/* mm block type */
typedef struct _zend_mm_block_info {
	size_t _size;	/* block的大小*/
	size_t _prev;	/* 计算前一个块有用到*/
} zend_mm_block_info;
 
 
typedef struct _zend_mm_block {
	zend_mm_block_info info;
} zend_mm_block;
 
typedef struct _zend_mm_small_free_block {	/* 双向链表 */
	zend_mm_block_info info;
	struct _zend_mm_free_block *prev_free_block;	/* 前一个块 */
	struct _zend_mm_free_block *next_free_block;	/* 后一个块 */
} zend_mm_small_free_block;	/* 小的空闲块*/
 
typedef struct _zend_mm_free_block {	/* 双向链表 + 树结构 */
	zend_mm_block_info info;
	struct _zend_mm_free_block *prev_free_block;	/* 前一个块 */
	struct _zend_mm_free_block *next_free_block;	/* 后一个块 */
 
	struct _zend_mm_free_block **parent;	/* 父结点 */
	struct _zend_mm_free_block *child[2];	/* 两个子结点*/
} zend_mm_free_block;
 
 
 
struct _zend_mm_heap {
	int                 use_zend_alloc;	/* 是否使用zend内存管理器 */
	void               *(*_malloc)(size_t);	/* 内存分配函数*/
	void                (*_free)(void*);	/* 内存释放函数*/
	void               *(*_realloc)(void*, size_t);
	size_t              free_bitmap;	/* 小块空闲内存标识 */
	size_t              large_free_bitmap;  /* 大块空闲内存标识*/
	size_t              block_size;		/* 一次内存分配的段大小，即ZEND_MM_SEG_SIZE指定的大小，默认为ZEND_MM_SEG_SIZE   (256 * 1024)*/
	size_t              compact_size;	/* 压缩操作边界值，为ZEND_MM_COMPACT指定大小，默认为 2 * 1024 * 1024*/
	zend_mm_segment    *segments_list;	/* 段指针列表 */
	zend_mm_storage    *storage;	/* 所调用的存储层 */
	size_t              real_size;	/* 堆的真实大小 */
	size_t              real_peak;	/* 堆真实大小的峰值 */
	size_t              limit;	/* 堆的内存边界 */
	size_t              size;	/* 堆大小 */
	size_t              peak;	/* 堆大小的峰值*/
	size_t              reserve_size;	/* 备用堆大小*/
	void               *reserve;	/* 备用堆 */
	int                 overflow;	/* 内存溢出数*/
	int                 internal;
#if ZEND_MM_CACHE
	unsigned int        cached;	/* 已缓存大小 */
	zend_mm_free_block *cache[ZEND_MM_NUM_BUCKETS];	/* 缓存数组/
#endif
	zend_mm_free_block *free_buckets[ZEND_MM_NUM_BUCKETS*2];	/* 小块空闲内存数组 */
	zend_mm_free_block *large_free_buckets[ZEND_MM_NUM_BUCKETS];	/* 大块空闲内存数组*/
	zend_mm_free_block *rest_buckets[2];	/* 剩余内存数组 */
 
};

static void alloc_globals_ctor(zend_alloc_globals *alloc_globals TSRMLS_DC)
{
	char *tmp;
	alloc_globals->mm_heap = zend_mm_startup();
 
	tmp = getenv("USE_ZEND_ALLOC");
	if (tmp) {
		alloc_globals->mm_heap->use_zend_alloc = zend_atoi(tmp, 0);
		if (!alloc_globals->mm_heap->use_zend_alloc) {	/* 如果不使用zend的内存管理器，同直接使用malloc函数*/
			alloc_globals->mm_heap->_malloc = malloc;
			alloc_globals->mm_heap->_free = free;
			alloc_globals->mm_heap->_realloc = realloc;
		}
	}
}

# define ZEND_MM_ALIGNMENT 8
 
#define ZEND_MM_ALIGNMENT_MASK ~(ZEND_MM_ALIGNMENT-1)
 
#define ZEND_MM_ALIGNED_SIZE(size)	(((size) + ZEND_MM_ALIGNMENT - 1) & ZEND_MM_ALIGNMENT_MASK)
 
#define ZEND_MM_ALIGNED_HEADER_SIZE			ZEND_MM_ALIGNED_SIZE(sizeof(zend_mm_block))
#define ZEND_MM_ALIGNED_FREE_HEADER_SIZE	ZEND_MM_ALIGNED_SIZE(sizeof(zend_mm_small_free_block))

#define ZEND_MM_NEXT_BLOCK(b)			ZEND_MM_BLOCK_AT(b, ZEND_MM_BLOCK_SIZE(b))
#define ZEND_MM_PREV_BLOCK(b)			ZEND_MM_BLOCK_AT(b, -(int)((b)->info._prev & ~ZEND_MM_TYPE_MASK))
 
#define ZEND_MM_BLOCK_AT(blk, offset)	((zend_mm_block *) (((char *) (blk))+(offset)))
#define ZEND_MM_BLOCK_SIZE(b)			((b)->info._size & ~ZEND_MM_TYPE_MASK)
#define ZEND_MM_TYPE_MASK		ZEND_MM_LONG_CONST(0x3)