mcxt.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

	(*context->methods->check) (context);
	for (child = context->firstchild; child != NULL; child = child->nextchild)
		MemoryContextCheck(child);
}
#endif

/*
 * MemoryContextContains
 *		Detect whether an allocated chunk of memory belongs to a given
 *		context or not.
 *
 * Caution: this test is reliable as long as 'pointer' does point to
 * a chunk of memory allocated from *some* context.  If 'pointer' points
 * at memory obtained in some other way, there is a small chance of a
 * false-positive result, since the bits right before it might look like
 * a valid chunk header by chance.
 */
bool
MemoryContextContains(MemoryContext context, void *pointer)
{
	StandardChunkHeader *header;

	/*
	 * Try to detect bogus pointers handed to us, poorly though we can.
	 * Presumably, a pointer that isn't MAXALIGNED isn't pointing at an
	 * allocated chunk.
	 */
	if (pointer == NULL || pointer != (void *) MAXALIGN(pointer))
		return false;

	/*
	 * OK, it's probably safe to look at the chunk header.
	 */
	header = (StandardChunkHeader *)
		((char *) pointer - STANDARDCHUNKHEADERSIZE);

	/*
	 * If the context link doesn't match then we certainly have a non-member
	 * chunk.  Also check for a reasonable-looking size as extra guard against
	 * being fooled by bogus pointers.
	 */
	if (header->context == context && AllocSizeIsValid(header->size))
		return true;
	return false;
}

/*--------------------
 * MemoryContextCreate
 *		Context-type-independent part of context creation.
 *
 * This is only intended to be called by context-type-specific
 * context creation routines, not by the unwashed masses.
 *
 * The context creation procedure is a little bit tricky because
 * we want to be sure that we don't leave the context tree invalid
 * in case of failure (such as insufficient memory to allocate the
 * context node itself).  The procedure goes like this:
 *	1.	Context-type-specific routine first calls MemoryContextCreate(),
 *		passing the appropriate tag/size/methods values (the methods
 *		pointer will ordinarily point to statically allocated data).
 *		The parent and name parameters usually come from the caller.
 *	2.	MemoryContextCreate() attempts to allocate the context node,
 *		plus space for the name.  If this fails we can ereport() with no
 *		damage done.
 *	3.	We fill in all of the type-independent MemoryContext fields.
 *	4.	We call the type-specific init routine (using the methods pointer).
 *		The init routine is required to make the node minimally valid
 *		with zero chance of failure --- it can't allocate more memory,
 *		for example.
 *	5.	Now we have a minimally valid node that can behave correctly
 *		when told to reset or delete itself.  We link the node to its
 *		parent (if any), making the node part of the context tree.
 *	6.	We return to the context-type-specific routine, which finishes
 *		up type-specific initialization.  This routine can now do things
 *		that might fail (like allocate more memory), so long as it's
 *		sure the node is left in a state that delete will handle.
 *
 * This protocol doesn't prevent us from leaking memory if step 6 fails
 * during creation of a top-level context, since there's no parent link
 * in that case.  However, if you run out of memory while you're building
 * a top-level context, you might as well go home anyway...
 *
 * Normally, the context node and the name are allocated from
 * TopMemoryContext (NOT from the parent context, since the node must
 * survive resets of its parent context!).	However, this routine is itself
 * used to create TopMemoryContext!  If we see that TopMemoryContext is NULL,
 * we assume we are creating TopMemoryContext and use malloc() to allocate
 * the node.
 *
 * Note that the name field of a MemoryContext does not point to
 * separately-allocated storage, so it should not be freed at context
 * deletion.
 *--------------------
 */
MemoryContext
MemoryContextCreate(NodeTag tag, Size size,
					MemoryContextMethods *methods,
					MemoryContext parent,
					const char *name)
{
	MemoryContext node;
	Size		needed = size + strlen(name) + 1;

	/* Get space for node and name */
	if (TopMemoryContext != NULL)
	{
		/* Normal case: allocate the node in TopMemoryContext */
		node = (MemoryContext) MemoryContextAlloc(TopMemoryContext,
												  needed);
	}
	else
	{
		/* Special case for startup: use good ol' malloc */
		node = (MemoryContext) malloc(needed);
		Assert(node != NULL);
	}

	/* Initialize the node as best we can */
	MemSet(node, 0, size);
	node->type = tag;
	node->methods = methods;
	node->parent = NULL;		/* for the moment */
	node->firstchild = NULL;
	node->nextchild = NULL;
	node->name = ((char *) node) + size;
	strcpy(node->name, name);

	/* Type-specific routine finishes any other essential initialization */
	(*node->methods->init) (node);

	/* OK to link node to parent (if any) */
	if (parent)
	{
		node->parent = parent;
		node->nextchild = parent->firstchild;
		parent->firstchild = node;
	}

	/* Return to type-specific creation routine to finish up */
	return node;
}

/*
 * MemoryContextAlloc
 *		Allocate space within the specified context.
 *
 * This could be turned into a macro, but we'd have to import
 * nodes/memnodes.h into postgres.h which seems a bad idea.
 */
void *
MemoryContextAlloc(MemoryContext context, Size size)
{
	AssertArg(MemoryContextIsValid(context));

	if (!AllocSizeIsValid(size))
		elog(ERROR, "invalid memory alloc request size %lu",
			 (unsigned long) size);

	return (*context->methods->alloc) (context, size);
}

/*
 * MemoryContextAllocZero
 *		Like MemoryContextAlloc, but clears allocated memory
 *
 *	We could just call MemoryContextAlloc then clear the memory, but this
 *	is a very common combination, so we provide the combined operation.
 */
void *
MemoryContextAllocZero(MemoryContext context, Size size)
{
	void	   *ret;

	AssertArg(MemoryContextIsValid(context));

	if (!AllocSizeIsValid(size))
		elog(ERROR, "invalid memory alloc request size %lu",
			 (unsigned long) size);

	ret = (*context->methods->alloc) (context, size);

	MemSetAligned(ret, 0, size);

	return ret;
}

/*
 * MemoryContextAllocZeroAligned
 *		MemoryContextAllocZero where length is suitable for MemSetLoop
 *
 *	This might seem overly specialized, but it's not because newNode()
 *	is so often called with compile-time-constant sizes.
 */
void *
MemoryContextAllocZeroAligned(MemoryContext context, Size size)
{
	void	   *ret;

	AssertArg(MemoryContextIsValid(context));

	if (!AllocSizeIsValid(size))
		elog(ERROR, "invalid memory alloc request size %lu",
			 (unsigned long) size);

	ret = (*context->methods->alloc) (context, size);

	MemSetLoop(ret, 0, size);

	return ret;
}

/*
 * pfree
 *		Release an allocated chunk.
 */
void
pfree(void *pointer)
{
	StandardChunkHeader *header;

	/*
	 * Try to detect bogus pointers handed to us, poorly though we can.
	 * Presumably, a pointer that isn't MAXALIGNED isn't pointing at an
	 * allocated chunk.
	 */
	Assert(pointer != NULL);
	Assert(pointer == (void *) MAXALIGN(pointer));

	/*
	 * OK, it's probably safe to look at the chunk header.
	 */
	header = (StandardChunkHeader *)
		((char *) pointer - STANDARDCHUNKHEADERSIZE);

	AssertArg(MemoryContextIsValid(header->context));

	(*header->context->methods->free_p) (header->context, pointer);
}

/*
 * repalloc
 *		Adjust the size of a previously allocated chunk.
 */
void *
repalloc(void *pointer, Size size)
{
	StandardChunkHeader *header;

	/*
	 * Try to detect bogus pointers handed to us, poorly though we can.
	 * Presumably, a pointer that isn't MAXALIGNED isn't pointing at an
	 * allocated chunk.
	 */
	Assert(pointer != NULL);
	Assert(pointer == (void *) MAXALIGN(pointer));

	/*
	 * OK, it's probably safe to look at the chunk header.
	 */
	header = (StandardChunkHeader *)
		((char *) pointer - STANDARDCHUNKHEADERSIZE);

	AssertArg(MemoryContextIsValid(header->context));

	if (!AllocSizeIsValid(size))
		elog(ERROR, "invalid memory alloc request size %lu",
			 (unsigned long) size);

	return (*header->context->methods->realloc) (header->context,
												 pointer, size);
}

/*
 * MemoryContextSwitchTo
 *		Returns the current context; installs the given context.
 *
 * This is inlined when using GCC.
 *
 * TODO: investigate supporting inlining for some non-GCC compilers.
 */
#ifndef __GNUC__

MemoryContext
MemoryContextSwitchTo(MemoryContext context)
{
	MemoryContext old;

	AssertArg(MemoryContextIsValid(context));

	old = CurrentMemoryContext;
	CurrentMemoryContext = context;
	return old;
}
#endif   /* ! __GNUC__ */

/*
 * MemoryContextStrdup
 *		Like strdup(), but allocate from the specified context
 */
char *
MemoryContextStrdup(MemoryContext context, const char *string)
{
	char	   *nstr;
	Size		len = strlen(string) + 1;

	nstr = (char *) MemoryContextAlloc(context, len);

	memcpy(nstr, string, len);

	return nstr;
}


#if defined(WIN32) || defined(__CYGWIN__)
/*
 *	Memory support routines for libpgport on Win32
 *
 *	Win32 can't load a library that DLLIMPORTs a variable
 *	if the link object files also DLLIMPORT the same variable.
 *	For this reason, libpgport can't reference CurrentMemoryContext
 *	in the palloc macro calls.
 *
 *	To fix this, we create several functions here that allow us to
 *	manage memory without doing the inline in libpgport.
 */
void *
pgport_palloc(Size sz)
{
	return palloc(sz);
}


char *
pgport_pstrdup(const char *str)
{
	return pstrdup(str);
}


/* Doesn't reference a DLLIMPORT variable, but here for completeness. */
void
pgport_pfree(void *pointer)
{
	pfree(pointer);
}

#endif