#muduo学习笔记(二)Reactor关键结构

目录

muduo学习笔记(二)Reactor关键结构


Reactor简述

什么是Reactor

Reactor是一种基于事件驱动的设计模式,即通过回调机制,我们将事件的接口注册到Reactor上,当事件发生之后,就会回调注册的接口。
Reactor必要的几个组件
Event Multiplexer事件分发器:即一些I/O复用机制select、poll、epoll等.程序将事件源注册到分发器上,等待事件的触发,做相应处理.
Handle事件源:用于标识一个事件,Linux上是文件描述符.
Reactor反应器:用于管理事件的调度及注册删除.当有激活的事件时,则调用回调函数处理,没有则继续事件循环.
event handler事件处理器:管理已注册事件和的调度,分成不同类型的事件(读/写,定时)当事件发生,调用对应的回调函数处理.

Reactor模型的优缺点

优点
1)响应快,不必为单个同步时间所阻塞,虽然Reactor本身依然是同步的;
2)编程相对简单,可以最大程度的避免复杂的多线程及同步问题,并且避免了多线程/进程的切换开销;
3)可扩展性,可以方便的通过增加Reactor实例个数来充分利用CPU资源;
4)可复用性,reactor框架本身与具体事件处理逻辑无关,具有很高的复用性;

缺点
Reactor模式在IO读写数据时还是在同一个线程中实现的,即使使用多个Reactor机制的情况下,那些共享一个Reactor的Channel如果出现一个长时间的数据读写,会影响这个Reactor中其他Channel的相应时间,比如在大文件传输时,IO操作就会影响其他Client的相应时间,因而对这种操作,使用传统的Thread-Per-Connection或许是一个更好的选择,或则此时使用Proactor模式。

poll简述

poll的使用方法与select相似,轮询多个文件描述符,有读写时设置相应的状态位,poll相比select优在没有最大文件描述符数量的限制.
# include <poll.h>
int poll ( struct pollfd * fds, unsigned int nfds, int timeout);

struct pollfd {
int fd;         /* 文件描述符 */
short events;         /* 等待的事件 */
short revents;       /* 实际发生了的事件 */
} ; 

  每一个pollfd结构体指定了一个被监视的文件描述符,可以传递多个结构体,指示poll()监视多个文件描述符。每个结构体的events域是监视该文件描述符的事件掩码,由用户来设置这个域。revents域是文件描述符的操作结果事件掩码,内核在调用返回时设置这个域。events域中请求的任何事件都可能在revents域中返回。合法的事件如下:

  POLLIN         有数据可读。
  POLLRDNORM      有普通数据可读。
  POLLRDBAND      有优先数据可读。
  POLLPRI         有紧迫数据可读。
  POLLOUT       写数据不会导致阻塞。
  POLLWRNORM      写普通数据不会导致阻塞。
  POLLWRBAND      写优先数据不会导致阻塞。
  POLLMSGSIGPOLL     消息可用。

poll使用样例

#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <errno.h>
#include <poll.h>

#define MAX_BUFFER_SIZE 1024
#define IN_FILES 1
#define MAX(a,b) ((a>b)?(a):(b))

int main(int argc ,char **argv)
{
  struct pollfd fds[3];
  char buf[1024];
  int i,res,real_read, maxfd;

  if((fds[0].fd=open("/dev/stdin",O_RDONLY|O_NONBLOCK)) < 0)
  {
    fprintf(stderr,"open data1 error:%s",strerror(errno));
    return 1;
  }

  for (i = 0; i < IN_FILES; i++)
  {
    fds[i].events = POLLIN | POLLPRI;
  }

  while(1) //|| fds[1].events || fds[2].events)
  {
    int ret = poll(fds, 1, 1000);
    if (ret < 0)
    {
      printf("Poll error : %s\n",strerror(errno));
      return 1;
    }

    if(ret == 0){
      printf("Poll timeout\n");
      continue;
    }

    for (i = 0; i< 1; i++)
    {
      if (fds[i].revents)
      {
        memset(buf, 0, MAX_BUFFER_SIZE);
        real_read = read(fds[i].fd, buf, MAX_BUFFER_SIZE);
        if (real_read < 0)
        {
          if (errno != EAGAIN)
          {
            printf("read eror : %s\n",strerror(errno));
            continue;
          }
        }
        else if (!real_read)
        {
          close(fds[i].fd);
          fds[i].events = 0;
        }
        else
        {
          if (i == 0)
          {
            buf[real_read] = '\0';
            printf("%s", buf);
            if ((buf[0] == 'q') || (buf[0] == 'Q'))
            {
              printf("quit\n");
              return 1;
            }
          }
          else
          {
            buf[real_read] = '\0';
            printf("%s", buf);
          }
        }
      }
    }
  }

  exit(0);
}

muduo Reactor关键结构

muduo Reactor最核心的事件分发机制, 即将IO multiplexing拿到的IO事件分发给各个文件描述符(fd)的事件处理函数。

Channel

Chanel目前我对它的理解是,它负责管理一个文件描述符(file descript)IO事件.
Channel会封装C的poll,把不同的IO事件分发到不同的回调:ReadCallBack、WriteCallBack等
每个Channel对象自始至终只属于一个EventLoop,因此每个Channel对象都只属于某一个IO线程。 每个Channel对象自始至终只负责一个文件描述符(fd) 的IO事件分发

#ifndef NET_CHANNEL_H
#define NET_CHANNEL_H

#include <functional>

#include "EventLoop.hh"

class Channel {
public:
  typedef std::function<void()> EventCallBack;
  Channel(EventLoop* loop, int fd);
  ~Channel();

  void handleEvent();
  void setReadCallBack(const EventCallBack& cb) { m_readCallBack = cb; }
  void setWriteCallBack(const EventCallBack& cb) { m_writeCallBack = cb; }
  void setErrorCallBack(const EventCallBack& cb) { m_errorCallBack = cb; }

  int fd() const { return m_fd; }
  int events() const { return m_events; }
  void set_revents(int revt) { m_revents = revt; }
  bool isNoneEvent() const { return m_events == kNoneEvent; }

  void eableReading() { m_events |=  kReadEvent; update(); }

  int index() { return m_index; }
  void set_index(int idx) { m_index =idx; }

  EventLoop* ownerLoop() { return m_pLoop; }

private:
  Channel& operator=(const Channel&);
  Channel(const Channel&);

  void update();

  static const int kNoneEvent;
  static const int kReadEvent;
  static const int kWriteEvent;

  EventLoop* m_pLoop;
  const int m_fd;
  int m_events;    // 等待的事件
  int m_revents;   // 实际发生了的事件
  int m_index;

  EventCallBack m_readCallBack;
  EventCallBack m_writeCallBack;
  EventCallBack m_errorCallBack;
};

#endif

//Channel.cpp

#include <poll.h>
#include "Channel.hh"
#include "Logger.hh"

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

Channel::Channel(EventLoop* loop, int fd)
  : m_pLoop(loop),
    m_fd(fd),
    m_events(0),
    m_revents(0),
    m_index(-1)
{

}

Channel::~Channel()
{

}

void Channel::update()
{
  m_pLoop->updateChannel(this);
}


void Channel::handleEvent()
{
  if(m_revents & POLLNVAL)
  {
    LOG_WARN << "Channel::handleEvent() POLLNVAL";
  }

  if(m_revents & (POLLERR | POLLNVAL)){
    if(m_errorCallBack) m_errorCallBack();
  }

  if(m_revents & (POLLIN | POLLPRI | POLLRDHUP)){
    if(m_readCallBack) m_readCallBack();
  }

  if(m_revents & POLLOUT){
    if(m_writeCallBack) m_writeCallBack();
  }

}

值得一提的就是 Channel::update()它会调用EventLoop::updateChannel(), 后者会转而调
用Poller::updateChannel()。Poller对象下面会讲,通过Poller::updateChannel()注册IO事件(即file descript).

Channel::handleEvent()是Channel的核心, 它由EventLoop::loop()调
用, 它的功能是根据revents发生事件的的值分别调用不同的用户回调。 这个函数以后还会扩充。

Poller

Poller class是IO multiplexing的封装。 它现在是个具体类,而在muduo中是个抽象基类,因为muduo同时支持poll(2)和epoll(4)两种IOmultiplexing机制。
Poller是EventLoop的间接成员,只供其自己在EventLoop的IO线程中调用,因此无须加锁。其生命期与EventLoop相等。
Poller并不拥有管理文件描述符事件的Channel, Channel在析构之前必须自己
unregister(EventLoop::removeChannel()) , 避免空悬指针

#ifndef _NET_POLLER_HH
#define _NET_POLLER_HH

#include <vector>
#include <map>

#include "TimeStamp.hh"
#include "EventLoop.hh"
#include "Channel.hh"

struct pollfd;

class Poller{
public:
  typedef std::vector<Channel*> ChannelList;

  Poller(EventLoop* loop);
  ~Poller();

  TimeStamp poll(int timeoutMs, ChannelList* activeChannels);

  void updateChannel(Channel* channel);

  void assertInLoopThread() { m_pOwerLoop->assertInLoopThread(); }

private:
  Poller& operator=(const Poller&);
  Poller(const Poller&);

  void fillActiveChannels(int numEvents, ChannelList* activeChannels) const;

  typedef std::vector<struct pollfd> PollFdList;
  typedef std::map<int, Channel*> ChannelMap;

  EventLoop* m_pOwerLoop;
  PollFdList m_pollfds;
  ChannelMap m_channels;

};

#endif

//Poller.cpp
#include "Poller.hh"
#include "Logger.hh"
#include <assert.h>
#include <poll.h>
#include <signal.h>

Poller::Poller(EventLoop* loop)
  : m_pOwerLoop(loop)
{

}

Poller::~Poller()
{

}

TimeStamp Poller::poll(int timeoutMs, ChannelList* activeChannels)
{
  LOG_TRACE << "Poller::poll()";
  int numEvents = ::poll(/*&*m_pollfds.begin()*/m_pollfds.data(), m_pollfds.size(), timeoutMs);
  TimeStamp now(TimeStamp::now());
  if(numEvents > 0){
    LOG_TRACE << numEvents << " events happended";
    fillActiveChannels(numEvents, activeChannels);
  }
  else if(numEvents == 0){
    LOG_TRACE << " nothing happended";
  }
  else{
    LOG_SYSERR << "Poller::poll()";
  }

  return now;
}

/*
 *fillActiveChannels()遍历m_pollfds, 找出有活动事件的fd, 把它对应
 *的Channel填入activeChannels。
 */

void Poller::fillActiveChannels(int numEvents, ChannelList* activeChannels) const
{
  for(PollFdList::const_iterator pfd = m_pollfds.begin();
      pfd != m_pollfds.end() && numEvents > 0; ++pfd)
  {
    if(pfd->revents > 0)
    {
      --numEvents;
      ChannelMap::const_iterator ch = m_channels.find(pfd->fd);
      assert(ch != m_channels.end());
      Channel* channel = ch->second;
      assert(channel->fd() == pfd->fd);
      channel->set_revents(pfd->revents);
      activeChannels->push_back(channel);
    }
  }
}

void Poller::updateChannel(Channel* channel)
{
  assertInLoopThread();
  LOG_TRACE << "fd= " << channel->fd() << " events" << channel->events();
  if(channel->index() < 0){
    //a new one , add to pollfds
    assert(m_channels.find(channel->fd()) == m_channels.end());
    struct pollfd pfd;
    pfd.fd = channel->fd();
    pfd.events = static_cast<short>(channel->events());
    pfd.revents = 0;
    m_pollfds.push_back(pfd);
    int idx = static_cast<int>(m_pollfds.size()) - 1;
    channel->set_index(idx);
    m_channels[pfd.fd] = channel;

  }
  else{
    //update existing one
    assert(m_channels.find(channel->fd()) != m_channels.end());
    assert(m_channels[channel->fd()] == channel);
    int idx = channel->index();
    assert(0 <= idx && idx < static_cast<int>(m_pollfds.size()));
    struct pollfd& pfd = m_pollfds[idx];
    assert(pfd.fd == channel->fd() || pfd.fd == -1);
    pfd.events = static_cast<short>(channel->events());
    pfd.revents = 0;
    if(channel->isNoneEvent()){
      //ignore this pollfd
      pfd.fd = -1;
    }
  }

}

EventLoop

EventLopp在上一篇文章写过,这里给出改动.

EventLoop 新增了quit()成员函数, 还加了几个数据成员,并在构造函数里初始化它们。注意EventLoop通过智能指针来间接持有poller.

+class Poller;
+class Channel;

class EventLoop
------------
    bool isInloopThread() const {return m_threadId == CurrentThread::tid(); }

    +void quit();
    +void updateChannel(Channel* channel);

    static EventLoop* getEventLoopOfCurrentThread();

private:
    EventLoop& operator=(const EventLoop&);
    EventLoop(const EventLoop&);

    void abortNotInLoopThread();

    +typedef std::vector<Channel*> ChannelList;

    bool m_looping;
    +bool m_quit;
    const pid_t m_threadId;
    +std::unique_ptr<Poller> m_poller;
    +ChannelList m_activeChannels;
};

//EventLoop.cpp
  m_threadId(CurrentThread::tid()),
 + m_poller(new Poller(this))
{
------
+void EventLoop::quit()
+{
+  m_quit = true;
+  //wakeup();
+}
+
+void EventLoop::updateChannel(Channel* channel)
+{
+  assert(channel->ownerLoop() == this);
+  assertInLoopThread();
+  m_poller->updateChannel(channel);
+}

上一篇文章的EventLoop->loop()什么也没做,现在它有了实实在在的使命,它调用Poller::poll()获得当前活动事件的Chanel列表, 然后依次调用每个Channel的handleEvent()函数

void EventLoop::loop()
{
  assert(!m_looping);
  assertInLoopThread();
  m_looping = true;
  m_quit = false;

  LOG_TRACE << "EventLoop " << this << " start loopig";

  while(!m_quit)
  {
    m_activeChannels.clear();
    m_poller->poll(1000, &m_activeChannels);
    for(ChannelList::iterator it = m_activeChannels.begin();
      it != m_activeChannels.end(); ++it)
    {
      (*it)->handleEvent();
    }

  }

  LOG_TRACE << "EventLoop " << this << " stop loopig";
  m_looping = false;

}

Reactor时序图

测试程序-单次触发的定时器

程序利用timerfd_create 把时间变成了一个文件描述符,该“文件”在定时器超时的那一刻变得可读,这样就能很方便地融入到 select/poll 框架中,用统一的方式来处理 IO 事件和超时事件,这也正是 Reactor 模式的长处。

#include <errno.h>
#include <thread>
#include <strings.h>

#include "EventLoop.hh"
#include "Channel.hh"
#include "Poller.hh"

//Reactor Test
//单次触发定时器
#include <sys/timerfd.h>

EventLoop* g_loop;

void timeout()
{
  printf("timeout!\n");
  g_loop->quit();
}

int main()
{

  EventLoop loop;
  g_loop = &loop;

  int timerfd = ::timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK |TFD_CLOEXEC);

  Channel channel(&loop, timerfd);
  channel.setReadCallBack(timeout);
  channel.eableReading();

  struct itimerspec howlong;
  bzero(&howlong, sizeof howlong);
  howlong.it_value.tv_sec = 3;
  timerfd_settime(timerfd, 0, &howlong, NULL);

  loop.loop();

  close(timerfd);

}
 ./test.out 
2018-10-31 22:25:54.532487 [TRACE] [EventLoop.cpp:16] [EventLoop] EventLoop Create 0x7FFEB9567CC0 in thread 3075
2018-10-31 22:25:54.533563 [TRACE] [Poller.cpp:64] [updateChannel] fd= 3 events3
2018-10-31 22:25:54.534000 [TRACE] [EventLoop.cpp:41] [loop] EventLoop 0x7FFEB9567CC0 start loopig
2018-10-31 22:25:54.534334 [TRACE] [Poller.cpp:20] [poll] Poller::poll()
2018-10-31 22:25:55.535827 [TRACE] [Poller.cpp:28] [poll]  nothing happended
2018-10-31 22:25:55.536287 [TRACE] [Poller.cpp:20] [poll] Poller::poll()
2018-10-31 22:25:56.538334 [TRACE] [Poller.cpp:28] [poll]  nothing happended
2018-10-31 22:25:56.538802 [TRACE] [Poller.cpp:20] [poll] Poller::poll()
2018-10-31 22:25:57.534175 [TRACE] [Poller.cpp:24] [poll] 1 events happended
timeout!
2018-10-31 22:25:57.534766 [TRACE] [EventLoop.cpp:55] [loop] EventLoop 0x7FFEB9567CC0 stop loopig