1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17

typedef struct zskiplist {
    struct zskiplistNode *header, *tail; // 指向跳表的头结点
    unsigned long length;				   // 跳跃表的总节点数量, 除了头节点以外的
    int level;							   // 跳跃表的高度
} zskiplist;



typedef struct zskiplistNode {
    sds ele; 							// 用于存储字符串类型的数据
    double score;						// 用于排序的值
    struct zskiplistNode *backward;	   // 后退指针	
    struct zskiplistLevel {
        struct zskiplistNode *forward; // 指向当前层的下一个节点
        unsigned int span               // 指向节点与本节点之间的元素个数
    } level[];
} zskiplistNode;

1

#define ZSKIPLIST_MAXLEVEL 64 /* Should be enough for 2^64 elements */

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17

/* Returns a random level for the new skiplist node we are going to create.
 * The return value of this function is between 1 and ZSKIPLIST_MAXLEVEL
 * (both inclusive), with a powerlaw-alike distribution where higher
 * levels are less likely to be returned. 
 **/
int zslRandomLevel(void) {
    // 初始化层级为1
    int level = 1;
    
    // 判断随机数的低16位是否小于(ZSKIPLIST_P * 0xFFFF)
    while ((random()&0xFFFF) < (ZSKIPLIST_P * 0xFFFF))
        // 条件成立，层级 level 增加 1，然后继续判断，直到条件不成立为止。
        level += 1;
    
    // 返回的层级不超过 ZSKIPLIST_MAXLEVEL，即使循环可能将 level 增加到比最大层级还高的值。
    return (level<ZSKIPLIST_MAXLEVEL) ? level : ZSKIPLIST_MAXLEVEL;
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17

/* Create a new skiplist. */
zskiplist *zslCreate(void) {
    int j;
    zskiplist *zsl;

    zsl = zmalloc(sizeof(*zsl));
    zsl->level = 1;
    zsl->length = 0;
    zsl->header = zslCreateNode(ZSKIPLIST_MAXLEVEL,0,NULL);
    for (j = 0; j < ZSKIPLIST_MAXLEVEL; j++) {
        zsl->header->level[j].forward = NULL;
        zsl->header->level[j].span = 0;
    }
    zsl->header->backward = NULL;
    zsl->tail = NULL;
    return zsl;
}

1
2
3
4
5
6
7
8

/* Create a skiplist node with the specified number of levels.
 * The SDS string 'ele' is referenced by the node after the call. */
zskiplistNode *zslCreateNode(int level, double score, sds ele) {
    zskiplistNode *zn = zmalloc(sizeof(*zn)+level*sizeof(struct zskiplistLevel));
    zn->score = score;
    zn->ele = ele;
    return zn;
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68

zskiplistNode *zslInsert(zskiplist *zsl, double score, sds ele) {
    zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
    unsigned int rank[ZSKIPLIST_MAXLEVEL];
    int i, level;

    serverAssert(!isnan(score));
    x = zsl->header;
    // 找到位置, 并更新update[] 和rank[]
    for (i = zsl->level-1; i >= 0; i--) {
        /* store rank that is crossed to reach the insert position */
        rank[i] = i == (zsl->level-1) ? 0 : rank[i+1];
        while (x->level[i].forward &&
                (x->level[i].forward->score < score ||
                    (x->level[i].forward->score == score &&
                    sdscmp(x->level[i].forward->ele,ele) < 0)))
        {
            rank[i] += x->level[i].span;
            x = x->level[i].forward;
        }
        update[i] = x;
    }
    /* we assume the element is not already inside, since we allow duplicated
     * scores, reinserting the same element should never happen since the
     * caller of zslInsert() should test in the hash table if the element is
     * already inside or not. */
    // 生成新的随机高度, 
    level = zslRandomLevel();
    
    // 判断当前的跳跃表的高度是否小于随机生成的level
    if (level > zsl->level) {
        // 调整跳表的高度
        for (i = zsl->level; i < level; i++) {
            rank[i] = 0;
            update[i] = zsl->header;
            update[i]->level[i].span = zsl->length;
        }
        zsl->level = level;
    }
    
    // 创建新节点x
    x = zslCreateNode(level,score,ele);
    for (i = 0; i < level; i++) {
        // 更新x竖向层级上的所有节点的forward属性
        x->level[i].forward = update[i]->level[i].forward;
        update[i]->level[i].forward = x;

        /* update span covered by update[i] as x is inserted here */
        x->level[i].span = update[i]->level[i].span - (rank[0] - rank[i]);
        update[i]->level[i].span = (rank[0] - rank[i]) + 1;
    }

    /* increment span for untouched levels */
    // 更新
    for (i = level; i < zsl->level; i++) {
        update[i]->level[i].span++;
    }

    // 更新backward
    x->backward = (update[0] == zsl->header) ? NULL : update[0];
    if (x->level[0].forward)
        x->level[0].forward->backward = x;
    else
        zsl->tail = x;
    
    // 增加总长度
    zsl->length++;
    return x;
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20

/* Internal function used by zslDelete, zslDeleteByScore and zslDeleteByRank */
void zslDeleteNode(zskiplist *zsl, zskiplistNode *x, zskiplistNode **update) {
    int i;
    for (i = 0; i < zsl->level; i++) {
        if (update[i]->level[i].forward == x) {
            update[i]->level[i].span += x->level[i].span - 1;
            update[i]->level[i].forward = x->level[i].forward;
        } else {
            update[i]->level[i].span -= 1;
        }
    }
    if (x->level[0].forward) {
        x->level[0].forward->backward = x->backward;
    } else {
        zsl->tail = x->backward;
    }
    while(zsl->level > 1 && zsl->header->level[zsl->level-1].forward == NULL)
        zsl->level--;
    zsl->length--;
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18

/* Free a whole skiplist. */
void zslFree(zskiplist *zsl) {
    zskiplistNode *node = zsl->header->level[0].forward, *next;

    zfree(zsl->header);
    while(node) {
        next = node->level[0].forward;
        zslFreeNode(node);
        node = next;
    }
    zfree(zsl);
}


void zslFreeNode(zskiplistNode *node) {
    sdsfree(node->ele);
    zfree(node);
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19

/* Lookup the key and create the sorted set if does not exist. */
zobj = lookupKeyWrite(c->db,key);
if (zobj == NULL) {
    if (xx) goto reply_to_client; /* No key + XX option: nothing to do. */
    if (server.zset_max_ziplist_entries == 0 ||
        server.zset_max_ziplist_value < sdslen(c->argv[scoreidx+1]->ptr))
    {
        
        zobj = createZsetObject();
    } else {
        zobj = createZsetZiplistObject();
    }
    dbAdd(c->db,key,zobj);
} else {
    if (zobj->type != OBJ_ZSET) {
        addReply(c,shared.wrongtypeerr);
        goto cleanup;
    }
}