void freeListObject(robj *o) {
    switch (o->encoding) {
    case REDIS_ENCODING_LINKEDLIST:
        listRelease((list*) o->ptr);
        break;
    case REDIS_ENCODING_ZIPLIST:
        zfree(o->ptr);
        break;
    default:
        redisPanic("Unknown list encoding type");
    }
}

/* Return random element from a non empty set.
 * The returned element can be a int64_t value if the set is encoded
 * as an "intset" blob of integers, or a redis object if the set
 * is a regular set.
 *
 * The caller provides both pointers to be populated with the right
 * object. The return value of the function is the object->encoding
 * field of the object and is used by the caller to check if the
 * int64_t pointer or the redis object pointer was populated.
 *
 * When an object is returned (the set was a real set) the ref count
 * of the object is not incremented so this function can be considered
 * copy on write friendly. */
int setTypeRandomElement(robj* setobj, robj** objele, int64_t* llele)
{
    if (setobj->encoding == REDIS_ENCODING_HT) {
        dictEntry* de = dictGetRandomKey(setobj->ptr);
        *objele = dictGetKey(de);
    } else if (setobj->encoding == REDIS_ENCODING_INTSET) {
        *llele = intsetRandom(setobj->ptr);
    } else {
        redisPanic("Unknown set encoding");
    }
    return setobj->encoding;
}

/* 执行后台的job,参数内包含着哪种type */
void *bioProcessBackgroundJobs(void *arg) {
    struct bio_job *job;
    unsigned long type = (unsigned long) arg;
    sigset_t sigset;

    /* Make the thread killable at any time, so that bioKillThreads()
     * can work reliably. */
    pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
    pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);

    pthread_mutex_lock(&bio_mutex[type]);
    /* Block SIGALRM so we are sure that only the main thread will
     * receive the watchdog signal. */
    sigemptyset(&sigset);
    sigaddset(&sigset, SIGALRM);
    if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
        redisLog(REDIS_WARNING,
            "Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno));

    while(1) {
        listNode *ln;

        /* The loop always starts with the lock hold. */
        if (listLength(bio_jobs[type]) == 0) {
            pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
            continue;
        }
        /* Pop the job from the queue. */
        //从工作列表中取出第一个job
        ln = listFirst(bio_jobs[type]);
        job = ln->value;
        /* It is now possible to unlock the background system as we know have
         * a stand alone job structure to process.*/
        pthread_mutex_unlock(&bio_mutex[type]);

        /* Process the job accordingly to its type. */
        //执行具体的工作
        if (type == REDIS_BIO_CLOSE_FILE) {
            close((long)job->arg1);
        } else if (type == REDIS_BIO_AOF_FSYNC) {
            aof_fsync((long)job->arg1);
        } else {
            redisPanic("Wrong job type in bioProcessBackgroundJobs().");
        }
        zfree(job);

        /* Lock again before reiterating the loop, if there are no longer
         * jobs to process we'll block again in pthread_cond_wait(). */
        pthread_mutex_lock(&bio_mutex[type]);
        listDelNode(bio_jobs[type],ln);
        bio_pending[type]--;
    }
}

void freeSetObject(robj *o) {
    switch (o->encoding) {
    case REDIS_ENCODING_HT:
        dictRelease((dict*) o->ptr);
        break;
    case REDIS_ENCODING_INTSET:
        zfree(o->ptr);
        break;
    default:
        redisPanic("Unknown set encoding type");
    }
}

void decrRefCount(void *obj) {
    robj *o = obj;

    /* Object is a swapped out value, or in the process of being loaded. */
    if (server.vm_enabled &&
        (o->storage == REDIS_VM_SWAPPED || o->storage == REDIS_VM_LOADING))
    {
        vmpointer *vp = obj;
        if (o->storage == REDIS_VM_LOADING) vmCancelThreadedIOJob(o);
        vmMarkPagesFree(vp->page,vp->usedpages);
        server.vm_stats_swapped_objects--;
        zfree(vp);
        return;
    }

    if (o->refcount <= 0) redisPanic("decrRefCount against refcount <= 0");
    /* Object is in memory, or in the process of being swapped out.
     *
     * If the object is being swapped out, abort the operation on
     * decrRefCount even if the refcount does not drop to 0: the object
     * is referenced at least two times, as value of the key AND as
     * job->val in the iojob. So if we don't invalidate the iojob, when it is
     * done but the relevant key was removed in the meantime, the
     * complete jobs handler will not find the key about the job and the
     * assert will fail. */
    if (server.vm_enabled && o->storage == REDIS_VM_SWAPPING)
        vmCancelThreadedIOJob(o);
    if (--(o->refcount) == 0) {
        switch(o->type) {
        case REDIS_STRING: freeStringObject(o); break;
        case REDIS_LIST: freeListObject(o); break;
        case REDIS_SET: freeSetObject(o); break;
        case REDIS_ZSET: freeZsetObject(o); break;
        case REDIS_HASH: freeHashObject(o); break;
        default: redisPanic("Unknown object type"); break;
        }
        o->ptr = NULL; /* defensive programming. We'll see NULL in traces. */
        zfree(o);
    }
}

void ltrimCommand(redisClient *c) {
    robj *o;
    long start, end, llen, j, ltrim, rtrim;
    list *list;
    listNode *ln;

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

    if ((o = lookupKeyWriteOrReply(c,c->argv[1],shared.ok)) == NULL ||
        checkType(c,o,REDIS_LIST)) return;
    llen = listTypeLength(o);

    /* 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) {
        /* Out of range start or start > end result in empty list */
        ltrim = llen;
        rtrim = 0;
    } else {
        if (end >= llen) end = llen-1;
        ltrim = start;
        rtrim = llen-end-1;
    }

    /* Remove list elements to perform the trim */
    if (o->encoding == REDIS_ENCODING_ZIPLIST) {
        o->ptr = ziplistDeleteRange(o->ptr,0,ltrim);
        o->ptr = ziplistDeleteRange(o->ptr,-rtrim,rtrim);
    } else if (o->encoding == REDIS_ENCODING_LINKEDLIST) {
        list = o->ptr;
        for (j = 0; j < ltrim; j++) {
            ln = listFirst(list);
            listDelNode(list,ln);
        }
        for (j = 0; j < rtrim; j++) {
            ln = listLast(list);
            listDelNode(list,ln);
        }
    } else {
        redisPanic("Unknown list encoding");
    }
    if (listTypeLength(o) == 0) dbDelete(c->db,c->argv[1]);
    signalModifiedKey(c->db,c->argv[1]);
    server.dirty++;
    addReply(c,shared.ok);
}

int setTypeIsMember(robj *subject, robj *value) {
    long long llval;
    if (subject->encoding == REDIS_ENCODING_HT) {
        return dictFind((dict*)subject->ptr,value) != NULL;
    } else if (subject->encoding == REDIS_ENCODING_INTSET) {
        if (isObjectRepresentableAsLongLong(value,&llval) == REDIS_OK) {
            return intsetFind((intset*)subject->ptr,llval);
        }
    } else {
        redisPanic("Unknown set encoding");
    }
    return 0;
}

setTypeIterator *setTypeInitIterator(robj *subject) {
    setTypeIterator *si = zmalloc(sizeof(setTypeIterator));
    si->subject = subject;
    si->encoding = subject->encoding;
    if (si->encoding == REDIS_ENCODING_HT) {
        si->di = dictGetIterator(subject->ptr);
    } else if (si->encoding == REDIS_ENCODING_INTSET) {
        si->ii = 0;
    } else {
        redisPanic("Unknown set encoding");
    }
    return si;
}

void *bioProcessBackgroundJobs(void *arg) {
    struct bio_job *job;
#ifdef _WIN32
    size_t type = (size_t) arg;
#else
    unsigned long type = (unsigned long) arg;
#endif
    sigset_t sigset;

    pthread_detach(pthread_self());
    pthread_mutex_lock(&bio_mutex[type]);
    /* Block SIGALRM so we are sure that only the main thread will
     * receive the watchdog signal. */
    sigemptyset(&sigset);
    sigaddset(&sigset, SIGALRM);
    if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
        redisLog(REDIS_WARNING,
            "Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno));

    while(1) {
        listNode *ln;

        /* The loop always starts with the lock hold. */
        if (listLength(bio_jobs[type]) == 0) {
            pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
            continue;
        }
        /* Pop the job from the queue. */
        ln = listFirst(bio_jobs[type]);
        job = ln->value;
        /* It is now possible to unlock the background system as we know have
         * a stand alone job structure to process.*/
        pthread_mutex_unlock(&bio_mutex[type]);

        /* Process the job accordingly to its type. */
        if (type == REDIS_BIO_CLOSE_FILE) {
            close((long)job->arg1);
        } else if (type == REDIS_BIO_AOF_FSYNC) {
            aof_fsync((long)job->arg1);
        } else {
            redisPanic("Wrong job type in bioProcessBackgroundJobs().");
        }
        zfree(job);

        /* Lock again before reiterating the loop, if there are no longer
         * jobs to process we'll block again in pthread_cond_wait(). */
        pthread_mutex_lock(&bio_mutex[type]);
        listDelNode(bio_jobs[type],ln);
        bio_pending[type]--;
    }
}

void *bioProcessBackgroundJobs(void *arg) {
	//bioInit创建一个进程，用来刷文件。arg参数就是这个线程对应应该处理的任务号，用来索引bio_jobs[type]
    struct bio_job *job;
    unsigned long type = (unsigned long) arg;//实际上就是jobid。序号
    sigset_t sigset;

    pthread_detach(pthread_self());
    pthread_mutex_lock(&bio_mutex[type]);//先锁一下，待会pthread_cond_wait
    /* Block SIGALRM so we are sure that only the main thread will
     * receive the watchdog signal. */
    sigemptyset(&sigset);
    sigaddset(&sigset, SIGALRM);
    if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
        redisLog(REDIS_WARNING, "Warning: can't mask SIGALRM in bio.c thread: %s", strerror(errno));

    while(1) {
        listNode *ln;

        /* The loop always starts with the lock hold. */
        if (listLength(bio_jobs[type]) == 0) {
	//已经加锁了，进入等待bio_condvar[type]不为0，并立即解锁，等待。
	//等其他线程pthread_cond_signal的时候，会通知这个线程，别等待了，从而再次加锁，返回。
            pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
            continue;
        }
        /* Pop the job from the queue. */
        ln = listFirst(bio_jobs[type]);//获取到了一个任务，处理值。
        job = ln->value;
        /* It is now possible to unlock the background system as we know have
         * a stand alone job structure to process.*/
        pthread_mutex_unlock(&bio_mutex[type]);

		//根据不同的任务类型，做响应的清理。
        /* Process the job accordingly to its type. */
        if (type == REDIS_BIO_CLOSE_FILE) {
            close((long)job->arg1);//关闭文件。
        } else if (type == REDIS_BIO_AOF_FSYNC) {
            aof_fsync((long)job->arg1);//同步刷新数据。
        } else {
            redisPanic("Wrong job type in bioProcessBackgroundJobs().");
        }
        zfree(job);

        /* Lock again before reiterating the loop, if there are no longer
         * jobs to process we'll block again in pthread_cond_wait(). */
        pthread_mutex_lock(&bio_mutex[type]);
        listDelNode(bio_jobs[type],ln);
        bio_pending[type]--;//递减这种类型的挂起计数。
    }
}

void decrRefCount(void *obj) {
		robj *o = obj;

		if (o->refcount <= 0) redisPanic("decrRefCount against refcount <= 0");
		/* Object is in memory, or in the process of being swapped out.
		 *
		 * If the object is being swapped out, abort the operation on
		 * decrRefCount even if the refcount does not drop to 0: the object
		 * is referenced at least two times, as value of the key AND as
		 * job->val in the iojob. So if we don't invalidate the iojob, when it is
		 * done but the relevant key was removed in the meantime, the
		 * complete jobs handler will not find the key about the job and the
		 * assert will fail. */
		if (o->refcount == 1) {
				switch(o->type) {
						case REDIS_STRING: freeStringObject(o); break;
						default: redisPanic("Unknown object type"); break;
				}
				zfree(o);
		} else {
				o->refcount--;
		}
}

/* Initialize an iterator at the specified index. */
listTypeIterator *listTypeInitIterator(robj *subject, long index, unsigned char direction) {
    listTypeIterator *li = zmalloc(sizeof(listTypeIterator));
    li->subject = subject;
    li->encoding = subject->encoding;
    li->direction = direction;
    if (li->encoding == REDIS_ENCODING_ZIPLIST) {
        li->zi = ziplistIndex(subject->ptr,index);
    } else if (li->encoding == REDIS_ENCODING_LINKEDLIST) {
        li->ln = listIndex(subject->ptr,index);
    } else {
        redisPanic("Unknown list encoding");
    }
    return li;
}

/* Move to the next entry in the set. Returns the object at the current
 * position.
 *
 * Since set elements can be internally be stored as redis objects or
 * simple arrays of integers, setTypeNext returns the encoding of the
 * set object you are iterating, and will populate the appropriate pointer
 * (objele) or (llele) accordingly.
 *
 * Note that both the objele and llele pointers should be passed and cannot
 * be NULL since the function will try to defensively populate the non
 * used field with values which are easy to trap if misused.
 *
 * When there are no longer elements -1 is returned.
 * Returned objects ref count is not incremented, so this function is
 * copy on write friendly. */
int setTypeNext(setTypeIterator *si, robj **objele, int64_t *llele) {
    if (si->encoding == REDIS_ENCODING_HT) {
        dictEntry *de = dictNext(si->di);
        if (de == NULL) return -1;
        *objele = dictGetKey(de);
        *llele = -123456789; /* Not needed. Defensive. */
    } else if (si->encoding == REDIS_ENCODING_INTSET) {
        if (!intsetGet(si->subject->ptr,si->ii++,llele))
            return -1;
        *objele = NULL; /* Not needed. Defensive. */
    } else {
        redisPanic("Wrong set encoding in setTypeNext");
    }
    return si->encoding;
}

inline static void zunionInterAggregate(double *target, double val, int aggregate) {
    if (aggregate == REDIS_AGGR_SUM) {
        *target = *target + val;
        /* The result of adding two doubles is NaN when one variable
         * is +inf and the other is -inf. When these numbers are added,
         * we maintain the convention of the result being 0.0. */
        if (isnan(*target)) *target = 0.0;
    } else if (aggregate == REDIS_AGGR_MIN) {
        *target = val < *target ? val : *target;
    } else if (aggregate == REDIS_AGGR_MAX) {
        *target = val > *target ? val : *target;
    } else {
        /* safety net */
        redisPanic("Unknown ZUNION/INTER aggregate type");
    }
}

/* The not copy on write friendly version but easy to use version
 * of setTypeNext() is setTypeNextObject(), returning new objects
 * or incrementing the ref count of returned objects. So if you don't
 * retain a pointer to this object you should call decrRefCount() against it.
 *
 * This function is the way to go for write operations where COW is not
 * an issue as the result will be anyway of incrementing the ref count. */
robj *setTypeNextObject(setTypeIterator *si) {
    int64_t intele;
    robj *objele;
    int encoding;

    encoding = setTypeNext(si,&objele,&intele);
    switch(encoding) {
        case -1:    return NULL;
        case REDIS_ENCODING_INTSET:
            return createStringObjectFromLongLong(intele);
        case REDIS_ENCODING_HT:
            incrRefCount(objele);
            return objele;
        default:
            redisPanic("Unsupported encoding");
    }
    return NULL; /* just to suppress warnings */
}

int setTypeRemove(robj *setobj, robj *value) {
    long long llval;
    if (setobj->encoding == REDIS_ENCODING_HT) {
        if (dictDelete(setobj->ptr,value) == DICT_OK) {
            if (htNeedsResize(setobj->ptr)) dictResize(setobj->ptr);
            return 1;
        }
    } else if (setobj->encoding == REDIS_ENCODING_INTSET) {
        if (isObjectRepresentableAsLongLong(value,&llval) == REDIS_OK) {
            int success;
            setobj->ptr = intsetRemove(setobj->ptr,llval,&success);
            if (success) return 1;
        }
    } else {
        redisPanic("Unknown set encoding");
    }
    return 0;
}

void lsetCommand(redisClient *c) {
	int slotnum = keyHashSlot(c->argv[1]->ptr, sdslen(c->argv[1]->ptr));
    robj *o = lookupKeyWriteOrReply(c,c->argv[1],shared.nokeyerr,slotnum);
    if (o == NULL || checkType(c,o,REDIS_LIST)) return;
    long index;
    robj *value = (c->argv[3] = tryObjectEncoding(c->argv[3]));

    if ((getLongFromObjectOrReply(c, c->argv[2], &index, NULL) != REDIS_OK))
        return;

    listTypeTryConversion(o,value);
    if (o->encoding == REDIS_ENCODING_ZIPLIST) {
        unsigned char *p, *zl = o->ptr;
        p = ziplistIndex(zl,index);
        if (p == NULL) {
            addReply(c,shared.outofrangeerr);
        } else {
            o->ptr = ziplistDelete(o->ptr,&p);
            value = getDecodedObject(value);
            o->ptr = ziplistInsert(o->ptr,p,value->ptr,sdslen(value->ptr));
            decrRefCount(value);
            addReply(c,shared.ok);
            signalModifiedKey(c->db,c->argv[1],slotnum);
            notifyKeyspaceEvent(REDIS_NOTIFY_LIST,"lset",c->argv[1],c->db->id);
            server.dirty++;
        }
    } else if (o->encoding == REDIS_ENCODING_LINKEDLIST) {
        listNode *ln = listIndex(o->ptr,index);
        if (ln == NULL) {
            addReply(c,shared.outofrangeerr);
        } else {
            decrRefCount((robj*)listNodeValue(ln));
            listNodeValue(ln) = value;
            incrRefCount(value);
            addReply(c,shared.ok);
            signalModifiedKey(c->db,c->argv[1],slotnum);
            notifyKeyspaceEvent(REDIS_NOTIFY_LIST,"lset",c->argv[1],c->db->id);
            server.dirty++;
        }
    } else {
        redisPanic("Unknown list encoding");
    }
}

void *bioProcessBackgroundJobs(void *arg) {
    struct bio_job *job;
#ifdef _WIN32
    size_t type = (size_t) arg;
#else
    unsigned long type = (unsigned long) arg;
#endif

    pthread_detach(pthread_self());
    pthread_mutex_lock(&bio_mutex[type]);
    while(1) {
        listNode *ln;

        /* The loop always starts with the lock hold. */
        if (listLength(bio_jobs[type]) == 0) {
            pthread_cond_wait(&bio_condvar[type],&bio_mutex[type]);
            continue;
        }
        /* Pop the job from the queue. */
        ln = listFirst(bio_jobs[type]);
        job = ln->value;
        /* It is now possible to unlock the background system as we know have
         * a stand alone job structure to process.*/
        pthread_mutex_unlock(&bio_mutex[type]);

        /* Process the job accordingly to its type. */
        if (type == REDIS_BIO_CLOSE_FILE) {
            close((long)(size_t)job->arg1);
        } else if (type == REDIS_BIO_AOF_FSYNC) {
            aof_fsync((long)(size_t)job->arg1);
        } else {
            redisPanic("Wrong job type in bioProcessBackgroundJobs().");
        }
        zfree(job);

        /* Lock again before reiterating the loop, if there are no longer
         * jobs to process we'll block again in pthread_cond_wait(). */
        pthread_mutex_lock(&bio_mutex[type]);
        listDelNode(bio_jobs[type],ln);
        bio_pending[type]--;
    }
}

/* Unblock a client calling the right function depending on the kind
 * of operation the client is blocking for. */
void unblockClient(redisClient *c) {
    if (c->btype == REDIS_BLOCKED_LIST) {
        unblockClientWaitingData(c);
    } else if (c->btype == REDIS_BLOCKED_WAIT) {
        unblockClientWaitingReplicas(c);
    } else {
        redisPanic("Unknown btype in unblockClient().");
    }
    /* Clear the flags, and put the client in the unblocked list so that
     * we'll process new commands in its query buffer ASAP. */
    c->flags &= ~REDIS_BLOCKED;
    c->btype = REDIS_BLOCKED_NONE;
    server.bpop_blocked_clients--;
    /* The client may already be into the unblocked list because of a previous
     * blocking operation, don't add back it into the list multiple times. */
    if (!(c->flags & REDIS_UNBLOCKED)) {
        c->flags |= REDIS_UNBLOCKED;
        listAddNodeTail(server.unblocked_clients,c);
    }
}

void listTypeConvert(robj *subject, int enc) {
    listTypeIterator *li;
    listTypeEntry entry;
    redisAssertWithInfo(NULL,subject,subject->type == REDIS_LIST);

    if (enc == REDIS_ENCODING_LINKEDLIST) {
        list *l = listCreate();
        listSetFreeMethod(l,decrRefCount);

        /* listTypeGet returns a robj with incremented refcount */
        li = listTypeInitIterator(subject,0,REDIS_TAIL);
        while (listTypeNext(li,&entry)) listAddNodeTail(l,listTypeGet(&entry));
        listTypeReleaseIterator(li);

        subject->encoding = REDIS_ENCODING_LINKEDLIST;
        zfree(subject->ptr);
        subject->ptr = l;
    } else {
        redisPanic("Unsupported list conversion");
    }
}