Redis原始碼分析（三十）--- pubsub釋出訂閱模式

TuxedoLinux發表於2018-06-01
Redis原始碼模式

Redis原始碼分析（三十）--- pubsub釋出訂閱模式


        今天學習了Redis中比較高大上的名詞，“釋出訂閱模式”，釋出訂閱模式這個詞在我最開始接觸聽說的時候是在JMS(Java Message Service)java訊息服務中聽說的。這個名次用通俗的一點話說，就是我訂閱了這類訊息，當只有這類的訊息進行廣播傳送的時候，我才會，其他的訊息直接過濾，保證了一個高效的傳輸效率。下面切入正題，學習一下Redis是如何實現這個釋出訂閱模式的。先看看裡面的簡單的API構造；

/*-----------------------------------------------------------------------------
 * Pubsub low level API
 *----------------------------------------------------------------------------*/
void freePubsubPattern(void *p) /* 釋放釋出訂閱的模式 */
int listMatchPubsubPattern(void *a, void *b) /* 釋出訂閱模式是否匹配 */
int clientSubscriptionsCount(redisClient *c) /* 返回客戶端的所訂閱的數量，包括channels + patterns管道和模式 */
int pubsubSubscribeChannel(redisClient *c, robj *channel) /* Client訂閱一個Channel管道 */
int pubsubUnsubscribeChannel(redisClient *c, robj *channel, int notify) /* 取消訂閱Client中的Channel */
int pubsubSubscribePattern(redisClient *c, robj *pattern) /* Client客戶端訂閱一種模式 */
int pubsubUnsubscribePattern(redisClient *c, robj *pattern, int notify) /* Client客戶端取消訂閱pattern模式 */
int pubsubUnsubscribeAllChannels(redisClient *c, int notify) /* 客戶端取消自身訂閱的所有Channel */
int pubsubUnsubscribeAllPatterns(redisClient *c, int notify) /* 客戶端取消訂閱所有的pattern模式 */
int pubsubPublishMessage(robj *channel, robj *message) /* 為所有訂閱了Channel的Client傳送訊息message */

/* ------------PUB/SUB API ---------------- */
void subscribeCommand(redisClient *c) /* 訂閱Channel的命令 */
void unsubscribeCommand(redisClient *c) /* 取消訂閱Channel的命令 */
void psubscribeCommand(redisClient *c) /* 訂閱模式命令 */
void punsubscribeCommand(redisClient *c) /* 取消訂閱模式命令 */
void publishCommand(redisClient *c) /* 釋出訊息命令 */
void pubsubCommand(redisClient *c) /* 釋出訂閱命令 */
在這裡面出現了高頻的詞Pattern(模式)和Channel(頻道,叫管道比較彆扭)，也就是說，後續所有的關於釋出訂閱的東東都是基於這2者展開進行的。現在大致講解一下在Redis中是如何實現此中模式的:

1.在RedisClient 內部維護了一個pubsub_channels的Channel列表，記錄了此客戶端所訂閱的頻道

2.在Server服務端，同樣維護著一個類似的變數叫做，pubsub_channels，這是一個dict字典變數，每一個Channel對應著一批訂閱了此頻道的Client，也就是Channel-->list of Clients

3.當一個Client publish一個message的時候，會先去服務端的pubsub_channels找相應的Channel，遍歷裡面的Client，然後傳送通知，即完成了整個釋出訂閱模式。

    我們可以簡單的看一下Redis訂閱一個Channel的方法實現；

/* Subscribe a client to a channel. Returns 1 if the operation succeeded, or
 * 0 if the client was already subscribed to that channel. */
/* Client訂閱一個Channel管道 */
int pubsubSubscribeChannel(redisClient *c, robj *channel) {
    struct dictEntry *de;
    list *clients = NULL;
    int retval = 0;

    /* Add the channel to the client -> channels hash table */
    //在Client的字典pubsub_channels中新增Channel
    if (dictAdd(c->pubsub_channels,channel,NULL) == DICT_OK) {
        retval = 1;
        incrRefCount(channel);
        /* Add the client to the channel -> list of clients hash table */
        //新增Clietn到server中的pubsub_channels，對應的列表中
        de = dictFind(server.pubsub_channels,channel);
        if (de == NULL) {
        	//如果此頻道的Client列表為空，則建立新列表並新增
            clients = listCreate();
            dictAdd(server.pubsub_channels,channel,clients);
            incrRefCount(channel);
        } else {
        	//否則，獲取這個頻道的客戶端列表，在尾部新增新的客戶端
            clients = dictGetVal(de);
        }
        listAddNodeTail(clients,c);
    }
    /* Notify the client */
    //新增給回覆客戶端
    addReply(c,shared.mbulkhdr[3]);
    addReply(c,shared.subscribebulk);
    addReplyBulk(c,channel);
    addReplyLongLong(c,clientSubscriptionsCount(c));
    return retval;
}
新增操作主要分2部，Client自身的內部維護的pubsub_channels的新增，是一個dict字典物件，然後，是server端維護的pubsub_channels中的client列表的新增。在進行Channel頻道的刪除的時候，也是執行的這2步驟操作:

/* Unsubscribe a client from a channel. Returns 1 if the operation succeeded, or
 * 0 if the client was not subscribed to the specified channel. */
/* 取消訂閱Client中的Channel */
int pubsubUnsubscribeChannel(redisClient *c, robj *channel, int notify) {
    struct dictEntry *de;
    list *clients;
    listNode *ln;
    int retval = 0;

    /* Remove the channel from the client -> channels hash table */
    incrRefCount(channel); /* channel may be just a pointer to the same object
                            we have in the hash tables. Protect it... */
    //字典刪除Client中pubsub_channels中的Channel
    if (dictDelete(c->pubsub_channels,channel) == DICT_OK) {
        retval = 1;
        /* Remove the client from the channel -> clients list hash table */
        //再移除Channel對應的Client列表
        de = dictFind(server.pubsub_channels,channel);
        redisAssertWithInfo(c,NULL,de != NULL);
        clients = dictGetVal(de);
        ln = listSearchKey(clients,c);
        redisAssertWithInfo(c,NULL,ln != NULL);
        listDelNode(clients,ln);
        if (listLength(clients) == 0) {
            /* Free the list and associated hash entry at all if this was
             * the latest client, so that it will be possible to abuse
             * Redis PUBSUB creating millions of channels. */
            dictDelete(server.pubsub_channels,channel);
        }
    }
    /* Notify the client */
    if (notify) {
        addReply(c,shared.mbulkhdr[3]);
        addReply(c,shared.unsubscribebulk);
        addReplyBulk(c,channel);
        addReplyLongLong(c,dictSize(c->pubsub_channels)+
                       listLength(c->pubsub_patterns));

    }
    decrRefCount(channel); /* it is finally safe to release it */
    return retval;
}
裡面還有對應的模式的訂閱和取消訂閱的操作，原理和channel完全一致，二者的區別在於，pattern是用來匹配的Channel的，這個是什麼意思呢。在後面會做出答案，接著看。最後看一個最最核心的方法，客戶端發步訊息方法:

/* Publish a message */
/* 為所有訂閱了Channel的Client傳送訊息message */
int pubsubPublishMessage(robj *channel, robj *message) {
    int receivers = 0;
    struct dictEntry *de;
    listNode *ln;
    listIter li;

    /* Send to clients listening for that channel */
    //找到Channel所對應的dictEntry
    de = dictFind(server.pubsub_channels,channel);
    if (de) {
    	//獲取此Channel對應的客戶單列表
        list *list = dictGetVal(de);
        listNode *ln;
        listIter li;

        listRewind(list,&li);
        while ((ln = listNext(&li)) != NULL) {
        	//依次取出List中的客戶單，新增訊息回覆
            redisClient *c = ln->value;

            addReply(c,shared.mbulkhdr[3]);
            addReply(c,shared.messagebulk);
            addReplyBulk(c,channel);
            //新增訊息回覆
            addReplyBulk(c,message);
            receivers++;
        }
    }
    /* Send to clients listening to matching channels */
    /* 傳送給嘗試匹配該Channel的客戶端訊息 */
    if (listLength(server.pubsub_patterns)) {
        listRewind(server.pubsub_patterns,&li);
        channel = getDecodedObject(channel);
        while ((ln = listNext(&li)) != NULL) {
            pubsubPattern *pat = ln->value;
			
			//客戶端的模式如果匹配了Channel，也會傳送訊息
            if (stringmatchlen((char*)pat->pattern->ptr,
                                sdslen(pat->pattern->ptr),
                                (char*)channel->ptr,
                                sdslen(channel->ptr),0)) {
                addReply(pat->client,shared.mbulkhdr[4]);
                addReply(pat->client,shared.pmessagebulk);
                addReplyBulk(pat->client,pat->pattern);
                addReplyBulk(pat->client,channel);
                addReplyBulk(pat->client,message);
                receivers++;
            }
        }
        decrRefCount(channel);
    }
    return receivers;
}
pattern的作用就在上面體現了，如果某種pattern匹配了Channel頻道，則模式的客戶端也會接收訊息。在server->pubsub_patterns中，pubsub_patterns是一個list列表，裡面的每一個pattern只對應一個Client,就是上面的pat->client，這一點和Channel還是有本質的區別的。講完釋出訂閱模式的基本操作後，順便把與此相關的notify通知類也稍稍講講，通知只有3個方法，
/* ----------------- API ------------------- */
int keyspaceEventsStringToFlags(char *classes) /* 鍵值字元型別轉為對應的Class型別 */
sds keyspaceEventsFlagsToString(int flags) /* 通過輸入的flag值類，轉為字元型別*/
void notifyKeyspaceEvent(int type, char *event, robj *key, int dbid) /* 釋出通知方法，分為2類，keySpace的通知，keyEvent的通知 */
涉及到string To flag 和flag To String 的轉換，也不知道這個會在哪裡用到；
/* Turn a string representing notification classes into an integer
 * representing notification classes flags xored.
 *
 * The function returns -1 if the input contains characters not mapping to
 * any class. */
/* 鍵值字元型別轉為對應的Class型別 */
int keyspaceEventsStringToFlags(char *classes) {
    char *p = classes;
    int c, flags = 0;

    while((c = *p++) != '\0') {
        switch(c) {
        case 'A': flags |= REDIS_NOTIFY_ALL; break;
        case 'g': flags |= REDIS_NOTIFY_GENERIC; break;
        case '$': flags |= REDIS_NOTIFY_STRING; break;
        case 'l': flags |= REDIS_NOTIFY_LIST; break;
        case 's': flags |= REDIS_NOTIFY_SET; break;
        case 'h': flags |= REDIS_NOTIFY_HASH; break;
        case 'z': flags |= REDIS_NOTIFY_ZSET; break;
        case 'x': flags |= REDIS_NOTIFY_EXPIRED; break;
        case 'e': flags |= REDIS_NOTIFY_EVICTED; break;
        case 'K': flags |= REDIS_NOTIFY_KEYSPACE; break;
        case 'E': flags |= REDIS_NOTIFY_KEYEVENT; break;
        default: return -1;
        }
    }
    return flags;
}
應該是響應鍵盤輸入的型別和Redis型別之間的轉換。在notify的方法還有一個event事件的通知方法:

/* The API provided to the rest of the Redis core is a simple function:
 *
 * notifyKeyspaceEvent(char *event, robj *key, int dbid);
 *
 * 'event' is a C string representing the event name.
 * 'key' is a Redis object representing the key name.
 * 'dbid' is the database ID where the key lives.  */
/* 釋出通知方法，分為2類，keySpace的通知，keyEvent的通知 */ 
void notifyKeyspaceEvent(int type, char *event, robj *key, int dbid) {
    sds chan;
    robj *chanobj, *eventobj;
    int len = -1;
    char buf[24];

    /* If notifications for this class of events are off, return ASAP. */
    if (!(server.notify_keyspace_events & type)) return;

    eventobj = createStringObject(event,strlen(event));
    
    //2種的通知形式，略有差別
    /* __keyspace@<db>__:<key> <event> notifications. */
    if (server.notify_keyspace_events & REDIS_NOTIFY_KEYSPACE) {
        chan = sdsnewlen("__keyspace@",11);
        len = ll2string(buf,sizeof(buf),dbid);
        chan = sdscatlen(chan, buf, len);
        chan = sdscatlen(chan, "__:", 3);
        chan = sdscatsds(chan, key->ptr);
        chanobj = createObject(REDIS_STRING, chan);
        //上述幾步操作，元件格式字串，最後釋出訊息，下面keyEvent的通知同理
        pubsubPublishMessage(chanobj, eventobj);
        decrRefCount(chanobj);
    }

    /* __keyevente@<db>__:<event> <key> notifications. */
    if (server.notify_keyspace_events & REDIS_NOTIFY_KEYEVENT) {
        chan = sdsnewlen("__keyevent@",11);
        if (len == -1) len = ll2string(buf,sizeof(buf),dbid);
        chan = sdscatlen(chan, buf, len);
        chan = sdscatlen(chan, "__:", 3);
        chan = sdscatsds(chan, eventobj->ptr);
        chanobj = createObject(REDIS_STRING, chan);
        pubsubPublishMessage(chanobj, key);
        decrRefCount(chanobj);
    }
    decrRefCount(eventobj);
}
有keySpace和keyEvent的2種事件通知。具體怎麼用，等後面碰到的時候在看看。

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