Implementation of Muduo accept connection, disconnection and sending data

Catalog

One 、TcpServer Accept new connection

1、TcpServer

2、TcpConnection

Two 、TcpConnection disconnect

3、 ... and 、TcpConnection send data

Four 、 How to limit the maximum number of concurrent connections to the server

5、 ... and 、 How to kick off idle connections

6、 ... and 、 Flow control when sending data

7、 ... and 、 Why? TcpConnection Object is used shared_ptr To manage objects

8、 ... and 、TcpConnection Of id How to store , When from client connection Receive the data , How to know id 

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muduo It's for Chen Shuo's personal use C++ Developed a network library , The code is of great learning value , The summary comes from books 《Linux Multithreaded server-side programming 》, Also written by Chen Shuo , Can cooperate with github Use code together .

muduo github website ：https://github.com/chenshuo/muduo

One 、TcpServer Accept new connection

1、TcpServer

TcpServer The sequence of function calls related to the new connection is shown in the following figure

 

Channel::handleEvent() The trigger condition is listening socket Can be read , Indicates that a new connection has arrived ,TcpServer The corresponding... Will be created for the new connection TcpConnection object . When a new connection arrives ,Acceptor Callbacks newConnection(), The latter creates TcpConnection object conn, Add it to connectionMap, Set it up callback, Call again conn->connectEstablished(), Which will call the user provided ConnectionCallback.

2、TcpConnection

yes muduo The core and most complex class ,TcpConnection Use Channel get socket Upper IO event , It will take care of itself writable event , But the readable The event passed MessageCallback Send to user ,TcpConnection Have Tcp socket, The destructor will close(fd).

Two 、TcpConnection disconnect

muduo Passive shutdown is available , That is, the other party closes the connection first , Local read() return 0, Trigger shutdown logic . You can also call TcpConnection Of forceClose() Member functions , For actively closing the connection , The latter will call handleClose() function , The process of function call is shown in the following figure ：

 

 

TcpServer Will send to TcpConnection register CloseCallback, Used to receive the message of disconnection .handleClose() The main function of is to call closeCallback_, This callback is bound to TcpServer::removeConnection(), The latter will put conn from ConnectionMap In the delete .

TcpConnection It didn't provide close() function , But use shutdown() function ,muduo The initiative to close the connection is divided into two steps ： If you want to take the initiative to close the connection , First turn off the local “ Write ” End , Wait until the other party closes the connection , Then close the local “ read ” End , such half-close Mainly to prevent closing the connection , The other party is still sending data .

3、 ... and 、TcpConnection send data

By calling TcpConnection::send() To send data , Because the message must be read and written in EventLoop The same thread of , Therefore, thread safety must be ensured , So in send When , It will first check whether it is in the current IO Threads , If so, call directly sendInLoop(), If not in a thread , Will be able to messsage A copy of , Pass to IO In thread sendInLoop() To send the .

sendInLoop() Will try to send data directly , If you send it all at once , Will not enable WriteCallback, If only part of the data is sent , Then put the remaining data into outputBuffer_, And began to focus on writable event , And then in handleWrite() Send the remaining data in .

Four 、 How to limit the maximum number of concurrent connections to the server

Prepare an idle file descriptor , When the file descriptor used by this process has reached the upper limit （Acceptor Of handleRead() perform accept, return errno by EMFILE）, First close the idle file descriptor , Get a quota for a file descriptor , Again accept() Get new socket The descriptor of the connection , And then immediately close() fall , This gracefully disconnects the client , Finally, reopen an idle file descriptor , hold “ pit ” Occupy , In case this happens again .

5、 ... and 、 How to kick off idle connections

Use timeing wheel, The approximate data structure is ：8 A barrel （hash set） A circular queue （ Timeout time 8s）. Put the first bucket 1 Connections that will time out in seconds , Put the second bucket 2 The connection that will time out after seconds, and so on , As soon as each connection receives the data, it puts itself into the 8 A barrel , Then in every second timer Disconnect the connection in the first bucket , Move this empty bucket to the end of the line . So you don't have to check all the connections every time .

The process of connection timeout being kicked out ：

 

Connection refresh ：

Concrete implementation , There is no connection in the bucket , It is Entry struct, Every Entry contain TcpConnection Of weak_ptr, When Entry The reference count of is decremented to 0, It means it doesn't exist in any box , The connection times out ,Entry The destructor of will disconnect .

6、 ... and 、 Flow control when sending data

muduo Set up WriteCompleteCallback() and HighWaterCallback() As “ Low water level callback ” and “ High water level callback ”, Called when the send buffer is empty WriteCompleteCallback(), When the length of the output buffer exceeds the size specified by the user , Just call HighWaterCallback().

7、 ... and 、 Why? TcpConnection Object is used shared_ptr To manage objects

Because from TCP The connection received a request Start , It may take some time for the program to process this connection , In order to confirm socket Connection is processing request Whether the period has been closed , Need to hold TcpConnection Reference count for object .

8、 ... and 、TcpConnection Of id How to store , When from client connection Receive the data , How to know id 

TcpConnection Of id Use std::map<int, TcpConnectionPtr> clientConns_ preservation id To client connection Mapping ,muduo Of TcpConnection Also use context function , Every TcpConnection There is one. boost::any member , Can be used to save and connection Bound arbitrary data , For example, connection. id, Connection last data arrival time , The user name represented by the connection .