sysv_shmem.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

/*-------------------------------------------------------------------------
 *
 * sysv_shmem.c
 *	  Implement shared memory using SysV facilities
 *
 * These routines represent a fairly thin layer on top of SysV shared
 * memory functionality.
 *
 * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/port/sysv_shmem.c,v 1.44 2005/10/15 02:49:22 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <errno.h>
#include <signal.h>
#include <unistd.h>
#include <sys/file.h>
#include <sys/stat.h>
#ifdef HAVE_SYS_IPC_H
#include <sys/ipc.h>
#endif
#ifdef HAVE_SYS_SHM_H
#include <sys/shm.h>
#endif
#ifdef HAVE_KERNEL_OS_H
#include <kernel/OS.h>
#endif

#include "miscadmin.h"
#include "storage/ipc.h"
#include "storage/pg_shmem.h"


typedef key_t IpcMemoryKey;		/* shared memory key passed to shmget(2) */
typedef int IpcMemoryId;		/* shared memory ID returned by shmget(2) */

#define IPCProtection	(0600)	/* access/modify by user only */

#ifdef SHM_SHARE_MMU			/* use intimate shared memory on Solaris */
#define PG_SHMAT_FLAGS			SHM_SHARE_MMU
#else
#define PG_SHMAT_FLAGS			0
#endif


unsigned long UsedShmemSegID = 0;
void	   *UsedShmemSegAddr = NULL;

static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
static void IpcMemoryDetach(int status, Datum shmaddr);
static void IpcMemoryDelete(int status, Datum shmId);
static PGShmemHeader *PGSharedMemoryAttach(IpcMemoryKey key,
					 IpcMemoryId *shmid);


/*
 *	InternalIpcMemoryCreate(memKey, size)
 *
 * Attempt to create a new shared memory segment with the specified key.
 * Will fail (return NULL) if such a segment already exists.  If successful,
 * attach the segment to the current process and return its attached address.
 * On success, callbacks are registered with on_shmem_exit to detach and
 * delete the segment when on_shmem_exit is called.
 *
 * If we fail with a failure code other than collision-with-existing-segment,
 * print out an error and abort.  Other types of errors are not recoverable.
 */
static void *
InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size)
{
	IpcMemoryId shmid;
	void	   *memAddress;

	shmid = shmget(memKey, size, IPC_CREAT | IPC_EXCL | IPCProtection);

	if (shmid < 0)
	{
		/*
		 * Fail quietly if error indicates a collision with existing segment.
		 * One would expect EEXIST, given that we said IPC_EXCL, but perhaps
		 * we could get a permission violation instead?  Also, EIDRM might
		 * occur if an old seg is slated for destruction but not gone yet.
		 */
		if (errno == EEXIST || errno == EACCES
#ifdef EIDRM
			|| errno == EIDRM
#endif
			)
			return NULL;

		/*
		 * Else complain and abort
		 */
		ereport(FATAL,
				(errmsg("could not create shared memory segment: %m"),
		  errdetail("Failed system call was shmget(key=%lu, size=%lu, 0%o).",
					(unsigned long) memKey, (unsigned long) size,
					IPC_CREAT | IPC_EXCL | IPCProtection),
				 (errno == EINVAL) ?
				 errhint("This error usually means that PostgreSQL's request for a shared memory "
		  "segment exceeded your kernel's SHMMAX parameter.  You can either "
						 "reduce the request size or reconfigure the kernel with larger SHMMAX.  "
				  "To reduce the request size (currently %lu bytes), reduce "
			   "PostgreSQL's shared_buffers parameter (currently %d) and/or "
						 "its max_connections parameter (currently %d).\n"
						 "If the request size is already small, it's possible that it is less than "
						 "your kernel's SHMMIN parameter, in which case raising the request size or "
						 "reconfiguring SHMMIN is called for.\n"
		"The PostgreSQL documentation contains more information about shared "
						 "memory configuration.",
						 (unsigned long) size, NBuffers, MaxBackends) : 0,
				 (errno == ENOMEM) ?
				 errhint("This error usually means that PostgreSQL's request for a shared "
				   "memory segment exceeded available memory or swap space. "
				  "To reduce the request size (currently %lu bytes), reduce "
			   "PostgreSQL's shared_buffers parameter (currently %d) and/or "
						 "its max_connections parameter (currently %d).\n"
		"The PostgreSQL documentation contains more information about shared "
						 "memory configuration.",
						 (unsigned long) size, NBuffers, MaxBackends) : 0,
				 (errno == ENOSPC) ?
				 errhint("This error does *not* mean that you have run out of disk space. "
						 "It occurs either if all available shared memory IDs have been taken, "
						 "in which case you need to raise the SHMMNI parameter in your kernel, "
		  "or because the system's overall limit for shared memory has been "
				 "reached.  If you cannot increase the shared memory limit, "
		  "reduce PostgreSQL's shared memory request (currently %lu bytes), "
			"by reducing its shared_buffers parameter (currently %d) and/or "
						 "its max_connections parameter (currently %d).\n"
		"The PostgreSQL documentation contains more information about shared "
						 "memory configuration.",
						 (unsigned long) size, NBuffers, MaxBackends) : 0));
	}

	/* Register on-exit routine to delete the new segment */
	on_shmem_exit(IpcMemoryDelete, Int32GetDatum(shmid));

	/* OK, should be able to attach to the segment */
	memAddress = shmat(shmid, NULL, PG_SHMAT_FLAGS);

	if (memAddress == (void *) -1)
		elog(FATAL, "shmat(id=%d) failed: %m", shmid);

	/* Register on-exit routine to detach new segment before deleting */
	on_shmem_exit(IpcMemoryDetach, PointerGetDatum(memAddress));

	/* Record key and ID in lockfile for data directory. */
	RecordSharedMemoryInLockFile((unsigned long) memKey,
								 (unsigned long) shmid);

	return memAddress;
}

/****************************************************************************/
/*	IpcMemoryDetach(status, shmaddr)	removes a shared memory segment		*/
/*										from process' address spaceq		*/
/*	(called as an on_shmem_exit callback, hence funny argument list)		*/
/****************************************************************************/
static void
IpcMemoryDetach(int status, Datum shmaddr)
{
	if (shmdt(DatumGetPointer(shmaddr)) < 0)
		elog(LOG, "shmdt(%p) failed: %m", DatumGetPointer(shmaddr));
}

/****************************************************************************/
/*	IpcMemoryDelete(status, shmId)		deletes a shared memory segment		*/
/*	(called as an on_shmem_exit callback, hence funny argument list)		*/
/****************************************************************************/
static void
IpcMemoryDelete(int status, Datum shmId)
{
	if (shmctl(DatumGetInt32(shmId), IPC_RMID, NULL) < 0)
		elog(LOG, "shmctl(%d, %d, 0) failed: %m",
			 DatumGetInt32(shmId), IPC_RMID);
}

/*
 * PGSharedMemoryIsInUse
 *
 * Is a previously-existing shmem segment still existing and in use?
 *
 * The point of this exercise is to detect the case where a prior postmaster
 * crashed, but it left child backends that are still running.	Therefore
 * we only care about shmem segments that are associated with the intended
 * DataDir.  This is an important consideration since accidental matches of
 * shmem segment IDs are reasonably common.
 */
bool
PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
{
	IpcMemoryId shmId = (IpcMemoryId) id2;
	struct shmid_ds shmStat;

#ifndef WIN32
	struct stat statbuf;
	PGShmemHeader *hdr;
#endif

	/*
	 * We detect whether a shared memory segment is in use by seeing whether
	 * it (a) exists and (b) has any processes are attached to it.
	 */
	if (shmctl(shmId, IPC_STAT, &shmStat) < 0)
	{
		/*
		 * EINVAL actually has multiple possible causes documented in the
		 * shmctl man page, but we assume it must mean the segment no longer
		 * exists.
		 */
		if (errno == EINVAL)
			return false;

		/*
		 * EACCES implies that the segment belongs to some other userid, which
		 * means it is not a Postgres shmem segment (or at least, not one that
		 * is relevant to our data directory).
		 */
		if (errno == EACCES)
			return false;

		/*
		 * Otherwise, we had better assume that the segment is in use. The
		 * only likely case is EIDRM, which implies that the segment has been
		 * IPC_RMID'd but there are still processes attached to it.
		 */
		return true;
	}

	/* If it has no attached processes, it's not in use */
	if (shmStat.shm_nattch == 0)
		return false;

	/*
	 * Try to attach to the segment and see if it matches our data directory.
	 * This avoids shmid-conflict problems on machines that are running
	 * several postmasters under the same userid.  On Windows, which doesn't
	 * have useful inode numbers, we can't do this so we punt and assume there
	 * is a conflict.
	 */
#ifndef WIN32
	if (stat(DataDir, &statbuf) < 0)