muduo之channel

         channel是muduo中的事件分发器，它只属于一个EventLoop,Channel类中保存着IO事件的类型以及对应的回调函数,每个channel只负责一个文件描述符，但它并不拥有这个文件描述符。channel是在epoll和TcpConnection之间起沟通作用，故也叫做通道，其它类通过调用channel的setCallbcak来和建立channel沟通关系。

Channel.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 an internal header file, you should not include this.

#ifndef MUDUO_NET_CHANNEL_H
#define MUDUO_NET_CHANNEL_H

#include "muduo/base/noncopyable.h"
#include "muduo/base/Timestamp.h"

#include <functional>
#include <memory>

namespace muduo
{
namespace net
{

class EventLoop;

///
/// A selectable I/O channel.
///
/// This class doesn't own the file descriptor.
/// The file descriptor could be a socket,
/// an eventfd, a timerfd, or a signalfd
class Channel : noncopyable
{
 public:
  typedef std::function<void()> EventCallback;
  typedef std::function<void(Timestamp)> ReadEventCallback;

  Channel(EventLoop* loop, int fd);
  ~Channel();

  void handleEvent(Timestamp receiveTime);
  void setReadCallback(ReadEventCallback cb)    		//读
  { readCallback_ = std::move(cb); }
  void setWriteCallback(EventCallback cb)				//写
  { writeCallback_ = std::move(cb); }
  void setCloseCallback(EventCallback cb)				//关闭
  { closeCallback_ = std::move(cb); }
  void setErrorCallback(EventCallback cb)				//出错
  { errorCallback_ = std::move(cb); }

  /// Tie this channel to the owner object managed by shared_ptr,
  /// prevent the owner object being destroyed in handleEvent.
  void tie(const std::shared_ptr<void>&);

  int fd() const { return fd_; }
  int events() const { return events_; }
  void set_revents(int revt) { revents_ = revt; } // used by pollers
  // int revents() const { return revents_; }
  bool isNoneEvent() const { return events_ == kNoneEvent; }

  void enableReading() { events_ |= kReadEvent; update(); }  //注册可读事件 
  void disableReading() { events_ &= ~kReadEvent; update(); }//销毁读事件
  void enableWriting() { events_ |= kWriteEvent; update(); } //注册可写事件
  void disableWriting() { events_ &= ~kWriteEvent; update(); }///销毁写事件
  void disableAll() { events_ = kNoneEvent; update(); }
  bool isWriting() const { return events_ & kWriteEvent; }
  bool isReading() const { return events_ & kReadEvent; }

  // for Poller
  int index() { return index_; }
  void set_index(int idx) { index_ = idx; }

  // for debug
  string reventsToString() const;
  string eventsToString() const;

  void doNotLogHup() { logHup_ = false; }

  EventLoop* ownerLoop() { return loop_; }
  void remove();

 private:
  static string eventsToString(int fd, int ev);

  void update();
  void handleEventWithGuard(Timestamp receiveTime);

  static const int kNoneEvent;  //无事件
  static const int kReadEvent;  //可读事件
  static const int kWriteEvent; //可写事件

  EventLoop* loop_;
  const int  fd_;
  int        events_;
  int        revents_; // it's the received event types of epoll or poll
  int        index_; // used by Poller.
  bool       logHup_;

  std::weak_ptr<void> tie_;
  bool tied_;
  bool eventHandling_;
  bool addedToLoop_;
  ReadEventCallback readCallback_;
  EventCallback writeCallback_;
  EventCallback closeCallback_;
  EventCallback errorCallback_;
};

}  // namespace net
}  // namespace muduo

#endif  // MUDUO_NET_CHANNEL_H

Channel.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/base/Logging.h"
#include "muduo/net/Channel.h"
#include "muduo/net/EventLoop.h"

#include <sstream>

#include <poll.h>

using namespace muduo;
using namespace muduo::net;

const int Channel::kNoneEvent = 0;
const int Channel::kReadEvent = POLLIN | POLLPRI;
const int Channel::kWriteEvent = POLLOUT;

//Channel(事件分发器),只属于一个EventLoop,Channel类中保存着IO事件的类型以及对应的回调函数,每个channel只负责一个文件描述符
Channel::Channel(EventLoop* loop, int fd__)
  : loop_(loop),        //channel所属的loop,一个channel只属于一个loop
    fd_(fd__),          //channel负责的文件描述符
    events_(0),         //注册的事件
    revents_(0),        //poller设置的就绪的事件
    index_(-1),         //被poller使用的下标
    logHup_(true),      //是否生成某些日志
    tied_(false),   用于tie()方法
    eventHandling_(false),          //处理handevent的标志
    addedToLoop_(false)		//是否正在循环监听中
{
}

Channel::~Channel()
{
  assert(!eventHandling_);
  assert(!addedToLoop_);
  if (loop_->isInLoopThread())
  {
    assert(!loop_->hasChannel(this));
  }
}

void Channel::tie(const std::shared_ptr<void>& obj)
{
  tie_ = obj;
  tied_ = true;
}

void Channel::update()   //调到loop_->updateChannel,再调用poll->updateChannel
{
  addedToLoop_ = true;
  loop_->updateChannel(this);
}

void Channel::remove()  //同上
{
  assert(isNoneEvent());
  addedToLoop_ = false;
  loop_->removeChannel(this);//移除ChannelMap里面的channel
}

//处理所有发生的事件，如果活着，底层调用handleEventWithGuard
void Channel::handleEvent(Timestamp receiveTime) 事件到来调用handleEvent处理
{
  std::shared_ptr<void> guard;       //守护
  if (tied_)
  {
    guard = tie_.lock();
    if (guard)
    {
      handleEventWithGuard(receiveTime);
    }
  }
  else
  {
    handleEventWithGuard(receiveTime);
  }
}

//处理所有发生的事件
//EPOLLIN ：表示对应的文件描述符可以读； 
//EPOLLOUT：表示对应的文件描述符可以写； 
//EPOLLPRI：表示对应的文件描述符有紧急的数据可读 
//EPOLLERR：表示对应的文件描述符发生错误； 
//EPOLLHUP：表示对应的文件描述符被挂断； 
//EPOLLET：表示对应的文件描述符有事件发生； 
void Channel::handleEventWithGuard(Timestamp receiveTime)
{					
  eventHandling_ = true;			
  LOG_TRACE << reventsToString();
  if ((revents_ & POLLHUP) && !(revents_ & POLLIN))  //判断返回事件类型
  {
    if (logHup_)
    {
      LOG_WARN << "fd = " << fd_ << " Channel::handle_event() POLLHUP";
    }
    if (closeCallback_) closeCallback_();
  }

  if (revents_ & POLLNVAL)                 //不合法文件描述符
  {
    LOG_WARN << "fd = " << fd_ << " Channel::handle_event() POLLNVAL";
  }

  if (revents_ & (POLLERR | POLLNVAL))
  {
    if (errorCallback_) errorCallback_();
  }
  if (revents_ & (POLLIN | POLLPRI | POLLRDHUP))   //POLLRDHUP是对端关闭连接事件，如shutdown等
  {
    if (readCallback_) readCallback_(receiveTime);
  }
  if (revents_ & POLLOUT)
  {
    if (writeCallback_) writeCallback_();
  }
  eventHandling_ = false;
}

string Channel::reventsToString() const
{
  return eventsToString(fd_, revents_);
}

string Channel::eventsToString() const
{
  return eventsToString(fd_, events_);
}

string Channel::eventsToString(int fd, int ev)
{
  std::ostringstream oss;
  oss << fd << ": ";
  if (ev & POLLIN)
    oss << "IN ";
  if (ev & POLLPRI)
    oss << "PRI ";
  if (ev & POLLOUT)
    oss << "OUT ";
  if (ev & POLLHUP)
    oss << "HUP ";
  if (ev & POLLRDHUP)
    oss << "RDHUP ";
  if (ev & POLLERR)
    oss << "ERR ";
  if (ev & POLLNVAL)
    oss << "NVAL ";

  return oss.str();
}