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概要 †

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引数 †

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実装 †

PGShmemHeader *
PGSharedMemoryCreate(Size size, bool makePrivate, int port)
{
	IpcMemoryKey NextShmemSegID;
	void	   *memAddress;
	PGShmemHeader *hdr;
	IpcMemoryId shmid;
#ifndef WIN32
	struct stat statbuf;
#endif
	/* Room for a header? */
	Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
	/* Make sure PGSharedMemoryAttach doesn't fail without need */
	UsedShmemSegAddr = NULL;
	/* Loop till we find a free IPC key */
	NextShmemSegID = port * 1000;
	for (NextShmemSegID++;; NextShmemSegID++)
	{
		/* Try to create new segment */
		memAddress = InternalIpcMemoryCreate(NextShmemSegID, size);
		if (memAddress)
			break;				/* successful create and attach */
		/* Check shared memory and possibly remove and recreate */
		if (makePrivate)		/* a standalone backend shouldn't do this */
			continue;
		if ((memAddress = PGSharedMemoryAttach(NextShmemSegID, &shmid)) == NULL)
			continue;			/* can't attach, not one of mine */
		/*
		 * If I am not the creator and it belongs to an extant process,
		 * continue.
		 */
		hdr = (PGShmemHeader *) memAddress;
		if (hdr->creatorPID != getpid())
		{
			if (kill(hdr->creatorPID, 0) == 0 || errno != ESRCH)
			{
				shmdt(memAddress);
				continue;		/* segment belongs to a live process */
			}
		}
		/*
		 * The segment appears to be from a dead Postgres process, or from a
		 * previous cycle of life in this same process.  Zap it, if possible.
		 * This probably shouldn't fail, but if it does, assume the segment
		 * belongs to someone else after all, and continue quietly.
		 */
		shmdt(memAddress);
		if (shmctl(shmid, IPC_RMID, NULL) < 0)
			continue;
		/*
		 * Now try again to create the segment.
		 */
		memAddress = InternalIpcMemoryCreate(NextShmemSegID, size);
		if (memAddress)
			break;				/* successful create and attach */
		/*
		 * Can only get here if some other process managed to create the same
		 * shmem key before we did.  Let him have that one, loop around to try
		 * next key.
		 */
	}
	/*
	 * OK, we created a new segment.  Mark it as created by this process. The
	 * order of assignments here is critical so that another Postgres process
	 * can't see the header as valid but belonging to an invalid PID!
	 */
	hdr = (PGShmemHeader *) memAddress;
	hdr->creatorPID = getpid();
	hdr->magic = PGShmemMagic;
#ifndef WIN32
	/* Fill in the data directory ID info, too */
	if (stat(DataDir, &statbuf) < 0)
		ereport(FATAL,
				(errcode_for_file_access(),
				 errmsg("could not stat data directory \"%s\": %m",
						DataDir)));
	hdr->device = statbuf.st_dev;
	hdr->inode = statbuf.st_ino;
#endif
	/*
	 * Initialize space allocation status for segment.
	 */
	hdr->totalsize = size;
	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
	/* Save info for possible future use */
	UsedShmemSegAddr = memAddress;
	UsedShmemSegID = (unsigned long) NextShmemSegID;
	return hdr;
}
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呼出元 †

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備考 †

/*
* PGSharedMemoryCreate
*
* Create a shared memory segment of the given size and initialize its
* standard header.  Also, register an on_shmem_exit callback to release
* the storage.
*
* Dead Postgres segments are recycled if found, but we do not fail upon
* collision with non-Postgres shmem segments.	The idea here is to detect and
* re-use keys that may have been assigned by a crashed postmaster or backend.
*
* makePrivate means to always create a new segment, rather than attach to
* or recycle any existing segment.
*
* The port number is passed for possible use as a key (for SysV, we use
* it to generate the starting shmem key).	In a standalone backend,
* zero will be passed.
*/
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履歴 †

更新日更新者更新内容
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2007/11/11testnoda/ページ作者PGSharedMemoryCreate()/postgresql-8.1.4より移行
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コメント †


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