Redis design and Implementation (VII) | publish & subscribe

Publish and subscribe

• summary

Redis The publish and subscribe function of is provided by PUBLISH、SUBSCRIBE、PSUBSCRIBE Wait for the order to make up .
Through execution SUBSCRIBE command , The client can subscribe to one or more channels , To become subscribers to these channels ( subscriber ): Whenever another client sends a message to the subscribed channel （message) when , All subscribers to the channel will receive this message .

• Command to use

#  If all three clients execute this , All three clients are subscribers to this channel 
SUBSCRIBE "news.it"
#  A client sends this , Then all three subscribers will receive 
PUBLISH "news.it" "hello"

• PSUBSCRIBE

This command allows the client to subscribe to one or more modes , Suppose as shown in the figure below A subscribe it,B subscribe et,C、D Subscribe to a ie Pattern , So it Channel sends messages ,C、D I will also receive ,
Wildcard ? Represents a placeholder ,* Represents any placeholder （ Include 0 individual ）,?* Represents more than one placeholder

# PSUBSCRIBE You can subscribe to one or more patterns , Similar to wildcards 
PSUBSCRIBE "news.?t"

1. Channel subscription and unsubscribe

• summary

Clients subscribing to the same channel will redisServer Structure in the form of a linked list pubsub_channels In the dictionary , Here's the picture

1.1 Subscribed Channels

• Add a dictionary , Will traverse all input channels

• Add the corresponding key of the channel , If the channel does not exist , Then there must be no bond , So I will add the key to the dictionary first
• If there is a channel , Then join the team directly

1.2 unsubscribe

• summary

This action is the reverse order of the subscription action just now

UNSUBSCRIBE " channel 1" " channel 2"

2. Mode subscription and unsubscribe

• summary

Mode subscription and unsubscribe will be in redisServer Of pubsub_patterns Properties of the , It is also a linked list , The structure of each node is pubsubPattern

• example

2.1 A subscription model

• step

1. Create a new one pubsubPattern structure , Structure pattern Property to the subscribed mode ,client Client with property set to subscription mode .
2. take pubsubPattern Structure added to pubsub_patterns The end of a list .

2.2 unsubscribe

• summary

Mode unsubscribe order PUNSUBSCRIBE yes PSUBSCRIBE Counter operation of orders : When a client unsubscribes from a certain mode or modes , The server will be pubsub_patterns Look up and delete those in the list pattern Property is unsubscribed mode , also client Property of the client executing the unsubscribe command pubsubPattern structure .

3. Send a message

• summary

When one Redis Client execution PUBLISH <channel> <message> Command will message message Send to channel channel When , The server needs to perform the following two actions :

1. The message is message Send to channel All subscribers to the channel .
2. If there are one or more modes pattern And channel channel Match , Then send the message message Send to pattern Subscribers to patterns .

4. View subscription messages

• summary

PUBSUB The order is Redis 2.8 One of the new orders , The client can view information about the channel or mode through this command , For example, how many subscribers a channel currently has , Or how many subscribers there are in a certain mode at present , And so on .

4.1 PUBSUB CHANNELS

• summary

PUBSUB CHANNELS <pattern>, The subcommand is used to return the channel that the server is currently subscribed to , among pattern It's optional

• No mode given , Then return to all subscribed channels
• Given mode , Then all channels that conform to the mode

4.2 PUBSUB NUMSUB

• summary

PUBSUB NUMSUB [channel-1 -2 ...-n] Sons command , Returns the number of subscribers of the corresponding channel , The bottom layer is to traverse the channel name corresponding to the dictionary , The length of the corresponding linked list

4.3 PUBSUB NUMPAT

• summary

PUBSUB NUMPAT The subcommand is used to return the number of currently subscribed modes of the server . This subcommand is done by returning pubsub patterns The length of the list to achieve , Because the length of the linked list is the number of subscription modes of the server ,