muduo库net源码分析一（网络编程本质）

TCP网络编程最本质的是处理三个半事件

1、连接建立：服务器accept（被动）接受连接，客户端connect（主动）发起连接。

2、连接断开：主动断开（close、shutdown），被动断开（read返回0）。

3、消息到达：文件描述符可读。

4、消息发送完毕：这算半个。对于低流量的服务，可不必关心这个事件，这里的发送完毕是指数据写入操作系统缓冲区，将由TCP协议栈负责数据的发送与重传，不代表对方已经接收到数据。对于高流量的程序，应用要在发送完毕后再发送，以免数据丢包。

一个套接字有两个缓冲区，一个接收缓冲区一个发送缓冲区，当一个套接字到来的时候先被内核缓冲区接收

接下来看muduo 对这三个半事件的封装

通过TcpServer 提供了三个成员函数来注册三个回调函数，连接成功和断开用了一个回调函数。

Echo 服务示例：

#include "examples/simple/echo/echo.h"#include "muduo/base/Logging.h"
#include "muduo/net/EventLoop.h"#include <unistd.h>// using namespace muduo;
// using namespace muduo::net;int main()
{LOG_INFO << "pid = " << getpid();muduo::net::EventLoop loop;muduo::net::InetAddress listenAddr(2007);EchoServer server(&loop, listenAddr);server.start();loop.loop();
}

#ifndef MUDUO_EXAMPLES_SIMPLE_ECHO_ECHO_H
#define MUDUO_EXAMPLES_SIMPLE_ECHO_ECHO_H#include "muduo/net/TcpServer.h"// RFC 862
class EchoServer
{public:EchoServer(muduo::net::EventLoop* loop,const muduo::net::InetAddress& listenAddr);void start();  // calls server_.start();private:void onConnection(const muduo::net::TcpConnectionPtr& conn);void onMessage(const muduo::net::TcpConnectionPtr& conn,muduo::net::Buffer* buf,muduo::Timestamp time);muduo::net::TcpServer server_;
};#endif  // MUDUO_EXAMPLES_SIMPLE_ECHO_ECHO_H

#include "examples/simple/echo/echo.h"#include "muduo/base/Logging.h"using std::placeholders::_1;
using std::placeholders::_2;
using std::placeholders::_3;// using namespace muduo;
// using namespace muduo::net;EchoServer::EchoServer(muduo::net::EventLoop* loop,const muduo::net::InetAddress& listenAddr): server_(loop, listenAddr, "EchoServer")
{server_.setConnectionCallback(std::bind(&EchoServer::onConnection, this, _1));server_.setMessageCallback(std::bind(&EchoServer::onMessage, this, _1, _2, _3));
}void EchoServer::start()
{server_.start();
}void EchoServer::onConnection(const muduo::net::TcpConnectionPtr& conn)
{LOG_INFO << "EchoServer - " << conn->peerAddress().toIpPort() << " -> "<< conn->localAddress().toIpPort() << " is "<< (conn->connected() ? "UP" : "DOWN");
}void EchoServer::onMessage(const muduo::net::TcpConnectionPtr& conn,muduo::net::Buffer* buf,muduo::Timestamp time)
{muduo::string msg(buf->retrieveAllAsString());LOG_INFO << conn->name() << " echo " << msg.size() << " bytes, "<< "data received at " << time.toString();conn->send(msg);
}

EventLoop的封装

one loop per thread意思是说每个线程最多只能有一个EventLoop对象。

EventLoop对象构造的时候，会检查当前线程是否已经创建了其他EventLoop对象，如果已创建，终止程序（LOG_FATAL）

EventLoop构造函数会记住本对象所属线程（threadId_）。

创建了EventLoop对象的线程称为IO线程，其功能是运行事件循环（EventLoop::loop）

#ifndef MUDUO_NET_EVENTLOOP_H
#define MUDUO_NET_EVENTLOOP_H#include <boost/noncopyable.hpp>#include <muduo/base/CurrentThread.h>
#include <muduo/base/Thread.h>namespace muduo
{
namespace net
{///
/// Reactor, at most one per thread.
///
/// This is an interface class, so don't expose too much details.
class EventLoop : boost::noncopyable
{public:EventLoop();~EventLoop();  // force out-line dtor, for scoped_ptr members.////// Loops forever.////// Must be called in the same thread as creation of the object.///void loop();void assertInLoopThread(){if (!isInLoopThread()){abortNotInLoopThread();}}bool isInLoopThread() const { return threadId_ == CurrentThread::tid(); }static EventLoop* getEventLoopOfCurrentThread();private:void abortNotInLoopThread();bool looping_; /* atomic */const pid_t threadId_;     // 当前对象所属线程ID
};}
}
#endif  // MUDUO_NET_EVENTLOOP_H

#include <muduo/net/EventLoop.h>#include <muduo/base/Logging.h>#include <poll.h>using namespace muduo;
using namespace muduo::net;namespace
{
// 当前线程EventLoop对象指针
// 线程局部存储
__thread EventLoop* t_loopInThisThread = 0;
}EventLoop* EventLoop::getEventLoopOfCurrentThread()
{return t_loopInThisThread;
}EventLoop::EventLoop(): looping_(false),threadId_(CurrentThread::tid())
{LOG_TRACE << "EventLoop created " << this << " in thread " << threadId_;// 如果当前线程已经创建了EventLoop对象，终止(LOG_FATAL)if (t_loopInThisThread){LOG_FATAL << "Another EventLoop " << t_loopInThisThread<< " exists in this thread " << threadId_;}else{t_loopInThisThread = this;}
}EventLoop::~EventLoop()
{t_loopInThisThread = NULL;
}// 事件循环，该函数不能跨线程调用
// 只能在创建该对象的线程中调用
void EventLoop::loop()
{assert(!looping_);// 断言当前处于创建该对象的线程中assertInLoopThread();looping_ = true;LOG_TRACE << "EventLoop " << this << " start looping";::poll(NULL, 0, 5*1000);LOG_TRACE << "EventLoop " << this << " stop looping";looping_ = false;
}void EventLoop::abortNotInLoopThread()
{LOG_FATAL << "EventLoop::abortNotInLoopThread - EventLoop " << this<< " was created in threadId_ = " << threadId_<< ", current thread id = " <<  CurrentThread::tid();
}