25muduo_net库源码分析（一）

1.TCP网络编程本质

TCP网络编程最本质是的处理三个半事件

（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。

2.什么都不做的EventLoop

（1）one loop   perthread意思是说每个线程最多只能有一个EventLoop对象。

（2）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）

（3）EventLoop构造函数会记住本对象所属线程（threadId_）。

（4）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）

3.EchoServer类图

4.代码

POD类型，__thread t_loopInThisThreadl，每个线程都有一个。

EventLoop.h

// Copyright 2010, Shuo Chen.  All rights reserved.
// http://code.google.com/p/muduo/
//
// Use of this source code is governed by a BSD-style license
// that can be found in the License file.

// Author: Shuo Chen (chenshuo at chenshuo dot com)
//
// This is a public header file, it must only include public header files.

#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

EventLoop.c

// Copyright 2010, Shuo Chen.  All rights reserved.
// http://code.google.com/p/muduo/
//
// Use of this source code is governed by a BSD-style license
// that can be found in the License file.

// Author: Shuo Chen (chenshuo at chenshuo dot com)

#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();
}

Reactor_test01.cc

#include <muduo/net/EventLoop.h>

#include <stdio.h>

using namespace muduo;
using namespace muduo::net;

void threadFunc()
{
	printf("threadFunc(): pid = %d, tid = %d\n",
		getpid(), CurrentThread::tid());

	EventLoop loop;
	loop.loop();
}

int main(void)
{
	printf("main(): pid = %d, tid = %d\n",
		getpid(), CurrentThread::tid());

	EventLoop loop;

	Thread t(threadFunc);
	t.start();

	loop.loop();
	t.join();
	return 0;
}

运行结果

Reactor_02.cc

这个是一个错误的例子，t线程没有自己的EventLoop对象

#include <muduo/net/EventLoop.h>

#include <stdio.h>

using namespace muduo;
using namespace muduo::net;

EventLoop* g_loop;

void threadFunc()
{
	g_loop->loop();
}

int main(void)
{
	EventLoop loop;
	g_loop = &loop;
	Thread t(threadFunc);
	t.start();
	t.join();
	return 0;
}

运行结果