Redis 】 【 publish and subscribe message

1.说明

在Redis2The publish-subscribe function is supported after the version,The publisher creates a channel,and send a message on it,All clients subscribed to the channel will receive the message（不出意外的情况下,但实际不一定）,The benefit of publish subscribe is to reduce unnecessary polling,The application scenario has an instant chat room、Public account subscription, etc.但Redis适合小型应用,If it is a large architecture,I believe it will still be usedrabbitMQ或者kafkaWait for more professionalMQqueue software.

Redis-server内部会维护一个字典,键是频道名,The value is a linked list that stores subscribers,Every time a message is published, the linked list is traversed for push.

2.订阅发布

我们打开一个redis终端,使用subscribe命令订阅频道,You may wish to open several terminals and subscribe to the same channel at the same time,For example, I open two terminals here and subscribe to itchatChannel的频道

# 订阅格式：subscribe 频道名
127.0.0.1:6379> subscribe chatChannel
Reading messages... (press Ctrl-C to quit)
1) "subscribe"
2) "chatChannel"
3) (integer) 1

再打开一个终端,使用publish命令发布消息,In this way, the terminal that subscribes to the channel will print the result

# 发布格式：publish 频道名 消息
127.0.0.1:6379> publish chatChannel "hello"
(integer) 2

结果如下图

Each client can subscribe to multiple channels at the same time,即subscribeThe parameter specifies multiple channels,另外也可以使用psubscribeCommand to subscribe to multiple channels（Seems to be called a pattern）,支持正则表达式

# 同时订阅 频道1、频道2、频道3
subscribe 频道1 频道2 频道3
# 订阅所有以“chat”开头的频道
psubscribe chat*

You can use it if you want to unsubscribeunsubscribe和punsubscribe命令,Usage is a command followed by a channel or matching pattern

3.代码实现

订阅消息,比如说订阅3Unsubscribe after that

from redis import Redis

r = Redis(host='localhost', port=6379, db=0)
p = r.pubsub()  # If you don't want to receive some other information, you can put the parameterignore_subscribe_messages改为True
p.subscribe("testChannel")  # If you want to subscribe to multiple channels at the same time,可以传入多个参数
# p.psubscribe("test*") # 模式匹配

i = 0
while True:
    msg = p.get_message()
    if msg:
        print("来电了: ", msg)
        i += 1
    if i > 2:
        break

# 取消订阅
p.unsubscribe()
# p.punsubscribe()
p.close()
r.close()

Posting a message is relatively simple

from redis import Redis

r = Redis(host='localhost', port=6379, db=0)
r.publish('testChannel', 'hello everybody')
r.close()