Muduo库源码剖析(九)——TcpConnection类

TcpConnection类

要点

TcpConnection表示的是“一次TCP连接”，它是不可再生的，一旦连接断开，这个TcpConnection对象就没啥用了。它的主要功能就是对 成功连接服务器的客户连接connfd 的封装。

一个TcpConnection 唯一对应一个Channel和Socket

Channel处理事件的一系列回调就是在 TcpConnection类中设置和实现的。

TcpConnection断开连接

muduo只有一种关闭连接的方式：被动关闭。即对方先关闭连接，本地read(2)返回0，触发关闭逻辑。函数调用流程如下

实现代码

代码量比较大，但是逻辑比较简单

// TcpConnection.h
#pragma once
#include "noncopyable.h"
#include "InetAddress.h"
#include "Callbacks.h"
#include "Buffer.h"
#include "Timestamp.h"

#include 
#include 
#include 

class Channel;
class EventLoop;
class Socket;

// TcpServer -> Acceptor -> 有一个新用户连接，通过accept得到connfd
// -> TcpConnection 设置回调 -> Channel -> Poller -> Channel的回调操作
// 对 成功与服务器建立连接所得的connfd的封装
class TcpConnection : noncopyable, public std::enable_shared_from_this<TcpConnection>
{
public:
    TcpConnection(EventLoop *loop,
                const std::string &nameArg,
                int sockfd,
                const InetAddress& localAddr,
                const InetAddress& peerAddr);
    ~TcpConnection();

    EventLoop* getLoop() const { return loop_; }
    // getLoopName
    const std::string& name() const { return name_; }
    const InetAddress& localAddress() const { return localAddr_; }
    const InetAddress& peerAddress() const { return peerAddr_; }

    bool connected() const { return state_ == kConnected; }

    // 发送数据
    void send(const std::string &buf);
    // 关闭连接
    void shutdown();

    void setConnectionCallback(const ConnectionCallback& cb) { connectionCallback_ = cb; }

    void setMessageCallback(const MessageCallback &cb) { messageCallback_ = cb; }
    
    void setWriteCompleteCallback(const WriteCompleteCallback &cb) { writeCompleteCallback_ = cb; }
    
    void setHighWaterMarkCallback(const HighWaterMarkCallback &cb, size_t highWaterMark) { highWaterMarkCallback_ = cb; highWaterMark_ = highWaterMark; }

    void setCloseCallback(const CloseCallback& cb) { closeCallback_ = cb; }

    // 连接建立
    void connectEstablished();
    // 连接销毁
    void connectDestroyed();

private:
    enum StateE { kDisconnected, kConnecting, kConnected, kDisconnecting };
    void setState(StateE state) { state_ = state; }

    void handleRead(Timestamp receiveTime);
    void handleWrite();
    void handleClose();
    void handleError();

    void sendInLoop(const void* message, size_t len);
    void shutdownInLoop();
    
    EventLoop *loop_; // 不是baseLoop，因为 TcpConnection都是在subLoop中管理
    const std::string name_;
    std::atomic_int state_;
    bool reading_;

    // 与Acceptor类似， Acceptor -> mainLoop , TcpConnection -> subLoop
    std::unique_ptr<Socket> socket_;
    std::unique_ptr<Channel> channel_;

    const InetAddress localAddr_;
    const InetAddress peerAddr_;

    ConnectionCallback connectionCallback_;
    MessageCallback messageCallback_; // 有读写消息时的回调
    WriteCompleteCallback writeCompleteCallback_;
    HighWaterMarkCallback highWaterMarkCallback_;
    CloseCallback closeCallback_;
    size_t highWaterMark_;

    Buffer inputBuffer_; // 接收数据的缓冲区
    Buffer outputBuffer_; // 发送数据的缓冲区
};

// TcpConnection.cc
#include "TcpConnection.h"
#include "Logger.h"
#include "Socket.h"
#include "Channel.h"
#include "EventLoop.h"

#include 
#include 
#include 
#include 
#include 
#include 
#include 

static EventLoop* CheckLoopNotNull(EventLoop *loop)
{
    if(loop == nullptr)
    {
        LOG_FATAL("%s:%s:%d TcpConnection Loop is null! \n", __FILE__, __FUNCTION__, __LINE__);
    }
    return loop;
}

TcpConnection::TcpConnection(EventLoop *loop,
                const std::string &nameArg,
                int sockfd,
                const InetAddress& localAddr,
                const InetAddress& peerAddr)
    : loop_(CheckLoopNotNull(loop))
    , name_(nameArg)
    , state_(kConnecting)
    , reading_(true)
    , socket_(new Socket(sockfd))
    , channel_(new Channel(loop, sockfd))
    , localAddr_(localAddr)
    , peerAddr_(peerAddr)
    , highWaterMark_(64*1024*1024) // 64M
{
    // 给channel设置相应回调
    // Poller 给 Channel通知感兴趣的事件发生，Channel会回调相应操作函数
    channel_->setReadCallback(
        std::bind(&TcpConnection::handleRead, this, std::placeholders::_1)
    );
    channel_->setWriteCallback(
        std::bind(&TcpConnection::handleWrite, this)
    );
    channel_->setCloseCallback(
        std::bind(&TcpConnection::handleClose, this)
    );
    channel_->setErrorCallback(
        std::bind(&TcpConnection::handleError, this)
    );

    LOG_INFO("TcpConnection::ctor[%s] at fd=%d\n", name_.c_str(), sockfd);
    socket_->setKeepAlive(true);
}

TcpConnection::~TcpConnection()
{
    LOG_INFO("TcpConnection::dtor[%s] at fd=%d state=%d\n",
     name_.c_str(), channel_->fd(), (int)state_);
}

void TcpConnection::send(const std::string &buf)
{
    if(state_ == kConnected)
    {
        if(loop_->isInLoopThread())
        {
            sendInLoop(buf.c_str(), buf.size());
        }
        else  // 唤醒Loop所属线程执行send
        {
            loop_->runInLoop(
                std::bind(
                    &TcpConnection::sendInLoop,
                    this,
                    buf.c_str(),
                    buf.size()
                )
            );
        }
    }
}

// 发送数据时，若应用写的快，内核发送满
// 需要把待发送数据写入缓冲区中
// 且设置了水位回调
void TcpConnection::sendInLoop(const void* data, size_t len)
{
    ssize_t nwrote = 0;
    size_t remaining = len; // 每一次写后，剩余没写的数据量
    bool faultError = false;

    // 之前调用过该 TcpConnection 的shutdown，不能再进行发送
    if(state_ == kDisconnected)
    {
        LOG_ERROR("disconnected, give up writing!");
        return;
    }

    // !!if no thing in output queue, try writing directly
    // 表示channel_第一次开始写数据， 且缓冲区无待发数据,则可以直接发data数据
    // 否则要将数据加入到 outputBuffer_ 后发送
    if(!channel_->isWriting() && outputBuffer_.readableBytes() == 0)
    {
        nwrote = ::write(channel_->fd(), data, len);
        if(nwrote >= 0)
        {
            remaining = len - nwrote;
            if(remaining == 0 && writeCompleteCallback_)
            {
                // 数据全部发完，不用给channel设置epollout事件
                loop_->queueInLoop(
                    std::bind(writeCompleteCallback_, shared_from_this())
                );
            }
        }
        else 
        {
            nwrote = 0;
            // EWOULDBLOCK没有数据的正常返回
            if(errno != EWOULDBLOCK)
            {
                LOG_ERROR("TcpConnection::sendInLoop");
                // SIGPIPE SIGRESET
                if(errno == EPIPE || errno == ECONNRESET)
                {
                    faultError = true; 
                }
            }
        }
    }

    // 说明本次write，并没把数据全发出，剩余数据需要保存到缓冲区中，然后给channel
    // 注册epollout事件，poller发现tcp的发送缓冲区有内容可发，会通知相应的sock--channel调用writeCallback_回调
    // 即调用 TcpConnection::handleWrite(),把发送缓冲区中数据全发送完成
    if(!faultError && remaining > 0)
    {
        // 目前发送缓冲区剩余待发送数据长度
        size_t oldLen = outputBuffer_.readableBytes();
        if(oldLen + remaining >= highWaterMark_
            && oldLen < highWaterMark_  // 上一次若已经超过高水位，不需要调用回调
            && highWaterMarkCallback_)
        {
            loop_->queueInLoop(
                std::bind(highWaterMarkCallback_, shared_from_this(), oldLen + remaining)
            );
        }
        outputBuffer_.append((char*)data + nwrote, remaining);
        if(!channel_->isWriting())
        {
            channel_->enableWriting(); // 一定要注册channel写事件，否则poller不会给channel通知epollout
        }
    }
}

void TcpConnection::shutdown()
{
    if(state_ == kConnected)
    {
        setState(kDisconnecting);
        loop_->runInLoop(
            std::bind(&TcpConnection::shutdownInLoop, this)
        );
    }
}

void TcpConnection::shutdownInLoop()
{
    // 保证优雅关闭，发完数据才关闭
    // 不关注channel_的写事件了，表明outputBuffer中数据已全部发送完成
    if(!channel_->isWriting())
    {
        socket_->shutdownWrite();
    }
}

void TcpConnection::connectEstablished()
{
    setState(kConnected);
    // 检测Channel对应的TcpConnection的生命期
    // 防止对应的Channel在销毁后仍被调用其回调
    channel_->tie(shared_from_this());
    channel_->enableReading(); // 向Poller注册Channel的epollin事件

    // 新连接建立，执行回调
    connectionCallback_(shared_from_this()); // 用户定义的函数
}

void TcpConnection::connectDestroyed()
{
    if(state_ == kConnected)
    {
        setState(kDisconnected);
        channel_->disableAll(); // 把对channel所有感兴趣的事件从Poller中删除掉
        connectionCallback_(shared_from_this()); //用户设置的回调
    }
    channel_->remove(); // 把channel从Poller中删掉（从map中删掉）
}

void TcpConnection::handleRead(Timestamp receiveTime)
{
    int savedErrno = 0;
    ssize_t n = inputBuffer_.readFd(channel_->fd(), &savedErrno);
    if(n > 0)
    {
        // 已建立连接的用户，有可读事件发生了，调用用户传入的回调操作onMessage
        messageCallback_(shared_from_this(), &inputBuffer_, receiveTime);
    }
    else if(n == 0) // 连接断开
    {
        handleClose();
    }
    else 
    {
        errno = savedErrno;
        LOG_ERROR("TcpConnection::handleRead");
        handleError();
    }
}

void TcpConnection::handleWrite()
{
    if(channel_->isWriting())
    {
        int savedErrno = 0;
        ssize_t n = outputBuffer_.writeFd(channel_->fd(), &savedErrno);
        if(n > 0)
        {
            outputBuffer_.retrieve(n);
            // 缓冲区内数据都发出了，则不需要再关注fd的可写事件了
            if(outputBuffer_.readableBytes() == 0)
            {
                channel_->disableWriting();
                if(writeCompleteCallback_)
                {
                    // 唤醒loop_对应线程执行回调
                    loop_->queueInLoop(
                        std::bind(writeCompleteCallback_, shared_from_this())
                    );
                }
                if(state_ == kDisconnecting) // 保证优雅关闭
                {
                    shutdownInLoop();
                }
            }
        }
        else 
        {
            LOG_ERROR("TcpConnection::handleWrite");
        }
    }
    else
    {
        LOG_ERROR("TcpConnection fd=%d is down no more writing \n", channel_->fd());
    }

}

void TcpConnection::handleClose()
{
    LOG_INFO("TcpConnection::handleClose fd = %d state=%d\n", channel_->fd(), (int)state_);
    setState(kDisconnected);
    channel_->disableAll();

    TcpConnectionPtr connPtr(shared_from_this());
    connectionCallback_(connPtr); //
    closeCallback_(connPtr); // 关闭连接的回调 执行的是TcpServer::removeConnection回调方法
}

void TcpConnection::handleError()
{
    int optval;
    socklen_t optlen = sizeof optval;
    int err = 0;
    // 获得错误码信息
    if(::getsockopt(channel_->fd(), SOL_SOCKET, SO_ERROR, &optval, &optlen) < 0)
    {
        err = errno;
    }
    else 
    {
        err = optval;
    }

    LOG_ERROR("TcpConnection::handleError name:%s - SO_ERROR:%d \n",name_.c_str(), err);
}

杂项

• 【TODO】TcpConnection 类 和 Channel 类 以及 Acceptor类的区别?

TcpConnection 是对一条建立起来的连接fd进行封装，而 Channel 是对于任意fd 的封装

TcpConnection 拥有 其对应的 Channel，反之不对。

Acceptor 可以认为是一个特殊的TcpConnection，它只处理读事件，即监听新连接的到来,它运行在 mainLoop上