postgresql之内存池-GenerationContext

创建GenerationContext

MemoryContext
GenerationContextCreate(MemoryContext parent,const char *name,Size blockSize)
{GenerationContext *set;
...set = (GenerationContext *) malloc(MAXALIGN(sizeof(GenerationContext)));
.../* Fill in GenerationContext-specific header fields */set->blockSize = blockSize;set->block = NULL;dlist_init(&set->blocks);/* Finally, do the type-independent part of context creation */MemoryContextCreate((MemoryContext) set,T_GenerationContext,&GenerationMethods,parent,name);return (MemoryContext) set;
}

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分配空间

分配空间大小大于block/8

计算需要分配空间
分配空间
初始化空间
将空间放入循环双向链表

if (chunk_size > set->blockSize / 8){Size		blksize = chunk_size + Generation_BLOCKHDRSZ + Generation_CHUNKHDRSZ;block = (GenerationBlock *) malloc(blksize);if (block == NULL)return NULL;context->mem_allocated += blksize;/* block with a single (used) chunk */block->blksize = blksize;block->nchunks = 1;block->nfree = 0;/* the block is completely full */block->freeptr = block->endptr = ((char *) block) + blksize;chunk = (GenerationChunk *) (((char *) block) + Generation_BLOCKHDRSZ);chunk->block = block;chunk->context = set;chunk->size = chunk_size;
.../* add the block to the list of allocated blocks */dlist_push_head(&set->blocks, &block->node);
...return GenerationChunkGetPointer(chunk);}

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分配空间小于等于block/8

block为空或block剩余空间不足，则创建新的block

/** Not an over-sized chunk. Is there enough space in the current block? If* not, allocate a new "regular" block.*/block = set->block;if ((block == NULL) ||(block->endptr - block->freeptr) < Generation_CHUNKHDRSZ + chunk_size){Size		blksize = set->blockSize;block = (GenerationBlock *) malloc(blksize);if (block == NULL)return NULL;context->mem_allocated += blksize;block->blksize = blksize;block->nchunks = 0;block->nfree = 0;block->freeptr = ((char *) block) + Generation_BLOCKHDRSZ;block->endptr = ((char *) block) + blksize;.../* add it to the doubly-linked list of blocks */dlist_push_head(&set->blocks, &block->node);/* and also use it as the current allocation block */set->block = block;}

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分配空间

chunk = (GenerationChunk *) block->freeptr;
...block->nchunks += 1;block->freeptr += (Generation_CHUNKHDRSZ + chunk_size);
...chunk->block = block;chunk->context = set;chunk->size = chunk_size;...return GenerationChunkGetPointer(chunk);

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释放空间

增加nfree计数

	GenerationContext *set = (GenerationContext *) context;GenerationChunk *chunk = GenerationPointerGetChunk(pointer);GenerationBlock *block;
...block = chunk->block;
.../* Reset context to NULL in freed chunks */chunk->context = NULL;
...block->nfree += 1;

如果nfree等于nchunks,删除节点，释放空间

	/* If there are still allocated chunks in the block, we're done. */if (block->nfree < block->nchunks)return;
/** The block is empty, so let's get rid of it. First remove it from the* list of blocks, then return it to malloc().*/dlist_delete(&block->node);/* Also make sure the block is not marked as the current block. */if (set->block == block)set->block = NULL;context->mem_allocated -= block->blksize;free(block);

销毁GenerationContext

遍历blocks，删除节点，释放节点空间
释放context

static void
GenerationReset(MemoryContext context)
{GenerationContext *set = (GenerationContext *) context;dlist_mutable_iter miter;
...dlist_foreach_modify(miter, &set->blocks){GenerationBlock *block = dlist_container(GenerationBlock, node, miter.cur);dlist_delete(miter.cur);context->mem_allocated -= block->blksize;
...free(block);}set->block = NULL;
...
}
/** GenerationDelete*		Free all memory which is allocated in the given context.*/
static void
GenerationDelete(MemoryContext context)
{/* Reset to release all the GenerationBlocks */GenerationReset(context);/* And free the context header */free(context);
}