1 /*-------------------------------------------------------------------------
4 * routines to manage per-process shared memory data structure
6 * Copyright (c) 1994, Regents of the University of California
10 * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.15 1997/02/12 05:23:54 scrappy Exp $
12 *-------------------------------------------------------------------------
15 * Each postgres backend gets one of these. We'll use it to
16 * clean up after the process should the process suddenly die.
20 * ProcSleep(), ProcWakeup(), ProcWakeupNext(),
21 * ProcQueueAlloc() -- create a shm queue for sleeping processes
22 * ProcQueueInit() -- create a queue without allocing memory
24 * Locking and waiting for buffers can cause the backend to be
25 * put to sleep. Whoever releases the lock, etc. wakes the
26 * process up again (and gives it an error code so it knows
27 * whether it was awoken on an error condition).
31 * ProcReleaseLocks -- frees the locks associated with this process,
32 * ProcKill -- destroys the shared memory state (and locks)
33 * associated with the process.
35 * 5/15/91 -- removed the buffer pool based lock chain in favor
36 * of a shared memory lock chain. The write-protection is
37 * more expensive if the lock chain is in the buffer pool.
38 * The only reason I kept the lock chain in the buffer pool
39 * in the first place was to allow the lock table to grow larger
40 * than available shared memory and that isn't going to work
41 * without a lot of unimplemented support anyway.
43 * 4/7/95 -- instead of allocating a set of 1 semaphore per process, we
44 * allocate a semaphore from a set of PROC_NSEMS_PER_SET semaphores
45 * shared among backends (we keep a few sets of semaphores around).
46 * This is so that we can support more backends. (system-wide semaphore
47 * sets run out pretty fast.) -ay 4/95
49 * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.15 1997/02/12 05:23:54 scrappy Exp $
57 #include <sys/types.h>
59 #if defined(sparc_solaris)
65 #include "miscadmin.h"
66 #include "libpq/pqsignal.h"
68 #include "access/xact.h"
69 #include "utils/hsearch.h"
71 #include "storage/ipc.h"
72 /* In Ultrix, sem.h must be included after ipc.h */
74 #include "storage/buf.h"
75 #include "storage/lock.h"
76 #include "storage/lmgr.h"
77 #include "storage/shmem.h"
78 #include "storage/spin.h"
79 #include "storage/proc.h"
82 * timeout (in seconds) for resolving possible deadlock
84 #ifndef DEADLOCK_TIMEOUT
85 #define DEADLOCK_TIMEOUT 60
88 /* --------------------
89 * Spin lock for manipulating the shared process data structure:
90 * ProcGlobal.... Adding an extra spin lock seemed like the smallest
91 * hack to get around reading and updating this structure in shared
92 * memory. -mer 17 July 1991
93 * --------------------
95 SPINLOCK ProcStructLock;
98 * For cleanup routines. Don't cleanup if the initialization
101 static bool ProcInitialized = FALSE;
103 static PROC_HDR *ProcGlobal = NULL;
107 static void ProcKill(int exitStatus, int pid);
108 static void ProcGetNewSemKeyAndNum(IPCKey *key, int *semNum);
109 static void ProcFreeSem(IpcSemaphoreKey semKey, int semNum);
112 * initializes the global process table. We put it here so that
113 * the postmaster can do this initialization. (ProcFreeAllSem needs
114 * to read this table on exiting the postmaster. If we have the first
115 * backend do this, starting up and killing the postmaster without
116 * starting any backends will be a problem.)
119 InitProcGlobal(IPCKey key)
123 /* attach to the free list */
124 ProcGlobal = (PROC_HDR *)
125 ShmemInitStruct("Proc Header",(unsigned)sizeof(PROC_HDR),&found);
127 /* --------------------
128 * We're the first - initialize.
129 * --------------------
135 ProcGlobal->numProcs = 0;
136 ProcGlobal->freeProcs = INVALID_OFFSET;
137 ProcGlobal->currKey = IPCGetProcessSemaphoreInitKey(key);
138 for (i=0; i < MAX_PROC_SEMS/PROC_NSEMS_PER_SET; i++)
139 ProcGlobal->freeSemMap[i] = 0;
143 /* ------------------------
144 * InitProc -- create a per-process data structure for this process
145 * used by the lock manager on semaphore queues.
146 * ------------------------
149 InitProcess(IPCKey key)
154 unsigned long location, myOffset;
156 /* ------------------
157 * Routine called if deadlock timer goes off. See ProcSleep()
161 pqsignal(SIGALRM, HandleDeadLock);
162 #endif /* WIN32 we'll have to figure out how to handle this later */
164 SpinAcquire(ProcStructLock);
166 /* attach to the free list */
167 ProcGlobal = (PROC_HDR *)
168 ShmemInitStruct("Proc Header",(unsigned)sizeof(PROC_HDR),&found);
170 /* this should not happen. InitProcGlobal() is called before this. */
171 elog(WARN, "InitProcess: Proc Header uninitialized");
176 SpinRelease(ProcStructLock);
177 elog(WARN,"ProcInit: you already exist");
181 /* try to get a proc from the free list first */
183 myOffset = ProcGlobal->freeProcs;
185 if (myOffset != INVALID_OFFSET)
187 MyProc = (PROC *) MAKE_PTR(myOffset);
188 ProcGlobal->freeProcs = MyProc->links.next;
192 /* have to allocate one. We can't use the normal binding
193 * table mechanism because the proc structure is stored
194 * by PID instead of by a global name (need to look it
195 * up by PID when we cleanup dead processes).
198 MyProc = (PROC *) ShmemAlloc((unsigned)sizeof(PROC));
201 SpinRelease(ProcStructLock);
202 elog (FATAL,"cannot create new proc: out of memory");
205 /* this cannot be initialized until after the buffer pool */
206 SHMQueueInit(&(MyProc->lockQueue));
207 MyProc->procId = ProcGlobal->numProcs;
208 ProcGlobal->numProcs++;
212 * zero out the spin lock counts and set the sLocks field for
213 * ProcStructLock to 1 as we have acquired this spinlock above but
214 * didn't record it since we didn't have MyProc until now.
216 memset(MyProc->sLocks, 0, sizeof(MyProc->sLocks));
217 MyProc->sLocks[ProcStructLock] = 1;
220 if (IsUnderPostmaster) {
226 ProcGetNewSemKeyAndNum(&semKey, &semNum);
228 semId = IpcSemaphoreCreate(semKey,
231 IpcSemaphoreDefaultStartValue,
235 * we might be reusing a semaphore that belongs to a dead
236 * backend. So be careful and reinitialize its value here.
238 semun.val = IpcSemaphoreDefaultStartValue;
239 semctl(semId, semNum, SETVAL, semun);
241 IpcSemaphoreLock(semId, semNum, IpcExclusiveLock);
242 MyProc->sem.semId = semId;
243 MyProc->sem.semNum = semNum;
244 MyProc->sem.semKey = semKey;
246 MyProc->sem.semId = -1;
249 /* ----------------------
251 * ----------------------
253 SpinRelease(ProcStructLock);
256 MyProc->xid = InvalidTransactionId;
262 * Start keeping spin lock stats from here on. Any botch before
263 * this initialization is forever botched
266 memset(MyProc->sLocks, 0, MAX_SPINS*sizeof(*MyProc->sLocks));
268 /* -------------------------
269 * Install ourselves in the binding table. The name to
270 * use is determined by the OS-assigned process id. That
271 * allows the cleanup process to find us after any untimely
273 * -------------------------
276 location = MAKE_OFFSET(MyProc);
277 if ((! ShmemPIDLookup(pid,&location)) || (location != MAKE_OFFSET(MyProc)))
279 elog(FATAL,"InitProc: ShmemPID table broken");
282 MyProc->errType = NO_ERROR;
283 SHMQueueElemInit(&(MyProc->links));
285 on_exitpg(ProcKill, (caddr_t)pid);
287 ProcInitialized = TRUE;
291 * ProcReleaseLocks() -- release all locks associated with this process
299 LockReleaseAll(1,&MyProc->lockQueue);
304 * used by the postmaster to clean up the global tables. This also frees
305 * up the semaphore used for the lmgr of the process. (We have to do
306 * this is the postmaster instead of doing a IpcSemaphoreKill on exiting
307 * the process because the semaphore set is shared among backends and
308 * we don't want to remove other's semaphores on exit.)
313 SHMEM_OFFSET location;
316 location = INVALID_OFFSET;
318 location = ShmemPIDDestroy(pid);
319 if (location == INVALID_OFFSET)
321 proc = (PROC *) MAKE_PTR(location);
323 SpinAcquire(ProcStructLock);
325 ProcFreeSem(proc->sem.semKey, proc->sem.semNum);
327 proc->links.next = ProcGlobal->freeProcs;
328 ProcGlobal->freeProcs = MAKE_OFFSET(proc);
330 SpinRelease(ProcStructLock);
336 * ProcKill() -- Destroy the per-proc data structure for
337 * this process. Release any of its held spin locks.
340 ProcKill(int exitStatus, int pid)
343 SHMEM_OFFSET location;
345 /* --------------------
346 * If this is a FATAL exit the postmaster will have to kill all the
347 * existing backends and reinitialize shared memory. So all we don't
348 * need to do anything here.
349 * --------------------
359 ShmemPIDLookup(pid,&location);
360 if (location == INVALID_OFFSET)
363 proc = (PROC *) MAKE_PTR(location);
365 if (proc != MyProc) {
366 Assert( pid != getpid() );
371 * Assume one lock table.
374 ProcReleaseSpins(proc);
375 LockReleaseAll(1,&proc->lockQueue);
378 LockReleaseAll(0,&proc->lockQueue);
382 * get off the wait queue
386 if (proc->links.next != INVALID_OFFSET) {
387 Assert(proc->waitLock->waitProcs.size > 0);
388 SHMQueueDelete(&(proc->links));
389 --proc->waitLock->waitProcs.size;
391 SHMQueueElemInit(&(proc->links));
398 * ProcQueue package: routines for putting processes to sleep
403 * ProcQueueAlloc -- alloc/attach to a shared memory process queue
405 * Returns: a pointer to the queue or NULL
406 * Side Effects: Initializes the queue if we allocated one
409 ProcQueueAlloc(char *name)
412 PROC_QUEUE *queue = (PROC_QUEUE *)
413 ShmemInitStruct(name,(unsigned)sizeof(PROC_QUEUE),&found);
421 ProcQueueInit(queue);
427 * ProcQueueInit -- initialize a shared memory process queue
430 ProcQueueInit(PROC_QUEUE *queue)
432 SHMQueueInit(&(queue->links));
439 * ProcSleep -- put a process to sleep
441 * P() on the semaphore should put us to sleep. The process
442 * semaphore is cleared by default, so the first time we try
443 * to acquire it, we sleep.
445 * ASSUME: that no one will fiddle with the queue until after
446 * we release the spin lock.
448 * NOTES: The process queue is now a priority queue for locking.
451 ProcSleep(PROC_QUEUE *queue,
459 #ifndef WIN32 /* figure this out later */
460 struct itimerval timeval, dummy;
463 proc = (PROC *) MAKE_PTR(queue->links.prev);
464 for (i=0;i<queue->size;i++)
466 if (proc->prio < prio)
467 proc = (PROC *) MAKE_PTR(proc->links.prev);
473 MyProc->token = token;
474 MyProc->waitLock = lock;
476 /* -------------------
477 * currently, we only need this for the ProcWakeup routines
478 * -------------------
480 TransactionIdStore((TransactionId) GetCurrentTransactionId(), &MyProc->xid);
482 /* -------------------
483 * assume that these two operations are atomic (because
485 * -------------------
487 SHMQueueInsertTL(&(proc->links),&(MyProc->links));
490 SpinRelease(spinlock);
493 * Postgres does not have any deadlock detection code and for this
494 * reason we must set a timer to wake up the process in the event of
495 * a deadlock. For now the timer is set for 1 minute and we assume that
496 * any process which sleeps for this amount of time is deadlocked and will
497 * receive a SIGALRM signal. The handler should release the processes
498 * semaphore and abort the current transaction.
500 * Need to zero out struct to set the interval and the micro seconds fields
505 memset(&timeval, 0, sizeof(struct itimerval));
506 timeval.it_value.tv_sec = DEADLOCK_TIMEOUT;
508 if (setitimer(ITIMER_REAL, &timeval, &dummy))
509 elog(FATAL, "ProcSleep: Unable to set timer for process wakeup");
513 * if someone wakes us between SpinRelease and IpcSemaphoreLock,
514 * IpcSemaphoreLock will not block. The wakeup is "saved" by
515 * the semaphore implementation.
518 IpcSemaphoreLock(MyProc->sem.semId, MyProc->sem.semNum, IpcExclusiveLock);
521 * We were awoken before a timeout - now disable the timer
525 timeval.it_value.tv_sec = 0;
528 if (setitimer(ITIMER_REAL, &timeval, &dummy))
529 elog(FATAL, "ProcSleep: Unable to diable timer for process wakeup");
533 * We were assumed to be in a critical section when we went
537 SpinAcquire(spinlock);
539 return(MyProc->errType);
544 * ProcWakeup -- wake up a process by releasing its private semaphore.
546 * remove the process from the wait queue and set its links invalid.
547 * RETURN: the next process in the wait queue.
550 ProcWakeup(PROC *proc, int errType)
553 /* assume that spinlock has been acquired */
555 if (proc->links.prev == INVALID_OFFSET ||
556 proc->links.next == INVALID_OFFSET)
557 return((PROC *) NULL);
559 retProc = (PROC *) MAKE_PTR(proc->links.prev);
561 /* you have to update waitLock->waitProcs.size yourself */
562 SHMQueueDelete(&(proc->links));
563 SHMQueueElemInit(&(proc->links));
565 proc->errType = errType;
567 IpcSemaphoreUnlock(proc->sem.semId, proc->sem.semNum, IpcExclusiveLock);
579 return( MyProc->procId );
583 * ProcLockWakeup -- routine for waking up processes when a lock is
587 ProcLockWakeup(PROC_QUEUE *queue, char *ltable, char *lock)
593 return(STATUS_NOT_FOUND);
595 proc = (PROC *) MAKE_PTR(queue->links.prev);
597 while ((LockResolveConflicts ((LOCKTAB *) ltable,
600 proc->xid) == STATUS_OK))
602 /* there was a waiting process, grant it the lock before waking it
603 * up. This will prevent another process from seizing the lock
604 * between the time we release the lock master (spinlock) and
605 * the time that the awoken process begins executing again.
607 GrantLock((LOCK *) lock, proc->token);
611 * ProcWakeup removes proc from the lock waiting process queue and
612 * returns the next proc in chain. If a writer just dropped
613 * its lock and there are several waiting readers, wake them all up.
615 proc = ProcWakeup(proc, NO_ERROR);
618 if (!proc || queue->size == 0)
625 /* Something is still blocking us. May have deadlocked. */
626 return(STATUS_NOT_FOUND);
630 ProcAddLock(SHM_QUEUE *elem)
632 SHMQueueInsertTL(&MyProc->lockQueue,elem);
635 /* --------------------
636 * We only get to this routine if we got SIGALRM after DEADLOCK_TIMEOUT
637 * while waiting for a lock to be released by some other process. After
638 * the one minute deadline we assume we have a deadlock and must abort
639 * this transaction. We must also indicate that I'm no longer waiting
640 * on a lock so that other processes don't try to wake me up and screw
642 * --------------------
645 HandleDeadLock(int sig)
652 /* ---------------------
653 * Check to see if we've been awoken by anyone in the interim.
655 * If we have we can return and resume our transaction -- happy day.
656 * Before we are awoken the process releasing the lock grants it to
657 * us so we know that we don't have to wait anymore.
659 * Damn these names are LONG! -mer
660 * ---------------------
662 if (IpcSemaphoreGetCount(MyProc->sem.semId, MyProc->sem.semNum) ==
663 IpcSemaphoreDefaultStartValue) {
669 * you would think this would be unnecessary, but...
671 * this also means we've been removed already. in some ports
672 * (e.g., sparc and aix) the semop(2) implementation is such that
673 * we can actually end up in this handler after someone has removed
674 * us from the queue and bopped the semaphore *but the test above
675 * fails to detect the semaphore update* (presumably something weird
676 * having to do with the order in which the semaphore wakeup signal
677 * and SIGALRM get handled).
679 if (MyProc->links.prev == INVALID_OFFSET ||
680 MyProc->links.next == INVALID_OFFSET) {
685 lock = MyProc->waitLock;
686 size = lock->waitProcs.size; /* so we can look at this in the core */
688 #ifdef DEADLOCK_DEBUG
692 /* ------------------------
693 * Get this process off the lock's wait queue
694 * ------------------------
696 Assert(lock->waitProcs.size > 0);
697 --lock->waitProcs.size;
698 SHMQueueDelete(&(MyProc->links));
699 SHMQueueElemInit(&(MyProc->links));
701 /* ------------------
702 * Unlock my semaphore so that the count is right for next time.
703 * I was awoken by a signal, not by someone unlocking my semaphore.
706 IpcSemaphoreUnlock(MyProc->sem.semId, MyProc->sem.semNum, IpcExclusiveLock);
709 * Set MyProc->errType to STATUS_ERROR so that we abort after
710 * returning from this handler.
713 MyProc->errType = STATUS_ERROR;
716 * if this doesn't follow the IpcSemaphoreUnlock then we get lock
717 * table corruption ("LockReplace: xid table corrupted") due to
718 * race conditions. i don't claim to understand this...
722 elog(NOTICE, "Timeout -- possible deadlock");
727 ProcReleaseSpins(PROC *proc)
736 for (i=0; i < (int)MAX_SPINS; i++)
740 Assert(proc->sLocks[i] == 1);
746 /*****************************************************************************
748 *****************************************************************************/
751 * ProcGetNewSemKeyAndNum -
752 * scan the free semaphore bitmap and allocate a single semaphore from
753 * a semaphore set. (If the semaphore set doesn't exist yet,
754 * IpcSemaphoreCreate will create it. Otherwise, we use the existing
758 ProcGetNewSemKeyAndNum(IPCKey *key, int *semNum)
761 int32 *freeSemMap = ProcGlobal->freeSemMap;
762 unsigned int fullmask;
765 * we hold ProcStructLock when entering this routine. We scan through
766 * the bitmap to look for a free semaphore.
768 fullmask = ~0 >> (32 - PROC_NSEMS_PER_SET);
769 for(i=0; i < MAX_PROC_SEMS/PROC_NSEMS_PER_SET; i++) {
773 if (freeSemMap[i] == fullmask)
774 continue; /* none free for this set */
776 for(j = 0; j < PROC_NSEMS_PER_SET; j++) {
777 if ((freeSemMap[i] & mask) == 0) {
779 * a free semaphore found. Mark it as allocated.
781 freeSemMap[i] |= mask;
783 *key = ProcGlobal->currKey + i;
791 /* if we reach here, all the semaphores are in use. */
792 elog(WARN, "InitProc: cannot allocate a free semaphore");
797 * free up our semaphore in the semaphore set. If we're the last one
798 * in the set, also remove the semaphore set.
801 ProcFreeSem(IpcSemaphoreKey semKey, int semNum)
805 int32 *freeSemMap = ProcGlobal->freeSemMap;
807 i = semKey - ProcGlobal->currKey;
808 mask = ~(1 << semNum);
809 freeSemMap[i] &= mask;
811 if (freeSemMap[i]==0)
812 IpcSemaphoreKill(semKey);
816 * ProcFreeAllSemaphores -
817 * on exiting the postmaster, we free up all the semaphores allocated
818 * to the lmgrs of the backends.
821 ProcFreeAllSemaphores()
824 int32 *freeSemMap = ProcGlobal->freeSemMap;
826 for(i=0; i < MAX_PROC_SEMS/PROC_NSEMS_PER_SET; i++) {
827 if (freeSemMap[i]!=0)
828 IpcSemaphoreKill(ProcGlobal->currKey + i);