Redis（三）：set/get 命令源碼解析

    // rF 代表 getCommand 是只讀命令，又快又準(zhǔn)，時(shí)間復(fù)雜度 O(1)或者O(log(n))    // wm 代表 setCommand 是個(gè)寫命令,當(dāng)心空間問題    {"get",getCommand,2,"rF",0,NULL,1,1,1,0,0}    {"set",setCommand,-3,"wm",0,NULL,1,1,1,0,0}

typedef struct dictType {    // hash 算法原型    unsigned int (*hashFunction)(const void *key);    void *(*keyDup)(void *privdata, const void *key);    void *(*valDup)(void *privdata, const void *obj);    int (*keyCompare)(void *privdata, const void *key1, const void *key2);    void (*keyDestructor)(void *privdata, void *key);    void (*valDestructor)(void *privdata, void *obj);} dictType;

/* Command table. sds string -> command struct pointer. */dictType commandTableDictType = {    // 即 dictSdsCaseHash 是 command 的hash算法實(shí)現(xiàn)    dictSdsCaseHash,            /* hash function */    NULL,                       /* key dup */    NULL,                       /* val dup */    dictSdsKeyCaseCompare,      /* key compare */    dictSdsDestructor,          /* key destructor */    NULL                        /* val destructor */};// server.c, 不區(qū)分大小寫的key hashunsigned int dictSdsCaseHash(const void *key) {    return dictGenCaseHashFunction((unsigned char*)key, sdslen((char*)key));}// dict.c, 不區(qū)分大小寫的key-hash算法: hash * 33 + c/* And a case insensitive hash function (based on djb hash) */unsigned int dictGenCaseHashFunction(const unsigned char *buf, int len) {    // static uint32_t dict_hash_function_seed = 5381;    unsigned int hash = (unsigned int)dict_hash_function_seed;
    while (len--)        hash = ((hash << 5) + hash) + (tolower(*buf++)); /* hash * 33 + c */    return hash;}

/* Db->dict, keys are sds strings, vals are Redis objects. */dictType dbDictType = {    // k 的hash算法實(shí)現(xiàn)    dictSdsHash,                /* hash function */    NULL,                       /* key dup */    NULL,                       /* val dup */    dictSdsKeyCompare,          /* key compare */    dictSdsDestructor,          /* key destructor */    dictObjectDestructor   /* val destructor */};// server.c, 調(diào)用 dict 的實(shí)現(xiàn)unsigned int dictSdsHash(const void *key) {    return dictGenHashFunction((unsigned char*)key, sdslen((char*)key));}// dict.c, 數(shù)據(jù)key的hash算法，或者通用的 string 的hashCode 算法/* MurmurHash2, by Austin Appleby * Note - This code makes a few assumptions about how your machine behaves - * 1. We can read a 4-byte value from any address without crashing * 2. sizeof(int) == 4 * * And it has a few limitations - * * 1. It will not work incrementally. * 2. It will not produce the same results on little-endian and big-endian *    machines. */unsigned int dictGenHashFunction(const void *key, int len) {    /* 'm' and 'r' are mixing constants generated offline.     They're not really 'magic', they just happen to work well.  */    uint32_t seed = dict_hash_function_seed;    const uint32_t m = 0x5bd1e995;    const int r = 24;
    /* Initialize the hash to a 'random' value */    uint32_t h = seed ^ len;
    /* Mix 4 bytes at a time into the hash */    const unsigned char *data = (const unsigned char *)key;    // 核心算法: step1. *m, ^k>>r, *m, *m, ^k, 每4位做一次運(yùn)算    while(len >= 4) {        uint32_t k = *(uint32_t*)data;
        k *= m;        k ^= k >> r;        k *= m;
        h *= m;        h ^= k;
        data += 4;        len -= 4;    }
    /* Handle the last few bytes of the input array  */    // step2. 倒數(shù)第三位 ^<<16, 第二位 ^<<8, 第一位 ^, 然后 *m    switch(len) {        case 3: h ^= data[2] << 16;        case 2: h ^= data[1] << 8;        case 1: h ^= data[0]; h *= m;    };
    /* Do a few final mixes of the hash to ensure the last few     * bytes are well-incorporated. */    // step3. 再混合 ^>>13, *m, ^>>15    h ^= h >> 13;    h *= m;    h ^= h >> 15;
    return (unsigned int)h;}

// t_string.cvoid getCommand(client *c) {    getGenericCommand(c);}int getGenericCommand(client *c) {    robj *o;    // 如果在kv里找不到，則直接響應(yīng)空，shared.nullbulk 作為全局常量的優(yōu)勢就體現(xiàn)出來了    // shared.nullbulk = createObject(OBJ_STRING,sdsnew("$-1\r\n"));    if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.nullbulk)) == NULL)        return C_OK;    // 找到對(duì)應(yīng)的數(shù)據(jù)，但是類型不匹配，說明不能使用 get 命令，響應(yīng)錯(cuò)誤信息    // shared.wrongtypeerr = "-WRONGTYPE Operation against a key holding the wrong kind of value\r\n"    if (o->type != OBJ_STRING) {        addReply(c,shared.wrongtypeerr);        return C_ERR;    } else {        // 正常情況則直接響應(yīng)結(jié)果即可        addReplyBulk(c,o);        return C_OK;    }}

// db.c, 查找某個(gè)key對(duì)應(yīng)的元素或者直接響應(yīng)客戶端robj *lookupKeyReadOrReply(client *c, robj *key, robj *reply) {    // 使用 c->db 對(duì)應(yīng)的數(shù)據(jù)庫進(jìn)行查詢，所以要求客戶端必須針對(duì)某db進(jìn)行操作，且不能跨庫操作是原理決定    robj *o = lookupKeyRead(c->db, key);    // 如果沒有查到數(shù)據(jù)就直接使用默認(rèn)的 reply, 響應(yīng)客戶端了    if (!o) addReply(c,reply);    return o;}// db.c, 讀取key 對(duì)應(yīng)值robj *lookupKeyRead(redisDb *db, robj *key) {    robj *val;    // 檢查過期情況，如果過期，則不用再查了    if (expireIfNeeded(db,key) == 1) {        /* Key expired. If we are in the context of a master, expireIfNeeded()         * returns 0 only when the key does not exist at all, so it's save         * to return NULL ASAP. */        if (server.masterhost == NULL) return NULL;
        /* However if we are in the context of a slave, expireIfNeeded() will         * not really try to expire the key, it only returns information         * about the "logical" status of the key: key expiring is up to the         * master in order to have a consistent view of master's data set.         *         * However, if the command caller is not the master, and as additional         * safety measure, the command invoked is a read-only command, we can         * safely return NULL here, and provide a more consistent behavior         * to clients accessign expired values in a read-only fashion, that         * will say the key as non exisitng.         *         * Notably this covers GETs when slaves are used to scale reads. */        if (server.current_client &&            server.current_client != server.master &&            server.current_client->cmd &&            server.current_client->cmd->flags & CMD_READONLY)        {            return NULL;        }    }    // 然后從db中查找對(duì)應(yīng)的key值，其實(shí)就是一個(gè) hash 查找    // 緩存命中統(tǒng)計(jì)    val = lookupKey(db,key);    if (val == NULL)        server.stat_keyspace_misses++;    else        server.stat_keyspace_hits++;    return val;}// db.c, 過期的處理有點(diǎn)復(fù)雜，我們稍后再看，先看 db 的查找key過程robj *lookupKey(redisDb *db, robj *key) {    // 直接在 db->dict 中進(jìn)行hash查找即可，前面已經(jīng)介紹完成，關(guān)鍵優(yōu)化點(diǎn)在增量rehash    dictEntry *de = dictFind(db->dict,key->ptr);    if (de) {        robj *val = dictGetVal(de);
        /* Update the access time for the ageing algorithm.         * Don't do it if we have a saving child, as this will trigger         * a copy on write madness. */        if (server.rdb_child_pid == -1 && server.aof_child_pid == -1)            val->lru = LRU_CLOCK();        return val;    } else {        return NULL;    }}
// db.c, 接下來看下，檢查過期情況int expireIfNeeded(redisDb *db, robj *key) {    mstime_t when = getExpire(db,key);    mstime_t now;
    if (when < 0) return 0; /* No expire for this key */
    /* Don't expire anything while loading. It will be done later. */    if (server.loading) return 0;
    /* If we are in the context of a Lua script, we claim that time is     * blocked to when the Lua script started. This way a key can expire     * only the first time it is accessed and not in the middle of the     * script execution, making propagation to slaves / AOF consistent.     * See issue #1525 on Github for more information. */    now = server.lua_caller ? server.lua_time_start : mstime();
    /* If we are running in the context of a slave, return ASAP:     * the slave key expiration is controlled by the master that will     * send us synthesized DEL operations for expired keys.     *     * Still we try to return the right information to the caller,     * that is, 0 if we think the key should be still valid, 1 if     * we think the key is expired at this time. */    if (server.masterhost != NULL) return now > when;
    /* Return when this key has not expired */    // 如果還沒到期就直接返回    if (now <= when) return 0;
    /* Delete the key */    server.stat_expiredkeys++;    // key過期，是一個(gè)寫動(dòng)作，需要傳播到 AOF 或者 slaves...    propagateExpire(db,key,server.lazyfree_lazy_expire);    // pub/sub 監(jiān)控通知    notifyKeyspaceEvent(NOTIFY_EXPIRED,        "expired",key,db->id);    // 同步刪除或者異步刪除, 稍后討論    return server.lazyfree_lazy_expire ? dbAsyncDelete(db,key) :                                         dbSyncDelete(db,key);}
/* Return the expire time of the specified key, or -1 if no expire * is associated with this key (i.e. the key is non volatile) */long long getExpire(redisDb *db, robj *key) {    dictEntry *de;    /* No expire? return ASAP */    // 查找過期隊(duì)列, 數(shù)據(jù)量小    if (dictSize(db->expires) == 0 ||       (de = dictFind(db->expires,key->ptr)) == NULL) return -1;
    /* The entry was found in the expire dict, this means it should also     * be present in the main dict (safety check). */    serverAssertWithInfo(NULL,key,dictFind(db->dict,key->ptr) != NULL);    // 返回到期時(shí)間戳, union 的應(yīng)用    return dictGetSignedIntegerVal(de);}
// 刪除過期數(shù)據(jù)key的兩種方式，同步+異步// db.c, 同步刪除, 刪除 expires 隊(duì)列和 dict 數(shù)據(jù)/* Delete a key, value, and associated expiration entry if any, from the DB */int dbSyncDelete(redisDb *db, robj *key) {    /* Deleting an entry from the expires dict will not free the sds of     * the key, because it is shared with the main dictionary. */    if (dictSize(db->expires) > 0) dictDelete(db->expires,key->ptr);    if (dictDelete(db->dict,key->ptr) == DICT_OK) {        if (server.cluster_enabled) slotToKeyDel(key);        return 1;    } else {        return 0;    }}// lazyfree.c, 異步刪除過期數(shù)據(jù), 一看就很復(fù)雜/* Delete a key, value, and associated expiration entry if any, from the DB. * If there are enough allocations to free the value object may be put into * a lazy free list instead of being freed synchronously. The lazy free list * will be reclaimed in a different bio.c thread. */#define LAZYFREE_THRESHOLD 64int dbAsyncDelete(redisDb *db, robj *key) {    /* Deleting an entry from the expires dict will not free the sds of     * the key, because it is shared with the main dictionary. */    if (dictSize(db->expires) > 0) dictDelete(db->expires,key->ptr);
    /* If the value is composed of a few allocations, to free in a lazy way     * is actually just slower... So under a certain limit we just free     * the object synchronously. */    dictEntry *de = dictFind(db->dict,key->ptr);    if (de) {        robj *val = dictGetVal(de);        // 判斷刪除的數(shù)據(jù)的影響范圍，與 數(shù)據(jù)類型有關(guān)，string為1，hash/set則計(jì)算count，list計(jì)算length        size_t free_effort = lazyfreeGetFreeEffort(val);
        /* If releasing the object is too much work, let's put it into the         * lazy free list. */        if (free_effort > LAZYFREE_THRESHOLD) {            // 將相關(guān)的數(shù)據(jù)放入隊(duì)列中，后臺(tái)任務(wù)慢慢刪除            atomicIncr(lazyfree_objects,1,&lazyfree_objects_mutex);            bioCreateBackgroundJob(BIO_LAZY_FREE,val,NULL,NULL);            // 自身則立即設(shè)置為 NULL            dictSetVal(db->dict,de,NULL);        }    }
    /* Release the key-val pair, or just the key if we set the val     * field to NULL in order to lazy free it later. */    if (dictDelete(db->dict,key->ptr) == DICT_OK) {        if (server.cluster_enabled) slotToKeyDel(key);        return 1;    } else {        return 0;    }}

// t_string.c, set 的所有用法都統(tǒng)一 setCommand, 多個(gè)參數(shù)共同解析為 flags/* SET key value [NX] [XX] [EX <seconds>] [PX <milliseconds>] */void setCommand(client *c) {    int j;    robj *expire = NULL;    int unit = UNIT_SECONDS;    int flags = OBJ_SET_NO_FLAGS;
    for (j = 3; j < c->argc; j++) {        char *a = c->argv[j]->ptr;        robj *next = (j == c->argc-1) ? NULL : c->argv[j+1];        // NX 與 XX 互斥        if ((a[0] == 'n' || a[0] == 'N') &&            (a[1] == 'x' || a[1] == 'X') && a[2] == '\0' &&            !(flags & OBJ_SET_XX))        {            flags |= OBJ_SET_NX;        } else if ((a[0] == 'x' || a[0] == 'X') &&                   (a[1] == 'x' || a[1] == 'X') && a[2] == '\0' &&                   !(flags & OBJ_SET_NX))        {            flags |= OBJ_SET_XX;        }         // PX 與 EX 互斥        else if ((a[0] == 'e' || a[0] == 'E') &&                   (a[1] == 'x' || a[1] == 'X') && a[2] == '\0' &&                   !(flags & OBJ_SET_PX) && next)        {            flags |= OBJ_SET_EX;            unit = UNIT_SECONDS;            expire = next;            j++;        } else if ((a[0] == 'p' || a[0] == 'P') &&                   (a[1] == 'x' || a[1] == 'X') && a[2] == '\0' &&                   !(flags & OBJ_SET_EX) && next)        {            flags |= OBJ_SET_PX;            unit = UNIT_MILLISECONDS;            expire = next;            j++;        } else {            addReply(c,shared.syntaxerr);            return;        }    }    // 嘗試壓縮 value 值以節(jié)省空間 (原始命令: set key value)    c->argv[2] = tryObjectEncoding(c->argv[2]);    setGenericCommand(c,flags,c->argv[1],c->argv[2],expire,unit,NULL,NULL);}// object.c, 壓縮字符串/* Try to encode a string object in order to save space */robj *tryObjectEncoding(robj *o) {    long value;    sds s = o->ptr;    size_t len;
    /* Make sure this is a string object, the only type we encode     * in this function. Other types use encoded memory efficient     * representations but are handled by the commands implementing     * the type. */    serverAssertWithInfo(NULL,o,o->type == OBJ_STRING);
    /* We try some specialized encoding only for objects that are     * RAW or EMBSTR encoded, in other words objects that are still     * in represented by an actually array of chars. */    if (!sdsEncodedObject(o)) return o;
    /* It's not safe to encode shared objects: shared objects can be shared     * everywhere in the "object space" of Redis and may end in places where     * they are not handled. We handle them only as values in the keyspace. */     if (o->refcount > 1) return o;
    /* Check if we can represent this string as a long integer.     * Note that we are sure that a string larger than 21 chars is not     * representable as a 32 nor 64 bit integer. */    len = sdslen(s);    // 針對(duì)小于21個(gè)字符串的字符，嘗試轉(zhuǎn)為 long 型    if (len <= 21 && string2l(s,len,&value)) {        /* This object is encodable as a long. Try to use a shared object.         * Note that we avoid using shared integers when maxmemory is used         * because every object needs to have a private LRU field for the LRU         * algorithm to work well. */        if ((server.maxmemory == 0 ||             (server.maxmemory_policy != MAXMEMORY_VOLATILE_LRU &&              server.maxmemory_policy != MAXMEMORY_ALLKEYS_LRU)) &&            value >= 0 &&            value < OBJ_SHARED_INTEGERS)        {            decrRefCount(o);            incrRefCount(shared.integers[value]);            return shared.integers[value];        } else {            if (o->encoding == OBJ_ENCODING_RAW) sdsfree(o->ptr);            o->encoding = OBJ_ENCODING_INT;            o->ptr = (void*) value;            return o;        }    }
    /* If the string is small and is still RAW encoded,     * try the EMBSTR encoding which is more efficient.     * In this representation the object and the SDS string are allocated     * in the same chunk of memory to save space and cache misses. */    // 44    if (len <= OBJ_ENCODING_EMBSTR_SIZE_LIMIT) {        robj *emb;
        if (o->encoding == OBJ_ENCODING_EMBSTR) return o;        // 使用 EMBSTR 編碼轉(zhuǎn)換，實(shí)際就是同一個(gè) s 返回        emb = createEmbeddedStringObject(s,sdslen(s));        decrRefCount(o);        return emb;    }
    /* We can't encode the object...     *     * Do the last try, and at least optimize the SDS string inside     * the string object to require little space, in case there     * is more than 10% of free space at the end of the SDS string.     *     * We do that only for relatively large strings as this branch     * is only entered if the length of the string is greater than     * OBJ_ENCODING_EMBSTR_SIZE_LIMIT. */    if (o->encoding == OBJ_ENCODING_RAW &&        sdsavail(s) > len/10)    {        o->ptr = sdsRemoveFreeSpace(o->ptr);    }
    /* Return the original object. */    return o;}// sds.c, 去除無用空間占用/* Reallocate the sds string so that it has no free space at the end. The * contained string remains not altered, but next concatenation operations * will require a reallocation. * * After the call, the passed sds string is no longer valid and all the * references must be substituted with the new pointer returned by the call. */sds sdsRemoveFreeSpace(sds s) {    void *sh, *newsh;    // s[-1] 指針不越界, 它是在新建一個(gè) sds 對(duì)象時(shí)，在該指針前一位寫入的值，確定sds類型    char type, oldtype = s[-1] & SDS_TYPE_MASK;    int hdrlen;    size_t len = sdslen(s);    // sdsHdrSize: sds頭部大小    sh = (char*)s-sdsHdrSize(oldtype);
    type = sdsReqType(len);    hdrlen = sdsHdrSize(type);    if (oldtype==type) {        newsh = s_realloc(sh, hdrlen+len+1);        if (newsh == NULL) return NULL;        s = (char*)newsh+hdrlen;    } else {        newsh = s_malloc(hdrlen+len+1);        if (newsh == NULL) return NULL;        memcpy((char*)newsh+hdrlen, s, len+1);        s_free(sh);        s = (char*)newsh+hdrlen;        s[-1] = type;        sdssetlen(s, len);    }    sdssetalloc(s, len);    return s;}
// t_string.c, expire 為超時(shí)時(shí)間設(shè)置void setGenericCommand(client *c, int flags, robj *key, robj *val, robj *expire, int unit, robj *ok_reply, robj *abort_reply) {    long long milliseconds = 0; /* initialized to avoid any harmness warning */
    if (expire) {        // 解析 expire 到 milliseconds 中        if (getLongLongFromObjectOrReply(c, expire, &milliseconds, NULL) != C_OK)            return;        if (milliseconds <= 0) {            addReplyErrorFormat(c,"invalid expire time in %s",c->cmd->name);            return;        }        if (unit == UNIT_SECONDS) milliseconds *= 1000;    }    // 語法限制檢測, NX 要求不存在, XX 要求存在    if ((flags & OBJ_SET_NX && lookupKeyWrite(c->db,key) != NULL) ||        (flags & OBJ_SET_XX && lookupKeyWrite(c->db,key) == NULL))    {        addReply(c, abort_reply ? abort_reply : shared.nullbulk);        return;    }    // 切實(shí)存儲(chǔ) kv    setKey(c->db,key,val);    server.dirty++;    // 設(shè)置超時(shí)    if (expire) setExpire(c->db,key,mstime()+milliseconds);    // 通知pub/sub變更    notifyKeyspaceEvent(NOTIFY_STRING,"set",key,c->db->id);    // 通知expire事件    if (expire) notifyKeyspaceEvent(NOTIFY_GENERIC,        "expire",key,c->db->id);    addReply(c, ok_reply ? ok_reply : shared.ok);}// object.c, int getLongLongFromObjectOrReply(client *c, robj *o, long long *target, const char *msg) {    long long value;    if (getLongLongFromObject(o, &value) != C_OK) {        if (msg != NULL) {            addReplyError(c,(char*)msg);        } else {            addReplyError(c,"value is not an integer or out of range");        }        return C_ERR;    }    *target = value;    return C_OK;}// object.c, int getLongLongFromObject(robj *o, long long *target) {    long long value;
    if (o == NULL) {        value = 0;    } else {        serverAssertWithInfo(NULL,o,o->type == OBJ_STRING);        // 將字符串轉(zhuǎn)換為 long 型，得到超時(shí)時(shí)間        if (sdsEncodedObject(o)) {            if (strict_strtoll(o->ptr,&value) == C_ERR) return C_ERR;        } else if (o->encoding == OBJ_ENCODING_INT) {            value = (long)o->ptr;        } else {            serverPanic("Unknown string encoding");        }    }    if (target) *target = value;    return C_OK;}

// db.c, set kv/* High level Set operation. This function can be used in order to set * a key, whatever it was existing or not, to a new object. * * 1) The ref count of the value object is incremented. * 2) clients WATCHing for the destination key notified. * 3) The expire time of the key is reset (the key is made persistent). */void setKey(redisDb *db, robj *key, robj *val) {    // 先查找，再更新    if (lookupKeyWrite(db,key) == NULL) {        // 新增 kv        dbAdd(db,key,val);    } else {        // 覆蓋 kv        dbOverwrite(db,key,val);    }    // 增加 value 的引用計(jì)數(shù)    incrRefCount(val);    // 新增的元素，移出過期隊(duì)列    removeExpire(db,key);    signalModifiedKey(db,key);}robj *lookupKeyWrite(redisDb *db, robj *key) {    // 先嘗試過期處理，再查找db (hash 查找 db->dic)    expireIfNeeded(db,key);    return lookupKey(db,key);}
// db.c, 添加kv/* Add the key to the DB. It's up to the caller to increment the reference * counter of the value if needed. * * The program is aborted if the key already exists. */void dbAdd(redisDb *db, robj *key, robj *val) {    sds copy = sdsdup(key->ptr);    // 添加到 db->dict 中    int retval = dictAdd(db->dict, copy, val);
    serverAssertWithInfo(NULL,key,retval == C_OK);    // list 類型的數(shù)據(jù)，進(jìn)行特殊處理（阻塞）    if (val->type == OBJ_LIST) signalListAsReady(db, key);    // 集群添加    if (server.cluster_enabled) slotToKeyAdd(key); }// db.c /* Slot to Key API. This is used by Redis Cluster in order to obtain in * a fast way a key that belongs to a specified hash slot. This is useful * while rehashing the cluster. */void slotToKeyAdd(robj *key) {    // hash 定位 slot, 下面我們簡單看下該算法    unsigned int hashslot = keyHashSlot(key->ptr,sdslen(key->ptr));
    sds sdskey = sdsdup(key->ptr);    // 添加key 到 server.cluster->slots_to_keys 的 跳表中    zslInsert(server.cluster->slots_to_keys,hashslot,sdskey);}// cluster.c, slot 定位算法, 其實(shí)就是 crc16算法與上 0x3FFF，該算法決定了 slot 最多只能有 16383 個(gè)/* We have 16384 hash slots. The hash slot of a given key is obtained * as the least significant 14 bits of the crc16 of the key. * * However if the key contains the {...} pattern, only the part between * { and } is hashed. This may be useful in the future to force certain * keys to be in the same node (assuming no resharding is in progress). */unsigned int keyHashSlot(char *key, int keylen) {    int s, e; /* start-end indexes of { and } */
    for (s = 0; s < keylen; s++)        if (key[s] == '{') break;
    /* No '{' ? Hash the whole key. This is the base case. */    if (s == keylen) return crc16(key,keylen) & 0x3FFF;
    /* '{' found? Check if we have the corresponding '}'. */    for (e = s+1; e < keylen; e++)        if (key[e] == '}') break;
    /* No '}' or nothing betweeen {} ? Hash the whole key. */    if (e == keylen || e == s+1) return crc16(key,keylen) & 0x3FFF;
    /* If we are here there is both a { and a } on its right. Hash     * what is in the middle between { and }. */    return crc16(key+s+1,e-s-1) & 0x3FFF;}
// db.c, 設(shè)置key的超時(shí)標(biāo)識(shí)void setExpire(redisDb *db, robj *key, long long when) {    dictEntry *kde, *de;
    /* Reuse the sds from the main dict in the expire dict */    kde = dictFind(db->dict,key->ptr);    serverAssertWithInfo(NULL,key,kde != NULL);    // 將需要超時(shí)檢測的 key 添加到 db->expires 隊(duì)列中    de = dictReplaceRaw(db->expires,dictGetKey(kde));    // 設(shè)置超時(shí)時(shí)間為 when    dictSetSignedIntegerVal(de,when);}// dict.h#define dictSetSignedIntegerVal(entry, _val_) \    do { entry->v.s64 = _val_; } while(0)