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 

// 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 

#include 
#include 

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 

#include 

#include 

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();
}