/*------------------------------------------------------------------------- * * proc.c * routines to manage per-process shared memory data structure * * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.157 2005/04/15 04:18:10 neilc Exp $ * *------------------------------------------------------------------------- */ /* * Interface (a): * ProcSleep(), ProcWakeup(), * ProcQueueAlloc() -- create a shm queue for sleeping processes * ProcQueueInit() -- create a queue without allocing memory * * Locking and waiting for buffers can cause the backend to be * put to sleep. Whoever releases the lock, etc. wakes the * process up again (and gives it an error code so it knows * whether it was awoken on an error condition). * * Interface (b): * * ProcReleaseLocks -- frees the locks associated with current transaction * * ProcKill -- destroys the shared memory state (and locks) * associated with the process. * * 5/15/91 -- removed the buffer pool based lock chain in favor * of a shared memory lock chain. The write-protection is * more expensive if the lock chain is in the buffer pool. * The only reason I kept the lock chain in the buffer pool * in the first place was to allow the lock table to grow larger * than available shared memory and that isn't going to work * without a lot of unimplemented support anyway. */ #include "postgres.h" #include #include #include #include "miscadmin.h" #include "access/xact.h" #include "storage/bufmgr.h" #include "storage/ipc.h" #include "storage/proc.h" #include "storage/sinval.h" #include "storage/spin.h" /* GUC variables */ int DeadlockTimeout = 1000; int StatementTimeout = 0; /* Pointer to this process's PGPROC struct, if any */ PGPROC *MyProc = NULL; /* * This spinlock protects the freelist of recycled PGPROC structures. * We cannot use an LWLock because the LWLock manager depends on already * having a PGPROC and a wait semaphore! But these structures are touched * relatively infrequently (only at backend startup or shutdown) and not for * very long, so a spinlock is okay. */ NON_EXEC_STATIC slock_t *ProcStructLock = NULL; /* Pointers to shared-memory structures */ static PROC_HDR *ProcGlobal = NULL; static PGPROC *DummyProcs = NULL; static bool waitingForLock = false; /* Mark these volatile because they can be changed by signal handler */ static volatile bool statement_timeout_active = false; static volatile bool deadlock_timeout_active = false; /* statement_fin_time is valid only if statement_timeout_active is true */ static struct timeval statement_fin_time; static void ProcKill(int code, Datum arg); static void DummyProcKill(int code, Datum arg); static bool CheckStatementTimeout(void); /* * Report shared-memory space needed by InitProcGlobal. */ int ProcGlobalShmemSize(int maxBackends) { int size = 0; size += MAXALIGN(sizeof(PROC_HDR)); /* ProcGlobal */ size += MAXALIGN(NUM_DUMMY_PROCS * sizeof(PGPROC)); /* DummyProcs */ size += MAXALIGN(maxBackends * sizeof(PGPROC)); /* MyProcs */ size += MAXALIGN(sizeof(slock_t)); /* ProcStructLock */ return size; } /* * Report number of semaphores needed by InitProcGlobal. */ int ProcGlobalSemas(int maxBackends) { /* We need a sema per backend, plus one for each dummy process. */ return maxBackends + NUM_DUMMY_PROCS; } /* * InitProcGlobal - * initializes the global process table. We put it here so that * the postmaster can do this initialization. * * We also create all the per-process semaphores we will need to support * the requested number of backends. We used to allocate semaphores * only when backends were actually started up, but that is bad because * it lets Postgres fail under load --- a lot of Unix systems are * (mis)configured with small limits on the number of semaphores, and * running out when trying to start another backend is a common failure. * So, now we grab enough semaphores to support the desired max number * of backends immediately at initialization --- if the sysadmin has set * MaxBackends higher than his kernel will support, he'll find out sooner * rather than later. * * Another reason for creating semaphores here is that the semaphore * implementation typically requires us to create semaphores in the * postmaster, not in backends. */ void InitProcGlobal(int maxBackends) { bool foundProcGlobal, foundDummy; /* Create or attach to the ProcGlobal shared structure */ ProcGlobal = (PROC_HDR *) ShmemInitStruct("Proc Header", sizeof(PROC_HDR), &foundProcGlobal); /* * Create or attach to the PGPROC structures for dummy (checkpoint) * processes, too. These do not get linked into the freeProcs list. */ DummyProcs = (PGPROC *) ShmemInitStruct("DummyProcs", NUM_DUMMY_PROCS * sizeof(PGPROC), &foundDummy); if (foundProcGlobal || foundDummy) { /* both should be present or neither */ Assert(foundProcGlobal && foundDummy); } else { /* * We're the first - initialize. */ PGPROC *procs; int i; ProcGlobal->freeProcs = INVALID_OFFSET; /* * Pre-create the PGPROC structures and create a semaphore for * each. */ procs = (PGPROC *) ShmemAlloc(maxBackends * sizeof(PGPROC)); if (!procs) ereport(FATAL, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of shared memory"))); MemSet(procs, 0, maxBackends * sizeof(PGPROC)); for (i = 0; i < maxBackends; i++) { PGSemaphoreCreate(&(procs[i].sem)); procs[i].links.next = ProcGlobal->freeProcs; ProcGlobal->freeProcs = MAKE_OFFSET(&procs[i]); } MemSet(DummyProcs, 0, NUM_DUMMY_PROCS * sizeof(PGPROC)); for (i = 0; i < NUM_DUMMY_PROCS; i++) { DummyProcs[i].pid = 0; /* marks dummy proc as not in use */ PGSemaphoreCreate(&(DummyProcs[i].sem)); } /* Create ProcStructLock spinlock, too */ ProcStructLock = (slock_t *) ShmemAlloc(sizeof(slock_t)); SpinLockInit(ProcStructLock); } } /* * InitProcess -- initialize a per-process data structure for this backend */ void InitProcess(void) { SHMEM_OFFSET myOffset; /* use volatile pointer to prevent code rearrangement */ volatile PROC_HDR *procglobal = ProcGlobal; /* * ProcGlobal should be set by a previous call to InitProcGlobal (if * we are a backend, we inherit this by fork() from the postmaster). */ if (procglobal == NULL) elog(PANIC, "proc header uninitialized"); if (MyProc != NULL) elog(ERROR, "you already exist"); /* * Try to get a proc struct from the free list. If this fails, we * must be out of PGPROC structures (not to mention semaphores). */ SpinLockAcquire(ProcStructLock); myOffset = procglobal->freeProcs; if (myOffset != INVALID_OFFSET) { MyProc = (PGPROC *) MAKE_PTR(myOffset); procglobal->freeProcs = MyProc->links.next; SpinLockRelease(ProcStructLock); } else { /* * If we reach here, all the PGPROCs are in use. This is one of * the possible places to detect "too many backends", so give the * standard error message. */ SpinLockRelease(ProcStructLock); ereport(FATAL, (errcode(ERRCODE_TOO_MANY_CONNECTIONS), errmsg("sorry, too many clients already"))); } /* * Initialize all fields of MyProc, except for the semaphore which was * prepared for us by InitProcGlobal. */ SHMQueueElemInit(&(MyProc->links)); MyProc->waitStatus = STATUS_OK; MyProc->xid = InvalidTransactionId; MyProc->xmin = InvalidTransactionId; MyProc->pid = MyProcPid; MyProc->databaseId = MyDatabaseId; MyProc->logRec.xrecoff = 0; MyProc->lwWaiting = false; MyProc->lwExclusive = false; MyProc->lwWaitLink = NULL; MyProc->waitLock = NULL; MyProc->waitProcLock = NULL; SHMQueueInit(&(MyProc->procLocks)); /* * Arrange to clean up at backend exit. */ on_shmem_exit(ProcKill, 0); /* * We might be reusing a semaphore that belonged to a failed process. * So be careful and reinitialize its value here. */ PGSemaphoreReset(&MyProc->sem); /* * Now that we have a PGPROC, we could try to acquire locks, so * initialize the deadlock checker. */ InitDeadLockChecking(); } /* * InitDummyProcess -- create a dummy per-process data structure * * This is called by checkpoint processes so that they will have a MyProc * value that's real enough to let them wait for LWLocks. The PGPROC and * sema that are assigned are the extra ones created during InitProcGlobal. * * Dummy processes are presently not expected to wait for real (lockmgr) * locks, nor to participate in sinval messaging. */ void InitDummyProcess(int proctype) { PGPROC *dummyproc; /* * ProcGlobal should be set by a previous call to InitProcGlobal (we * inherit this by fork() from the postmaster). */ if (ProcGlobal == NULL || DummyProcs == NULL) elog(PANIC, "proc header uninitialized"); if (MyProc != NULL) elog(ERROR, "you already exist"); Assert(proctype >= 0 && proctype < NUM_DUMMY_PROCS); dummyproc = &DummyProcs[proctype]; /* * dummyproc should not presently be in use by anyone else */ if (dummyproc->pid != 0) elog(FATAL, "DummyProc[%d] is in use by PID %d", proctype, dummyproc->pid); MyProc = dummyproc; /* * Initialize all fields of MyProc, except MyProc->sem which was set * up by InitProcGlobal. */ MyProc->pid = MyProcPid; /* marks dummy proc as in use by me */ SHMQueueElemInit(&(MyProc->links)); MyProc->waitStatus = STATUS_OK; MyProc->xid = InvalidTransactionId; MyProc->xmin = InvalidTransactionId; MyProc->databaseId = MyDatabaseId; MyProc->logRec.xrecoff = 0; MyProc->lwWaiting = false; MyProc->lwExclusive = false; MyProc->lwWaitLink = NULL; MyProc->waitLock = NULL; MyProc->waitProcLock = NULL; SHMQueueInit(&(MyProc->procLocks)); /* * Arrange to clean up at process exit. */ on_shmem_exit(DummyProcKill, Int32GetDatum(proctype)); /* * We might be reusing a semaphore that belonged to a failed process. * So be careful and reinitialize its value here. */ PGSemaphoreReset(&MyProc->sem); } /* * Cancel any pending wait for lock, when aborting a transaction. * * Returns true if we had been waiting for a lock, else false. * * (Normally, this would only happen if we accept a cancel/die * interrupt while waiting; but an ereport(ERROR) while waiting is * within the realm of possibility, too.) */ bool LockWaitCancel(void) { /* Nothing to do if we weren't waiting for a lock */ if (!waitingForLock) return false; /* Turn off the deadlock timer, if it's still running (see ProcSleep) */ disable_sig_alarm(false); /* Unlink myself from the wait queue, if on it (might not be anymore!) */ LWLockAcquire(LockMgrLock, LW_EXCLUSIVE); if (MyProc->links.next != INVALID_OFFSET) { /* We could not have been granted the lock yet */ Assert(MyProc->waitStatus == STATUS_ERROR); RemoveFromWaitQueue(MyProc); } else { /* * Somebody kicked us off the lock queue already. Perhaps they * granted us the lock, or perhaps they detected a deadlock. If * they did grant us the lock, we'd better remember it in our * local lock table. */ if (MyProc->waitStatus == STATUS_OK) GrantAwaitedLock(); } waitingForLock = false; LWLockRelease(LockMgrLock); /* * Reset the proc wait semaphore to zero. This is necessary in the * scenario where someone else granted us the lock we wanted before we * were able to remove ourselves from the wait-list. The semaphore * will have been bumped to 1 by the would-be grantor, and since we * are no longer going to wait on the sema, we have to force it back * to zero. Otherwise, our next attempt to wait for a lock will fall * through prematurely. */ PGSemaphoreReset(&MyProc->sem); /* * Return true even if we were kicked off the lock before we were able * to remove ourselves. */ return true; } /* * ProcReleaseLocks() -- release locks associated with current transaction * at main transaction commit or abort * * At main transaction commit, we release all locks except session locks. * At main transaction abort, we release all locks including session locks; * this lets us clean up after a VACUUM FULL failure. * * At subtransaction commit, we don't release any locks (so this func is not * needed at all); we will defer the releasing to the parent transaction. * At subtransaction abort, we release all locks held by the subtransaction; * this is implemented by retail releasing of the locks under control of * the ResourceOwner mechanism. * * Note that user locks are not released in any case. */ void ProcReleaseLocks(bool isCommit) { if (!MyProc) return; /* If waiting, get off wait queue (should only be needed after error) */ LockWaitCancel(); /* Release locks */ LockReleaseAll(DEFAULT_LOCKMETHOD, !isCommit); } /* * ProcKill() -- Destroy the per-proc data structure for * this process. Release any of its held LW locks. */ static void ProcKill(int code, Datum arg) { /* use volatile pointer to prevent code rearrangement */ volatile PROC_HDR *procglobal = ProcGlobal; Assert(MyProc != NULL); /* Release any LW locks I am holding */ LWLockReleaseAll(); /* * Make real sure we release any buffer locks and pins we might be * holding, too. It is pretty ugly to do this here and not in a * shutdown callback registered by the bufmgr ... but we must do this * *after* LWLockReleaseAll and *before* zapping MyProc. */ AtProcExit_Buffers(); /* Get off any wait queue I might be on */ LockWaitCancel(); /* Remove from the standard lock table */ LockReleaseAll(DEFAULT_LOCKMETHOD, true); #ifdef USER_LOCKS /* Remove from the user lock table */ LockReleaseAll(USER_LOCKMETHOD, true); #endif SpinLockAcquire(ProcStructLock); /* Return PGPROC structure (and semaphore) to freelist */ MyProc->links.next = procglobal->freeProcs; procglobal->freeProcs = MAKE_OFFSET(MyProc); /* PGPROC struct isn't mine anymore */ MyProc = NULL; SpinLockRelease(ProcStructLock); } /* * DummyProcKill() -- Cut-down version of ProcKill for dummy (checkpoint) * processes. The PGPROC and sema are not released, only marked * as not-in-use. */ static void DummyProcKill(int code, Datum arg) { int proctype = DatumGetInt32(arg); PGPROC *dummyproc; Assert(proctype >= 0 && proctype < NUM_DUMMY_PROCS); dummyproc = &DummyProcs[proctype]; Assert(MyProc == dummyproc); /* Release any LW locks I am holding */ LWLockReleaseAll(); /* Release buffer locks and pins, too */ AtProcExit_Buffers(); /* I can't be on regular lock queues, so needn't check */ /* Mark dummy proc no longer in use */ MyProc->pid = 0; /* PGPROC struct isn't mine anymore */ MyProc = NULL; } /* * ProcQueue package: routines for putting processes to sleep * and waking them up */ /* * ProcQueueAlloc -- alloc/attach to a shared memory process queue * * Returns: a pointer to the queue or NULL * Side Effects: Initializes the queue if we allocated one */ #ifdef NOT_USED PROC_QUEUE * ProcQueueAlloc(char *name) { bool found; PROC_QUEUE *queue = (PROC_QUEUE *) ShmemInitStruct(name, sizeof(PROC_QUEUE), &found); if (!queue) return NULL; if (!found) ProcQueueInit(queue); return queue; } #endif /* * ProcQueueInit -- initialize a shared memory process queue */ void ProcQueueInit(PROC_QUEUE *queue) { SHMQueueInit(&(queue->links)); queue->size = 0; } /* * ProcSleep -- put a process to sleep * * Caller must have set MyProc->heldLocks to reflect locks already held * on the lockable object by this process (under all XIDs). * * Locktable's masterLock must be held at entry, and will be held * at exit. * * Result: STATUS_OK if we acquired the lock, STATUS_ERROR if not (deadlock). * * ASSUME: that no one will fiddle with the queue until after * we release the masterLock. * * NOTES: The process queue is now a priority queue for locking. * * P() on the semaphore should put us to sleep. The process * semaphore is normally zero, so when we try to acquire it, we sleep. */ int ProcSleep(LockMethod lockMethodTable, LOCKMODE lockmode, LOCK *lock, PROCLOCK *proclock) { LWLockId masterLock = lockMethodTable->masterLock; PROC_QUEUE *waitQueue = &(lock->waitProcs); LOCKMASK myHeldLocks = MyProc->heldLocks; bool early_deadlock = false; PGPROC *proc; int i; /* * Determine where to add myself in the wait queue. * * Normally I should go at the end of the queue. However, if I already * hold locks that conflict with the request of any previous waiter, * put myself in the queue just in front of the first such waiter. * This is not a necessary step, since deadlock detection would move * me to before that waiter anyway; but it's relatively cheap to * detect such a conflict immediately, and avoid delaying till * deadlock timeout. * * Special case: if I find I should go in front of some waiter, check to * see if I conflict with already-held locks or the requests before * that waiter. If not, then just grant myself the requested lock * immediately. This is the same as the test for immediate grant in * LockAcquire, except we are only considering the part of the wait * queue before my insertion point. */ if (myHeldLocks != 0) { LOCKMASK aheadRequests = 0; proc = (PGPROC *) MAKE_PTR(waitQueue->links.next); for (i = 0; i < waitQueue->size; i++) { /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { /* Must I wait for him ? */ if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) { /* * Yes, so we have a deadlock. Easiest way to clean * up correctly is to call RemoveFromWaitQueue(), but * we can't do that until we are *on* the wait queue. * So, set a flag to check below, and break out of * loop. Also, record deadlock info for later * message. */ RememberSimpleDeadLock(MyProc, lockmode, lock, proc); early_deadlock = true; break; } /* I must go before this waiter. Check special case. */ if ((lockMethodTable->conflictTab[lockmode] & aheadRequests) == 0 && LockCheckConflicts(lockMethodTable, lockmode, lock, proclock, MyProc, NULL) == STATUS_OK) { /* Skip the wait and just grant myself the lock. */ GrantLock(lock, proclock, lockmode); GrantAwaitedLock(); return STATUS_OK; } /* Break out of loop to put myself before him */ break; } /* Nope, so advance to next waiter */ aheadRequests |= LOCKBIT_ON(proc->waitLockMode); proc = (PGPROC *) MAKE_PTR(proc->links.next); } /* * If we fall out of loop normally, proc points to waitQueue head, * so we will insert at tail of queue as desired. */ } else { /* I hold no locks, so I can't push in front of anyone. */ proc = (PGPROC *) &(waitQueue->links); } /* * Insert self into queue, ahead of the given proc (or at tail of * queue). */ SHMQueueInsertBefore(&(proc->links), &(MyProc->links)); waitQueue->size++; lock->waitMask |= LOCKBIT_ON(lockmode); /* Set up wait information in PGPROC object, too */ MyProc->waitLock = lock; MyProc->waitProcLock = proclock; MyProc->waitLockMode = lockmode; MyProc->waitStatus = STATUS_ERROR; /* initialize result for error */ /* * If we detected deadlock, give up without waiting. This must agree * with CheckDeadLock's recovery code, except that we shouldn't * release the semaphore since we haven't tried to lock it yet. */ if (early_deadlock) { RemoveFromWaitQueue(MyProc); return STATUS_ERROR; } /* mark that we are waiting for a lock */ waitingForLock = true; /* * Release the locktable's masterLock. * * NOTE: this may also cause us to exit critical-section state, possibly * allowing a cancel/die interrupt to be accepted. This is OK because * we have recorded the fact that we are waiting for a lock, and so * LockWaitCancel will clean up if cancel/die happens. */ LWLockRelease(masterLock); /* * Set timer so we can wake up after awhile and check for a deadlock. * If a deadlock is detected, the handler releases the process's * semaphore and sets MyProc->waitStatus = STATUS_ERROR, allowing us * to know that we must report failure rather than success. * * By delaying the check until we've waited for a bit, we can avoid * running the rather expensive deadlock-check code in most cases. */ if (!enable_sig_alarm(DeadlockTimeout, false)) elog(FATAL, "could not set timer for process wakeup"); /* * If someone wakes us between LWLockRelease and PGSemaphoreLock, * PGSemaphoreLock will not block. The wakeup is "saved" by the * semaphore implementation. Note also that if CheckDeadLock is * invoked but does not detect a deadlock, PGSemaphoreLock() will * continue to wait. There used to be a loop here, but it was useless * code... * * We pass interruptOK = true, which eliminates a window in which * cancel/die interrupts would be held off undesirably. This is a * promise that we don't mind losing control to a cancel/die interrupt * here. We don't, because we have no shared-state-change work to do * after being granted the lock (the grantor did it all). We do have * to worry about updating the locallock table, but if we lose control * to an error, LockWaitCancel will fix that up. */ PGSemaphoreLock(&MyProc->sem, true); /* * Disable the timer, if it's still running */ if (!disable_sig_alarm(false)) elog(FATAL, "could not disable timer for process wakeup"); /* * Re-acquire the locktable's masterLock. We have to do this to hold * off cancel/die interrupts before we can mess with waitingForLock * (else we might have a missed or duplicated locallock update). */ LWLockAcquire(masterLock, LW_EXCLUSIVE); /* * We no longer want LockWaitCancel to do anything. */ waitingForLock = false; /* * If we got the lock, be sure to remember it in the locallock table. */ if (MyProc->waitStatus == STATUS_OK) GrantAwaitedLock(); /* * We don't have to do anything else, because the awaker did all the * necessary update of the lock table and MyProc. */ return MyProc->waitStatus; } /* * ProcWakeup -- wake up a process by releasing its private semaphore. * * Also remove the process from the wait queue and set its links invalid. * RETURN: the next process in the wait queue. * * XXX: presently, this code is only used for the "success" case, and only * works correctly for that case. To clean up in failure case, would need * to twiddle the lock's request counts too --- see RemoveFromWaitQueue. */ PGPROC * ProcWakeup(PGPROC *proc, int waitStatus) { PGPROC *retProc; /* assume that masterLock has been acquired */ /* Proc should be sleeping ... */ if (proc->links.prev == INVALID_OFFSET || proc->links.next == INVALID_OFFSET) return NULL; /* Save next process before we zap the list link */ retProc = (PGPROC *) MAKE_PTR(proc->links.next); /* Remove process from wait queue */ SHMQueueDelete(&(proc->links)); (proc->waitLock->waitProcs.size)--; /* Clean up process' state and pass it the ok/fail signal */ proc->waitLock = NULL; proc->waitProcLock = NULL; proc->waitStatus = waitStatus; /* 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, NULL) == 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 BackendId */ void ProcSendSignal(BackendId procId) { PGPROC *proc = BackendIdGetProc(procId); 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; } 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 = 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 = 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; 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; 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; }