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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;
}
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呼出元 †

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/*
*	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.
*/
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