//初始化列表类型的迭代器为一个指定的下标
listTypeIterator *listTypeInitIterator(robj *subject, long index,
unsigned char direction) {
listTypeIterator *li = zmalloc(sizeof(listTypeIterator)); //分配空间
//设置迭代器的各个成员的初始值
li->subject = subject;
li->encoding = subject->encoding;
li->direction = direction;
li->iter = NULL; //quicklist迭代器为空
/* LIST_HEAD means start at TAIL and move *towards* head.
* LIST_TAIL means start at HEAD and move *towards tail. */
//获得迭代方向
int iter_direction =
direction == LIST_HEAD ? AL_START_TAIL : AL_START_HEAD;
//对列表对象编码为quicklist类型操作
if (li->encoding == OBJ_ENCODING_QUICKLIST) {
//将迭代器和下标为index的quicklistNode结合，迭代器指向该节点
li->iter = quicklistGetIteratorAtIdx(li->subject->ptr,
iter_direction, index);
} else {
serverPanic("Unknown list encoding");
}
return li;
}
/* Initialize an iterator at the specified index. */
listTypeIterator *listTypeInitIterator(robj *subject, long index,
unsigned char direction) {
listTypeIterator *li = zmalloc(sizeof(listTypeIterator));
li->subject = subject;
li->encoding = subject->encoding;
li->direction = direction;
li->iter = NULL;
/* LIST_HEAD means start at TAIL and move *towards* head.
* LIST_TAIL means start at HEAD and move *towards tail. */
int iter_direction =
direction == LIST_HEAD ? AL_START_TAIL : AL_START_HEAD;
if (li->encoding == OBJ_ENCODING_QUICKLIST) {
li->iter = quicklistGetIteratorAtIdx(li->subject->ptr,
iter_direction, index);
} else {
serverPanic("Unknown list encoding");
}
return li;
}
