feat: Add bpop cmd

[SamuelSze1]

Summary by CodeRabbit

Release Notes

• New Features

  • Introduced BLPop and BRPop commands for blocking list pop operations.
  • Added functionality to block clients while waiting for keys and to unblock them after operations.
  • Implemented a method to manage evicted blocked connections, enhancing connection management.

• Bug Fixes

  • Improved handling of client state updates during rename and list operations.

• Documentation

  • Updated command table to include new blocking operations and their functionalities.

These enhancements improve the efficiency and responsiveness of client interactions with the system.

[coderabbitai]

Walkthrough

The changes introduce new methods and classes to enhance the functionality of the BaseCmd and KiwiDB classes for managing blocked connections in a multi-database context. Notable additions include methods for blocking clients while waiting for data, unblocking connections, and handling expired connections. New command classes for blocking list pop operations are also defined, along with modifications to existing command handling functions to incorporate these features. Overall, the updates improve the system's ability to manage concurrent data access and manipulation.

Changes

Files	Change Summary
src/base_cmd.cc, src/base_cmd.h	Introduced methods BlockThisClientToWaitLRPush, ServeAndUnblockConns, and IsExpired in BaseCmd and BlockedConnNode classes. Added command names kCmdNameBLPop, kCmdNameBRPop, and structures BlockKey, BlockKeyHash for managing blocked connections.
src/cmd_admin.cc	Added method calls to set the client's key and invoke ServeAndUnblockConns after successful data push operations.
src/cmd_keys.cc	Updated RenameCmd::DoCmd to set the client's key and call ServeAndUnblockConns after a successful rename operation.
src/cmd_list.cc, src/cmd_list.h	Modified DoCmd methods for LPushCmd, RPoplpushCmd, and RPushCmd to include calls to ServeAndUnblockConns. Introduced new classes BLPopCmd and BRPopCmd with relevant methods and member variables for blocking operations.
src/cmd_table_manager.cc	Registered new commands BLPop and BRPop in the command table with a parameter count of -3.
src/kiwi.cc, src/kiwi.h	Added method ScanEvictedBlockedConnsOfBlrpop for managing evicted blocked connections, and methods to access the blocked connections map and mutex. Introduced member variables for managing blocked connections.

Sequence Diagram(s)

sequenceDiagram
    participant Client
    participant BaseCmd
    participant KiwiDB

    Client->>BaseCmd: Request to Block Client
    BaseCmd->>KiwiDB: BlockThisClientToWaitLRPush(keys, expire_time, client, type)
    KiwiDB-->>BaseCmd: Client Blocked
    BaseCmd->>Client: Confirmation of Blocking

    Client->>BaseCmd: Request to Unblock Client
    BaseCmd->>KiwiDB: ServeAndUnblockConns(client)
    KiwiDB-->>BaseCmd: Connections Unblocked
    BaseCmd->>Client: Confirmation of Unblocking

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Poem

🐰 In the garden where bunnies play,
New commands hop in, brightening the day!
Block and unblock, a dance so sweet,
With each little change, our code's a treat!
Hooray for the features that help us thrive,
In the world of code, we joyfully dive! 🌼

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Recent review details

Commits

Files that changed from the base of the PR and between ff31360 and d525c40.

Files selected for processing (9)

• src/base_cmd.cc (2 hunks)
• src/base_cmd.h (4 hunks)
• src/cmd_admin.cc (1 hunks)
• src/cmd_keys.cc (1 hunks)
• src/cmd_list.cc (3 hunks)
• src/cmd_list.h (1 hunks)
• src/cmd_table_manager.cc (1 hunks)
• src/kiwi.cc (3 hunks)
• src/kiwi.h (2 hunks)

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[SamuelSze1]

增加blpop和brpop指令，步骤为下
1.首先尝试直接lpop或rpop，如果list中有数据就直接返回，否则进入下一步
2.调用BlockThisClientToWaitLRPush将client放入key_to_blocked_conns_中对应的key的阻塞队列中
3.在执行向list中添加元素的cmd后调用ServeAndUnblockConns，将list的元素根据key_to_blocked_conns_中对应的key的阻塞队列的顺序执行对应的lpop或rpop并把结果发回给client
4.注册了一个线程每隔250ms调用ScanEvictedBlockedConnsOfBlrpop，遍历所有key_to_blocked_conns_并删除已经超时的或被执行的链接并返回给client
5.因为blpop只能可以输入多个list作为参数，但最后只能返回一个list的元素，所以在BlockedConnNode中有一个std::shared_ptr<std::atomic>,在BlockThisClientToWaitLRPush中会给对应同一个bpop指令的BlockedConnNode一个指向同一个原子变量的指针，当一个BlockedConnNode被从队列中取出来的时候会把这个变量设为true，阻止其他BlockedConnNode被执行

[luky116]

BlockThisClientToWaitLRPush 这个方法没有看到哪里有调用

[luky116]

看 pika 那边用到了这个方法， 可以补齐