Redis的发布与订阅主要是实现客户端订阅一个频道或者模式，当某客户端向一个频道发送消息时，该频道或者匹配模式订阅者都能够收到消息。
频道的订阅与退订
Redis在服务器结构体中的pubsub_channels字典中保存了所有的频道订阅关系。pubsub_channels键为频道，值为订阅的客户端组成的链表。
客户端结构体的pubsub_channels保存了客户端订阅的所有频道，pubsub_channels的键为频道，值为空。
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struct redisServer {
// ...
dict *pubsub_channels; // 保存所有的频道订阅关系
// ...
}
struct redisClient {
// ...
dict *pubsub_channels; // 记录客户端订阅的频道
// ...
}
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订阅
源码如下
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// 订阅命令处理函数
void subscribeCommand(redisClient *c) {
int j;
// 遍历指令中的所有频道
for (j = 1; j < c->argc; j++)
pubsubSubscribeChannel(c,c->argv[j]);
c->flags |= REDIS_PUBSUB;
}
// 设置客户端c订阅频道channel
int pubsubSubscribeChannel(redisClient *c, robj *channel) {
dictEntry *de;
list *clients = NULL;
int retval = 0;
/* Add the channel to the client -> channels hash table */
// 将channels加倒c->c->pubsub_channels的字典里
if (dictAdd(c->pubsub_channels,channel,NULL) == DICT_OK) {
retval = 1;
incrRefCount(channel);
/* Add the client to the channel -> list of clients hash table */
// 找出服务器中的频道
de = dictFind(server.pubsub_channels,channel);
// 不存在就添加一个频道
// 获取客户端链表
if (de == NULL) {
clients = listCreate();
dictAdd(server.pubsub_channels,channel,clients);
incrRefCount(channel);
} else {
clients = dictGetVal(de);
}
// 添加到客户端链表尾部
listAddNodeTail(clients,c);
}
/* Notify the client */
// 回复客户端
addReply(c,shared.mbulkhdr[3]);
addReply(c,shared.subscribebulk);
addReplyBulk(c,channel);
addReplyLongLong(c,clientSubscriptionsCount(c));
return retval;
}
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退订
源码如下
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void unsubscribeCommand(redisClient *c) {
if (c->argc == 1) {
// 退订所有频道
pubsubUnsubscribeAllChannels(c,1);
} else {
int j;
// 遍历频道一一退订
for (j = 1; j < c->argc; j++)
pubsubUnsubscribeChannel(c,c->argv[j],1);
}
if (clientSubscriptionsCount(c) == 0) c->flags &= ~REDIS_PUBSUB;
}
// 退订所有频道
int pubsubUnsubscribeAllChannels(redisClient *c, int notify) {
dictIterator *di = dictGetSafeIterator(c->pubsub_channels);
dictEntry *de;
int count = 0;
// 遍历一一退订
while((de = dictNext(di)) != NULL) {
robj *channel = dictGetKey(de);
count += pubsubUnsubscribeChannel(c,channel,notify);
}
/* We were subscribed to nothing? Still reply to the client. */
if (notify && count == 0) {
addReply(c,shared.mbulkhdr[3]);
addReply(c,shared.unsubscribebulk);
addReply(c,shared.nullbulk);
addReplyLongLong(c,dictSize(c->pubsub_channels)+
listLength(c->pubsub_patterns));
}
dictReleaseIterator(di);
return count;
}
// 客户端退订频道
int pubsubUnsubscribeChannel(redisClient *c, robj *channel, int notify) {
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... */
// 移除客户端字典中频道的订阅
if (dictDelete(c->pubsub_channels,channel) == DICT_OK) {
retval = 1;
/* Remove the client from the channel -> clients list hash table */
// 找到服务器频道
de = dictFind(server.pubsub_channels,channel);
redisAssertWithInfo(c,NULL,de != NULL);
clients = dictGetVal(de); // 获取链表
ln = listSearchKey(clients,c); // 寻找链表中的订阅
redisAssertWithInfo(c,NULL,ln != NULL);
listDelNode(clients,ln); // 删除节点
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. */
// 删除节点后 链表为空 删除字典中的节点
dictDelete(server.pubsub_channels,channel);
}
}
/* Notify the client */
// 回复客户端
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;
}
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模式的订阅与退订
Redis在服务器结构体中的pubsub_patterns链表中保存了所有订阅模式关系。使用pubsubPattern结构的数据作为节点。
客户端结构体的pubsub_patterns保存了客户端订阅的所有模式，节点使用pubsubPattern结构的数据。
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struct redisServer {
// ...
list *pubsub_patterns; // 所有订阅模式关系
// ...
}
struct redisClient {
// ...
list *pubsub_patterns; // 订阅模式关系
// ...
}
typedef struct pubsubPattern {
client *client; // 订阅模式的客户端
robj *pattern; // 被订阅模式
} pubsubPattern;
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订阅
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// 订阅模式
void psubscribeCommand(redisClient *c) {
int j;
// 遍历命令中的模式
for (j = 1; j < c->argc; j++)
pubsubSubscribePattern(c,c->argv[j]);
c->flags |= REDIS_PUBSUB;
}
// 设置客户端c订阅模式pattern
int pubsubSubscribePattern(redisClient *c, robj *pattern) {
int retval = 0;
// 客户端模式链表中查找模式
// 为空则创建
if (listSearchKey(c->pubsub_patterns,pattern) == NULL) {
retval = 1;
pubsubPattern *pat;
// 客户端模式链表尾部添加模式
listAddNodeTail(c->pubsub_patterns,pattern);
incrRefCount(pattern);
// 服务端模式链表尾部添加模式
pat = zmalloc(sizeof(*pat));
pat->pattern = getDecodedObject(pattern);
pat->client = c;
listAddNodeTail(server.pubsub_patterns,pat);
}
/* Notify the client */
addReply(c,shared.mbulkhdr[3]);
addReply(c,shared.psubscribebulk);
addReplyBulk(c,pattern);
addReplyLongLong(c,clientSubscriptionsCount(c));
return retval;
}
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退订
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// 退订模式
void punsubscribeCommand(redisClient *c) {
if (c->argc == 1) {
// 退订所有模式
pubsubUnsubscribeAllPatterns(c,1);
} else {
int j;
// 退订命令中的模式
for (j = 1; j < c->argc; j++)
pubsubUnsubscribePattern(c,c->argv[j],1);
}
if (clientSubscriptionsCount(c) == 0) c->flags &= ~REDIS_PUBSUB;
}
// 退订客户端c订阅的所有模式
int pubsubUnsubscribeAllPatterns(redisClient *c, int notify) {
listNode *ln;
listIter li;
int count = 0;
// 遍历，一一退订
listRewind(c->pubsub_patterns,&li);
while ((ln = listNext(&li)) != NULL) {
robj *pattern = ln->value;
count += pubsubUnsubscribePattern(c,pattern,notify);
}
if (notify && count == 0) {
/* We were subscribed to nothing? Still reply to the client. */
addReply(c,shared.mbulkhdr[3]);
addReply(c,shared.punsubscribebulk);
addReply(c,shared.nullbulk);
addReplyLongLong(c,dictSize(c->pubsub_channels)+
listLength(c->pubsub_patterns));
}
return count;
}
// 取消客户端c对模式pattern的订阅
int pubsubUnsubscribePattern(redisClient *c, robj *pattern, int notify) {
listNode *ln;
pubsubPattern pat;
int retval = 0;
incrRefCount(pattern); /* Protect the object. May be the same we remove */
// 订阅了才进行操作
if ((ln = listSearchKey(c->pubsub_patterns,pattern)) != NULL) {
retval = 1;
// 从客户端订阅中删除
listDelNode(c->pubsub_patterns,ln);
pat.client = c;
pat.pattern = pattern;
// 从服务端订阅中删除
ln = listSearchKey(server.pubsub_patterns,&pat);
listDelNode(server.pubsub_patterns,ln);
}
/* Notify the client */
if (notify) {
addReply(c,shared.mbulkhdr[3]);
addReply(c,shared.punsubscribebulk);
addReplyBulk(c,pattern);
addReplyLongLong(c,dictSize(c->pubsub_channels)+
listLength(c->pubsub_patterns));
}
decrRefCount(pattern);
return retval;
}
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发送消息
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// 发布消息
void publishCommand(redisClient *c) {
int receivers = pubsubPublishMessage(c->argv[1],c->argv[2]);
// 暂时不考虑集群
if (server.cluster_enabled)
clusterPropagatePublish(c->argv[1],c->argv[2]);
else
forceCommandPropagation(c,REDIS_PROPAGATE_REPL);
addReplyLongLong(c,receivers);
}
// 将消息发送到所有订阅了频道的客户端
int pubsubPublishMessage(robj *channel, robj *message) {
int receivers = 0;
dictEntry *de;
listNode *ln;
listIter li;
/* Send to clients listening for that channel */
// 先查找订阅了频道的
de = dictFind(server.pubsub_channels,channel);
if (de) {
// 获取链表
list *list = dictGetVal(de);
listNode *ln;
listIter li;
// 遍历链表 发送消息
listRewind(list,&li);
while ((ln = listNext(&li)) != NULL) {
redisClient *c = ln->value;
addReply(c,shared.mbulkhdr[3]);
addReply(c,shared.messagebulk);
addReplyBulk(c,channel);
addReplyBulk(c,message);
receivers++;
}
}
/* Send to clients listening to matching channels */
if (listLength(server.pubsub_patterns)) {
// 遍历模式链表
listRewind(server.pubsub_patterns,&li);
channel = getDecodedObject(channel);
while ((ln = listNext(&li)) != NULL) {
pubsubPattern *pat = ln->value;
// 匹配模式 发送消息
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;
}
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