void spopCommand(redisClient *c) {
    robj *set, *ele;
    int64_t llele;
    int encoding;

    if ((set = lookupKeyWriteOrReply(c,c->argv[1],shared.nullbulk)) == NULL ||
        checkType(c,set,REDIS_SET)) return;

    encoding = setTypeRandomElement(set,&ele,&llele);
    if (encoding == REDIS_ENCODING_INTSET) {
        addReplyBulkLongLong(c,llele);
        set->ptr = intsetRemove(set->ptr,llele,NULL);
    } else {
        addReplyBulk(c,ele);
        setTypeRemove(set,ele);
    }
    if (setTypeSize(set) == 0) dbDelete(c->db,c->argv[1]);
    touchWatchedKey(c->db,c->argv[1]);
    server.dirty++;
}

void expireGenericCommand(redisClient *c, robj *key, robj *param, long offset) {
    dictEntry *de;
    long seconds;

    if (getLongFromObjectOrReply(c, param, &seconds, NULL) != REDIS_OK) return;

    seconds -= offset;

    de = dictFind(c->db->dict,key->ptr);
    if (de == NULL) {
        addReply(c,shared.czero);
        return;
    }
    /* EXPIRE with negative TTL, or EXPIREAT with a timestamp into the past
     * should never be executed as a DEL when load the AOF or in the context
     * of a slave instance.
     *
     * Instead we take the other branch of the IF statement setting an expire
     * (possibly in the past) and wait for an explicit DEL from the master. */
    if (seconds <= 0 && !server.loading && !server.masterhost) {
        robj *aux;

        redisAssert(dbDelete(c->db,key));
        server.dirty++;

        /* Replicate/AOF this as an explicit DEL. */
        aux = createStringObject("DEL",3);
        rewriteClientCommandVector(c,2,aux,key);
        decrRefCount(aux);
        touchWatchedKey(c->db,key);
        addReply(c, shared.cone);
        return;
    } else {
        time_t when = time(NULL)+seconds;
        setExpire(c->db,key,when);
        addReply(c,shared.cone);
        touchWatchedKey(c->db,key);
        server.dirty++;
        return;
    }
}

void moveCommand(redisClient *c) {
    robj *o;
    redisDb *src, *dst;
    int srcid;

    /* Obtain source and target DB pointers */
    src = c->db;
    srcid = c->db->id;
    if (selectDb(c,atoi(c->argv[2]->ptr)) == REDIS_ERR) {
        addReply(c,shared.outofrangeerr);
        return;
    }
    dst = c->db;
    selectDb(c,srcid); /* Back to the source DB */

    /* If the user is moving using as target the same
     * DB as the source DB it is probably an error. */
    if (src == dst) {
        addReply(c,shared.sameobjecterr);
        return;
    }

    /* Check if the element exists and get a reference */
    o = lookupKeyWrite(c->db,c->argv[1]);
    if (!o) {
        addReply(c,shared.czero);
        return;
    }

    /* Try to add the element to the target DB */
    if (dbAdd(dst,c->argv[1],o) == REDIS_ERR) {
        addReply(c,shared.czero);
        return;
    }
    incrRefCount(o);

    /* OK! key moved, free the entry in the source DB */
    dbDelete(src,c->argv[1]);
    server.dirty++;
    addReply(c,shared.cone);
}

void zremrangebyscoreCommand(redisClient *c) {
    double min;
    double max;
    long deleted;
    robj *zsetobj;
    zset *zs;

    if ((getDoubleFromObjectOrReply(c, c->argv[2], &min, NULL) != REDIS_OK) ||
        (getDoubleFromObjectOrReply(c, c->argv[3], &max, NULL) != REDIS_OK)) return;

    if ((zsetobj = lookupKeyWriteOrReply(c,c->argv[1],shared.czero)) == NULL ||
        checkType(c,zsetobj,REDIS_ZSET)) return;

    zs = zsetobj->ptr;
    deleted = zslDeleteRangeByScore(zs->zsl,min,max,zs->dict);
    if (htNeedsResize(zs->dict)) dictResize(zs->dict);
    if (dictSize(zs->dict) == 0) dbDelete(c->db,c->argv[1]);
    if (deleted) touchWatchedKey(c->db,c->argv[1]);
    server.dirty += deleted;
    addReplyLongLong(c,deleted);
}

void lremCommand(redisClient *c) {
    robj *subject, *obj;
    obj = c->argv[3] = tryObjectEncoding(c->argv[3]);
    int toremove = atoi(c->argv[2]->ptr);
    int removed = 0;
    listTypeEntry entry;

    subject = lookupKeyWriteOrReply(c,c->argv[1],shared.czero);
    if (subject == NULL || checkType(c,subject,REDIS_LIST)) return;

    /* Make sure obj is raw when we're dealing with a ziplist */
    if (subject->encoding == REDIS_ENCODING_ZIPLIST)
        obj = getDecodedObject(obj);

    listTypeIterator *li;
    if (toremove < 0) {
        toremove = -toremove;
        li = listTypeInitIterator(subject,-1,REDIS_HEAD);
    } else {
        li = listTypeInitIterator(subject,0,REDIS_TAIL);
    }

    while (listTypeNext(li,&entry)) {
        if (listTypeEqual(&entry,obj)) {
            listTypeDelete(&entry);
            server.dirty++;
            removed++;
            if (toremove && removed == toremove) break;
        }
    }
    listTypeReleaseIterator(li);

    /* Clean up raw encoded object */
    if (subject->encoding == REDIS_ENCODING_ZIPLIST)
        decrRefCount(obj);

    if (listTypeLength(subject) == 0) dbDelete(c->db,c->argv[1]);
    addReplyLongLong(c,removed);
    if (removed) signalModifiedKey(c->db,c->argv[1]);
}

void popGenericCommand(redisClient *c, int where) {
    robj *o = lookupKeyWriteOrReply(c,c->argv[1],shared.nullbulk);
    if (o == NULL || checkType(c,o,REDIS_LIST)) return;

    robj *value = listTypePop(o,where);
    if (value == NULL) {
        addReply(c,shared.nullbulk);
    } else {
        char *event = (where == REDIS_HEAD) ? "lpop" : "rpop";

        addReplyBulk(c,value);
        decrRefCount(value);
        notifyKeyspaceEvent(REDIS_NOTIFY_LIST,event,c->argv[1],c->db->id);
        if (listTypeLength(o) == 0) {
            notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",
                                c->argv[1],c->db->id);
            dbDelete(c->db,c->argv[1]);
        }
        signalModifiedKey(c->db,c->argv[1]);
        server.dirty++;
    }
}

void rpoplpushCommand(redisClient *c) {
    robj *sobj, *value;
    if ((sobj = lookupKeyWriteOrReply(c,c->argv[1],shared.nullbulk)) == NULL ||
        checkType(c,sobj,REDIS_LIST)) return;

    if (listTypeLength(sobj) == 0) {
        addReply(c,shared.nullbulk);
    } else {
        robj *dobj = lookupKeyWrite(c->db,c->argv[2]);
        if (dobj && checkType(c,dobj,REDIS_LIST)) return;
        value = listTypePop(sobj,REDIS_TAIL);
        rpoplpushHandlePush(c,c->argv[2],dobj,value);

        /* listTypePop returns an object with its refcount incremented */
        decrRefCount(value);

        /* Delete the source list when it is empty */
        if (listTypeLength(sobj) == 0) dbDelete(c->db,c->argv[1]);
        touchWatchedKey(c->db,c->argv[1]);
        server.dirty++;
    }
}

void sremCommand(redisClient *c) {
    robj *set;
    int j, deleted = 0;

    if ((set = lookupKeyWriteOrReply(c,c->argv[1],shared.czero)) == NULL ||
        checkType(c,set,REDIS_SET)) return;

    for (j = 2; j < c->argc; j++) {
        if (setTypeRemove(set,c->argv[j])) {
            deleted++;
            if (setTypeSize(set) == 0) {
                dbDelete(c->db,c->argv[1]);
                break;
            }
        }
    }
    if (deleted) {
        signalModifiedKey(c->db,c->argv[1]);
        server.dirty += deleted;
    }
    addReplyLongLong(c,deleted);
}

int expireIfNeeded(redisDb *db, robj *key) {
    mstime_t when = getExpire(db,key);//微秒
    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 */
    if (now <= when) return 0;

    /* Delete the key */
    server.stat_expiredkeys++;

    propagateExpire(db,key);
    //事件函数的处理
    notifyKeyspaceEvent(REDIS_NOTIFY_EXPIRED,
                        "expired",key,db->id);
    //删除该键
    return dbDelete(db,key);
}

void rpoplpushCommand(redisClient *c) {
    robj *sobj, *value;
    int slotnum1 = keyHashSlot(c->argv[1]->ptr, sdslen(c->argv[1]->ptr));
    int slotnum2 = keyHashSlot(c->argv[2]->ptr, sdslen(c->argv[2]->ptr));
    if ((sobj = lookupKeyWriteOrReply(c,c->argv[1],shared.nullbulk,slotnum1)) == NULL ||
        checkType(c,sobj,REDIS_LIST)) return;

    if (listTypeLength(sobj) == 0) {
        /* This may only happen after loading very old RDB files. Recent
         * versions of Redis delete keys of empty lists. */
        addReply(c,shared.nullbulk);
    } else {
        robj *dobj = lookupKeyWrite(c->db,c->argv[2],slotnum2);
        robj *touchedkey = c->argv[1];

        if (dobj && checkType(c,dobj,REDIS_LIST)) return;
        value = listTypePop(sobj,REDIS_TAIL);
        /* We saved touched key, and protect it, since rpoplpushHandlePush
         * may change the client command argument vector (it does not
         * currently). */
        incrRefCount(touchedkey);
        rpoplpushHandlePush(c,c->argv[2],dobj,value,slotnum2);

        /* listTypePop returns an object with its refcount incremented */
        decrRefCount(value);

        /* Delete the source list when it is empty */
        notifyKeyspaceEvent(REDIS_NOTIFY_LIST,"rpop",touchedkey,c->db->id);
        if (listTypeLength(sobj) == 0) {
            dbDelete(c->db,touchedkey,slotnum1);
            notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",
                                touchedkey,c->db->id);
        }
        signalModifiedKey(c->db,touchedkey,slotnum1);
        decrRefCount(touchedkey);
        server.dirty++;
    }
}

void zremrangebyrankCommand(redisClient *c) {
    long start;
    long end;
    int llen;
    long deleted;
    robj *zsetobj;
    zset *zs;

    if ((getLongFromObjectOrReply(c, c->argv[2], &start, NULL) != REDIS_OK) ||
        (getLongFromObjectOrReply(c, c->argv[3], &end, NULL) != REDIS_OK)) return;

    if ((zsetobj = lookupKeyWriteOrReply(c,c->argv[1],shared.czero)) == NULL ||
        checkType(c,zsetobj,REDIS_ZSET)) return;
    zs = zsetobj->ptr;
    llen = zs->zsl->length;

    /* convert negative indexes */
    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);
        return;
    }
    if (end >= llen) end = llen-1;

    /* increment start and end because zsl*Rank functions
     * use 1-based rank */
    deleted = zslDeleteRangeByRank(zs->zsl,start+1,end+1,zs->dict);
    if (htNeedsResize(zs->dict)) dictResize(zs->dict);
    if (dictSize(zs->dict) == 0) dbDelete(c->db,c->argv[1]);
    if (deleted) touchWatchedKey(c->db,c->argv[1]);
    server.dirty += deleted;
    addReplyLongLong(c, deleted);
}

void zremrangebyscoreCommand(redisClient *c) {
    zrangespec range;
    long deleted;
    robj *o;
    zset *zs;

    /* Parse the range arguments. */
    if (zslParseRange(c->argv[2],c->argv[3],&range) != REDIS_OK) {
        addReplyError(c,"min or max is not a double");
        return;
    }

    if ((o = lookupKeyWriteOrReply(c,c->argv[1],shared.czero)) == NULL ||
        checkType(c,o,REDIS_ZSET)) return;

    zs = o->ptr;
    deleted = zslDeleteRangeByScore(zs->zsl,range,zs->dict);
    if (htNeedsResize(zs->dict)) dictResize(zs->dict);
    if (dictSize(zs->dict) == 0) dbDelete(c->db,c->argv[1]);
    if (deleted) touchWatchedKey(c->db,c->argv[1]);
    server.dirty += deleted;
    addReplyLongLong(c,deleted);
}

void rpoplpushCommand(redisClient *c) {
    robj *sobj, *value;
    if ((sobj = lookupKeyWriteOrReply(c,c->argv[1],shared.nullbulk)) == NULL ||
        checkType(c,sobj,REDIS_LIST)) return;

    if (listTypeLength(sobj) == 0) {
        /* This may only happen after loading very old RDB files. Recent
         * versions of Redis delete keys of empty lists. */
        addReply(c,shared.nullbulk);
    } else {
        robj *dobj = lookupKeyWrite(c->db,c->argv[2]);
        robj *touchedkey = c->argv[1];

        if (dobj && checkType(c,dobj,REDIS_LIST)) return;
        value = listTypePop(sobj,REDIS_TAIL);
        /* We saved touched key, and protect it, since rpoplpushHandlePush
         * may change the client command argument vector. */
        incrRefCount(touchedkey);
        rpoplpushHandlePush(c,c,c->argv[2],dobj,value);

        /* listTypePop returns an object with its refcount incremented */
        decrRefCount(value);

        /* Delete the source list when it is empty */
        if (listTypeLength(sobj) == 0) dbDelete(c->db,touchedkey);
        signalModifiedKey(c->db,touchedkey);
        decrRefCount(touchedkey);
        server.dirty++;

        /* Replicate this as a simple RPOP since the LPUSH side is replicated
         * by rpoplpushHandlePush() call if needed (it may not be needed
         * if a client is blocking wait a push against the list). */
        rewriteClientCommandVector(c,2,
            resetRefCount(createStringObject("RPOP",4)),
            c->argv[1]);
    }
}

int expireIfNeeded(redisDb *db, robj *key) {
    time_t when = getExpire(db,key);

    if (when < 0) return 0; /* No expire for this key */

    /* 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 time(NULL) > when;
    }

    /* Return when this key has not expired */
    if (time(NULL) <= when) return 0;

    /* Delete the key */
    server.stat_expiredkeys++;
    propagateExpire(db,key);
    return dbDelete(db,key);
}

void delCommand(redisClient *c) {
    int deleted = 0, j;

    for (j = 1; j < c->argc; j++) {
        if (server.ds_enabled) {
            lookupKeyRead(c->db,c->argv[j]);
            /* FIXME: this can be optimized a lot, no real need to load
             * a possibly huge value. */
        }
        if (dbDelete(c->db,c->argv[j])) {
            signalModifiedKey(c->db,c->argv[j]);
            server.dirty++;
            deleted++;
        } else if (server.ds_enabled) {
            if (cacheKeyMayExist(c->db,c->argv[j]) &&
                dsExists(c->db,c->argv[j]))
            {
                cacheScheduleIO(c->db,c->argv[j],REDIS_IO_SAVE);
                deleted = 1;
            }
        }
    }
    addReplyLongLong(c,deleted);
}

//.........这里部分代码省略.........
            } else {
                zfree(src);
                addReply(c,shared.syntaxerr);
                return;
            }
        }
    }

    /* sort sets from the smallest to largest, this will improve our
     * algorithm's performance */
    qsort(src,setnum,sizeof(zsetopsrc),qsortCompareZsetopsrcByCardinality);

    dstobj = createZsetObject();
    dstzset = dstobj->ptr;

    if (op == REDIS_OP_INTER) {
        /* skip going over all entries if the smallest zset is NULL or empty */
        if (src[0].dict && dictSize(src[0].dict) > 0) {
            /* precondition: as src[0].dict is non-empty and the zsets are ordered
             * from small to large, all src[i > 0].dict are non-empty too */
            di = dictGetIterator(src[0].dict);
            while((de = dictNext(di)) != NULL) {
                double score, value;

                score = src[0].weight * zunionInterDictValue(de);
                for (j = 1; j < setnum; j++) {
                    dictEntry *other = dictFind(src[j].dict,dictGetEntryKey(de));
                    if (other) {
                        value = src[j].weight * zunionInterDictValue(other);
                        zunionInterAggregate(&score,value,aggregate);
                    } else {
                        break;
                    }
                }

                /* Only continue when present in every source dict. */
                if (j == setnum) {
                    robj *o = dictGetEntryKey(de);
                    znode = zslInsert(dstzset->zsl,score,o);
                    incrRefCount(o); /* added to skiplist */
                    dictAdd(dstzset->dict,o,&znode->score);
                    incrRefCount(o); /* added to dictionary */
                }
            }
            dictReleaseIterator(di);
        }
    } else if (op == REDIS_OP_UNION) {
        for (i = 0; i < setnum; i++) {
            if (!src[i].dict) continue;

            di = dictGetIterator(src[i].dict);
            while((de = dictNext(di)) != NULL) {
                double score, value;

                /* skip key when already processed */
                if (dictFind(dstzset->dict,dictGetEntryKey(de)) != NULL)
                    continue;

                /* initialize score */
                score = src[i].weight * zunionInterDictValue(de);

                /* because the zsets are sorted by size, its only possible
                 * for sets at larger indices to hold this entry */
                for (j = (i+1); j < setnum; j++) {
                    dictEntry *other = dictFind(src[j].dict,dictGetEntryKey(de));
                    if (other) {
                        value = src[j].weight * zunionInterDictValue(other);
                        zunionInterAggregate(&score,value,aggregate);
                    }
                }

                robj *o = dictGetEntryKey(de);
                znode = zslInsert(dstzset->zsl,score,o);
                incrRefCount(o); /* added to skiplist */
                dictAdd(dstzset->dict,o,&znode->score);
                incrRefCount(o); /* added to dictionary */
            }
            dictReleaseIterator(di);
        }
    } else {
        /* unknown operator */
        redisAssert(op == REDIS_OP_INTER || op == REDIS_OP_UNION);
    }

    if (dbDelete(c->db,dstkey)) {
        touchWatchedKey(c->db,dstkey);
        touched = 1;
        server.dirty++;
    }
    if (dstzset->zsl->length) {
        dbAdd(c->db,dstkey,dstobj);
        addReplyLongLong(c, dstzset->zsl->length);
        if (!touched) touchWatchedKey(c->db,dstkey);
        server.dirty++;
    } else {
        decrRefCount(dstobj);
        addReply(c, shared.czero);
    }
    zfree(src);
}

//函数会在redis每次执行完单个命令，事务块或lua脚本之后被调用
//对于所有被阻塞在client的key来说，只要key被执行了PUSH，那么这个key会被加入到server.ready_keys中
//处理client的阻塞状态
void handleClientsBlockedOnLists(void) {
    //只要server.ready_keys还有要解除阻塞的key，就循环遍历server.ready_keys链表
    while(listLength(server.ready_keys) != 0) {
        list *l;

        /* Point server.ready_keys to a fresh list and save the current one
         * locally. This way as we run the old list we are free to call
         * signalListAsReady() that may push new elements in server.ready_keys
         * when handling clients blocked into BRPOPLPUSH. */
        //备份一个server.ready_keys链表
        l = server.ready_keys;
        //生成一个新的空链表
        server.ready_keys = listCreate();

        //只要链表中还有就绪的key
        while(listLength(l) != 0) {
            listNode *ln = listFirst(l);    //链表头结点地址
            readyList *rl = ln->value;      //保存链表节点的值，每个值都是readyList结构

            /* First of all remove this key from db->ready_keys so that
             * we can safely call signalListAsReady() against this key. */
            //从rl->db->ready_keys中删除就绪的key
            dictDelete(rl->db->ready_keys,rl->key);

            /* If the key exists and it's a list, serve blocked clients
             * with data. */
            //以读操作将就绪key的值读出来
            robj *o = lookupKeyWrite(rl->db,rl->key);
            //读出的value对象必须是列表类型
            if (o != NULL && o->type == OBJ_LIST) {
                dictEntry *de;

                /* We serve clients in the same order they blocked for
                 * this key, from the first blocked to the last. */
                // blocking_keys是一个字典，字典的键是造成client阻塞的键，字典的值是链表，保存被阻塞的client
                // 根据key取出被阻塞的client
                de = dictFind(rl->db->blocking_keys,rl->key);
                // 链表非空
                if (de) {
                    // 获取de节点的值
                    list *clients = dictGetVal(de);
                    // 获取链表的长度
                    int numclients = listLength(clients);

                    //遍历链表的所有节点
                    while(numclients--) {
                        // 第一个client节点地址
                        listNode *clientnode = listFirst(clients);
                        // 取出节点的值，是一个client类型
                        client *receiver = clientnode->value;
                        // 从client类型中的target获得要PUSH出的dstkey，该键保存在target中
                        robj *dstkey = receiver->bpop.target;
                        // 获取弹出的位置，根据BRPOPLPUSH命令
                        int where = (receiver->lastcmd &&
                                     receiver->lastcmd->proc == blpopCommand) ?
                                    LIST_HEAD : LIST_TAIL;
                        // 从列表中弹出元素
                        robj *value = listTypePop(o,where);

                        // 弹出成功
                        if (value) {
                            /* Protect receiver->bpop.target, that will be
                             * freed by the next unblockClient()
                             * call. */
                            //增加dstkey的引用计数，保护该键，在unblockClient函数中释放
                            if (dstkey) incrRefCount(dstkey);
                            //取消client的阻塞状态
                            unblockClient(receiver);

                            // 将value推入造成client阻塞的键上，
                            if (serveClientBlockedOnList(receiver,
                                rl->key,dstkey,rl->db,value,
                                where) == C_ERR)
                            {
                                /* If we failed serving the client we need
                                 * to also undo the POP operation. */
                                    // 如果推入失败，则需要键弹出的value还原回去
                                    listTypePush(o,value,where);
                            }
                            // 释放dstkey和value
                            if (dstkey) decrRefCount(dstkey);
                            decrRefCount(value);
                        } else {
                            break;
                        }
                    }
                }

                // 如果弹出了所有元素，将key从数据库中删除
                if (listTypeLength(o) == 0) {
                    dbDelete(rl->db,rl->key);
                }
                /* We don't call signalModifiedKey() as it was already called
                 * when an element was pushed on the list. */
            }

            /* Free this item. */
//.........这里部分代码省略.........

// BRPOP BLPOP 命令的底层实现
//  BLPOP key [key ...] timeout
void blockingPopGenericCommand(client *c, int where) {
    robj *o;
    mstime_t timeout;
    int j;

    // 以秒为单位取出timeout值
    if (getTimeoutFromObjectOrReply(c,c->argv[c->argc-1],&timeout,UNIT_SECONDS)
        != C_OK) return;

    //遍历所有的key
    for (j = 1; j < c->argc-1; j++) {
        //以写操作取出当前key的值
        o = lookupKeyWrite(c->db,c->argv[j]);
        // value对象不为空
        if (o != NULL) {
            // 如果value对象的类型不是列表类型，发送类型错误信息
            if (o->type != OBJ_LIST) {
                addReply(c,shared.wrongtypeerr);
                return;
            } else {
                // 列表长度不为0
                if (listTypeLength(o) != 0) {
                    /* Non empty list, this is like a non normal [LR]POP. */
                    // 保存事件名称
                    char *event = (where == LIST_HEAD) ? "lpop" : "rpop";
                    // 保存弹出的value对象
                    robj *value = listTypePop(o,where);
                    serverAssert(value != NULL);

                    // 发送回复给client
                    addReplyMultiBulkLen(c,2);
                    addReplyBulk(c,c->argv[j]);
                    addReplyBulk(c,value);
                    // 释放value
                    decrRefCount(value);
                    // 发送事件通知
                    notifyKeyspaceEvent(NOTIFY_LIST,event,
                                        c->argv[j],c->db->id);
                    //如果弹出元素后列表为空
                    if (listTypeLength(o) == 0) {
                        //从数据库中删除当前的key
                        dbDelete(c->db,c->argv[j]);
                        // 发送"del"的事件通知
                        notifyKeyspaceEvent(NOTIFY_GENERIC,"del",
                                            c->argv[j],c->db->id);
                    }
                    //数据库的键被修改，发送信号
                    signalModifiedKey(c->db,c->argv[j]);
                    //更新脏键
                    server.dirty++;

                    /* Replicate it as an [LR]POP instead of B[LR]POP. */
                    // 传播一个[LR]POP 而不是B[LR]POP
                    rewriteClientCommandVector(c,2,
                        (where == LIST_HEAD) ? shared.lpop : shared.rpop,
                        c->argv[j]);
                    return;
                }
            }
        }
    }

    /* If we are inside a MULTI/EXEC and the list is empty the only thing
     * we can do is treating it as a timeout (even with timeout 0). */
    // 如果命令在一个事务中执行，则发送一个空回复以避免死等待
    if (c->flags & CLIENT_MULTI) {
        addReply(c,shared.nullmultibulk);
        return;
    }

    /* If the list is empty or the key does not exists we must block */
    // 参数中的所有键都不存在，则阻塞这些键
    blockForKeys(c, c->argv + 1, c->argc - 2, timeout, NULL);
}

void sunionDiffGenericCommand(redisClient *c, robj **setkeys, int setnum, robj *dstkey, int op) {
    robj **sets = zmalloc(sizeof(robj*)*setnum);
    setTypeIterator *si;
    robj *ele, *dstset = NULL;
    int j, cardinality = 0;

    for (j = 0; j < setnum; j++) {
        robj *setobj = dstkey ?
            lookupKeyWrite(c->db,setkeys[j]) :
            lookupKeyRead(c->db,setkeys[j]);
        if (!setobj) {
            sets[j] = NULL;
            continue;
        }
        if (checkType(c,setobj,REDIS_SET)) {
            zfree(sets);
            return;
        }
        sets[j] = setobj;
    }

    /* We need a temp set object to store our union. If the dstkey
     * is not NULL (that is, we are inside an SUNIONSTORE operation) then
     * this set object will be the resulting object to set into the target key*/
    dstset = createIntsetObject();

    /* Iterate all the elements of all the sets, add every element a single
     * time to the result set */
    for (j = 0; j < setnum; j++) {
        if (op == REDIS_OP_DIFF && j == 0 && !sets[j]) break; /* result set is empty */
        if (!sets[j]) continue; /* non existing keys are like empty sets */

        si = setTypeInitIterator(sets[j]);
        while((ele = setTypeNextObject(si)) != NULL) {
            if (op == REDIS_OP_UNION || j == 0) {
                if (setTypeAdd(dstset,ele)) {
                    cardinality++;
                }
            } else if (op == REDIS_OP_DIFF) {
                if (setTypeRemove(dstset,ele)) {
                    cardinality--;
                }
            }
            decrRefCount(ele);
        }
        setTypeReleaseIterator(si);

        /* Exit when result set is empty. */
        if (op == REDIS_OP_DIFF && cardinality == 0) break;
    }

    /* Output the content of the resulting set, if not in STORE mode */
    if (!dstkey) {
        addReplyMultiBulkLen(c,cardinality);
        si = setTypeInitIterator(dstset);
        while((ele = setTypeNextObject(si)) != NULL) {
            addReplyBulk(c,ele);
            decrRefCount(ele);
        }
        setTypeReleaseIterator(si);
        decrRefCount(dstset);
    } else {
        /* If we have a target key where to store the resulting set
         * create this key with the result set inside */
        dbDelete(c->db,dstkey);
        if (setTypeSize(dstset) > 0) {
            dbAdd(c->db,dstkey,dstset);
            addReplyLongLong(c,setTypeSize(dstset));
        } else {
            decrRefCount(dstset);
            addReply(c,shared.czero);
        }
        touchWatchedKey(c->db,dstkey);
        server.dirty++;
    }
    zfree(sets);
}

void sinterGenericCommand(redisClient *c, robj **setkeys, unsigned long setnum, robj *dstkey) {
    robj **sets = zmalloc(sizeof(robj*)*setnum);
    setTypeIterator *si;
    robj *eleobj, *dstset = NULL;
    int64_t intobj;
    void *replylen = NULL;
    unsigned long j, cardinality = 0;
    int encoding;

    for (j = 0; j < setnum; j++) {
        robj *setobj = dstkey ?
            lookupKeyWrite(c->db,setkeys[j]) :
            lookupKeyRead(c->db,setkeys[j]);
        if (!setobj) {
            zfree(sets);
            if (dstkey) {
                if (dbDelete(c->db,dstkey)) {
                    touchWatchedKey(c->db,dstkey);
                    server.dirty++;
                }
                addReply(c,shared.czero);
            } else {
                addReply(c,shared.emptymultibulk);
            }
            return;
        }
        if (checkType(c,setobj,REDIS_SET)) {
            zfree(sets);
            return;
        }
        sets[j] = setobj;
    }
    /* Sort sets from the smallest to largest, this will improve our
     * algorithm's performace */
    qsort(sets,setnum,sizeof(robj*),qsortCompareSetsByCardinality);

    /* The first thing we should output is the total number of elements...
     * since this is a multi-bulk write, but at this stage we don't know
     * the intersection set size, so we use a trick, append an empty object
     * to the output list and save the pointer to later modify it with the
     * right length */
    if (!dstkey) {
        replylen = addDeferredMultiBulkLength(c);
    } else {
        /* If we have a target key where to store the resulting set
         * create this key with an empty set inside */
        dstset = createIntsetObject();
    }

    /* Iterate all the elements of the first (smallest) set, and test
     * the element against all the other sets, if at least one set does
     * not include the element it is discarded */
    si = setTypeInitIterator(sets[0]);
    while((encoding = setTypeNext(si,&eleobj,&intobj)) != -1) {
        for (j = 1; j < setnum; j++) {
            if (encoding == REDIS_ENCODING_INTSET) {
                /* intset with intset is simple... and fast */
                if (sets[j]->encoding == REDIS_ENCODING_INTSET &&
                    !intsetFind((intset*)sets[j]->ptr,intobj))
                {
                    break;
                /* in order to compare an integer with an object we
                 * have to use the generic function, creating an object
                 * for this */
                } else if (sets[j]->encoding == REDIS_ENCODING_HT) {
                    eleobj = createStringObjectFromLongLong(intobj);
                    if (!setTypeIsMember(sets[j],eleobj)) {
                        decrRefCount(eleobj);
                        break;
                    }
                    decrRefCount(eleobj);
                }
            } else if (encoding == REDIS_ENCODING_HT) {
                /* Optimization... if the source object is integer
                 * encoded AND the target set is an intset, we can get
                 * a much faster path. */
                if (eleobj->encoding == REDIS_ENCODING_INT &&
                    sets[j]->encoding == REDIS_ENCODING_INTSET &&
                    !intsetFind((intset*)sets[j]->ptr,(long)eleobj->ptr))
                {
                    break;
                /* else... object to object check is easy as we use the
                 * type agnostic API here. */
                } else if (!setTypeIsMember(sets[j],eleobj)) {
                    break;
                }
            }
        }

        /* Only take action when all sets contain the member */
        if (j == setnum) {
            if (!dstkey) {
                if (encoding == REDIS_ENCODING_HT)
                    addReplyBulk(c,eleobj);
                else
                    addReplyBulkLongLong(c,intobj);
                cardinality++;
            } else {
                if (encoding == REDIS_ENCODING_INTSET) {
                    eleobj = createStringObjectFromLongLong(intobj);
//.........这里部分代码省略.........