Hello everyone , I'm cabbage . This article is mainly for explanation Redis Publish and subscribe messages , If you get something after reading the article , You can support bloggers three times in a row ~, Hee hee .

One 、 What is publish and subscribe

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• Redis Publish subscribe (pub/sub) It's a kind of Message communication mode ： sender (pub) Send a message , subscriber (sub) receive messages .

• characteristic ：Redis Clients can subscribe to any number of channels .

• It's like fans pay attention to me , When I finish writing the article and publish it , You open it CSDN You will also receive my articles . here , I am the sender （pub）; Fans are subscribers （sub）.

Structure diagram is as follows ： The publisher sends his message to redis The server , Subscribers from redis Get the message published by the publisher from the server

Two 、Redis Publish and subscribe to

• To facilitate the later explanation of the use of publish and subscribe command lines , Let me introduce briefly with two pictures redis Realize the overall process of publishing and subscribing .

• The client can subscribe to channels, as shown in the figure below ：

• When you post a message to this channel , The message is sent to the subscribing client , Here's the picture ：

3、 ... and 、redis Publish and subscribe to common commands

• The following table lists them redis Publish and subscribe to common commands ：
  

Four 、 Order actual combat

• In the demo redis Before publishing and subscribing to messages , We need to open two clients , One acts as a News Publisher , One acts as a message recipient .

1、 Basic use

• First use a client to subscribe to the channel csdn_blog, Waiting for news ：

127.0.0.1:6379> SUBSCRIBE csdn_blog 
Reading messages... (press Ctrl-C to quit)
1) "subscribe"
2) "csdn_blog"
3) (integer) 1

• Then a client is csdn_blog Channel sends messages hello,cabbage：

127.0.0.1:6379> PUBLISH csdn_blog "hello,cabbage"
(integer) 1

• Finally, the receiver receives the message ：

1) "message" 
2) "csdn_blog"    #  The channel where the message is received 
3) "hello,cabbage"   #  Messages received 

2、 Subscribe to qualified channels

• Subscribe to csdn The first channel ,* For any character

127.0.0.1:6379> PSUBSCRIBE csdn*
Reading messages... (press Ctrl-C to quit)
1) "psubscribe"
2) "csdn*"
3) (integer) 1

• Publishers post messages on two channels ：

127.0.0.1:6379> PUBLISH csdn_blog "hello"
(integer) 1
127.0.0.1:6379> PUBLISH csdn_sing "sing"
(integer) 1

• Finally, subscribers receive messages from two channels ：

1) "pmessage"
2) "csdn*"
3) "csdn_blog"
4) "hello"
1) "pmessage"
2) "csdn*"
3) "csdn_sing"
4) "sing"

3、 View active channels

• Subscribers subscribe to two channels ：

127.0.0.1:6379> SUBSCRIBE csdn_one csdn_two
Reading messages... (press Ctrl-C to quit)
1) "subscribe"
2) "csdn_one"
3) (integer) 1
1) "subscribe"
2) "csdn_two"
3) (integer) 2

• Publishers send messages on three channels ：

127.0.0.1:6379> PUBLISH csdn_one "one"
(integer) 1
127.0.0.1:6379> PUBLISH csdn_two "two"
(integer) 1
127.0.0.1:6379> PUBLISH csdn_three "three"
(integer) 0

• Show active channels on the publisher client ：

127.0.0.1:6379> PUBSUB channels
1) "csdn_one"
2) "csdn_two"

5、 ... and 、 Principle of publishing and subscribing

• Every Redis The server processes all maintain a... That represents the state of the server redis.h/redisServer structure , Structural pubsub_channels Property is a dictionary , This dictionary is used to save subscription channel information , among , Dictionary Key is the channel being subscribed to , And the dictionary is The value is a linked list , All clients subscribing to this channel are saved in the linked list .

1、 Subscription channel principle

• Suppose there is a channel as shown in the figure below and a client subscribing to the channel ： It is clear from the picture ,channelA Three people subscribe to the channel ;channelB No one subscribes to the channel ;channelC Two people subscribe to the channel .

• When the client clientF call SUBSCRIBE On command , The program will place the client and the channel to be subscribed in pubsub_channels It's related in the dictionary . Execute the following instructions , The corresponding result graph is ：

127.0.0.1:6379> SUBSCRIBE channelB channelC channelA

• Conclusion ： adopt pubsub_channels Dictionaries , The program just checks whether a channel is the key of the dictionary , You can know if the channel is being subscribed by the client ; Just take the value of a key , You can get the information of all clients who subscribe to the channel .

2、 Principle of publishing information

• Principle that ： When calling PUBLISH channel message command , The procedure is based first on channel Key to dictionary , Then send the information to all clients in the dictionary value chain .

• For the image above , If the client channelA Carry out orders PUBLISH channelA “hello,cabbage”, that clientA,clientB,clientC,clientF All four clients will receive "hello,cabbage" Information , By traversing all clients of the subscription channel .

3、 Unsubscribe information principle

• principle ： Use UNSUBSCRIBE The command can unsubscribe the specified channel , This command performs the reverse operation of subscription ： It is from pubsub_channels Given channel of Dictionary （ key ） in , Delete information about the current client , In this way, the channel information will not be sent to this client .

Reference article ：http://t.zoukankan.com/rxbook-p-12652198.html

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