aset.c

来自「PostgreSQL7.4.6 for Linux」· C语言 代码 · 共 1,125 行 · 第 1/3 页

 * Actually, this routine has some discretion about what to do.
 * It should mark all allocated chunks freed, but it need not necessarily
 * give back all the resources the set owns.  Our actual implementation is
 * that we hang onto any "keeper" block specified for the set.	In this way,
 * we don't thrash malloc() when a context is repeatedly reset after small
 * allocations, which is typical behavior for per-tuple contexts.
 */
static void
AllocSetReset(MemoryContext context)
{
	AllocSet	set = (AllocSet) context;
	AllocBlock	block = set->blocks;

	AssertArg(AllocSetIsValid(set));

#ifdef MEMORY_CONTEXT_CHECKING
	/* Check for corruption and leaks before freeing */
	AllocSetCheck(context);
#endif

	/* Clear chunk freelists */
	MemSet(set->freelist, 0, sizeof(set->freelist));
	/* New blocks list is either empty or just the keeper block */
	set->blocks = set->keeper;

	while (block != NULL)
	{
		AllocBlock	next = block->next;

		if (block == set->keeper)
		{
			/* Reset the block, but don't return it to malloc */
			char	   *datastart = ((char *) block) + ALLOC_BLOCKHDRSZ;

#ifdef CLOBBER_FREED_MEMORY
			/* Wipe freed memory for debugging purposes */
			memset(datastart, 0x7F, block->freeptr - datastart);
#endif
			block->freeptr = datastart;
			block->next = NULL;
		}
		else
		{
			/* Normal case, release the block */
#ifdef CLOBBER_FREED_MEMORY
			/* Wipe freed memory for debugging purposes */
			memset(block, 0x7F, block->freeptr - ((char *) block));
#endif
			free(block);
		}
		block = next;
	}
}

/*
 * AllocSetDelete
 *		Frees all memory which is allocated in the given set,
 *		in preparation for deletion of the set.
 *
 * Unlike AllocSetReset, this *must* free all resources of the set.
 * But note we are not responsible for deleting the context node itself.
 */
static void
AllocSetDelete(MemoryContext context)
{
	AllocSet	set = (AllocSet) context;
	AllocBlock	block = set->blocks;

	AssertArg(AllocSetIsValid(set));

#ifdef MEMORY_CONTEXT_CHECKING
	/* Check for corruption and leaks before freeing */
	AllocSetCheck(context);
#endif

	/* Make it look empty, just in case... */
	MemSet(set->freelist, 0, sizeof(set->freelist));
	set->blocks = NULL;
	set->keeper = NULL;

	while (block != NULL)
	{
		AllocBlock	next = block->next;

#ifdef CLOBBER_FREED_MEMORY
		/* Wipe freed memory for debugging purposes */
		memset(block, 0x7F, block->freeptr - ((char *) block));
#endif
		free(block);
		block = next;
	}
}

/*
 * AllocSetAlloc
 *		Returns pointer to allocated memory of given size; memory is added
 *		to the set.
 */
static void *
AllocSetAlloc(MemoryContext context, Size size)
{
	AllocSet	set = (AllocSet) context;
	AllocBlock	block;
	AllocChunk	chunk;
	AllocChunk	priorfree;
	int			fidx;
	Size		chunk_size;
	Size		blksize;

	AssertArg(AllocSetIsValid(set));

	/*
	 * If requested size exceeds maximum for chunks, allocate an entire
	 * block for this request.
	 */
	if (size > ALLOC_CHUNK_LIMIT)
	{
		chunk_size = MAXALIGN(size);
		blksize = chunk_size + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ;
		block = (AllocBlock) malloc(blksize);
		if (block == NULL)
		{
			MemoryContextStats(TopMemoryContext);
			ereport(ERROR,
					(errcode(ERRCODE_OUT_OF_MEMORY),
					 errmsg("out of memory"),
					 errdetail("Failed on request of size %lu.",
							   (unsigned long) size)));
		}
		block->aset = set;
		block->freeptr = block->endptr = ((char *) block) + blksize;

		chunk = (AllocChunk) (((char *) block) + ALLOC_BLOCKHDRSZ);
		chunk->aset = set;
		chunk->size = chunk_size;
#ifdef MEMORY_CONTEXT_CHECKING
		chunk->requested_size = size;
		/* set mark to catch clobber of "unused" space */
		if (size < chunk_size)
			((char *) AllocChunkGetPointer(chunk))[size] = 0x7E;
#endif

		/*
		 * Stick the new block underneath the active allocation block, so
		 * that we don't lose the use of the space remaining therein.
		 */
		if (set->blocks != NULL)
		{
			block->next = set->blocks->next;
			set->blocks->next = block;
		}
		else
		{
			block->next = NULL;
			set->blocks = block;
		}

		AllocAllocInfo(set, chunk);
		return AllocChunkGetPointer(chunk);
	}

	/*
	 * Request is small enough to be treated as a chunk.  Look in the
	 * corresponding free list to see if there is a free chunk we could
	 * reuse.
	 */
	fidx = AllocSetFreeIndex(size);
	priorfree = NULL;
	for (chunk = set->freelist[fidx]; chunk; chunk = (AllocChunk) chunk->aset)
	{
		if (chunk->size >= size)
			break;
		priorfree = chunk;
	}

	/*
	 * If one is found, remove it from the free list, make it again a
	 * member of the alloc set and return its data address.
	 */
	if (chunk != NULL)
	{
		if (priorfree == NULL)
			set->freelist[fidx] = (AllocChunk) chunk->aset;
		else
			priorfree->aset = chunk->aset;

		chunk->aset = (void *) set;

#ifdef MEMORY_CONTEXT_CHECKING
		chunk->requested_size = size;
		/* set mark to catch clobber of "unused" space */
		if (size < chunk->size)
			((char *) AllocChunkGetPointer(chunk))[size] = 0x7E;
#endif

		AllocAllocInfo(set, chunk);
		return AllocChunkGetPointer(chunk);
	}

	/*
	 * Choose the actual chunk size to allocate.
	 */
	chunk_size = 1 << (fidx + ALLOC_MINBITS);
	Assert(chunk_size >= size);

	/*
	 * If there is enough room in the active allocation block, we will put
	 * the chunk into that block.  Else must start a new one.
	 */
	if ((block = set->blocks) != NULL)
	{
		Size		availspace = block->endptr - block->freeptr;

		if (availspace < (chunk_size + ALLOC_CHUNKHDRSZ))
		{
			/*
			 * The existing active (top) block does not have enough room
			 * for the requested allocation, but it might still have a
			 * useful amount of space in it.  Once we push it down in the
			 * block list, we'll never try to allocate more space from it.
			 * So, before we do that, carve up its free space into chunks
			 * that we can put on the set's freelists.
			 *
			 * Because we can only get here when there's less than
			 * ALLOC_CHUNK_LIMIT left in the block, this loop cannot
			 * iterate more than ALLOCSET_NUM_FREELISTS-1 times.
			 */
			while (availspace >= ((1 << ALLOC_MINBITS) + ALLOC_CHUNKHDRSZ))
			{
				Size		availchunk = availspace - ALLOC_CHUNKHDRSZ;
				int			a_fidx = AllocSetFreeIndex(availchunk);

				/*
				 * In most cases, we'll get back the index of the next
				 * larger freelist than the one we need to put this chunk
				 * on.	The exception is when availchunk is exactly a
				 * power of 2.
				 */
				if (availchunk != (1 << (a_fidx + ALLOC_MINBITS)))
				{
					a_fidx--;
					Assert(a_fidx >= 0);
					availchunk = (1 << (a_fidx + ALLOC_MINBITS));
				}

				chunk = (AllocChunk) (block->freeptr);

				block->freeptr += (availchunk + ALLOC_CHUNKHDRSZ);
				availspace -= (availchunk + ALLOC_CHUNKHDRSZ);

				chunk->size = availchunk;
#ifdef MEMORY_CONTEXT_CHECKING
				chunk->requested_size = 0;		/* mark it free */
#endif
				chunk->aset = (void *) set->freelist[a_fidx];
				set->freelist[a_fidx] = chunk;
			}

			/* Mark that we need to create a new block */
			block = NULL;
		}
	}

	/*
	 * Time to create a new regular (multi-chunk) block?
	 */
	if (block == NULL)
	{
		Size		required_size;

		if (set->blocks == NULL)
		{
			/* First block of the alloc set, use initBlockSize */
			blksize = set->initBlockSize;
		}
		else
		{
			/*
			 * Use first power of 2 that is larger than previous block,
			 * but not more than the allowed limit.  (We don't simply double
			 * the prior block size, because in some cases this could be a
			 * funny size, eg if very first allocation was for an odd-sized
			 * large chunk.)
			 */
			Size	pblksize = set->blocks->endptr - ((char *) set->blocks);

			blksize = set->initBlockSize;
			while (blksize <= pblksize)
				blksize <<= 1;
			if (blksize > set->maxBlockSize)
				blksize = set->maxBlockSize;
		}

		/*
		 * If initBlockSize is less than ALLOC_CHUNK_LIMIT, we could need
		 * more space... but try to keep it a power of 2.
		 */
		required_size = chunk_size + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ;
		while (blksize < required_size)
			blksize <<= 1;

		/* Try to allocate it */
		block = (AllocBlock) malloc(blksize);

		/*
		 * We could be asking for pretty big blocks here, so cope if
		 * malloc fails.  But give up if there's less than a meg or so
		 * available...
		 */
		while (block == NULL && blksize > 1024 * 1024)
		{
			blksize >>= 1;
			if (blksize < required_size)
				break;
			block = (AllocBlock) malloc(blksize);
		}

		if (block == NULL)
		{
			MemoryContextStats(TopMemoryContext);
			ereport(ERROR,
					(errcode(ERRCODE_OUT_OF_MEMORY),
					 errmsg("out of memory"),
					 errdetail("Failed on request of size %lu.",
							   (unsigned long) size)));
		}

		block->aset = set;
		block->freeptr = ((char *) block) + ALLOC_BLOCKHDRSZ;
		block->endptr = ((char *) block) + blksize;

		/*
		 * If this is the first block of the set, make it the "keeper"
		 * block. Formerly, a keeper block could only be created during
		 * context creation, but allowing it to happen here lets us have
		 * fast reset cycling even for contexts created with
		 * minContextSize = 0; that way we don't have to force space to be
		 * allocated in contexts that might never need any space.  Don't
		 * mark an oversize block as a keeper, however.
		 */
		if (set->blocks == NULL && blksize == set->initBlockSize)
		{
			Assert(set->keeper == NULL);
			set->keeper = block;
		}

		block->next = set->blocks;
		set->blocks = block;
	}

	/*
	 * OK, do the allocation
	 */
	chunk = (AllocChunk) (block->freeptr);

	block->freeptr += (chunk_size + ALLOC_CHUNKHDRSZ);
	Assert(block->freeptr <= block->endptr);

	chunk->aset = (void *) set;
	chunk->size = chunk_size;
#ifdef MEMORY_CONTEXT_CHECKING
	chunk->requested_size = size;
	/* set mark to catch clobber of "unused" space */
	if (size < chunk->size)
		((char *) AllocChunkGetPointer(chunk))[size] = 0x7E;
#endif

	AllocAllocInfo(set, chunk);
	return AllocChunkGetPointer(chunk);
}

/*
 * AllocSetFree
 *		Frees allocated memory; memory is removed from the set.
 */