Redis（八）：zset/zadd/zrange/zrembyscore 命令源碼解析

/* ZSETs use a specialized version of Skiplists */typedef struct zskiplistNode {    sds ele;    double score;    struct zskiplistNode *backward;    struct zskiplistLevel {        struct zskiplistNode *forward;        unsigned int span;    } level[];} zskiplistNode;// 跳躍鏈表typedef struct zskiplist {    struct zskiplistNode *header, *tail;    unsigned long length;    int level;} zskiplist;// zset 主數(shù)據(jù)結(jié)構(gòu)，dict + zskiplisttypedef struct zset {    dict *dict;    zskiplist *zsl;} zset;// zset 在合適場(chǎng)景下，將先使用 ziplist 存儲(chǔ)數(shù)據(jù)typedef struct zlentry {    unsigned int prevrawlensize, prevrawlen;    unsigned int lensize, len;    unsigned int headersize;    unsigned char encoding;    unsigned char *p;} zlentry;

// 用法: ZADD key score1 member1 [score2 member2]// t_zset.cvoid zaddCommand(client *c) {    // zadd 的多個(gè)參數(shù)變形, 使用 flags 進(jìn)行區(qū)分復(fù)用    zaddGenericCommand(c,ZADD_NONE);}void zaddGenericCommand(client *c, int flags) {    static char *nanerr = "resulting score is not a number (NaN)";    robj *key = c->argv[1];    robj *zobj;    sds ele;    double score = 0, *scores = NULL, curscore = 0.0;    int j, elements;    int scoreidx = 0;    /* The following vars are used in order to track what the command actually     * did during the execution, to reply to the client and to trigger the     * notification of keyspace change. */    int added = 0;      /* Number of new elements added. */    int updated = 0;    /* Number of elements with updated score. */    int processed = 0;  /* Number of elements processed, may remain zero with                           options like XX. */
    /* Parse options. At the end 'scoreidx' is set to the argument position     * of the score of the first score-element pair. */    // 從第三位置開(kāi)始嘗試解析特殊標(biāo)識(shí)（用法規(guī)范）    // 按位與到 flags 中    scoreidx = 2;    while(scoreidx < c->argc) {        char *opt = c->argv[scoreidx]->ptr;        // NX: 不更新已存在的元素，只做添加操作        if (!strcasecmp(opt,"nx")) flags |= ZADD_NX;        // XX: 只做更新操作，不做添加操作        else if (!strcasecmp(opt,"xx")) flags |= ZADD_XX;        // CH: 將返回值從添加的新元素?cái)?shù)修改為已更改元素的總數(shù)。更改的元素是第添加的新元素以及已為其更新分?jǐn)?shù)的現(xiàn)有元素。因此，命令行中指定的具有與過(guò)去相同分?jǐn)?shù)的元素將不計(jì)算在內(nèi)。注意：通常，ZADD的返回值僅計(jì)算添加的新元素的數(shù)量。        else if (!strcasecmp(opt,"ch")) flags |= ZADD_CH;        // INCR: 使用指定元素增加指定分?jǐn)?shù), 與 ZINCRBY 類似，此場(chǎng)景下，只允許操作一個(gè)元素        else if (!strcasecmp(opt,"incr")) flags |= ZADD_INCR;        else break;        scoreidx++;    }
    /* Turn options into simple to check vars. */    int incr = (flags & ZADD_INCR) != 0;    int nx = (flags & ZADD_NX) != 0;    int xx = (flags & ZADD_XX) != 0;    int ch = (flags & ZADD_CH) != 0;
    /* After the options, we expect to have an even number of args, since     * we expect any number of score-element pairs. */    // 把特殊標(biāo)識(shí)去除后，剩下的參數(shù)列表應(yīng)該2n數(shù)，即 score-element 一一配對(duì)的，否則語(yǔ)法錯(cuò)誤    elements = c->argc-scoreidx;    if (elements % 2) {        addReply(c,shared.syntaxerr);        return;    }    elements /= 2; /* Now this holds the number of score-element pairs. */
    /* Check for incompatible options. */    // 互斥項(xiàng)    if (nx && xx) {        addReplyError(c,            "XX and NX options at the same time are not compatible");        return;    }    // 語(yǔ)法檢查，INCR 只能針對(duì)1個(gè)元素操作    if (incr && elements > 1) {        addReplyError(c,            "INCR option supports a single increment-element pair");        return;    }
    /* Start parsing all the scores, we need to emit any syntax error     * before executing additions to the sorted set, as the command should     * either execute fully or nothing at all. */    // 解析所有的 score 值為double類型，賦值到 scores 中    scores = zmalloc(sizeof(double)*elements);    for (j = 0; j < elements; j++) {        if (getDoubleFromObjectOrReply(c,c->argv[scoreidx+j*2],&scores[j],NULL)            != C_OK) goto cleanup;    }
    /* Lookup the key and create the sorted set if does not exist. */    // 語(yǔ)法檢查    zobj = lookupKeyWrite(c->db,key);    if (zobj == NULL) {        if (xx) goto reply_to_client; /* No key + XX option: nothing to do. */        // 創(chuàng)建原始key對(duì)象        // 默認(rèn) zset_max_ziplist_entries=OBJ_ZSET_MAX_ZIPLIST_ENTRIES: 128        // 默認(rèn) zset_max_ziplist_value=OBJ_ZSET_MAX_ZIPLIST_VALUE: 64        // 所以此處默認(rèn)主要是檢查 第1個(gè)member的長(zhǎng)度是大于 64        if (server.zset_max_ziplist_entries == 0 ||            server.zset_max_ziplist_value < sdslen(c->argv[scoreidx+1]->ptr))        {            // 2. 通用情況使用 dict+quicklist 型的zset             zobj = createZsetObject();        } else {            // 1. 元素比較小的情況下創(chuàng)建 ziplist 型的 zset            zobj = createZsetZiplistObject();        }        // 將對(duì)象添加到db中，后續(xù)所有操作針對(duì) zobj 操作即是對(duì)db的操作 (引用傳遞)        dbAdd(c->db,key,zobj);    } else {        if (zobj->type != OBJ_ZSET) {            addReply(c,shared.wrongtypeerr);            goto cleanup;        }    }    // 一個(gè)個(gè)元素循環(huán)添加    for (j = 0; j < elements; j++) {        score = scores[j];
        ele = c->argv[scoreidx+1+j*2]->ptr;        // 分當(dāng)前zobj的編碼不同進(jìn)行添加 (ziplist, skiplist)        // 3. ZIPLIST 編碼下的zset添加操作        if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {            unsigned char *eptr;            // 3.1. 查找是否存在要添加的元素 （確定添加或更新）            if ((eptr = zzlFind(zobj->ptr,ele,&curscore)) != NULL) {                if (nx) continue;                if (incr) {                    score += curscore;                    if (isnan(score)) {                        addReplyError(c,nanerr);                        goto cleanup;                    }                }
                /* Remove and re-insert when score changed. */                if (score != curscore) {                    // 3.2. 元素更新操作，先刪再插入                    zobj->ptr = zzlDelete(zobj->ptr,eptr);                    zobj->ptr = zzlInsert(zobj->ptr,ele,score);                    server.dirty++;                    updated++;                }                processed++;            } else if (!xx) {                /* Optimize: check if the element is too large or the list                 * becomes too long *before* executing zzlInsert. */                zobj->ptr = zzlInsert(zobj->ptr,ele,score);                // 5. 超過(guò)一條件后，做 ziplist->skiplist 轉(zhuǎn)換                // 默認(rèn) 元素個(gè)數(shù)>128, 當(dāng)前元素>64                // 這兩個(gè)判斷不會(huì)重復(fù)嗎？？?jī)蓚€(gè)原因: 1. 轉(zhuǎn)換函數(shù)內(nèi)部會(huì)重新判定; 2. 下一次循環(huán)時(shí)不會(huì)再走當(dāng)前邏輯;                if (zzlLength(zobj->ptr) > server.zset_max_ziplist_entries)                    zsetConvert(zobj,OBJ_ENCODING_SKIPLIST);                if (sdslen(ele) > server.zset_max_ziplist_value)                    zsetConvert(zobj,OBJ_ENCODING_SKIPLIST);                server.dirty++;                added++;                processed++;            }        }         // 4. skiplist 下的zset元素添加        else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {            zset *zs = zobj->ptr;            zskiplistNode *znode;            dictEntry *de;            // 判斷ele是否已存在，使用hash查找，快速            de = dictFind(zs->dict,ele);            if (de != NULL) {                if (nx) continue;                curscore = *(double*)dictGetVal(de);
                if (incr) {                    score += curscore;                    if (isnan(score)) {                        addReplyError(c,nanerr);                        /* Don't need to check if the sorted set is empty                         * because we know it has at least one element. */                        goto cleanup;                    }                }
                /* Remove and re-insert when score changes. */                // 先刪再插入 skiplist                if (score != curscore) {                    zskiplistNode *node;                    serverAssert(zslDelete(zs->zsl,curscore,ele,&node));                    znode = zslInsert(zs->zsl,score,node->ele);                    /* We reused the node->ele SDS string, free the node now                     * since zslInsert created a new one. */                    node->ele = NULL;                    zslFreeNode(node);                    /* Note that we did not removed the original element from                     * the hash table representing the sorted set, so we just                     * update the score. */                    // 更新dict中的分?jǐn)?shù)引用                    dictGetVal(de) = &znode->score; /* Update score ptr. */                    server.dirty++;                    updated++;                }                processed++;            } else if (!xx) {                ele = sdsdup(ele);                znode = zslInsert(zs->zsl,score,ele);                // 添加skiplist的同時(shí)，也往 dict 中添加一份數(shù)據(jù)，因?yàn)閔ash的查找永遠(yuǎn)是最快的                serverAssert(dictAdd(zs->dict,ele,&znode->score) == DICT_OK);                server.dirty++;                added++;                processed++;            }        } else {            serverPanic("Unknown sorted set encoding");        }    }
reply_to_client:    if (incr) { /* ZINCRBY or INCR option. */        if (processed)            addReplyDouble(c,score);        else            addReply(c,shared.nullbulk);    } else { /* ZADD. */        addReplyLongLong(c,ch ? added+updated : added);    }
cleanup:    zfree(scores);    if (added || updated) {        signalModifiedKey(c->db,key);        notifyKeyspaceEvent(NOTIFY_ZSET,            incr ? "zincr" : "zadd", key, c->db->id);    }}
// 1. 元素比較小的情況下創(chuàng)建 ziplist 型的 zset// object.c, 創(chuàng)建ziplist 的zsetrobj *createZsetZiplistObject(void) {    unsigned char *zl = ziplistNew();    robj *o = createObject(OBJ_ZSET,zl);    o->encoding = OBJ_ENCODING_ZIPLIST;    return o;}// 2. 創(chuàng)建通用的 zset 實(shí)例// object.crobj *createZsetObject(void) {    zset *zs = zmalloc(sizeof(*zs));    robj *o;    // zsetDictType 稍有不同    zs->dict = dictCreate(&zsetDictType,NULL);    // 首次遇到 skiplist, 咱去瞅瞅是如何創(chuàng)建的    zs->zsl = zslCreate();    o = createObject(OBJ_ZSET,zs);    o->encoding = OBJ_ENCODING_SKIPLIST;    return o;}// server.c, zset創(chuàng)建時(shí)使用的dict類型，與hash有不同/* Sorted sets hash (note: a skiplist is used in addition to the hash table) */dictType zsetDictType = {    dictSdsHash,               /* hash function */    NULL,                      /* key dup */    NULL,                      /* val dup */    dictSdsKeyCompare,         /* key compare */    NULL,                      /* Note: SDS string shared & freed by skiplist */    NULL                       /* val destructor */};// 創(chuàng)建 skiplist 對(duì)象/* Create a new skiplist. */zskiplist *zslCreate(void) {    int j;    zskiplist *zsl;
    zsl = zmalloc(sizeof(*zsl));    zsl->level = 1;    zsl->length = 0;    // 創(chuàng)建header節(jié)點(diǎn)，ZSKIPLIST_MAXLEVEL 32    zsl->header = zslCreateNode(ZSKIPLIST_MAXLEVEL,0,NULL);    // 初始化header    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;}/* 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;}

// 3. ZIPLIST 編碼下的zset添加操作// 3.1. 查找是否存在要添加的元素 （確定添加或更新）// t_zset.c, 查找指定eleunsigned char *zzlFind(unsigned char *zl, sds ele, double *score) {    unsigned char *eptr = ziplistIndex(zl,0), *sptr;    // 遍歷所有ziplist    // 可見(jiàn)，此時(shí)的ziplist并沒(méi)有表現(xiàn)出有序啊    while (eptr != NULL) {        // eptr 相當(dāng)于是 key        // sptr 相當(dāng)于score        sptr = ziplistNext(zl,eptr);        serverAssert(sptr != NULL);
        if (ziplistCompare(eptr,(unsigned char*)ele,sdslen(ele))) {            /* Matching element, pull out score. */            // 找到相應(yīng)的 key 后，解析下一值，即 score            if (score != NULL) *score = zzlGetScore(sptr);            return eptr;        }        /* Move to next element. */        // 移動(dòng)兩次對(duì)象，才會(huì)到下一元素(因?yàn)榇鎯?chǔ)是 key-score 相鄰存儲(chǔ))        eptr = ziplistNext(zl,sptr);    }    return NULL;}// t_zset.c, 獲取元素的scoredouble zzlGetScore(unsigned char *sptr) {    unsigned char *vstr;    unsigned int vlen;    long long vlong;    char buf[128];    double score;
    serverAssert(sptr != NULL);    serverAssert(ziplistGet(sptr,&vstr,&vlen,&vlong));    // 帶小數(shù)點(diǎn)不帶小數(shù)點(diǎn)    if (vstr) {        memcpy(buf,vstr,vlen);        buf[vlen] = '\0';        // 做類型轉(zhuǎn)換        score = strtod(buf,NULL);    } else {        score = vlong;    }
    return score;}
// 3.2. 元素更新操作，先刪再插入// t_zset.c/* Delete (element,score) pair from ziplist. Use local copy of eptr because we * don't want to modify the one given as argument. */unsigned char *zzlDelete(unsigned char *zl, unsigned char *eptr) {    unsigned char *p = eptr;
    /* TODO: add function to ziplist API to delete N elements from offset. */    zl = ziplistDelete(zl,&p);    zl = ziplistDelete(zl,&p);    return zl;}// 添加 ele-score 到 ziplist 中/* Insert (element,score) pair in ziplist. This function assumes the element is * not yet present in the list. */unsigned char *zzlInsert(unsigned char *zl, sds ele, double score) {    unsigned char *eptr = ziplistIndex(zl,0), *sptr;    double s;    // 在上面查找時(shí)，我們看到ziplist也是遍歷，以為是無(wú)序的ziplist    // 然而實(shí)際上，插入時(shí)是維護(hù)了順序的喲    while (eptr != NULL) {        sptr = ziplistNext(zl,eptr);        serverAssert(sptr != NULL);        s = zzlGetScore(sptr);        // 找到第一個(gè)比score大的位置，在其前面插入 ele-score        if (s > score) {            /* First element with score larger than score for element to be             * inserted. This means we should take its spot in the list to             * maintain ordering. */            zl = zzlInsertAt(zl,eptr,ele,score);            break;        } else if (s == score) {            /* Ensure lexicographical ordering for elements. */            // 當(dāng)分?jǐn)?shù)相同時(shí)，按字典順序排列            if (zzlCompareElements(eptr,(unsigned char*)ele,sdslen(ele)) > 0) {                zl = zzlInsertAt(zl,eptr,ele,score);                break;            }        }
        /* Move to next element. */        eptr = ziplistNext(zl,sptr);    }
    /* Push on tail of list when it was not yet inserted. */    // 以上遍歷完成都沒(méi)有找到相應(yīng)位置，說(shuō)明當(dāng)前score是最大值，將其插入尾部    if (eptr == NULL)        zl = zzlInsertAt(zl,NULL,ele,score);    return zl;}// 在eptr的前面插入 ele-scoreunsigned char *zzlInsertAt(unsigned char *zl, unsigned char *eptr, sds ele, double score) {    unsigned char *sptr;    char scorebuf[128];    int scorelen;    size_t offset;
    scorelen = d2string(scorebuf,sizeof(scorebuf),score);    if (eptr == NULL) {        // 直接插入到尾部        zl = ziplistPush(zl,(unsigned char*)ele,sdslen(ele),ZIPLIST_TAIL);        zl = ziplistPush(zl,(unsigned char*)scorebuf,scorelen,ZIPLIST_TAIL);    } else {        /* Keep offset relative to zl, as it might be re-allocated. */        offset = eptr-zl;        // 直接在 eptr 位置添加 ele, 其他元素后移        zl = ziplistInsert(zl,eptr,(unsigned char*)ele,sdslen(ele));        eptr = zl+offset;
        /* Insert score after the element. */        // 此時(shí)的 eptr 已經(jīng)插入ele之后的位置，后移一位后，就可以找到 score 的存儲(chǔ)位置        serverAssert((sptr = ziplistNext(zl,eptr)) != NULL);        zl = ziplistInsert(zl,sptr,(unsigned char*)scorebuf,scorelen);    }    return zl;}
// 4. skiplist 下的zset元素添加// 4.1. 添加元素// t_zset.c, 添加 ele-score 到 skiplist 中/* Insert a new node in the skiplist. Assumes the element does not already * exist (up to the caller to enforce that). The skiplist takes ownership * of the passed SDS string 'ele'. */zskiplistNode *zslInsert(zskiplist *zsl, double score, sds ele) {    // ZSKIPLIST_MAXLEVEL 32    zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;    unsigned int rank[ZSKIPLIST_MAXLEVEL];    int i, level;
    serverAssert(!isnan(score));    x = zsl->header;    // 初始 zsl->level = 1    // 從header的最高層開(kāi)始遍歷    for (i = zsl->level-1; i >= 0; i--) {        /* store rank that is crossed to reach the insert position */        // 計(jì)算出每層可以插入的位置        rank[i] = i == (zsl->level-1) ? 0 : rank[i+1];        // 當(dāng)前l(fā)evel的score小于需要添加的元素時(shí)，往前推進(jìn)skiplist        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. */    // 得到一隨機(jī)的level, 決定要寫的節(jié)點(diǎn)數(shù)    // 如果當(dāng)前的level過(guò)小，則變更level, 重新初始化大的level    level = zslRandomLevel();    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;    }    // 構(gòu)建新的 skiplist 節(jié)點(diǎn)，為每一層節(jié)點(diǎn)添加同樣的數(shù)據(jù)    x = zslCreateNode(level,score,ele);    for (i = 0; i < level; i++) {        // 讓i層的節(jié)點(diǎn)與x關(guān)聯(lián)        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 */    // 如果當(dāng)前l(fā)evel較小，則存在有的level未賦值情況，需要主動(dòng)+1    for (i = level; i < zsl->level; i++) {        update[i]->level[i].span++;    }    // 關(guān)聯(lián)好header后，設(shè)置backward指針    x->backward = (update[0] == zsl->header) ? NULL : update[0];    if (x->level[0].forward)        x->level[0].forward->backward = x;    else        // 同有后繼節(jié)點(diǎn)，說(shuō)明是尾節(jié)點(diǎn)，賦值tail        zsl->tail = x;    zsl->length++;    return x;}

// 補(bǔ)充，我們看一下隨機(jī)level的計(jì)算算法// t_zset.c/* 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) {    int level = 1;    // n次隨機(jī)值得到 level, ZSKIPLIST_P:0.25    // 按隨機(jī)概率，應(yīng)該是有1/4的命中概率（如果不是呢？？）    while ((random()&0xFFFF) < (ZSKIPLIST_P * 0xFFFF))        level += 1;    return (level<ZSKIPLIST_MAXLEVEL) ? level : ZSKIPLIST_MAXLEVEL;}

// t_zset.c, 刪除skiplist的指定節(jié)點(diǎn)/* Delete an element with matching score/element from the skiplist. * The function returns 1 if the node was found and deleted, otherwise * 0 is returned. * * If 'node' is NULL the deleted node is freed by zslFreeNode(), otherwise * it is not freed (but just unlinked) and *node is set to the node pointer, * so that it is possible for the caller to reuse the node (including the * referenced SDS string at node->ele). */int zslDelete(zskiplist *zsl, double score, sds ele, zskiplistNode **node) {    zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;    int i;
    x = zsl->header;    // 與添加時(shí)查找對(duì)應(yīng)位置一樣，先進(jìn)行遍歷，找到最每個(gè)層級(jí)最接近 node 的位置    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 &&                     sdscmp(x->level[i].forward->ele,ele) < 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. */    // 進(jìn)行精確比對(duì)，相同才進(jìn)行刪除    x = x->level[0].forward;    if (x && score == x->score && sdscmp(x->ele,ele) == 0) {        // 執(zhí)行刪除動(dòng)作        zslDeleteNode(zsl, x, update);        if (!node)            zslFreeNode(x);        else            *node = x;        return 1;    }    return 0; /* not found */}// 刪除 x對(duì)應(yīng)的節(jié)點(diǎn)// update 是node的每一層級(jí)對(duì)應(yīng)的前驅(qū)節(jié)點(diǎn)/* 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 {            // 不相等說(shuō)明該層不存在指向 x 的引用            update[i]->level[i].span -= 1;        }    }    // 更新第0層尾節(jié)點(diǎn)指針    if (x->level[0].forward) {        x->level[0].forward->backward = x->backward;    } else {        zsl->tail = x->backward;    }    // 降低 skiplist 的層級(jí)，直到第一個(gè)非空的節(jié)點(diǎn)為止    while(zsl->level > 1 && zsl->header->level[zsl->level-1].forward == NULL)        zsl->level--;    zsl->length--;}

// t_zset.c, 編碼類型轉(zhuǎn)換void zsetConvert(robj *zobj, int encoding) {    zset *zs;    zskiplistNode *node, *next;    sds ele;    double score;    // 編碼相同，直接返回    if (zobj->encoding == encoding) return;    // ziplist -> skiplist 轉(zhuǎn)換    if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {        unsigned char *zl = zobj->ptr;        unsigned char *eptr, *sptr;        unsigned char *vstr;        unsigned int vlen;        long long vlong;
        if (encoding != OBJ_ENCODING_SKIPLIST)            serverPanic("Unknown target encoding");
        zs = zmalloc(sizeof(*zs));        zs->dict = dictCreate(&zsetDictType,NULL);        zs->zsl = zslCreate();
        eptr = ziplistIndex(zl,0);        serverAssertWithInfo(NULL,zobj,eptr != NULL);        sptr = ziplistNext(zl,eptr);        serverAssertWithInfo(NULL,zobj,sptr != NULL);
        while (eptr != NULL) {            score = zzlGetScore(sptr);            serverAssertWithInfo(NULL,zobj,ziplistGet(eptr,&vstr,&vlen,&vlong));            if (vstr == NULL)                ele = sdsfromlonglong(vlong);            else                ele = sdsnewlen((char*)vstr,vlen);            // 依次插入 skiplist 和 dict 中即可            node = zslInsert(zs->zsl,score,ele);            serverAssert(dictAdd(zs->dict,ele,&node->score) == DICT_OK);            // zzlNext 封裝了同時(shí)迭代 eptr 和 sptr 方法            zzlNext(zl,&eptr,&sptr);        }
        zfree(zobj->ptr);        zobj->ptr = zs;        zobj->encoding = OBJ_ENCODING_SKIPLIST;    }    // skiplist -> ziplist 逆向轉(zhuǎn)換    else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {        unsigned char *zl = ziplistNew();        if (encoding != OBJ_ENCODING_ZIPLIST)            serverPanic("Unknown target encoding");
        /* Approach similar to zslFree(), since we want to free the skiplist at         * the same time as creating the ziplist. */        zs = zobj->ptr;        dictRelease(zs->dict);        node = zs->zsl->header->level[0].forward;        zfree(zs->zsl->header);        zfree(zs->zsl);        // 正向迭代轉(zhuǎn)換        while (node) {            zl = zzlInsertAt(zl,NULL,node->ele,node->score);            next = node->level[0].forward;            zslFreeNode(node);            node = next;        }
        zfree(zs);        zobj->ptr = zl;        zobj->encoding = OBJ_ENCODING_ZIPLIST;    } else {        serverPanic("Unknown sorted set encoding");    }}// 基于ziplist, 同時(shí)迭代 ele-score/* Move to next entry based on the values in eptr and sptr. Both are set to * NULL when there is no next entry. */void zzlNext(unsigned char *zl, unsigned char **eptr, unsigned char **sptr) {    unsigned char *_eptr, *_sptr;    serverAssert(*eptr != NULL && *sptr != NULL);
    _eptr = ziplistNext(zl,*sptr);    if (_eptr != NULL) {        _sptr = ziplistNext(zl,_eptr);        serverAssert(_sptr != NULL);    } else {        /* No next entry. */        _sptr = NULL;    }
    *eptr = _eptr;    *sptr = _sptr;}

// 用法: ZRANGE key start stop [WITHSCORES]// t_zset.cvoid zrangeCommand(client *c) {    zrangeGenericCommand(c,0);}
void zrangeGenericCommand(client *c, int reverse) {    robj *key = c->argv[1];    robj *zobj;    int withscores = 0;    long start;    long end;    int llen;    int rangelen;
    if ((getLongFromObjectOrReply(c, c->argv[2], &start, NULL) != C_OK) ||        (getLongFromObjectOrReply(c, c->argv[3], &end, NULL) != C_OK)) return;
    if (c->argc == 5 && !strcasecmp(c->argv[4]->ptr,"withscores")) {        withscores = 1;    } else if (c->argc >= 5) {        addReply(c,shared.syntaxerr);        return;    }
    if ((zobj = lookupKeyReadOrReply(c,key,shared.emptymultibulk)) == NULL         || checkType(c,zobj,OBJ_ZSET)) return;
    /* Sanitize indexes. */    // 小于0，則代表反向查詢，但實(shí)際的輸出順序不是按此值運(yùn)算的（提供了 reverse 方法）    llen = zsetLength(zobj);    if (start < 0) start = llen+start;    if (end < 0) end = llen+end;    if (start < 0) start = 0;
    /* Invariant: start >= 0, so this test will be true when end < 0.     * The range is empty when start > end or start >= length. */    if (start > end || start >= llen) {        addReply(c,shared.emptymultibulk);        return;    }    if (end >= llen) end = llen-1;    rangelen = (end-start)+1;
    /* Return the result in form of a multi-bulk reply */    addReplyMultiBulkLen(c, withscores ? (rangelen*2) : rangelen);    // 同樣，分 ZIPLIST 和 SKIPLIST 編碼分別實(shí)現(xiàn)    if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {        unsigned char *zl = zobj->ptr;        unsigned char *eptr, *sptr;        unsigned char *vstr;        unsigned int vlen;        long long vlong;        // ziplist 以 ele-score 方式存儲(chǔ)，所以步長(zhǎng)是 2        if (reverse)            eptr = ziplistIndex(zl,-2-(2*start));        else            eptr = ziplistIndex(zl,2*start);
        serverAssertWithInfo(c,zobj,eptr != NULL);        sptr = ziplistNext(zl,eptr);        // 依次迭代輸出        while (rangelen--) {            serverAssertWithInfo(c,zobj,eptr != NULL && sptr != NULL);            serverAssertWithInfo(c,zobj,ziplistGet(eptr,&vstr,&vlen,&vlong));            if (vstr == NULL)                addReplyBulkLongLong(c,vlong);            else                addReplyBulkCBuffer(c,vstr,vlen);
            if (withscores)                addReplyDouble(c,zzlGetScore(sptr));            // ziplist 提供正向迭代，返回迭代功能，其實(shí)就是 offset的加減問(wèn)題            if (reverse)                zzlPrev(zl,&eptr,&sptr);            else                zzlNext(zl,&eptr,&sptr);        }
    } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {        zset *zs = zobj->ptr;        zskiplist *zsl = zs->zsl;        zskiplistNode *ln;        sds ele;
        /* Check if starting point is trivial, before doing log(N) lookup. */        // 反向使用 tail 迭代，否則使用header迭代        if (reverse) {            ln = zsl->tail;            if (start > 0)                // 獲取下標(biāo)元素應(yīng)該只是一個(gè)迭代循環(huán)問(wèn)題,不過(guò)還是稍微細(xì)看一下skiplist實(shí)現(xiàn)                ln = zslGetElementByRank(zsl,llen-start);        } else {            ln = zsl->header->level[0].forward;            if (start > 0)                ln = zslGetElementByRank(zsl,start+1);        }
        while(rangelen--) {            serverAssertWithInfo(c,zobj,ln != NULL);            ele = ln->ele;            addReplyBulkCBuffer(c,ele,sdslen(ele));            if (withscores)                addReplyDouble(c,ln->score);            // 直接正向或反向迭代即可            ln = reverse ? ln->backward : ln->level[0].forward;        }    } else {        serverPanic("Unknown sorted set encoding");    }}// 根據(jù)排名查找元素/* Finds an element by its rank. The rank argument needs to be 1-based. */zskiplistNode* zslGetElementByRank(zskiplist *zsl, unsigned long rank) {    zskiplistNode *x;    unsigned long traversed = 0;    int i;
    x = zsl->header;    // 好像沒(méi)有相像中的簡(jiǎn)單哦    // 請(qǐng)仔細(xì)品    for (i = zsl->level-1; i >= 0; i--) {        while (x->level[i].forward && (traversed + x->level[i].span) <= rank)        {            // span 的作用？？            traversed += x->level[i].span;            x = x->level[i].forward;        }        if (traversed == rank) {            return x;        }    }    return NULL;}

// t_zset.c, void zremrangebyscoreCommand(client *c) {    // 幾個(gè)范圍刪除，都復(fù)用 zremrangeGenericCommand    // ZRANGE_RANK/ZRANGE_SCORE/ZRANGE_LEX    zremrangeGenericCommand(c,ZRANGE_SCORE);}void zremrangeGenericCommand(client *c, int rangetype) {    robj *key = c->argv[1];    robj *zobj;    int keyremoved = 0;    unsigned long deleted = 0;    // score 存儲(chǔ)使用另外的數(shù)據(jù)結(jié)構(gòu)    zrangespec range;    zlexrangespec lexrange;    long start, end, llen;
    /* Step 1: Parse the range. */    // 解析參數(shù)，除了 rank 方式的查詢，其他兩個(gè)都使用 另外的專門數(shù)據(jù)結(jié)構(gòu)存儲(chǔ)參數(shù)    if (rangetype == ZRANGE_RANK) {        if ((getLongFromObjectOrReply(c,c->argv[2],&start,NULL) != C_OK) ||            (getLongFromObjectOrReply(c,c->argv[3],&end,NULL) != C_OK))            return;    } else if (rangetype == ZRANGE_SCORE) {        if (zslParseRange(c->argv[2],c->argv[3],&range) != C_OK) {            addReplyError(c,"min or max is not a float");            return;        }    } else if (rangetype == ZRANGE_LEX) {        if (zslParseLexRange(c->argv[2],c->argv[3],&lexrange) != C_OK) {            addReplyError(c,"min or max not valid string range item");            return;        }    }
    /* Step 2: Lookup & range sanity checks if needed. */    if ((zobj = lookupKeyWriteOrReply(c,key,shared.czero)) == NULL ||        checkType(c,zobj,OBJ_ZSET)) goto cleanup;
    if (rangetype == ZRANGE_RANK) {        /* Sanitize indexes. */        llen = zsetLength(zobj);        if (start < 0) start = llen+start;        if (end < 0) end = llen+end;        if (start < 0) start = 0;
        /* Invariant: start >= 0, so this test will be true when end < 0.         * The range is empty when start > end or start >= length. */        if (start > end || start >= llen) {            addReply(c,shared.czero);            goto cleanup;        }        if (end >= llen) end = llen-1;    }
    /* Step 3: Perform the range deletion operation. */    if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {        // 針對(duì)不同的刪除類型，使用不同的刪除方法        // 所以，這段代碼的復(fù)用體現(xiàn)在哪里呢？？？        switch(rangetype) {        case ZRANGE_RANK:            zobj->ptr = zzlDeleteRangeByRank(zobj->ptr,start+1,end+1,&deleted);            break;        case ZRANGE_SCORE:            // 3.1. 我們只看 score 的刪除 --ziplist            zobj->ptr = zzlDeleteRangeByScore(zobj->ptr,&range,&deleted);            break;        case ZRANGE_LEX:            zobj->ptr = zzlDeleteRangeByLex(zobj->ptr,&lexrange,&deleted);            break;        }        if (zzlLength(zobj->ptr) == 0) {            dbDelete(c->db,key);            keyremoved = 1;        }    } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {        zset *zs = zobj->ptr;        switch(rangetype) {        case ZRANGE_RANK:            deleted = zslDeleteRangeByRank(zs->zsl,start+1,end+1,zs->dict);            break;        case ZRANGE_SCORE:            // 3.2. skiplist 的刪除rangeByScore 方法            deleted = zslDeleteRangeByScore(zs->zsl,&range,zs->dict);            break;        case ZRANGE_LEX:            deleted = zslDeleteRangeByLex(zs->zsl,&lexrange,zs->dict);            break;        }        if (htNeedsResize(zs->dict)) dictResize(zs->dict);        if (dictSize(zs->dict) == 0) {            dbDelete(c->db,key);            keyremoved = 1;        }    } else {        serverPanic("Unknown sorted set encoding");    }
    /* Step 4: Notifications and reply. */    if (deleted) {        char *event[3] = {"zremrangebyrank","zremrangebyscore","zremrangebylex"};        signalModifiedKey(c->db,key);        notifyKeyspaceEvent(NOTIFY_ZSET,event[rangetype],key,c->db->id);        if (keyremoved)            notifyKeyspaceEvent(NOTIFY_GENERIC,"del",key,c->db->id);    }    server.dirty += deleted;    addReplyLongLong(c,deleted);
cleanup:    if (rangetype == ZRANGE_LEX) zslFreeLexRange(&lexrange);}// server.h, 范圍查詢參數(shù)存儲(chǔ)/* Struct to hold a inclusive/exclusive range spec by score comparison. */typedef struct {    double min, max;    int minex, maxex; /* are min or max exclusive? */} zrangespec;
// 3.1. ziplist 的刪除range方法// t_zset.cunsigned char *zzlDeleteRangeByScore(unsigned char *zl, zrangespec *range, unsigned long *deleted) {    unsigned char *eptr, *sptr;    double score;    unsigned long num = 0;    if (deleted != NULL) *deleted = 0;    // 找到首個(gè)在范圍內(nèi)的指針，進(jìn)行迭代    eptr = zzlFirstInRange(zl,range);    if (eptr == NULL) return zl;
    /* When the tail of the ziplist is deleted, eptr will point to the sentinel     * byte and ziplistNext will return NULL. */    while ((sptr = ziplistNext(zl,eptr)) != NULL) {        score = zzlGetScore(sptr);        // 肯定是比 min 大的，所以只需確認(rèn)比 max 小即可        if (zslValueLteMax(score,range)) {            /* Delete both the element and the score. */            zl = ziplistDelete(zl,&eptr);            zl = ziplistDelete(zl,&eptr);            num++;        } else {            /* No longer in range. */            break;        }    }
    if (deleted != NULL) *deleted = num;    return zl;}
/* Find pointer to the first element contained in the specified range. * Returns NULL when no element is contained in the range. */unsigned char *zzlFirstInRange(unsigned char *zl, zrangespec *range) {    unsigned char *eptr = ziplistIndex(zl,0), *sptr;    double score;
    /* If everything is out of range, return early. */    // 比較第1個(gè)元素和最后 一個(gè)元素，即可確認(rèn)是否在范圍內(nèi)    if (!zzlIsInRange(zl,range)) return NULL;
    while (eptr != NULL) {        sptr = ziplistNext(zl,eptr);        serverAssert(sptr != NULL);
        score = zzlGetScore(sptr);        // score >= min        if (zslValueGteMin(score,range)) {            /* Check if score <= max. */            if (zslValueLteMax(score,range))                return eptr;            return NULL;        }
        /* Move to next element. */        eptr = ziplistNext(zl,sptr);    }
    return NULL;}// 檢查zl是否在range范圍內(nèi)// 檢查第1個(gè)分?jǐn)?shù)和最后一個(gè)數(shù)即可/* Returns if there is a part of the zset is in range. Should only be used * internally by zzlFirstInRange and zzlLastInRange. */int zzlIsInRange(unsigned char *zl, zrangespec *range) {    unsigned char *p;    double score;
    /* Test for ranges that will always be empty. */    if (range->min > range->max ||            (range->min == range->max && (range->minex || range->maxex)))        return 0;
    p = ziplistIndex(zl,-1); /* Last score. */    if (p == NULL) return 0; /* Empty sorted set */    score = zzlGetScore(p);    // scoreMax >= min    if (!zslValueGteMin(score,range))        return 0;
    p = ziplistIndex(zl,1); /* First score. */    serverAssert(p != NULL);    score = zzlGetScore(p);    // scoreMin <= max    if (!zslValueLteMax(score,range))        return 0;
    return 1;}
// 3.2. 刪除 skiplist 中的range元素/* 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. */unsigned long zslDeleteRangeByScore(zskiplist *zsl, zrangespec *range, dict *dict) {    zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;    unsigned long removed = 0;    int i;
    x = zsl->header;    // 找出每層小于 range->min 的元素    for (i = zsl->level-1; i >= 0; i--) {        while (x->level[i].forward && (range->minex ?            x->level[i].forward->score <= range->min :            x->level[i].forward->score < range->min))                x = x->level[i].forward;        update[i] = x;    }
    /* Current node is the last with score < or <= min. */    x = x->level[0].forward;    // 從第0層開(kāi)始，依次刪除引用，刪除元素    // 同有找到符合條件的元素時(shí)，一次循環(huán)也不會(huì)成立    /* Delete nodes while in range. */    while (x &&           (range->maxex ? x->score < range->max : x->score <= range->max))    {        // 保留下一次迭代        zskiplistNode *next = x->level[0].forward;        zslDeleteNode(zsl,x,update);        // 同步刪除 dict 數(shù)據(jù)        dictDelete(dict,x->ele);        zslFreeNode(x); /* Here is where x->ele is actually released. */        removed++;        x = next;    }    return removed;}