if (server.zset_max_ziplist_entries == 0 ||
server.zset_max_ziplist_value < sdslen(c->argv[scoreidx+1]->ptr)){zobj = createZsetObject(); //创建zset} else {zobj = createZsetZiplistObject();//创建ziplist}

/* Insert item at "p". */unsigned char *__ziplistInsert(unsigned char *zl, unsigned char *p, unsigned char *s, unsigned int slen) {size_t curlen = intrev32ifbe(ZIPLIST_BYTES(zl)), reqlen;unsigned int prevlensize, prevlen = 0;size_t offset;int nextdiff = 0;unsigned char encoding = 0;long long value = 123456789; /* initialized to avoid warning. Using a valuethat is easy to see if for some reasonwe use it uninitialized. */zlentry tail;/* Find out prevlen for the entry that is inserted. *///插入位置前面一个entry节点占用的字节数prevlenif (p[0] != ZIP_END) {//插入节点不在末尾节点,直接从p的前面字节读
ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);} else {//插入节点在末尾位置,找到末尾节点
unsigned char *ptail = ZIPLIST_ENTRY_TAIL(zl);if (ptail[0] != ZIP_END) {prevlen = zipRawEntryLength(ptail);}}/* See if the entry can be encoded */if (zipTryEncoding(s,slen,&value,&encoding)) {//判断s是否可以转化为整数,并将整数值和enconding分别存在value和encoding指针/* 'encoding' is set to the appropriate integer encoding */reqlen = zipIntSize(encoding);//整数值长度
} else {/* 'encoding' is untouched, however zipStoreEntryEncoding will use the* string length to figure out how to encode it. */reqlen = slen;//字符串长度
}/* We need space for both the length of the previous entry and* the length of the payload. *///得出新插入节点占用的总字节数reqlen
reqlen += zipStorePrevEntryLength(NULL,prevlen);reqlen += zipStoreEntryEncoding(NULL,encoding,slen);/* When the insert position is not equal to the tail, we need to* make sure that the next entry can hold this entry's length in* its prevlen field. *///插入新节点不在末尾位置,则插入位置p所指向的entry节点的prevlen,//值会变成新插入节点的总长度,且prevlen所占用的字节数可能会变化,//nextdiff表示新插入节点下一节点的prevlen需要空间的变化,负值表示变小,//正值表示扩大int forcelarge = 0;nextdiff = (p[0] != ZIP_END) ? zipPrevLenByteDiff(p,reqlen) : 0;if (nextdiff == -4 && reqlen < 4) {nextdiff = 0;forcelarge = 1;}/* Store offset because a realloc may change the address of zl. */offset = p-zl;zl = ziplistResize(zl,curlen+reqlen+nextdiff);//重新分配空间,并将zl的每字节都填充到新分配的内存中
p = zl+offset;//将p后面的数据项进行移动/* Apply memory move when necessary and update tail offset. */if (p[0] != ZIP_END) {/* Subtract one because of the ZIP_END bytes */memmove(p+reqlen,p-nextdiff,curlen-offset-1+nextdiff);/* Encode this entry's raw length in the next entry. */if (forcelarge)//设置下一个节点的prevlen
zipStorePrevEntryLengthLarge(p+reqlen,reqlen);elsezipStorePrevEntryLength(p+reqlen,reqlen);/* Update offset for tail */ZIPLIST_TAIL_OFFSET(zl) =intrev32ifbe(intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))+reqlen);/* When the tail contains more than one entry, we need to take* "nextdiff" in account as well. Otherwise, a change in the* size of prevlen doesn't have an effect on the *tail* offset. */zipEntry(p+reqlen, &tail);if (p[reqlen+tail.headersize+tail.len] != ZIP_END) {ZIPLIST_TAIL_OFFSET(zl) =intrev32ifbe(intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))+nextdiff);}} else {/* This element will be the new tail. */ZIPLIST_TAIL_OFFSET(zl) = intrev32ifbe(p-zl);}/* When nextdiff != 0, the raw length of the next entry has changed, so* we need to cascade the update throughout the ziplist */if (nextdiff != 0) {offset = p-zl;zl = __ziplistCascadeUpdate(zl,p+reqlen);p = zl+offset;}/* Write the entry *///将新数据项放入插入位置
p += zipStorePrevEntryLength(p,prevlen);p += zipStoreEntryEncoding(p,encoding,slen);if (ZIP_IS_STR(encoding)) {memcpy(p,s,slen);} else {zipSaveInteger(p,value,encoding);}ZIPLIST_INCR_LENGTH(zl,1);return zl;}

typedef struct zset {dict *dict;//字典
zskiplist *zsl;//跳表

} zset;

int zslRandomLevel(void) {//随机生成节点层数,当第i层节点存在时，第i+1节点存在的概率为ZSKIPLIST_P = 1/4//ZSKIPLIST_MAXLEVEL 64,表示节点的最大层数int level = 1;while ((random()&0xFFFF) < (ZSKIPLIST_P * 0xFFFF))level += 1;return (level<ZSKIPLIST_MAXLEVEL) ? level : ZSKIPLIST_MAXLEVEL;}

/* ZSETs use a specialized version of Skiplists */typedef struct zskiplistNode {sds ele;//实际存储的数据double score;//分值struct zskiplistNode *backward;//后退指针,指向前一个节点struct zskiplistLevel {struct zskiplistNode *forward;//前进指针,指向下一个节点
unsigned long span;//跨度,表示该层链表的这一节点到下一节点跨越的节点数,用于计算rank
} level[];//层级数组,每个层级都有到下一个节点的指针和跨度

} zskiplistNode;//跳表节点
typedef struct zskiplist {struct zskiplistNode *header, *tail;//跳表头节点和尾节点
unsigned long length;//跳表元素个数int level;//跳表的最高层数(不包括头节点,头节点实际上并不存储数据)

} zskiplist;

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;for (i = zsl->level-1; i >= 0; i--) {/* store rank that is crossed to reach the insert position *///rank[i]初始化为rank[i+1],所以rank[i]-rank[i+1]表示在i层走过的节点数
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;}// 记录将要和新节点相连接的节点,x表示新节点在i层连接的上一节点
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. */level = zslRandomLevel();//随机生成此节点的层数if (level > zsl->level) {for (i = zsl->level; i < level; i++) {rank[i] = 0;update[i] = zsl->header;update[i]->level[i].span = zsl->length;}zsl->level = level;}x = zslCreateNode(level,score,ele);for (i = 0; i < level; i++) {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 *///rank[0]表示0层链表，插入节点x左边的节点数//rank[i]表示i层链表,插入节点x左边的节点数//rank[0] - rank[i]+1表示i层链表,x前一节点到x的跨度
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 *///在level及之上的每层,update[i]到下一节点的距离由于插入了x节点而加1for (i = level; i < zsl->level; i++) {update[i]->level[i].span++;}//更新后退指针
x->backward = (update[0] == zsl->header) ? NULL : update[0];if (x->level[0].forward)x->level[0].forward->backward = x;elsezsl->tail = x;zsl->length++;return x;}