.span - 1;
update[i]->level[i].forward = x->level[i].forward;
} else {
update[i]->level[i].span -= 1;
}
}
if (x->level[0].forward) {//处理前驱节点
x->level[0].forward->backward = x->backward;
} else {//否则，更新tail
zsl->tail = x->backward;
}
//收缩level
while(zsl->level > 1 && zsl->header->level[zsl->level-1].forward == NULL)
zsl->level--;
zsl->length--;
}
4.6 zslDelete
/* Delete an element with matching score/object from the skiplist. */
//根据score, obj来删除节点
int zslDelete(zskiplist *zsl, double score, robj *obj) {
zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
int i;
x = zsl->header;
// 遍历所有层，记录删除节点后需要被修改的节点到 update 数组
for (i = zsl->level-1; i >= 0; i--) {
while (x->level[i].forward &&
(x->level[i].forward->score < score ||
(x->level[i].forward->score == score &&
compareStringObjects(x->level[i].forward->obj,obj) < 0)))
x = x->level[i].forward;
update[i] = x;
}
/* We may have multiple elements with the same score, what we need
* is to find the element with both the right score and object. */
x = x->level[0].forward;
// 因为多个不同的 member 可能有相同的 score
// 所以要确保 x 的 member 和 score 都匹配时，才进行删除
if (x && score == x->score && equalStringObjects(x->obj,obj)) {
zslDeleteNode(zsl, x, update);
zslFreeNode(x);
return 1;
} else {
return 0; /* not found */
}
return 0; /* not found */
}
4.8 zslFirstInRange
/* Find the first node that is contained in the specified range.
* Returns NULL when no element is contained in the range. */
//找到跳跃表中第一个符合给定范围的元素
zskiplistNode *zslFirstInRange(zskiplist *zsl, zrangespec range) {
zskiplistNode *x;
int i;
/* If everything is out of range, return early. */
if (!zslIsInRange(zsl,&range)) return NULL;
x = zsl->header;
for (i = zsl->level-1; i >= 0; i--) {
/* Go forward while *OUT* of range. */
while (x->level[i].forward &&
!zslValueGteMin(x->level[i].forward->score,&range))
x = x->level[i].forward;
}
/* This is an inner range, so the next node cannot be NULL. */
x = x->level[0].forward;
redisAssert(x != NULL);
/* Check if score <= max. */
if (!zslValueLteMax(x->score,&range)) return NULL;
return x;
}
4.9 zslLastInRange
/* Find the last node that is contained in the specified range.
* Returns NULL when no element is contained in the range. */
//找到跳跃表中最后一个符合给定范围的元素
zskiplistNode *zslLastInRange(zskiplist *zsl, zrangespec range) {
zskiplistNode *x;
int i;
/* If everything is out of range, return early. */
if (!zslIsInRange(zsl,&range)) return NULL;
x = zsl->header;
for (i = zsl->level-1; i >= 0; i--) {
/* Go forward while *IN* range. */
while (x->level[i].forward &&
zslValueLteMax(x->level[i].forward->score,&range))
x = x->level[i].forward;
}
/* This is an inner range, so this node cannot be NULL. */
redisAssert(x != NULL);
/* Check if score >= min. */
if (!zslValueGteMin(x->score,&range)) return NULL;
return x;
}
4.10 zslDeleteRangeByScore
/* Delete all the elements with score between min and max from the skiplist.
* Min and max are inclusive, so a score >= min || score <= max is deleted.
* Note that this function takes the reference to the hash table view of the
* sorted set, in order to remove the elements from the hash table too. */
//删除给定范围内的