proc.c

关系型数据库 Postgresql 6.5.2

/*-------------------------------------------------------------------------
 *
 * proc.c
 *	  routines to manage per-process shared memory data structure
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /usr/local/cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.57 1999/05/25 22:42:03 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
/*
 *	Each postgres backend gets one of these.  We'll use it to
 *	clean up after the process should the process suddenly die.
 *
 *
 * Interface (a):
 *		ProcSleep(), ProcWakeup(), ProcWakeupNext(),
 *		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 this process,
 * 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.
 *
 * 4/7/95 -- instead of allocating a set of 1 semaphore per process, we
 *		allocate a semaphore from a set of PROC_NSEMS_PER_SET semaphores
 *		shared among backends (we keep a few sets of semaphores around).
 *		This is so that we can support more backends. (system-wide semaphore
 *		sets run out pretty fast.)				  -ay 4/95
 *
 * $Header: /usr/local/cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.57 1999/05/25 22:42:03 momjian Exp $
 */
#include <sys/time.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
#include <sys/types.h>

#if defined(solaris_sparc)
#include <sys/ipc.h>
#include <sys/sem.h>
#endif

#include "postgres.h"
#include "miscadmin.h"
#include "libpq/pqsignal.h"

#include "access/xact.h"
#include "utils/hsearch.h"

#include "storage/ipc.h"
/* In Ultrix, sem.h must be included after ipc.h */
#include <sys/sem.h>
#include "storage/buf.h"
#include "storage/lock.h"
#include "storage/lmgr.h"
#include "storage/shmem.h"
#include "storage/spin.h"
#include "storage/proc.h"
#include "utils/trace.h"

static void HandleDeadLock(int sig);
static void ProcFreeAllSemaphores(void);

#define DeadlockCheckTimer pg_options[OPT_DEADLOCKTIMEOUT]

/* --------------------
 * Spin lock for manipulating the shared process data structure:
 * ProcGlobal.... Adding an extra spin lock seemed like the smallest
 * hack to get around reading and updating this structure in shared
 * memory. -mer 17 July 1991
 * --------------------
 */
SPINLOCK	ProcStructLock;

/*
 * For cleanup routines.  Don't cleanup if the initialization
 * has not happened.
 */
static bool ProcInitialized = FALSE;

static PROC_HDR *ProcGlobal = NULL;

PROC	   *MyProc = NULL;

static void ProcKill(int exitStatus, int pid);
static void ProcGetNewSemKeyAndNum(IPCKey *key, int *semNum);
static void ProcFreeSem(IpcSemaphoreKey semKey, int semNum);

static char *DeadLockMessage = "Deadlock detected -- See the lock(l) manual page for a possible cause.";

/*
 * InitProcGlobal -
 *	  initializes the global process table. We put it here so that
 *	  the postmaster can do this initialization. (ProcFreeAllSemaphores needs
 *	  to read this table on exiting the postmaster. If we have the first
 *	  backend do this, starting up and killing the postmaster without
 *	  starting any backends will be a problem.)
 *
 *	  We also allocate 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.
 */
void
InitProcGlobal(IPCKey key, int maxBackends)
{
	bool		found = false;

	/* attach to the free list */
	ProcGlobal = (PROC_HDR *)
		ShmemInitStruct("Proc Header", (unsigned) sizeof(PROC_HDR), &found);

	/* --------------------
	 * We're the first - initialize.
	 * XXX if found should ever be true, it is a sign of impending doom ...
	 * ought to complain if so?
	 * --------------------
	 */
	if (!found)
	{
		int			i;

		ProcGlobal->freeProcs = INVALID_OFFSET;
		ProcGlobal->currKey = IPCGetProcessSemaphoreInitKey(key);
		for (i = 0; i < MAX_PROC_SEMS / PROC_NSEMS_PER_SET; i++)
			ProcGlobal->freeSemMap[i] = 0;

		/*
		 * Arrange to delete semas on exit --- set this up now so that we
		 * will clean up if pre-allocation fails...
		 */
		on_shmem_exit(ProcFreeAllSemaphores, NULL);

		/*
		 * Pre-create the semaphores for the first maxBackends processes,
		 * unless we are running as a standalone backend.
		 */
		if (key != PrivateIPCKey)
		{
			for (i = 0;
				 i < (maxBackends + PROC_NSEMS_PER_SET - 1) / PROC_NSEMS_PER_SET;
				 i++)
			{
				IPCKey		semKey = ProcGlobal->currKey + i;
				int			semId;
				int			semstat;

				semId = IpcSemaphoreCreate(semKey,
										   PROC_NSEMS_PER_SET,
										   IPCProtection,
										   IpcSemaphoreDefaultStartValue,
										   0,
										   &semstat);
				/* mark this sema set allocated */
				ProcGlobal->freeSemMap[i] = (1 << PROC_NSEMS_PER_SET);
			}
		}
	}
}

/* ------------------------
 * InitProc -- create a per-process data structure for this process
 * used by the lock manager on semaphore queues.
 * ------------------------
 */
void
InitProcess(IPCKey key)
{
	bool		found = false;
	int			semstat;
	unsigned long location,
				myOffset;

	/* ------------------
	 * Routine called if deadlock timer goes off. See ProcSleep()
	 * ------------------
	 */
	pqsignal(SIGALRM, HandleDeadLock);

	SpinAcquire(ProcStructLock);

	/* attach to the free list */
	ProcGlobal = (PROC_HDR *)
		ShmemInitStruct("Proc Header", (unsigned) sizeof(PROC_HDR), &found);
	if (!found)
	{
		/* this should not happen. InitProcGlobal() is called before this. */
		elog(ERROR, "InitProcess: Proc Header uninitialized");
	}

	if (MyProc != NULL)
	{
		SpinRelease(ProcStructLock);
		elog(ERROR, "ProcInit: you already exist");
		return;
	}

	/* try to get a proc from the free list first */

	myOffset = ProcGlobal->freeProcs;

	if (myOffset != INVALID_OFFSET)
	{
		MyProc = (PROC *) MAKE_PTR(myOffset);
		ProcGlobal->freeProcs = MyProc->links.next;
	}
	else
	{

		/*
		 * have to allocate one.  We can't use the normal shmem index
		 * table mechanism because the proc structure is stored by PID
		 * instead of by a global name (need to look it up by PID when we
		 * cleanup dead processes).
		 */

		MyProc = (PROC *) ShmemAlloc((unsigned) sizeof(PROC));
		if (!MyProc)
		{
			SpinRelease(ProcStructLock);
			elog(FATAL, "cannot create new proc: out of memory");
		}

		/* this cannot be initialized until after the buffer pool */
		SHMQueueInit(&(MyProc->lockQueue));
	}

	/*
	 * zero out the spin lock counts and set the sLocks field for
	 * ProcStructLock to 1 as we have acquired this spinlock above but
	 * didn't record it since we didn't have MyProc until now.
	 */
	MemSet(MyProc->sLocks, 0, sizeof(MyProc->sLocks));
	MyProc->sLocks[ProcStructLock] = 1;


	if (IsUnderPostmaster)
	{
		IPCKey		semKey;
		int			semNum;
		int			semId;
		union semun semun;

		ProcGetNewSemKeyAndNum(&semKey, &semNum);

		/*
		 * Note: because of the pre-allocation done in InitProcGlobal,
		 * this call should always attach to an existing semaphore. It
		 * will (try to) create a new group of semaphores only if the
		 * postmaster tries to start more backends than it said it would.
		 */
		semId = IpcSemaphoreCreate(semKey,
								   PROC_NSEMS_PER_SET,
								   IPCProtection,
								   IpcSemaphoreDefaultStartValue,
								   0,
								   &semstat);

		/*
		 * we might be reusing a semaphore that belongs to a dead backend.
		 * So be careful and reinitialize its value here.
		 */
		semun.val = IpcSemaphoreDefaultStartValue;
		semctl(semId, semNum, SETVAL, semun);

		IpcSemaphoreLock(semId, semNum, IpcExclusiveLock);
		MyProc->sem.semId = semId;
		MyProc->sem.semNum = semNum;
		MyProc->sem.semKey = semKey;
	}
	else
		MyProc->sem.semId = -1;

	/* ----------------------
	 * Release the lock.
	 * ----------------------
	 */
	SpinRelease(ProcStructLock);

	MyProc->pid = MyProcPid;
	MyProc->xid = InvalidTransactionId;
	MyProc->xmin = InvalidTransactionId;

	/* ----------------
	 * Start keeping spin lock stats from here on.	Any botch before
	 * this initialization is forever botched
	 * ----------------
	 */
	MemSet(MyProc->sLocks, 0, MAX_SPINS * sizeof(*MyProc->sLocks));

	/* -------------------------
	 * Install ourselves in the shmem index table.	The name to
	 * use is determined by the OS-assigned process id.  That
	 * allows the cleanup process to find us after any untimely
	 * exit.
	 * -------------------------
	 */
	location = MAKE_OFFSET(MyProc);
	if ((!ShmemPIDLookup(MyProcPid, &location)) || (location != MAKE_OFFSET(MyProc)))
		elog(FATAL, "InitProc: ShmemPID table broken");

	MyProc->errType = NO_ERROR;
	SHMQueueElemInit(&(MyProc->links));

	on_shmem_exit(ProcKill, (caddr_t) MyProcPid);

	ProcInitialized = TRUE;
}

/*
 * ProcReleaseLocks() -- release all locks associated with this process
 *
 */
void
ProcReleaseLocks()
{
	if (!MyProc)
		return;
	LockReleaseAll(1, &MyProc->lockQueue);
}

/*
 * ProcRemove -
 *	  used by the postmaster to clean up the global tables. This also frees
 *	  up the semaphore used for the lmgr of the process. (We have to do
 *	  this is the postmaster instead of doing a IpcSemaphoreKill on exiting
 *	  the process because the semaphore set is shared among backends and
 *	  we don't want to remove other's semaphores on exit.)
 */
bool
ProcRemove(int pid)
{
	SHMEM_OFFSET location;
	PROC	   *proc;

	location = INVALID_OFFSET;

	location = ShmemPIDDestroy(pid);
	if (location == INVALID_OFFSET)
		return FALSE;
	proc = (PROC *) MAKE_PTR(location);

	SpinAcquire(ProcStructLock);

	ProcFreeSem(proc->sem.semKey, proc->sem.semNum);

	proc->links.next = ProcGlobal->freeProcs;
	ProcGlobal->freeProcs = MAKE_OFFSET(proc);

	SpinRelease(ProcStructLock);

	return TRUE;
}

/*
 * ProcKill() -- Destroy the per-proc data structure for
 *		this process. Release any of its held spin locks.
 */
static void
ProcKill(int exitStatus, int pid)
{
	PROC	   *proc;
	SHMEM_OFFSET location;

	/* --------------------
	 * If this is a FATAL exit the postmaster will have to kill all the
	 * existing backends and reinitialize shared memory.  So all we don't
	 * need to do anything here.
	 * --------------------
	 */
	if (exitStatus != 0)
		return;

	ShmemPIDLookup(MyProcPid, &location);
	if (location == INVALID_OFFSET)
		return;

	proc = (PROC *) MAKE_PTR(location);

	Assert(proc == MyProc || pid != MyProcPid);

	MyProc = NULL;

	/* ---------------
	 * Assume one lock table.
	 * ---------------
	 */
	ProcReleaseSpins(proc);
	LockReleaseAll(DEFAULT_LOCKMETHOD, &proc->lockQueue);

#ifdef USER_LOCKS

	/*
	 * Assume we have a second lock table.
	 */
	LockReleaseAll(USER_LOCKMETHOD, &proc->lockQueue);
#endif

	/* ----------------
	 * get off the wait queue
	 * ----------------
	 */
	LockLockTable();
	if (proc->links.next != INVALID_OFFSET)
	{
		Assert(proc->waitLock->waitProcs.size > 0);
		SHMQueueDelete(&(proc->links));
		--proc->waitLock->waitProcs.size;
	}
	SHMQueueElemInit(&(proc->links));
	UnlockLockTable();

	return;
}

/*
 * 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, (unsigned) 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
 *
 * P() on the semaphore should put us to sleep.  The process
 * semaphore is cleared by default, so the first time we try