Redis 发布订阅 -- Redis 设计与实现

客官°小女子只卖身不卖艺 2022-05-28 05:48 225阅读 0赞

# 订阅与发布 #

Redis 通过 [PUBLISH][] 、 [SUBSCRIBE][] 等命令实现了订阅与发布模式， 这个功能提供两种信息机制， 分别是订阅/发布到频道和订阅/发布到模式， 下文先讨论订阅/发布到频道的实现， 再讨论订阅/发布到模式的实现。

## 频道的订阅与信息发送 ##

Redis 的 [SUBSCRIBE][] 命令可以让客户端订阅任意数量的频道， 每当有新信息发送到被订阅的频道时， 信息就会被发送给所有订阅指定频道的客户端。

作为例子， 下图展示了频道 `channel1` ， 以及订阅这个频道的三个客户端 —— `client2` 、 `client5` 和 `client1` 之间的关系：

![digraph pubsub\_relation \{    rankdir = BT;    node \[style = filled\];    edge \[style = bold\];    channel1 \[label = "channel1", fillcolor = "\#A8E270"\];    node \[shape = box, fillcolor = "\#95BBE3"\];    client2 \[label = "client2"\];    client5 \[label = "client5"\];    client1 \[label = "client1"\];    client2 -> channel1 \[label = "subscribe"\];    client5 -> channel1 \[label = "subscribe"\];    client1 -> channel1 \[label = "subscribe"\];\}][digraph pubsub_relation _ rankdir _ BT_ node _style _ filled_ edge _style _ bold_ channel1 _label _ _channel1_ fillcolor _ _A8E270_ node _shape _ box_ fillcolor _ _95BBE3_ client2 _label _ _client2_ client5 _label _ _client5_ client1 _label _ _client1_ client2 -_ channel1 _label _ _subscribe_ client5 -_ channel1 _label _ _subscribe_ client1 -_ channel1 _label _ _subscribe]

当有新消息通过 [PUBLISH][] 命令发送给频道 `channel1` 时， 这个消息就会被发送给订阅它的三个客户端：

![digraph send\_message\_to\_subscriber \{        node \[style = filled\];    edge \[style = "dashed, bold"\];        message \[label = "PUBLISH channel1 message", shape = plaintext, fillcolor = "\#FADCAD"\];    message -> channel1 \[color = "\#B22222\]"\];    channel1 \[label = "channel1", fillcolor = "\#A8E270"\];    node \[shape = box\];    client2 \[label = "client2", fillcolor = "\#95BBE3"\];    client5 \[label = "client5", fillcolor = "\#95BBE3"\];    client1 \[label = "client1", fillcolor = "\#95BBE3"\];    /\*    client2 -> channel1 \[label = "subscribe"\];    client5 -> channel1 \[label = "subscribe"\];    client1 -> channel1 \[label = "subscribe"\];    \*/    channel1 -> client2 \[label = "message", color = "\#B22222"\];    channel1 -> client5 \[label = "message", color = "\#B22222"\];    channel1 -> client1 \[label = "message", color = "\#B22222"\];\}][digraph send_message_to_subscriber _ node _style _ filled_ edge _style _ _dashed_ bold_ message _label _ _PUBLISH channel1 message_ shape _ plaintext_ fillcolor _ _FADCAD_ message -_ channel1 _color _ _B22222_ channel1 _label _ _channel1_ fillcolor _ _A8E270_ node _shape _ box_ client2 _label _ _client2_ fillcolor _ _95BBE3_ client5 _label _ _client5_ fillcolor _ _95BBE3_ client1 _label _ _client1_ fillcolor _ _95BBE3_ _ client2 -_ channel1 _label _ _subscribe_ client5 -_ channel1 _label _ _subscribe_ client1 -_ channel1 _label _ _subscribe_ _ channel1 -_ client2 _label _ _message_ color _ _B22222_ channel1 -_ client5 _label _ _message_ color _ _B22222_ channel1 -_ client1 _label _ _message_ color _ _B22222]

在后面的内容中， 我们将探讨 [SUBSCRIBE][] 和 [PUBLISH][] 命令的实现， 以及这套订阅与发布机制的运作原理。

## 订阅频道 ##

每个 Redis 服务器进程都维持着一个表示服务器状态的 `redis.h/redisServer` 结构， 结构的 `pubsub_channels` 属性是一个字典， 这个字典就用于保存订阅频道的信息：

struct redisServer {
          
        // ...
        dict *pubsub_channels;
        // ...
    };

其中，字典的键为正在被订阅的频道， 而字典的值则是一个链表， 链表中保存了所有订阅这个频道的客户端。

比如说，在下图展示的这个 `pubsub_channels` 示例中， `client2` 、 `client5` 和 `client1` 就订阅了 `channel1` ， 而其他频道也分别被别的客户端所订阅：

![digraph pubsub \{    rankdir = LR;    node \[shape = record, style = filled\];    edge \[style = bold\];    // keys    pubsub \[label = "pubsub\_channels |<channel1> channel1 |<channel2> channel2 |<channel3> channel3 | ... |<channelN> channelN", fillcolor = "\#A8E270"\];    // clients blocking for channel1    client1 \[label = "client1", fillcolor = "\#95BBE3"\];    client5 \[label = "client5", fillcolor = "\#95BBE3"\];    client2 \[label = "client2", fillcolor = "\#95BBE3"\];    null\_1 \[label = "NULL", shape = plaintext\];        pubsub:channel1 -> client2;    client2 -> client5;    client5 -> client1;    client1 -> null\_1;    // clients blocking for channel2    client7 \[label = "client7", fillcolor = "\#95BBE3"\];    null\_2 \[label = "NULL", shape = plaintext\];    pubsub:channel2 -> client7;    client7 -> null\_2;    // channel    client3 \[label = "client3", fillcolor = "\#95BBE3"\];    client4 \[label = "client4", fillcolor = "\#95BBE3"\];    client6 \[label = "client6", fillcolor = "\#95BBE3"\];    null\_3 \[label = "NULL", shape = plaintext\];    pubsub:channel3 -> client3;    client3 -> client4;    client4 -> client6;    client6 -> null\_3;\}][digraph pubsub _ rankdir _ LR_ node _shape _ record_ style _ filled_ edge _style _ bold_ _ keys pubsub _label _ _pubsub_channels _channel1_ channel1 _channel2_ channel2 _channel3_ channel3 _ ... _channelN_ channelN_ fillcolor _ _A8E270_ _ clients blocking for channel1 client1 _label _ _client1_ fillcolor _ _95BBE3_ client5 _label _ _client5_ fillcolor _ _95BBE3_ client2 _label _ _client2_ fillcolor _ _95BBE3_ null_1 _label _ _NULL_ shape _ plaintext_ pubsub_channel1 -_ client2_ client2 -_ client5_ client5 -_ client1_ client1 -_ null_1_ _ clients blocking for channel2 client7 _label _ _client7_ fillcolor _ _95BBE3_ null_2 _label _ _NULL_ shape _ plaintext_ pubsub_channel2 -_ client7_ client7 -_ null_2_ _ channel client3 _label _ _client3_ fillcolor _ _95BBE3_ client4 _label _ _client4_ fillcolor _ _95BBE3_ client6 _label _ _client6_ fillcolor _ _95BBE3_ null_3 _label _ _NULL_ shape _ plaintext_ pubsub_channel3 -_ client3_ client3 -_ client4_ client4 -_ client6_ client6 -_ null_3]

当客户端调用 [SUBSCRIBE][] 命令时， 程序就将客户端和要订阅的频道在 `pubsub_channels` 字典中关联起来。

举个例子，如果客户端 `client10086` 执行命令 `SUBSCRIBE channel1 channel2 channel3` ，那么前面展示的 `pubsub_channels` 将变成下面这个样子：

![digraph new\_subscribe \{    rankdir = LR;    node \[shape = record, style = filled\];    edge \[style = bold\];    // keys    pubsub \[label = "pubsub\_channels |<channel1> channel1 |<channel2> channel2 |<channel3> channel3 | ... |<channelN> channelN", fillcolor = "\#A8E270"\];    // clients blocking for channel1    client1 \[label = "client1", fillcolor = "\#95BBE3"\];    client5 \[label = "client5", fillcolor = "\#95BBE3"\];    client2 \[label = "client2", fillcolor = "\#95BBE3"\];    client10086 \[label = "client10086", fillcolor = "\#FFC1C1"\];    client10086\_1 \[label = "client10086", fillcolor = "\#FFC1C1"\];    client10086\_2 \[label = "client10086", fillcolor = "\#FFC1C1"\];    null\_1 \[label = "NULL", shape = plaintext\];    null\_2 \[label = "NULL", shape = plaintext\];    null\_3 \[label = "NULL", shape = plaintext\];        pubsub:channel1 -> client2;    client2 -> client5;    client5 -> client1;    client1 -> client10086;    client10086 -> null\_1;    // clients blocking for channel2    client7 \[label = "client7", fillcolor = "\#95BBE3"\];    pubsub:channel2 -> client7;    client7 -> client10086\_1;    client10086\_1 -> null\_2;    // channel    client3 \[label = "client3", fillcolor = "\#95BBE3"\];    client4 \[label = "client4", fillcolor = "\#95BBE3"\];    client6 \[label = "client6", fillcolor = "\#95BBE3"\];    pubsub:channel3 -> client3;    client3 -> client4;    client4 -> client6;    client6 -> client10086\_2;    client10086\_2 -> null\_3;\}][digraph new_subscribe _ rankdir _ LR_ node _shape _ record_ style _ filled_ edge _style _ bold_ _ keys pubsub _label _ _pubsub_channels _channel1_ channel1 _channel2_ channel2 _channel3_ channel3 _ ... _channelN_ channelN_ fillcolor _ _A8E270_ _ clients blocking for channel1 client1 _label _ _client1_ fillcolor _ _95BBE3_ client5 _label _ _client5_ fillcolor _ _95BBE3_ client2 _label _ _client2_ fillcolor _ _95BBE3_ client10086 _label _ _client10086_ fillcolor _ _FFC1C1_ client10086_1 _label _ _client10086_ fillcolor _ _FFC1C1_ client10086_2 _label _ _client10086_ fillcolor _ _FFC1C1_ null_1 _label _ _NULL_ shape _ plaintext_ null_2 _label _ _NULL_ shape _ plaintext_ null_3 _label _ _NULL_ shape _ plaintext_ pubsub_channel1 -_ client2_ client2 -_ client5_ client5 -_ client1_ client1 -_ client10086_ client10086 -_ null_1_ _ clients blocking for channel2 client7 _label _ _client7_ fillcolor _ _95BBE3_ pubsub_channel2 -_ client7_ client7 -_ client10086_1_ client10086_1 -_ null_2_ _ channel client3 _label _ _client3_ fillcolor _ _95BBE3_ client4 _label _ _client4_ fillcolor _ _95BBE3_ client6 _label _ _client6_ fillcolor _ _95BBE3_ pubsub_channel3 -_ client3_ client3 -_ client4_ client4 -_ client6_ client6 -_ client10086_2_ client10086_2 -_ null_3]

[SUBSCRIBE][] 命令的行为可以用伪代码表示如下：

def SUBSCRIBE(client, channels):
    
        # 遍历所有输入频道
        for channel in channels:
    
            # 将客户端添加到链表的末尾
            redisServer.pubsub_channels[channel].append(client)

通过 `pubsub_channels` 字典， 程序只要检查某个频道是否为字典的键， 就可以知道该频道是否正在被客户端订阅； 只要取出某个键的值， 就可以得到所有订阅该频道的客户端的信息。

## 发送信息到频道 ##

了解了 `pubsub_channels` 字典的结构之后， 解释 [PUBLISH][] 命令的实现就非常简单了： 当调用 `PUBLISH channel message` 命令， 程序首先根据 `channel` 定位到字典的键， 然后将信息发送给字典值链表中的所有客户端。

比如说，对于以下这个 `pubsub_channels` 实例， 如果某个客户端执行命令 `PUBLISH channel1 "hello moto"` ，那么 `client2` 、 `client5` 和 `client1` 三个客户端都将接收到 `"hello moto"` 信息：

[PUBLISH][] 命令的实现可以用以下伪代码来描述：

def PUBLISH(channel, message):
    
        # 遍历所有订阅频道 channel 的客户端
        for client in server.pubsub_channels[channel]:
    
            # 将信息发送给它们
            send_message(client, message)

## 退订频道 ##

使用 [UNSUBSCRIBE][] 命令可以退订指定的频道， 这个命令执行的是订阅的反操作： 它从 `pubsub_channels` 字典的给定频道（键）中， 删除关于当前客户端的信息， 这样被退订频道的信息就不会再发送给这个客户端。

## 模式的订阅与信息发送 ##

当使用 [PUBLISH][] 命令发送信息到某个频道时， 不仅所有订阅该频道的客户端会收到信息， 如果有某个/某些模式和这个频道匹配的话， 那么所有订阅这个/这些频道的客户端也同样会收到信息。

下图展示了一个带有频道和模式的例子， 其中 `tweet.shop.*` 模式匹配了 `tweet.shop.kindle` 频道和 `tweet.shop.ipad` 频道， 并且有不同的客户端分别订阅它们三个：

当有信息发送到 `tweet.shop.kindle` 频道时， 信息除了发送给 `clientX` 和 `clientY` 之外， 还会发送给订阅 `tweet.shop.*` 模式的 `client123` 和 `client256` ：

![digraph send\_message\_to\_pattern \{      node \[style = filled\];    edge \[style = bold\];    // tweet.shop.ipad    ipad \[label = "tweet.shop.ipad", fillcolor = "\#A8E270"\];    ipad -> pattern \[label = "match", dir = back\];    node \[shape = box\];    ipad -> client3333 \[label = "subscribe", dir = back\];    ipad -> client4444 \[label = "subscribe", dir = back\];    ipad -> client5555 \[label = "subscribe", dir = back\];    node \[shape = plaintext\];    message \[label = "PUBLISH tweet.shop.kindle message", fillcolor = "\#FADCAD"\];    kindle \[label = "tweet.shop.kindle", shape = ellipse, fillcolor = "\#A8E270"\];    pattern \[label = "tweet.shop.\*", shape = octagon\];    message -> kindle \[style = "bold, dashed", color = "\#B22222"\];    kindle -> pattern \[style = "bold, dashed", color = "\#B22222"\];    node \[shape = box\];    kindle -> clientX \[style = "bold, dashed", color = "\#B22222", label = "message"\];    kindle -> clientY \[style = "bold, dashed", color = "\#B22222", label = "message"\];    pattern -> client123 \[label = "message", style = "bold, dashed", color = "\#B22222"\];    pattern -> client256 \[label = "message", style = "bold, dashed", color = "\#B22222"\];    // client color    client123 \[fillcolor = "\#95BBE3"\];    client256 \[fillcolor = "\#95BBE3"\];    clientX \[fillcolor = "\#95BBE3"\];    clientY \[fillcolor = "\#95BBE3"\];    client3333 \[fillcolor = "\#95BBE3"\];    client4444 \[fillcolor = "\#95BBE3"\];    client5555 \[fillcolor = "\#95BBE3"\];\}][digraph send_message_to_pattern _ node _style _ filled_ edge _style _ bold_ _ tweet.shop.ipad ipad _label _ _tweet.shop.ipad_ fillcolor _ _A8E270_ ipad -_ pattern _label _ _match_ dir _ back_ node _shape _ box_ ipad -_ client3333 _label _ _subscribe_ dir _ back_ ipad -_ client4444 _label _ _subscribe_ dir _ back_ ipad -_ client5555 _label _ _subscribe_ dir _ back_ node _shape _ plaintext_ message _label _ _PUBLISH tweet.shop.kindle message_ fillcolor _ _FADCAD_ kindle _label _ _tweet.shop.kindle_ shape _ ellipse_ fillcolor _ _A8E270_ pattern _label _ _tweet.shop._ shape _ octagon_ message -_ kindle _style _ _bold_ dashed_ color _ _B22222_ kindle -_ pattern _style _ _bold_ dashed_ color _ _B22222_ node _shape _ box_ kindle -_ clientX _style _ _bold_ dashed_ color _ _B22222_ label _ _message_ kindle -_ clientY _style _ _bold_ dashed_ color _ _B22222_ label _ _message_ pattern -_ client123 _label _ _message_ style _ _bold_ dashed_ color _ _B22222_ pattern -_ client256 _label _ _message_ style _ _bold_ dashed_ color _ _B22222_ _ client color client123 _fillcolor _ _95BBE3_ client256 _fillcolor _ _95BBE3_ clientX _fillcolor _ _95BBE3_ clientY _fillcolor _ _95BBE3_ client3333 _fillcolor _ _95BBE3_ client4444 _fillcolor _ _95BBE3_ client5555 _fillcolor _ _95BBE3]

另一方面， 如果接收到信息的是频道 `tweet.shop.ipad` ， 那么 `client123` 和 `client256` 同样会收到信息：

![digraph pattern\_relation \{        rankdir = BT;    node \[style = filled\];    edge \[style = bold\];    kindle \[label = "tweet.shop.kindle", fillcolor = "\#A8E270"\];    ipad \[label = "tweet.shop.ipad", fillcolor = "\#A8E270"\];    node \[shape = octagon\];    pattern \[label = "tweet.shop.\*"\];    pattern -> kindle \[label = "match"\];    pattern -> ipad \[style = "bold, dashed", color = "\#B22222", dir = back\];    node \[shape = box\];    client123 -> pattern \[label = "message", dir = back, style= "bold, dashed", color = "\#B22222"\];    client256 -> pattern \[label = "message", dir = back, style= "bold, dashed", color = "\#B22222"\];    clientX -> kindle \[label = "subscribe"\];    clientY -> kindle \[label = "subscribe"\];    client3333 -> ipad \[label = "message", style = "bold, dashed", color = "\#B22222", dir = back\];    client4444 -> ipad \[label = "message", style = "bold, dashed", color = "\#B22222", dir = back\];    client5555 -> ipad \[label = "message", style = "bold, dashed", color = "\#B22222", dir = back\];    // new    publish \[label = "PUBLISH tweet.shop.ipad message", shape = plaintext, fillcolor = "\#FADCAD"\];    ipad -> publish \[style = "bold, dashed", color = "\#B22222", dir = back\];    // client color    client123 \[fillcolor = "\#95BBE3"\];    client256 \[fillcolor = "\#95BBE3"\];    clientX \[fillcolor = "\#95BBE3"\];    clientY \[fillcolor = "\#95BBE3"\];    client3333 \[fillcolor = "\#95BBE3"\];    client4444 \[fillcolor = "\#95BBE3"\];    client5555 \[fillcolor = "\#95BBE3"\];\}][digraph pattern_relation _ rankdir _ BT_ node _style _ filled_ edge _style _ bold_ kindle _label _ _tweet.shop.kindle_ fillcolor _ _A8E270_ ipad _label _ _tweet.shop.ipad_ fillcolor _ _A8E270_ node _shape _ octagon_ pattern _label _ _tweet.shop._ pattern -_ kindle _label _ _match_ pattern -_ ipad _style _ _bold_ dashed_ color _ _B22222_ dir _ back_ node _shape _ box_ client123 -_ pattern _label _ _message_ dir _ back_ style_ _bold_ dashed_ color _ _B22222_ client256 -_ pattern _label _ _message_ dir _ back_ style_ _bold_ dashed_ color _ _B22222_ clientX -_ kindle _label _ _subscribe_ clientY -_ kindle _label _ _subscribe_ client3333 -_ ipad _label _ _message_ style _ _bold_ dashed_ color _ _B22222_ dir _ back_ client4444 -_ ipad _label _ _message_ style _ _bold_ dashed_ color _ _B22222_ dir _ back_ client5555 -_ ipad _label _ _message_ style _ _bold_ dashed_ color _ _B22222_ dir _ back_ _ new publish _label _ _PUBLISH tweet.shop.ipad message_ shape _ plaintext_ fillcolor _ _FADCAD_ ipad -_ publish _style _ _bold_ dashed_ color _ _B22222_ dir _ back_ _ client color client123 _fillcolor _ _95BBE3_ client256 _fillcolor _ _95BBE3_ clientX _fillcolor _ _95BBE3_ clientY _fillcolor _ _95BBE3_ client3333 _fillcolor _ _95BBE3_ client4444 _fillcolor _ _95BBE3_ client5555 _fillcolor _ _95BBE3]

## 订阅模式 ##

`redisServer.pubsub_patterns` 属性是一个链表，链表中保存着所有和模式相关的信息：

struct redisServer {
          
        // ...
        list *pubsub_patterns;
        // ...
    };

链表中的每个节点都包含一个 `redis.h/pubsubPattern` 结构：

typedef struct pubsubPattern {
          
        redisClient *client;
        robj *pattern;
    } pubsubPattern;

`client` 属性保存着订阅模式的客户端，而 `pattern` 属性则保存着被订阅的模式。

每当调用 `PSUBSCRIBE` 命令订阅一个模式时， 程序就创建一个包含客户端信息和被订阅模式的 `pubsubPattern` 结构， 并将该结构添加到 `redisServer.pubsub_patterns` 链表中。

作为例子，下图展示了一个包含两个模式的 `pubsub_patterns` 链表， 其中 `client123` 和 `client256` 都正在订阅 `tweet.shop.*` 模式：

![digraph publish\_pattern \{        rankdir = LR;    node \[shape = record, style = filled\];    edge \[style = bold\];    redisServer \[label = "redisServer| ... |<pubsub\_patterns> pubsub\_patterns | ...", fillcolor = "\#A8E270"\];    pubsubPattern\_1 \[label = "pubsubPattern | client \\n client123 | pattern \\n tweet.shop.\*", fillcolor = "\#95BBE3"\];    pubsubPattern\_2 \[label = "pubsubPattern | client \\n client256 | pattern \\n tweet.shop.\*", fillcolor = "\#95BBE3"\];    redisServer:pubsub\_patterns -> pubsubPattern\_1;    pubsubPattern\_1 -> pubsubPattern\_2;\}][digraph publish_pattern _ rankdir _ LR_ node _shape _ record_ style _ filled_ edge _style _ bold_ redisServer _label _ _redisServer_ ... _pubsub_patterns_ pubsub_patterns _ ..._ fillcolor _ _A8E270_ pubsubPattern_1 _label _ _pubsubPattern _ client _n client123 _ pattern _n tweet.shop._ fillcolor _ _95BBE3_ pubsubPattern_2 _label _ _pubsubPattern _ client _n client256 _ pattern _n tweet.shop._ fillcolor _ _95BBE3_ redisServer_pubsub_patterns -_ pubsubPattern_1_ pubsubPattern_1 -_ pubsubPattern_2]

如果这时客户端 `client10086` 执行 `PSUBSCRIBE broadcast.list.*` ， 那么 `pubsub_patterns` 链表将被更新成这样：

![digraph pubsub\_pattern \{        rankdir = LR;    node \[shape = record, style = filled\];    edge \[style = bold\];    redisServer \[label = "redisServer| ... |<pubsub\_patterns> pubsub\_patterns | ...", fillcolor = "\#A8E270"\];    pubsubPattern\_1 \[label = "pubsubPattern | client \\n client123 | pattern \\n tweet.shop.\*", fillcolor = "\#95BBE3"\];    pubsubPattern\_2 \[label = "pubsubPattern | client \\n client256 | pattern \\n tweet.shop.\*", fillcolor = "\#95BBE3"\];    pubsubPattern\_3 \[label = "pubsubPattern | client \\n client10086 | pattern \\n broadcast.live.\*", fillcolor = "\#FFC1C1"\];    redisServer:pubsub\_patterns -> pubsubPattern\_1;    pubsubPattern\_1 -> pubsubPattern\_2;    pubsubPattern\_2 -> pubsubPattern\_3;\}][digraph pubsub_pattern _ rankdir _ LR_ node _shape _ record_ style _ filled_ edge _style _ bold_ redisServer _label _ _redisServer_ ... _pubsub_patterns_ pubsub_patterns _ ..._ fillcolor _ _A8E270_ pubsubPattern_1 _label _ _pubsubPattern _ client _n client123 _ pattern _n tweet.shop._ fillcolor _ _95BBE3_ pubsubPattern_2 _label _ _pubsubPattern _ client _n client256 _ pattern _n tweet.shop._ fillcolor _ _95BBE3_ pubsubPattern_3 _label _ _pubsubPattern _ client _n client10086 _ pattern _n broadcast.live._ fillcolor _ _FFC1C1_ redisServer_pubsub_patterns -_ pubsubPattern_1_ pubsubPattern_1 -_ pubsubPattern_2_ pubsubPattern_2 -_ pubsubPattern_3]

通过遍历整个 `pubsub_patterns` 链表，程序可以检查所有正在被订阅的模式，以及订阅这些模式的客户端。

## 发送信息到模式 ##

发送信息到模式的工作也是由 [PUBLISH][] 命令进行的， 在前面讲解频道的时候， 我们给出了这样一段伪代码， 说它定义了 [PUBLISH][] 命令的行为：

但是，这段伪代码并没有完整描述 [PUBLISH][] 命令的行为， 因为 [PUBLISH][] 除了将 `message` 发送到所有订阅 `channel` 的客户端之外， 它还会将 `channel` 和 `pubsub_patterns` 中的模式进行对比， 如果 `channel` 和某个模式匹配的话， 那么也将 `message` 发送到订阅那个模式的客户端。

完整描述 [PUBLISH][] 功能的伪代码定于如下：

def PUBLISH(channel, message):
    
        # 遍历所有订阅频道 channel 的客户端
        for client in server.pubsub_channels[channel]:
    
            # 将信息发送给它们
            send_message(client, message)
    
        # 取出所有模式，以及订阅模式的客户端
        for pattern, client in server.pubsub_patterns:
    
            # 如果 channel 和模式匹配
            if match(channel, pattern):
    
                # 那么也将信息发给订阅这个模式的客户端
                send_message(client, message)

举个例子，如果 Redis 服务器的 `pubsub_patterns` 状态如下：

那么当某个客户端发送信息 `"Amazon Kindle, $69."` 到 `tweet.shop.kindle` 频道时， 除了所有订阅了 `tweet.shop.kindle` 频道的客户端会收到信息之外， 客户端 `client123` 和 `client256` 也同样会收到信息， 因为这两个客户端订阅的 `tweet.shop.*` 模式和 `tweet.shop.kindle` 频道匹配。

## 退订模式 ##

使用 [PUNSUBSCRIBE][] 命令可以退订指定的模式， 这个命令执行的是订阅模式的反操作： 程序会删除 `redisServer.pubsub_patterns` 链表中， 所有和被退订模式相关联的 `pubsubPattern` 结构， 这样客户端就不会再收到和模式相匹配的频道发来的信息。

## 小结 ##

*  订阅信息由服务器进程维持的 `redisServer.pubsub_channels` 字典保存，字典的键为被订阅的频道，字典的值为订阅频道的所有客户端。
 *  当有新消息发送到频道时，程序遍历频道（键）所对应的（值）所有客户端，然后将消息发送到所有订阅频道的客户端上。
 *  订阅模式的信息由服务器进程维持的 `redisServer.pubsub_patterns` 链表保存，链表的每个节点都保存着一个 `pubsubPattern` 结构，结构中保存着被订阅的模式，以及订阅该模式的客户端。程序通过遍历链表来查找某个频道是否和某个模式匹配。
 *  当有新消息发送到频道时，除了订阅频道的客户端会收到消息之外，所有订阅了匹配频道的模式的客户端，也同样会收到消息。
 *  退订频道和退订模式分别是订阅频道和订阅模式的反操作。

[PUBLISH]: http://redis.readthedocs.org/en/latest/pub_sub/publish.html#publish
[SUBSCRIBE]: http://redis.readthedocs.org/en/latest/pub_sub/subscribe.html#subscribe
[digraph pubsub_relation _ rankdir _ BT_ node _style _ filled_ edge _style _ bold_ channel1 _label _ _channel1_ fillcolor _ _A8E270_ node _shape _ box_ fillcolor _ _95BBE3_ client2 _label _ _client2_ client5 _label _ _client5_ client1 _label _ _client1_ client2 -_ channel1 _label _ _subscribe_ client5 -_ channel1 _label _ _subscribe_ client1 -_ channel1 _label _ _subscribe]: /images/20220528/9fdad8648883473a8ba264b477949ec1.png
[digraph send_message_to_subscriber _ node _style _ filled_ edge _style _ _dashed_ bold_ message _label _ _PUBLISH channel1 message_ shape _ plaintext_ fillcolor _ _FADCAD_ message -_ channel1 _color _ _B22222_ channel1 _label _ _channel1_ fillcolor _ _A8E270_ node _shape _ box_ client2 _label _ _client2_ fillcolor _ _95BBE3_ client5 _label _ _client5_ fillcolor _ _95BBE3_ client1 _label _ _client1_ fillcolor _ _95BBE3_ _ client2 -_ channel1 _label _ _subscribe_ client5 -_ channel1 _label _ _subscribe_ client1 -_ channel1 _label _ _subscribe_ _ channel1 -_ client2 _label _ _message_ color _ _B22222_ channel1 -_ client5 _label _ _message_ color _ _B22222_ channel1 -_ client1 _label _ _message_ color _ _B22222]: /images/20220528/2c7ceeb047bc41339995604bad7b9189.png
[digraph pubsub _ rankdir _ LR_ node _shape _ record_ style _ filled_ edge _style _ bold_ _ keys pubsub _label _ _pubsub_channels _channel1_ channel1 _channel2_ channel2 _channel3_ channel3 _ ... _channelN_ channelN_ fillcolor _ _A8E270_ _ clients blocking for channel1 client1 _label _ _client1_ fillcolor _ _95BBE3_ client5 _label _ _client5_ fillcolor _ _95BBE3_ client2 _label _ _client2_ fillcolor _ _95BBE3_ null_1 _label _ _NULL_ shape _ plaintext_ pubsub_channel1 -_ client2_ client2 -_ client5_ client5 -_ client1_ client1 -_ null_1_ _ clients blocking for channel2 client7 _label _ _client7_ fillcolor _ _95BBE3_ null_2 _label _ _NULL_ shape _ plaintext_ pubsub_channel2 -_ client7_ client7 -_ null_2_ _ channel client3 _label _ _client3_ fillcolor _ _95BBE3_ client4 _label _ _client4_ fillcolor _ _95BBE3_ client6 _label _ _client6_ fillcolor _ _95BBE3_ null_3 _label _ _NULL_ shape _ plaintext_ pubsub_channel3 -_ client3_ client3 -_ client4_ client4 -_ client6_ client6 -_ null_3]: /images/20220528/45a6d00118cf4e7c9c9586ebd66a3f6a.png
[digraph new_subscribe _ rankdir _ LR_ node _shape _ record_ style _ filled_ edge _style _ bold_ _ keys pubsub _label _ _pubsub_channels _channel1_ channel1 _channel2_ channel2 _channel3_ channel3 _ ... _channelN_ channelN_ fillcolor _ _A8E270_ _ clients blocking for channel1 client1 _label _ _client1_ fillcolor _ _95BBE3_ client5 _label _ _client5_ fillcolor _ _95BBE3_ client2 _label _ _client2_ fillcolor _ _95BBE3_ client10086 _label _ _client10086_ fillcolor _ _FFC1C1_ client10086_1 _label _ _client10086_ fillcolor _ _FFC1C1_ client10086_2 _label _ _client10086_ fillcolor _ _FFC1C1_ null_1 _label _ _NULL_ shape _ plaintext_ null_2 _label _ _NULL_ shape _ plaintext_ null_3 _label _ _NULL_ shape _ plaintext_ pubsub_channel1 -_ client2_ client2 -_ client5_ client5 -_ client1_ client1 -_ client10086_ client10086 -_ null_1_ _ clients blocking for channel2 client7 _label _ _client7_ fillcolor _ _95BBE3_ pubsub_channel2 -_ client7_ client7 -_ client10086_1_ client10086_1 -_ null_2_ _ channel client3 _label _ _client3_ fillcolor _ _95BBE3_ client4 _label _ _client4_ fillcolor _ _95BBE3_ client6 _label _ _client6_ fillcolor _ _95BBE3_ pubsub_channel3 -_ client3_ client3 -_ client4_ client4 -_ client6_ client6 -_ client10086_2_ client10086_2 -_ null_3]: /images/20220528/761fa2ac7443455f8e6c87548f28ea10.png
[UNSUBSCRIBE]: http://redis.readthedocs.org/en/latest/pub_sub/unsubscribe.html#unsubscribe
[digraph pattern_relation _ rankdir _ BT_ node _style _ filled_ edge _style _ bold_ kindle _label _ _tweet.shop.kindle_ fillcolor _ _A8E270_ ipad _label _ _tweet.shop.ipad_ fillcolor _ _A8E270_ node _shape _ octagon_ pattern _label _ _tweet.shop._ pattern -_ kindle _label _ _match_ pattern -_ ipad _label _ _match_ node _shape _ box_ client123 _fillcolor _ _95BBE3_ client256 _fillcolor _ _95BBE3_ clientX _fillcolor _ _95BBE3_ clientY _fillcolor _ _95BBE3_ client3333 _fillcolor _ _95BBE3_ client4444 _fillcolor _ _95BBE3_ client5555 _fillcolor _ _95BBE3_ client123 -_ pattern _label _ _subscribe_ client256 -_ pattern _label _ _subscribe_ clientX -_ kindle _label _ _subscribe_ clientY -_ kindle _label _ _subscribe_ client3333 -_ ipad _label _ _subscribe_ client4444 -_ ipad _label _ _subscribe_ client5555 -_ ipad _label _ _subscribe]: /images/20220528/14938ec3accc4f19996c55e0e6919298.png
[digraph send_message_to_pattern _ node _style _ filled_ edge _style _ bold_ _ tweet.shop.ipad ipad _label _ _tweet.shop.ipad_ fillcolor _ _A8E270_ ipad -_ pattern _label _ _match_ dir _ back_ node _shape _ box_ ipad -_ client3333 _label _ _subscribe_ dir _ back_ ipad -_ client4444 _label _ _subscribe_ dir _ back_ ipad -_ client5555 _label _ _subscribe_ dir _ back_ node _shape _ plaintext_ message _label _ _PUBLISH tweet.shop.kindle message_ fillcolor _ _FADCAD_ kindle _label _ _tweet.shop.kindle_ shape _ ellipse_ fillcolor _ _A8E270_ pattern _label _ _tweet.shop._ shape _ octagon_ message -_ kindle _style _ _bold_ dashed_ color _ _B22222_ kindle -_ pattern _style _ _bold_ dashed_ color _ _B22222_ node _shape _ box_ kindle -_ clientX _style _ _bold_ dashed_ color _ _B22222_ label _ _message_ kindle -_ clientY _style _ _bold_ dashed_ color _ _B22222_ label _ _message_ pattern -_ client123 _label _ _message_ style _ _bold_ dashed_ color _ _B22222_ pattern -_ client256 _label _ _message_ style _ _bold_ dashed_ color _ _B22222_ _ client color client123 _fillcolor _ _95BBE3_ client256 _fillcolor _ _95BBE3_ clientX _fillcolor _ _95BBE3_ clientY _fillcolor _ _95BBE3_ client3333 _fillcolor _ _95BBE3_ client4444 _fillcolor _ _95BBE3_ client5555 _fillcolor _ _95BBE3]: /images/20220528/96007be9197c4c7ea0df35bf8fce9e6e.png
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[PUNSUBSCRIBE]: http://redis.readthedocs.org/en/latest/pub_sub/punsubscribe.html#punsubscribe