PHP引用计数与写时复制

[php]代码库

zval *get_var_and_separate(char *varname, int varname_len TSRMLS_DC)
{
	zval **varval, *varcopy;
	if (zend_hash_find(EG(active_symbol_table),varname, varname_len + 1, (void**)&varval) == FAILURE)
	{
		/* 如果在符号表里找不到这个变量则直接return */
		return NULL;
	}

	if ((*varval)->refcount < 2)
	{	
		//如果这个变量的zval部分的refcount小于2，代表没有别的变量在用，return
		return *varval;
	}
	
	/* 否则，复制一份zval*的值 */
	MAKE_STD_ZVAL(varcopy);
	varcopy = *varval;
	
	/* Duplicate any allocated structures within the zval* */
	zval_copy_ctor(varcopy);

	/* 从符号表中删除原来的变量
	 * This will decrease the refcount of varval in the process
	 */
	zend_hash_del(EG(active_symbol_table), varname, varname_len + 1);

	/* 初始化新的zval的refcount，并在符号表中重新添加此变量信息，并将其值与我们的新zval相关联。*/
	varcopy->refcount = 1;
	varcopy->is_ref = 0;
	zend_hash_add(EG(active_symbol_table), varname, varname_len + 1,&varcopy, sizeof(zval*), NULL);
	
	/* 返回新zval的地址 */
	return varcopy;
}