muduo源码剖析之EventLoopThread

简介

EventLoopThread类包装了一个thread类和一个EventLoop类,(one loop per thread)是封装了一个EventLoop的独立线程

主要成员及属性解析

意为I/O线程类，EventLoopThread可以创建一个IO线程，通过startLoop返回一个IO线程的loop，threadFunc中开启loop循环，

源码剖析

这个类比较简单,代码都写了注释,不多说

EventLoopThread.h

#ifndef MUDUO_NET_EVENTLOOPTHREAD_H
#define MUDUO_NET_EVENTLOOPTHREAD_H

#include "muduo/base/Condition.h"
#include "muduo/base/Mutex.h"
#include "muduo/base/Thread.h"

namespace muduo
{
namespace net
{

class EventLoop;

class EventLoopThread : noncopyable
{
 public:
  typedef std::function<void(EventLoop*)> ThreadInitCallback;

  EventLoopThread(const ThreadInitCallback& cb = ThreadInitCallback(),
                  const string& name = string());
  ~EventLoopThread();
  EventLoop* startLoop();//通过此接口启动io线程,返回subloop

 private:
  void threadFunc();//线程调用函数,进入loop

  EventLoop* loop_ GUARDED_BY(mutex_);//subloop
  bool exiting_;//loop退出标志
  Thread thread_;
  MutexLock mutex_;
  Condition cond_ GUARDED_BY(mutex_);
  ThreadInitCallback callback_;//线程初始化时调用的函数,不设置则不会调用
};

}  // namespace net
}  // namespace muduo

#endif  // MUDUO_NET_EVENTLOOPTHREAD_H

EventLoopThread.cc

// 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/EventLoopThread.h"
 
#include "muduo/net/EventLoop.h"
 
using namespace muduo;
using namespace muduo::net;
 
EventLoopThread::EventLoopThread(const ThreadInitCallback& cb,
                                 const string& name)
  : loop_(NULL),      //loop未启动为NULL
    exiting_(false),	//
    thread_(std::bind(&EventLoopThread::threadFunc, this), name),   //绑定线程运行函数
    mutex_(),
    cond_(mutex_),
    callback_(cb)
{
}
 
EventLoopThread::~EventLoopThread()
{
  exiting_ = true;
  if (loop_ != NULL) // not 100% race-free, eg. threadFunc could be running callback_.
  {
    // still a tiny chance to call destructed object, if threadFunc exits just now.
    // but when EventLoopThread destructs, usually programming is exiting anyway.
    loop_->quit();
    thread_.join();   //等待线程退出
  }
}
 
EventLoop* EventLoopThread::startLoop()
{
  assert(!thread_.started());
  thread_.start(); //调用pthread_create创建线程,此时有两个线程在运行
  //一个是调用EventLoopThread::startLoop()的线程，一个是执行EventLoopThread::threadFunc()的线程（IO线程）
 
  EventLoop* loop = NULL;
  {
    MutexLockGuard lock(mutex_);
    while (loop_ == NULL)
    {
      cond_.wait();     //须要等待EventLoop对象的创建
    }
    loop = loop_;       //IO线程创建loop_赋给主线程
  }
  
  return loop;          //主线程返回IO线程创建的EventLoop对象
}
 
void EventLoopThread::threadFunc()            //创建线程时会调用这个函数
{
  EventLoop loop;       //IO线程也要创建EventLoop对象,还要通知主线程已经创建完毕
 
  if (callback_)//如果设置了cb则diao'y
  {
    callback_(&loop);     //将定义好的loop传入回调
  }
 
  {
    MutexLockGuard lock(mutex_);
    // loop_指针指向了一个栈上的对象，threadFunc函数退出之后。这个指针就失效了
    // threadFunc函数退出，就意味着线程退出了，EventLoopThread对象也就没有存在的价值了
    // 因而不会有什么大的问题
    loop_ = &loop;
    cond_.notify();     //创建好，发送通知
  }
 
  loop.loop();          // 会在这里循环，直到EventLoopThread析构。此后不再使用loop_訪问EventLoop了
  //assert(exiting_);
  MutexLockGuard lock(mutex_);
  loop_ = NULL;
}