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);
}

void spopCommand(redisClient *c) {
    robj *set, *ele, *aux;
    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) {
        ele = createStringObjectFromLongLong(llele);
        set->ptr = intsetRemove(set->ptr,llele,NULL);
    } else {
        incrRefCount(ele);
        setTypeRemove(set,ele);
    }
    notifyKeyspaceEvent(REDIS_NOTIFY_SET,"spop",c->argv[1],c->db->id);

    /* Replicate/AOF this command as an SREM operation */
    aux = createStringObject("SREM",4);
    rewriteClientCommandVector(c,3,aux,c->argv[1],ele);
    decrRefCount(ele);
    decrRefCount(aux);

    addReplyBulk(c,ele);
    if (setTypeSize(set) == 0) {
        dbDelete(c->db,c->argv[1]);
        notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",c->argv[1],c->db->id);
    }
    signalModifiedKey(c->db,c->argv[1]);
    server.dirty++;
}

void sremCommand(redisClient *c) {
    robj *set;
    int j, deleted = 0, keyremoved = 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]);
                keyremoved = 1;
                break;
            }
        }
    }
    if (deleted) {
        signalModifiedKey(c->db,c->argv[1]);
        notifyKeyspaceEvent(REDIS_NOTIFY_SET,"srem",c->argv[1],c->db->id);
        if (keyremoved)
            notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",c->argv[1],
                                c->db->id);
        server.dirty += deleted;
    }
    addReplyLongLong(c,deleted);
}

void scardCommand(redisClient *c) {
    robj *o;

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

    addReplyLongLong(c,setTypeSize(o));
}

void smoveCommand(client *c) {
    robj *srcset, *dstset, *ele;
    srcset = lookupKeyWrite(c->db,c->argv[1]);
    dstset = lookupKeyWrite(c->db,c->argv[2]);
    ele = c->argv[3];

    /* If the source key does not exist return 0 */
    if (srcset == NULL) {
        addReply(c,shared.czero);
        return;
    }

    /* If the source key has the wrong type, or the destination key
     * is set and has the wrong type, return with an error. */
    if (checkType(c,srcset,OBJ_SET) ||
        (dstset && checkType(c,dstset,OBJ_SET))) return;

    /* If srcset and dstset are equal, SMOVE is a no-op */
    if (srcset == dstset) {
        addReply(c,setTypeIsMember(srcset,ele->ptr) ?
            shared.cone : shared.czero);
        return;
    }

    /* If the element cannot be removed from the src set, return 0. */
    if (!setTypeRemove(srcset,ele->ptr)) {
        addReply(c,shared.czero);
        return;
    }
    notifyKeyspaceEvent(NOTIFY_SET,"srem",c->argv[1],c->db->id);

    /* Remove the src set from the database when empty */
    if (setTypeSize(srcset) == 0) {
        dbDelete(c->db,c->argv[1]);
        notifyKeyspaceEvent(NOTIFY_GENERIC,"del",c->argv[1],c->db->id);
    }

    /* Create the destination set when it doesn't exist */
    if (!dstset) {
        dstset = setTypeCreate(ele->ptr);
        dbAdd(c->db,c->argv[2],dstset);
    }

    signalModifiedKey(c->db,c->argv[1]);
    signalModifiedKey(c->db,c->argv[2]);
    server.dirty++;

    /* An extra key has changed when ele was successfully added to dstset */
    if (setTypeAdd(dstset,ele->ptr)) {
        server.dirty++;
        notifyKeyspaceEvent(NOTIFY_SET,"sadd",c->argv[2],c->db->id);
    }
    addReply(c,shared.cone);
}

/*SMOVE source destination member*/
void smoveCommand(redisClient *c) {//将member元素从source集合移动到destination集合
    robj *srcset, *dstset, *ele;
    srcset = lookupKeyWrite(c->db,c->argv[1]);
    dstset = lookupKeyWrite(c->db,c->argv[2]);
    ele = c->argv[3] = tryObjectEncoding(c->argv[3]);

    /* If the source key does not exist return 0 */
    if (srcset == NULL) {
        addReply(c,shared.czero);
        return;
    }

    /* If the source key has the wrong type, or the destination key
     * is set and has the wrong type, return with an error. */
    if (checkType(c,srcset,REDIS_SET) ||
        (dstset && checkType(c,dstset,REDIS_SET))) return;

    /* If srcset and dstset are equal, SMOVE is a no-op */
    if (srcset == dstset) {
        addReply(c,shared.cone);
        return;
    }

    /* If the element cannot be removed from the src set, return 0. */
    if (!setTypeRemove(srcset,ele)) {//从源集合中删除member元素
        addReply(c,shared.czero);
        return;
    }
    notifyKeyspaceEvent(REDIS_NOTIFY_SET,"srem",c->argv[1],c->db->id);

    /* Remove the src set from the database when empty */
    if (setTypeSize(srcset) == 0) {//移除member元素后，源集合为空，删除
        dbDelete(c->db,c->argv[1]);
        notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",c->argv[1],c->db->id);
    }
    signalModifiedKey(c->db,c->argv[1]);
    signalModifiedKey(c->db,c->argv[2]);
    server.dirty++;

    /* Create the destination set when it doesn't exist */
    if (!dstset) {//目标集合不存在，则新建
        dstset = setTypeCreate(ele);
        dbAdd(c->db,c->argv[2],dstset);
    }

    /* An extra key has changed when ele was successfully added to dstset */
    if (setTypeAdd(dstset,ele)) {//添加member元素到目标集合
        server.dirty++;
        notifyKeyspaceEvent(REDIS_NOTIFY_SET,"sadd",c->argv[2],c->db->id);
    }
    addReply(c,shared.cone);
}

void smoveCommand(redisClient* c)
{
    robj* srcset, *dstset, *ele;
    srcset = lookupKeyWrite(c->db, c->argv[1]);
    dstset = lookupKeyWrite(c->db, c->argv[2]);
    ele = c->argv[3] = tryObjectEncoding(c->argv[3]);

    /* If the source key does not exist return 0 */
    if (srcset == NULL) {
        addReply(c, shared.czero);
        return;
    }

    /* If the source key has the wrong type, or the destination key
     * is set and has the wrong type, return with an error. */
    if (checkType(c, srcset, REDIS_SET) ||
        (dstset && checkType(c, dstset, REDIS_SET))) {
        return;
    }

    /* If srcset and dstset are equal, SMOVE is a no-op */
    if (srcset == dstset) {
        addReply(c, shared.cone);
        return;
    }

    /* If the element cannot be removed from the src set, return 0. */
    if (!setTypeRemove(srcset, ele)) {
        addReply(c, shared.czero);
        return;
    }

    /* Remove the src set from the database when empty */
    if (setTypeSize(srcset) == 0) {
        dbDelete(c->db, c->argv[1]);
    }
    signalModifiedKey(c->db, c->argv[1]);
    signalModifiedKey(c->db, c->argv[2]);
    server.dirty++;

    /* Create the destination set when it doesn't exist */
    if (!dstset) {
        dstset = setTypeCreate(ele);
        dbAdd(c->db, c->argv[2], dstset);
    }

    /* An extra key has changed when ele was successfully added to dstset */
    if (setTypeAdd(dstset, ele)) {
        server.dirty++;
    }
    addReply(c, shared.cone);
}

void spopCommand(client *c) {
    robj *set, *ele, *aux;
    sds sdsele;
    int64_t llele;
    int encoding;

    if (c->argc == 3) {
        spopWithCountCommand(c);
        return;
    } else if (c->argc > 3) {
        addReply(c,shared.syntaxerr);
        return;
    }

    /* Make sure a key with the name inputted exists, and that it's type is
     * indeed a set */
    if ((set = lookupKeyWriteOrReply(c,c->argv[1],shared.nullbulk)) == NULL ||
        checkType(c,set,OBJ_SET)) return;

    /* Get a random element from the set */
    encoding = setTypeRandomElement(set,&sdsele,&llele);

    /* Remove the element from the set */
    if (encoding == OBJ_ENCODING_INTSET) {
        ele = createStringObjectFromLongLong(llele);
        set->ptr = intsetRemove(set->ptr,llele,NULL);
    } else {
        ele = createStringObject(sdsele,sdslen(sdsele));
        setTypeRemove(set,ele->ptr);
    }

    notifyKeyspaceEvent(NOTIFY_SET,"spop",c->argv[1],c->db->id);

    /* Replicate/AOF this command as an SREM operation */
    aux = createStringObject("SREM",4);
    rewriteClientCommandVector(c,3,aux,c->argv[1],ele);
    decrRefCount(aux);

    /* Add the element to the reply */
    addReplyBulk(c,ele);
    decrRefCount(ele);

    /* Delete the set if it's empty */
    if (setTypeSize(set) == 0) {
        dbDelete(c->db,c->argv[1]);
        notifyKeyspaceEvent(NOTIFY_GENERIC,"del",c->argv[1],c->db->id);
    }

    /* Set has been modified */
    signalModifiedKey(c->db,c->argv[1]);
    server.dirty++;
}

void sremCommand(redisClient *c) {
    robj *set;

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

    c->argv[2] = tryObjectEncoding(c->argv[2]);
    if (setTypeRemove(set,c->argv[2])) {
        if (setTypeSize(set) == 0) dbDelete(c->db,c->argv[1]);
        touchWatchedKey(c->db,c->argv[1]);
        server.dirty++;
        addReply(c,shared.cone);
    } else {
        addReply(c,shared.czero);
    }
}

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++;
}

//.........这里部分代码省略.........
            return;
        }
        if (checkType(c,setobj,OBJ_SET)) {
            zfree(sets);
            return;
        }
        sets[j] = setobj;
    }
    /* Sort sets from the smallest to largest, this will improve our
     * algorithm's performance */
    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,&elesds,&intobj)) != -1) {
        for (j = 1; j < setnum; j++) {
            if (sets[j] == sets[0]) continue;
            if (encoding == OBJ_ENCODING_INTSET) {
                /* intset with intset is simple... and fast */
                if (sets[j]->encoding == OBJ_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 == OBJ_ENCODING_HT) {
                    elesds = sdsfromlonglong(intobj);
                    if (!setTypeIsMember(sets[j],elesds)) {
                        sdsfree(elesds);
                        break;
                    }
                    sdsfree(elesds);
                }
            } else if (encoding == OBJ_ENCODING_HT) {
                if (!setTypeIsMember(sets[j],elesds)) {
                    break;
                }
            }
        }

        /* Only take action when all sets contain the member */
        if (j == setnum) {
            if (!dstkey) {
                if (encoding == OBJ_ENCODING_HT)
                    addReplyBulkCBuffer(c,elesds,sdslen(elesds));
                else
                    addReplyBulkLongLong(c,intobj);
                cardinality++;
            } else {
                if (encoding == OBJ_ENCODING_INTSET) {
                    elesds = sdsfromlonglong(intobj);
                    setTypeAdd(dstset,elesds);
                    sdsfree(elesds);
                } else {
                    setTypeAdd(dstset,elesds);
                }
            }
        }
    }
    setTypeReleaseIterator(si);

    if (dstkey) {
        /* Store the resulting set into the target, if the intersection
         * is not an empty set. */
        int deleted = dbDelete(c->db,dstkey);
        if (setTypeSize(dstset) > 0) {
            dbAdd(c->db,dstkey,dstset);
            addReplyLongLong(c,setTypeSize(dstset));
            notifyKeyspaceEvent(NOTIFY_SET,"sinterstore",
                dstkey,c->db->id);
        } else {
            decrRefCount(dstset);
            addReply(c,shared.czero);
            if (deleted)
                notifyKeyspaceEvent(NOTIFY_GENERIC,"del",
                    dstkey,c->db->id);
        }
        signalModifiedKey(c->db,dstkey);
        server.dirty++;
    } else {
        setDeferredMultiBulkLength(c,replylen,cardinality);
    }
    zfree(sets);
}

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;
    int diff_algo = 1;

    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;
    }

    /* Select what DIFF algorithm to use.
     *
     * Algorithm 1 is O(N*M) where N is the size of the element first set
     * and M the total number of sets.
     *
     * Algorithm 2 is O(N) where N is the total number of elements in all
     * the sets.
     *
     * We compute what is the best bet with the current input here. */
    if (op == REDIS_OP_DIFF && sets[0]) {
        long long algo_one_work = 0, algo_two_work = 0;

        for (j = 0; j < setnum; j++) {
            if (sets[j] == NULL) continue;

            algo_one_work += setTypeSize(sets[0]);
            algo_two_work += setTypeSize(sets[j]);
        }

        /* Algorithm 1 has better constant times and performs less operations
         * if there are elements in common. Give it some advantage. */
        algo_one_work /= 2;
        diff_algo = (algo_one_work <= algo_two_work) ? 1 : 2;

        if (diff_algo == 1 && setnum > 1) {
            /* With algorithm 1 it is better to order the sets to subtract
             * by decreasing size, so that we are more likely to find
             * duplicated elements ASAP. */
            qsort(sets+1,setnum-1,sizeof(robj*),
                qsortCompareSetsByRevCardinality);
        }
    }

    /* 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();

    if (op == REDIS_OP_UNION) {
        /* Union is trivial, just add every element of every set to the
         * temporary set. */
        for (j = 0; j < setnum; j++) {
            if (!sets[j]) continue; /* non existing keys are like empty sets */

            si = setTypeInitIterator(sets[j]);
            while((ele = setTypeNextObject(si)) != NULL) {
                if (setTypeAdd(dstset,ele)) cardinality++;
                decrRefCount(ele);
            }
            setTypeReleaseIterator(si);
        }
    } else if (op == REDIS_OP_DIFF && sets[0] && diff_algo == 1) {
        /* DIFF Algorithm 1:
         *
         * We perform the diff by iterating all the elements of the first set,
         * and only adding it to the target set if the element does not exist
         * into all the other sets.
         *
         * This way we perform at max N*M operations, where N is the size of
         * the first set, and M the number of sets. */
        si = setTypeInitIterator(sets[0]);
        while((ele = setTypeNextObject(si)) != NULL) {
            for (j = 1; j < setnum; j++) {
                if (!sets[j]) continue; /* no key is an empty set. */
                if (sets[j] == sets[0]) break; /* same set! */
                if (setTypeIsMember(sets[j],ele)) break;
            }
            if (j == setnum) {
                /* There is no other set with this element. Add it. */
                setTypeAdd(dstset,ele);
                cardinality++;
            }
            decrRefCount(ele);
        }
        setTypeReleaseIterator(si);
    } else if (op == REDIS_OP_DIFF && sets[0] && diff_algo == 2) {
        /* DIFF Algorithm 2:
         *
//.........这里部分代码省略.........

//.........这里部分代码省略.........
     * 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 */
    /**
        求多个集合交集的算法思想：
        首先按照集合元素个数对集合进行qsort，然后遍历排序后的第一个集合中的元素，查看该元素在
        其他集合中是否存在，如果在其他集合中都存在，那么该元素为一个结果
    */
    si = setTypeInitIterator(sets[0]);
    while((encoding = setTypeNext(si,&eleobj,&intobj)) != -1) {
        for (j = 1; j < setnum; j++) {
            if (sets[j] == sets[0]) continue;//这段代码没意义啊
            if (encoding == REDIS_ENCODING_INTSET) {//intset
                /* intset with intset is simple... and fast */
                //集合sets[j]编码为intset
                if (sets[j]->encoding == REDIS_ENCODING_INTSET &&
                    !intsetFind((intset*)sets[j]->ptr,intobj))//在集合sets[j]中没有找到集合sets[0]的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) {//集合sets[j]编码为HT，sets[0]为INTSET
                    eleobj = createStringObjectFromLongLong(intobj);//将sets[0]中的intobj转换为sds
                    if (!setTypeIsMember(sets[j],eleobj)) {//如果eleobj不在集合sets[j]中
                        decrRefCount(eleobj);
                        break;
                    }
                    decrRefCount(eleobj);
                }
            } else if (encoding == REDIS_ENCODING_HT) {//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 {//添加到临时目标集合
                if (encoding == REDIS_ENCODING_INTSET) {
                    eleobj = createStringObjectFromLongLong(intobj);
                    setTypeAdd(dstset,eleobj);
                    decrRefCount(eleobj);
                } else {
                    setTypeAdd(dstset,eleobj);
                }
            }
        }
    }
    setTypeReleaseIterator(si);

    if (dstkey) {
        /* Store the resulting set into the target, if the intersection
         * is not an empty set. */
        int deleted = dbDelete(c->db,dstkey);//覆盖原来的目标集合
        if (setTypeSize(dstset) > 0) {
            dbAdd(c->db,dstkey,dstset);
            addReplyLongLong(c,setTypeSize(dstset));
            notifyKeyspaceEvent(REDIS_NOTIFY_SET,"sinterstore",
                dstkey,c->db->id);
        } else {//空集
            decrRefCount(dstset);
            addReply(c,shared.czero);
            if (deleted)
                notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",
                    dstkey,c->db->id);
        }
        signalModifiedKey(c->db,dstkey);
        server.dirty++;
    } else {
        setDeferredMultiBulkLength(c,replylen,cardinality);
    }
    zfree(sets);
}

/* This is used by SDIFF and in this case we can receive NULL that should
 * be handled as empty sets. */
int qsortCompareSetsByRevCardinality(const void *s1, const void *s2) {
    robj *o1 = *(robj**)s1, *o2 = *(robj**)s2;

    return  (o2 ? setTypeSize(o2) : 0) - (o1 ? setTypeSize(o1) : 0);
}

void srandmemberWithCountCommand(redisClient *c) {
    long l;
    unsigned long count, size;
    int uniq = 1;
    robj *set, *ele;
    int64_t llele;
    int encoding;

    dict *d;

    if (getLongFromObjectOrReply(c,c->argv[2],&l,NULL) != REDIS_OK) return;
    if (l >= 0) {
        count = (unsigned) l;
    } else {
        /* A negative count means: return the same elements multiple times
         * (i.e. don't remove the extracted element after every extraction). */
        count = -l;
        uniq = 0;
    }

    if ((set = lookupKeyReadOrReply(c,c->argv[1],shared.emptymultibulk))
        == NULL || checkType(c,set,REDIS_SET)) return;
    size = setTypeSize(set);

    /* If count is zero, serve it ASAP to avoid special cases later. */
    if (count == 0) {
        addReply(c,shared.emptymultibulk);
        return;
    }

    /* CASE 1: The count was negative, so the extraction method is just:
     * "return N random elements" sampling the whole set every time.
     * This case is trivial and can be served without auxiliary data
     * structures. */
    if (!uniq) {
        addReplyMultiBulkLen(c,count);
        while(count--) {
            encoding = setTypeRandomElement(set,&ele,&llele);
            if (encoding == REDIS_ENCODING_INTSET) {
                addReplyBulkLongLong(c,llele);
            } else {
                addReplyBulk(c,ele);
            }
        }
        return;
    }

    /* CASE 2:
     * The number of requested elements is greater than the number of
     * elements inside the set: simply return the whole set. */
    if (count >= size) {
        sunionDiffGenericCommand(c,c->argv+1,1,NULL,REDIS_OP_UNION);
        return;
    }

    /* For CASE 3 and CASE 4 we need an auxiliary dictionary. */
    d = dictCreate(&setDictType,NULL);

    /* CASE 3:
     * The number of elements inside the set is not greater than
     * SRANDMEMBER_SUB_STRATEGY_MUL times the number of requested elements.
     * In this case we create a set from scratch with all the elements, and
     * subtract random elements to reach the requested number of elements.
     *
     * This is done because if the number of requsted elements is just
     * a bit less than the number of elements in the set, the natural approach
     * used into CASE 3 is highly inefficient. */
    if (count*SRANDMEMBER_SUB_STRATEGY_MUL > size) {
        setTypeIterator *si;

        /* Add all the elements into the temporary dictionary. */
        si = setTypeInitIterator(set);
        while((encoding = setTypeNext(si,&ele,&llele)) != -1) {
            int retval = DICT_ERR;

            if (encoding == REDIS_ENCODING_INTSET) {
                retval = dictAdd(d,createStringObjectFromLongLong(llele),NULL);
            } else if (ele->encoding == REDIS_ENCODING_RAW) {
                retval = dictAdd(d,dupStringObject(ele),NULL);
            } else if (ele->encoding == REDIS_ENCODING_INT) {
                retval = dictAdd(d,
                    createStringObjectFromLongLong((long)ele->ptr),NULL);
            }
            redisAssert(retval == DICT_OK);
        }
        setTypeReleaseIterator(si);
        redisAssert(dictSize(d) == size);

        /* Remove random elements to reach the right count. */
        while(size > count) {
            dictEntry *de;

            de = dictGetRandomKey(d);
            dictDelete(d,dictGetKey(de));
            size--;
        }
    }

    /* CASE 4: We have a big set compared to the requested number of elements.
     * In this case we can simply get random elements from the set and add
//.........这里部分代码省略.........

void spopWithCountCommand(redisClient *c) {
    long l;
    unsigned long count, size;
    robj *set;

    /* Get the count argument */
    if (getLongFromObjectOrReply(c,c->argv[2],&l,NULL) != REDIS_OK) return;
    if (l >= 0) {
        count = (unsigned) l;
    } else {
        addReply(c,shared.outofrangeerr);
        return;
    }

    /* Make sure a key with the name inputted exists, and that it's type is
     * indeed a set. Otherwise, return nil */
    if ((set = lookupKeyReadOrReply(c,c->argv[1],shared.emptymultibulk))
        == NULL || checkType(c,set,REDIS_SET)) return;

    /* If count is zero, serve an empty multibulk ASAP to avoid special
     * cases later. */
    if (count == 0) {
        addReply(c,shared.emptymultibulk);
        return;
    }

    size = setTypeSize(set);

    /* Generate an SPOP keyspace notification */
    notifyKeyspaceEvent(REDIS_NOTIFY_SET,"spop",c->argv[1],c->db->id);
    server.dirty += count;

    /* CASE 1:
     * The number of requested elements is greater than or equal to
     * the number of elements inside the set: simply return the whole set. */
    if (count >= size) {
        /* We just return the entire set */
        sunionDiffGenericCommand(c,c->argv+1,1,NULL,REDIS_OP_UNION);

        /* Delete the set as it is now empty */
        dbDelete(c->db,c->argv[1]);
        notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",c->argv[1],c->db->id);

        /* Propagate this command as an DEL operation */
        rewriteClientCommandVector(c,2,shared.del,c->argv[1]);
        signalModifiedKey(c->db,c->argv[1]);
        server.dirty++;
        return;
    }

    /* Case 2 and 3 require to replicate SPOP as a set of SERM commands.
     * Prepare our replication argument vector. Also send the array length
     * which is common to both the code paths. */
    robj *propargv[3];
    propargv[0] = createStringObject("SREM",4);
    propargv[1] = c->argv[1];
    addReplyMultiBulkLen(c,count);

    /* Common iteration vars. */
    robj *objele;
    int encoding;
    int64_t llele;
    unsigned long remaining = size-count; /* Elements left after SPOP. */

    /* If we are here, the number of requested elements is less than the
     * number of elements inside the set. Also we are sure that count < size.
     * Use two different strategies.
     *
     * CASE 2: The number of elements to return is small compared to the
     * set size. We can just extract random elements and return them to
     * the set. */
    if (remaining*SPOP_MOVE_STRATEGY_MUL > count) {
        while(count--) {
            encoding = setTypeRandomElement(set,&objele,&llele);
            if (encoding == REDIS_ENCODING_INTSET) {
                objele = createStringObjectFromLongLong(llele);
            } else {
                incrRefCount(objele);
            }

            /* Return the element to the client and remove from the set. */
            addReplyBulk(c,objele);
            setTypeRemove(set,objele);

            /* Replicate/AOF this command as an SREM operation */
            propargv[2] = objele;
            alsoPropagate(server.sremCommand,c->db->id,propargv,3,
                REDIS_PROPAGATE_AOF|REDIS_PROPAGATE_REPL);
            decrRefCount(objele);
        }
    } else {
    /* CASE 3: The number of elements to return is very big, approaching
     * the size of the set itself. After some time extracting random elements
     * from such a set becomes computationally expensive, so we use
     * a different strategy, we extract random elements that we don't
     * want to return (the elements that will remain part of the set),
     * creating a new set as we do this (that will be stored as the original
     * set). Then we return the elements left in the original set and
     * release it. */
        robj *newset = NULL;
//.........这里部分代码省略.........

int qsortCompareSetsByCardinality(const void *s1, const void *s2) {
    return setTypeSize(*(robj**)s1)-setTypeSize(*(robj**)s2);
}

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);
}

//.........这里部分代码省略.........
            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);
                    setTypeAdd(dstset,eleobj);
                    decrRefCount(eleobj);
                } else {
                    setTypeAdd(dstset,eleobj);
                }
            }
        }
    }
    setTypeReleaseIterator(si);

    if (dstkey) {
        /* Store the resulting set into the target, if the intersection
         * is not an empty set. */
        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++;
    } else {
        setDeferredMultiBulkLength(c,replylen,cardinality);
    }
    zfree(sets);
}