the postmaster to clean up the global tables. This also frees
362 * up the semaphore used for the lmgr of the process. (We have to do
363 * this is the postmaster instead of doing a IpcSemaphoreKill on exiting
364 * the process because the semaphore set is shared among backends and
365 * we don't want to remove other's semaphores on exit.)
370 SHMEM_OFFSET location;
373 location = INVALID_OFFSET;
375 location = ShmemPIDDestroy(pid);
376 if (location == INVALID_OFFSET)
378 proc = (PROC *) MAKE_PTR(location);
380 SpinAcquire(ProcStructLock);
382 ProcFreeSem(proc->sem.semKey, proc->sem.semNum);
384 proc->links.next = ProcGlobal->freeProcs;
385 ProcGlobal->freeProcs = MAKE_OFFSET(proc);
387 SpinRelease(ProcStructLock);
393 * ProcKill() -- Destroy the per-proc data structure for
394 * this process. Release any of its held spin locks.
397 ProcKill(int exitStatus, int pid)
400 SHMEM_OFFSET location;
402 /* --------------------
403 * If this is a FATAL exit the postmaster will have to kill all the
404 * existing backends and reinitialize shared memory. So all we don't
405 * need to do anything here.
406 * --------------------
411 ShmemPIDLookup(MyProcPid, &location);
412 if (location == INVALID_OFFSET)
415 proc = (PROC *) MAKE_PTR(location);
417 Assert(proc == MyProc || pid != MyProcPid);
422 * Assume one lock table.
425 ProcReleaseSpins(proc);
426 LockReleaseAll(DEFAULT_LOCKMETHOD, &proc->lockQueue);
431 * Assume we have a second lock table.
433 LockReleaseAll(USER_LOCKMETHOD, &proc->lockQueue);
437 * get off the wait queue
440 GetOffWaitqueue(proc);
446 * ProcQueue package: routines for putting processes to sleep
451 * ProcQueueAlloc -- alloc/attach to a shared memory process queue
453 * Returns: a pointer to the queue or NULL
454 * Side Effects: Initializes the queue if we allocated one
458 ProcQueueAlloc(char *name)
461 PROC_QUEUE *queue = (PROC_QUEUE *)
462 ShmemInitStruct(name, (unsigned) sizeof(PROC_QUEUE), &found);
467 ProcQueueInit(queue);
474 * ProcQueueInit -- initialize a shared memory process queue
477 ProcQueueInit(PROC_QUEUE *queue)
479 SHMQueueInit(&(queue->links));
485 * Handling cancel request while waiting for lock
488 static bool lockWaiting = false;
490 SetWaitingForLock(bool waiting)
492 if (waiting == lockWaiting)
494 lockWaiting = waiting;
497 /* The lock was already released ? */
498 if (MyProc->links.next == INVALID_OFFSET)
503 if (QueryCancel) /* cancel request pending */
505 if (GetOffWaitqueue(MyProc))
508 elog(ERROR, "Query cancel requested while waiting lock");
516 struct itimerval timeval,
522 /* Deadlock timer off */
523 MemSet(&timeval, 0, sizeof(struct itimerval));
524 setitimer(ITIMER_REAL, &timeval, &dummy);
525 if (GetOffWaitqueue(MyProc))
526 elog(ERROR, "Query cancel requested while waiting lock");
530 * ProcSleep -- put a process to sleep
532 * P() on the semaphore should put us to sleep. The process
533 * semaphore is cleared by default, so the first time we try
534 * to acquire it, we sleep.
536 * ASSUME: that no one will fiddle with the queue until after
537 * we release the spin lock.
539 * NOTES: The process queue is now a priority queue for locking.
542 ProcSleep(PROC_QUEUE *waitQueue,/* lock->waitProcs */
543 LOCKMETHODCTL *lockctl,
544 int token, /* lockmode */
548 SPINLOCK spinlock = lockctl->masterLock;
550 int myMask = (1 << token);
551 int waitMask = lock->waitMask;
552 int aheadHolders[MAX_LOCKMODES];
553 bool selfConflict = (lockctl->conflictTab[token] & myMask),
555 bool deadlock_checked = false;
556 struct itimerval timeval,
559 MyProc->token = token;
560 MyProc->waitLock = lock;
562 proc = (PROC *) MAKE_PTR(waitQueue->links.prev);
564 /* if we don't conflict with any waiter - be first in queue */
565 if (!(lockctl->conflictTab[token] & waitMask))
568 for (i = 1; i < MAX_LOCKMODES; i++)
569 aheadHolders[i] = lock->activeHolders[i];
570 (aheadHolders[token])++;
572 for (i = 0; i < waitQueue->size; i++)
574 /* am I waiting for him ? */
575 if (lockctl->conflictTab[token] & proc->holdLock)
577 /* is he waiting for me ? */
578 if (lockctl->conflictTab[proc->token] & MyProc->holdLock)
580 MyProc->errType = STATUS_ERROR;
581 elog(NOTICE, DeadLockMessage);
584 /* being waiting for him - go past */
586 /* if he waits for me */
587 else if (lockctl->conflictTab[proc->token] & MyProc->holdLock)
589 /* if conflicting locks requested */
590 else if (lockctl->conflictTab[proc->token] & myMask)
594 * If I request non self-conflicting lock and there are others
595 * requesting the same lock just before me - stay here.
597 if (!selfConflict && prevSame)
602 * Last attempt to don't move any more: if we don't conflict with
603 * rest waiters in queue.
605 else if (!(lockctl->conflictTab[token] & waitMask))
608 prevSame = (proc->token == token);
609 (aheadHolders[proc->token])++;
610 if (aheadHolders[proc->token] == lock->holders[proc->token])
611 waitMask &= ~(1 << proc->token);
612 proc = (PROC *) MAKE_PTR(proc->links.prev);
616 /* -------------------
617 * assume that these two operations are atomic (because
619 * -------------------
621 SHMQueueInsertTL(&(proc->links), &(MyProc->links));
624 lock->waitMask |= myMask;
625 SpinRelease(spinlock);
628 * We set this so we can wake up periodically and check for a deadlock.
629 * If a deadlock is detected, the handler releases the processes
630 * semaphore and aborts the current transaction.
632 * Need to zero out struct to set the interval and the micro seconds fields
636 MemSet(&timeval, 0, sizeof(struct itimerval));
637 timeval.it_value.tv_sec = DeadlockTimeout / 1000;
638 timeval.it_value.tv_usec = (DeadlockTimeout % 1000) * 1000;
640 SetWaitingForLock(true);
643 MyProc->errType = NO_ERROR; /* reset flag after deadlock check */
645 if (!deadlock_checked)
646 if (setitimer(ITIMER_REAL, &timeval, &dummy))
647 elog(FATAL, "ProcSleep: Unable to set timer for process wakeup");
648 deadlock_checked = true;
651 * if someone wakes us between SpinRelease and IpcSemaphoreLock,
652 * IpcSemaphoreLock will not block. The wakeup is "saved" by
653 * the semaphore implementation.
656 IpcSemaphoreLock(MyProc->sem.semId, MyProc->sem.semNum,
658 } while (MyProc->errType == STATUS_NOT_FOUND); /* sleep after deadlock
663 * We were awoken before a timeout - now disable the timer
666 timeval.it_value.tv_sec = 0;
667 timeval.it_value.tv_usec = 0;
668 if (setitimer(ITIMER_REAL, &timeval, &dummy))
669 elog(FATAL, "ProcSleep: Unable to diable timer for process wakeup");
672 * We were assumed to be in a critical section when we went
676 SpinAcquire(spinlock);
681 /* Just to get meaningful debug messages from DumpLocks() */
682 MyProc->waitLock = (LOCK *) NULL;
685 return MyProc->errType;
690 * ProcWakeup -- wake up a process by releasing its private semaphore.
692 * remove the process from the wait queue and set its links invalid.
693 * RETURN: the next process in the wait queue.
696 ProcWakeup(PROC *proc, int errType)
700 /* assume that spinlock has been acquired */
702 if (proc->links.prev == INVALID_OFFSET ||
703 proc->links.next == INVALID_OFFSET)
704 return (PROC *) NULL;
706 retProc = (PROC *) MAKE_PTR(proc->links.prev);
708 /* you have to update waitLock->waitProcs.size yourself */
709 SHMQueueDelete(&(proc->links));
710 SHMQueueElemInit(&(proc->links));
712 proc->errType = errType;
714 IpcSemaphoreUnlock(proc->sem.semId, proc->sem.semNum, IpcExclusiveLock);
720 * ProcLockWakeup -- routine for waking up processes when a lock is
724 ProcLockWakeup(PROC_QUEUE *queue, LOCKMETHOD lockmethod, LOCK *lock)
728 int last_locktype = 0;
729 int queue_size = queue->size;
731 Assert(queue->size >= 0);
734 return STATUS_NOT_FOUND;
736 proc = (PROC *) MAKE_PTR(queue->links.prev);
737 while ((queue_size--) && (proc))
741 * This proc will conflict as the previous one did, don't even
744 if (proc->token == last_locktype)
748 * Does this proc conflict with locks held by others ?
750 if (LockResolveConflicts(lockmethod,
754 (XIDLookupEnt *) NULL) != STATUS_OK)
758 last_locktype = proc->token;
763 * there was a waiting process, grant it the lock before waking it
764 * up. This will prevent another process from seizing the lock
765 * between the time we release the lock master (spinlock) and the
766 * time that the awoken process begins executing again.
768 GrantLock(lock, proc->token);
771 * ProcWakeup removes proc from the lock waiting process queue and
772 * returns the next proc in chain.
777 proc = ProcWakeup(proc, NO_ERROR);
780 Assert(queue->size >= 0);
786 /* Something is still blocking us. May have deadlocked. */
788 if (lock->tag.lockmethod == USER_LOCKMETHOD ? Trace_userlocks : Trace_locks)
790 elog(DEBUG, "ProcLockWakeup: lock(%lx) can't wake up any process", MAKE_OFFSET(lock));
795 return STATUS_NOT_FOUND;
800 ProcAddLock(SHM_QUEUE *elem)
802 SHMQueueInsertTL(&MyProc->lockQueue, elem);
805 /* --------------------
806 * We only get to this routine if we got SIGALRM after DeadlockTimeout
807 * while waiting for a lock to be released by some other process. If we have
808 * a real deadlock, we must also indicate that I'm no longer waiting
809 * on a lock so that other processes don't try to wake me up and screw
811 * --------------------
814 HandleDeadLock(SIGNAL_ARGS)
820 /* ---------------------
821 * Check to see if we've been awoken by anyone in the interim.
823 * If we have we can return and resume our transaction -- happy day.
824 * Before we are awoken the process releasing the lock grants it to
825 * us so we know that we don't have to wait anymore.
827 * Damn these names are LONG! -mer
828 * ---------------------
830 if (IpcSemaphoreGetCount(MyProc->sem.semId, MyProc->sem.semNum) ==
831 IpcSemaphoreDefaultStartValue)
838 * you would think this would be unnecessary, but...
840 * this also means we've been removed already. in some ports (e.g.,
841 * sparc and aix) the semop(2) implementation is such that we can
842 * actually end up in this handler after someone has removed us from
843 * the queue and bopped the semaphore *but the test above fails to
844 * detect the semaphore update* (presumably something weird having to
845 * do with the order in which the semaphore wakeup signal and SIGALRM
848 if (MyProc->links.prev == INVALID_OFFSET ||
849 MyProc->links.next == INVALID_OFFSET)
860 MyProc->errType = STATUS_NOT_FOUND;
861 if (!DeadLockCheck(MyProc, MyProc->waitLock))
867 mywaitlock = MyProc->waitLock;
869 /* ------------------------
870 * Get this process off the lock's wait queue
871 * ------------------------
873 Assert(mywaitlock->waitProcs.size > 0);
875 --mywaitlock->waitProcs.size;
876 SHMQueueDelete(&(MyProc->links));
877 SHMQueueElemInit(&(MyProc->links));
879 /* ------------------
880 * Unlock my semaphore so that the count is right for next time.
881 * I was awoken by a signal, not by someone unlocking my semaphore.
884 IpcSemaphoreUnlock(MyProc->sem.semId, MyProc->sem.semNum,
888 * Set MyProc->errType to STATUS_ERROR so that we abort after
889 * returning from this handler.
892 MyProc->errType = STATUS_ERROR;
895 * if this doesn't follow the IpcSemaphoreUnlock then we get lock
896 * table corruption ("LockReplace: xid table corrupted") due to race
897 * conditions. i don't claim to understand this...
901 elog(NOTICE, DeadLockMessage);
906 ProcReleaseSpins(PROC *proc)
915 for (i = 0; i < (int) MAX_SPINS; i++)
919 Assert(proc->sLocks[i] == 1);
926 /*****************************************************************************
928 *****************************************************************************/
931 * ProcGetNewSemKeyAndNum -
932 * scan the free semaphore bitmap and allocate a single semaphore from
933 * a semaphore set. (If the semaphore set doesn't exist yet,
934 * IpcSemaphoreCreate will create it. Otherwise, we use the existing
938 ProcGetNewSemKeyAndNum(IPCKey *key, int *semNum)
941 int32 *freeSemMap = ProcGlobal->freeSemMap;
942 int32 fullmask = (1 << (PROC_NSEMS_PER_SET + 1)) - 1;
945 * we hold ProcStructLock when entering this routine. We scan through
946 * the bitmap to look for a free semaphore.
949 for (i = 0; i < MAX_PROC_SEMS / PROC_NSEMS_PER_SET; i++)
954 if (freeSemMap[i] == fullmask)
955 continue; /* this set is fully allocated */
957 for (j = 0; j < PROC_NSEMS_PER_SET; j++)
959 if ((freeSemMap[i] & mask) == 0)
963 * a free semaphore found. Mark it as allocated. Also set
964 * the bit indicating whole set is allocated.
966 freeSemMap[i] |= mask + (1 << PROC_NSEMS_PER_SET);
968 *key = ProcGlobal->currKey + i;
976 /* if we reach here, all the semaphores are in use. */
977 elog(ERROR, "InitProc: cannot allocate a free semaphore");
982 * free up our semaphore in the semaphore set.
985 ProcFreeSem(IpcSemaphoreKey semKey, int semNum)
989 int32 *freeSemMap = ProcGlobal->freeSemMap;
991 i = semKey - ProcGlobal->currKey;
992 mask = ~(1 << semNum);
993 freeSemMap[i] &= mask;
996 * Formerly we'd release a semaphore set if it was now completely
997 * unused, but now we keep the semaphores to ensure we won't run out
998 * when starting new backends --- cf. InitProcGlobal. Note that the
999 * PROC_NSEMS_PER_SET+1'st bit of the freeSemMap entry remains set to
1000 * indicate it is still allocated; ProcFreeAllSemaphores() needs that.
1005 * ProcFreeAllSemaphores -
1006 * called at shmem_exit time, ie when exiting the postmaster or
1007 * destroying shared state for a failed set of backends.
1008 * Free up all the semaphores allocated to the lmgrs of the backends.
1011 ProcFreeAllSemaphores()
1014 int32 *freeSemMap = ProcGlobal->freeSemMap;
1016 for (i = 0; i < MAX_PROC_SEMS / PROC_NSEMS_PER_SET; i++)
1018 if (freeSemMap[i] != 0)
1019 IpcSemaphoreKill(ProcGlobal->currKey + i);