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<title>Muduo : Reactor(EventLoop, Channel, Poller)</title>
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<a href="/muduo-reactoreventloop-channel-poller.html" rel="bookmark"
title="Permalink to Muduo : Reactor(EventLoop, Channel, Poller)">Muduo : Reactor(EventLoop, Channel, Poller)</a></h2>
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<abbr class="published" title="2016-08-10T11:00:00+08:00">
三 10 八月 2016
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<address class="vcard author">By
<a class="url fn" href="/author/hongjincao.html"> hongjin.cao</a>
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<blockquote>
<p>Linux多线程服务器编程 6.4.1</p>
<p>TCP网络编程最本质的是处理<code>三个半事件</code>:</p>
<ol>
<li>
<p>连接的建立, 包括server accept新连接,客户端成功connect.TCP连接一旦建立,server和client的地位是相等的,可以各自收发数据.</p>
</li>
<li>
<p>连接的断开,包括主动断开(close,shutdown)和被动断开(read返回0)</p>
</li>
<li>
<p>消息到达,文件描述符可读.(对该事件的处理方式决定了网络编程的风格,阻塞还是非阻塞?如何处理分包?应用层缓冲如何设计?)</p>
</li>
</ol>
<p>3.5 消息发送完毕,这算半个,这里的发送完毕是指将数据写入操作系统的缓冲区,将由TCP协议栈负责数据的发送和重传,不代表对方已经接收到数据.</p>
</blockquote>
<p>接下来就来学习下muduo是如何处理这<code>三个半事件的</code></p>
<h1>Reactor Pattern</h1>
<p><code>《Linux高性能服务器编程》</code>的8.4小节中介绍了Reactor和Proactor,Reactor是向工作线程通知<code>事件的发生</code>,而Proactor则是通知<code>事件的完成</code>.</p>
<p>TODO: 总结<a href="https://en.wikipedia.org/wiki/Reactor_pattern">Reactor</a></p>
<p>muduo也是基于Reactor模型的.</p>
<h1>muduo 的Reactor</h1>
<p><img alt="这里写图片描述" src="https://lh3.googleusercontent.com/LS86ZKntcADnDQdezB-26s0kBTn34LgFWwgsaP77BEKZwUBLqOoAZT6yRrjFcBsrMR9hjV-N8nhZ7qvWYNI3zJ3Ofe9yGIGdz8kwDkGBjCc3RCdNh_QqAICu0b7qETT7sgGzOqRLaPci7H1SAT7jsJVhdXsASJoqayHjAk5_lK2ZBQQt31rfZpUms7J5DcODEIwvg7teog10colnwKkT0vRSTtJD54pXimYvbi0fB0qrElyTepiz90Ox9o6esof4eIn1hHvOqtQMX4l84tL5EhH-vN3fmmHl5GhD1wdKAKVlPmDnJblPe6JtDE9fGFHTzDWKhKtllzpAjlsMIi2hVlpNyfXfUcH3S-94bG5SPoNBvNigv9sQVD7xaCOlxPZ2UeNvv-gXiGmGgadmixo0kZdcTYmtlFDcbEJC-1DHQx4v_yTHU5IzRP44JNyMfqRK5_0-q5Oe2H2J7WIhvawtm1K3EWFmnQNUErtU6L7ULQXTiCB-AcomI6h5RfeqsqSxAPaoqGoAJO8jhrxrf7-asqBfHJYtR40dpmnW8vSCOkaNxBCVrlUvqtNF0KM84oPt73g1BkMnCgzK69ATR63KgNhDbAFtzQ=w944-h576-no"></p>
<h1>EventLoop</h1>
<p>为了保证每个线程只有一个EventLoop，EventLoop会记录创建它的线程ID，并且使用<code>__thread</code>（TLS线程局部存储）来记录当前线程创建的EventLoop对象的指针。当某线程创建了超过一个EventLoop时,就结束程序。这样就能保证一个线程只有一个EventLoop,即<code>one loop per thread</code></p>
<p>EventLoop会进行事件循环，使用某种IO Multiplexing技术（select、poll、epoll）监听关心的文件描述符fds是否发生了关注的事件，然后调用相应的handler。因此线程会阻塞在此，当然也可以设置超时时间。 为了能及时唤醒该线程，可以让EventLoop自身也有一个fd，关注它的readable事件，想将EventLoop所在线程唤醒时，只需要向该fd进行写操作即可。</p>
<p>EventLoop的生命周期与所在线程相同，不必是heap上的。此外，将拥有EventLoop的线程称为<code>IO线程</code>，应为该线程只关心socket fd上的IO。其他线程可以称为‘工作线程’，负责业务逻辑。</p>
<p><code>activeChannels_</code>用来存放发生了事件的Channel的集合，通过poller来获得（poller负责设置Channel发生了什么事件）。然后调用每个Channel的<code>handleEvent</code>来处理发生的事件，<code>handleEvent</code>根据poller设置的发生事件，调用想用的处理函数。</p>
<p>最主要的事件循环就是这样的：</p>
<div class="highlight"><pre><span></span><span class="kt">void</span> <span class="n">EventLoop</span><span class="o">::</span><span class="n">loop</span><span class="p">()</span>
<span class="p">{</span>
<span class="c1">// ...</span>
<span class="k">while</span> <span class="p">(</span><span class="o">!</span><span class="n">quit_</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">activeChannels_</span><span class="p">.</span><span class="n">clear</span><span class="p">();</span>
<span class="c1">// 通过poller获取就绪的channel，放到activeChannels_中，poller会将发生的事件类型填写到channel的revents_中，供Channel::handleEvent使用</span>
<span class="n">pollReturnTime_</span> <span class="o">=</span> <span class="n">poller_</span><span class="o">-></span><span class="n">poll</span><span class="p">(</span><span class="n">kPollTimeMs</span><span class="p">,</span> <span class="o">&</span><span class="n">activeChannels_</span><span class="p">);</span>
<span class="o">++</span><span class="n">iteration_</span><span class="p">;</span>
<span class="n">eventHandling_</span> <span class="o">=</span> <span class="nb">true</span><span class="p">;</span>
<span class="k">for</span> <span class="p">(</span><span class="n">ChannelList</span><span class="o">::</span><span class="n">iterator</span> <span class="n">it</span> <span class="o">=</span> <span class="n">activeChannels_</span><span class="p">.</span><span class="n">begin</span><span class="p">();</span>
<span class="n">it</span> <span class="o">!=</span> <span class="n">activeChannels_</span><span class="p">.</span><span class="n">end</span><span class="p">();</span> <span class="o">++</span><span class="n">it</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">currentActiveChannel_</span> <span class="o">=</span> <span class="o">*</span><span class="n">it</span><span class="p">;</span>
<span class="c1">// 调用channel的事件处理函数handleEvent，根据poller设置的发生的事件类型，调用相应的用户回调函数</span>
<span class="n">currentActiveChannel_</span><span class="o">-></span><span class="n">handleEvent</span><span class="p">(</span><span class="n">pollReturnTime_</span><span class="p">);</span>
<span class="p">}</span>
<span class="n">currentActiveChannel_</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
<span class="n">eventHandling_</span> <span class="o">=</span> <span class="nb">false</span><span class="p">;</span>
<span class="c1">// ...</span>
<span class="p">}</span>
<span class="c1">//...</span>
<span class="p">}</span>
</pre></div>
<h1>Channel</h1>
<p>每个Channel只负责一个文件描述符fd的IO事件分发，但它不拥有这个fd，也不在析构时关闭该fd。Channel会把不同的IO事件分发给不同的回调函数，如ReadCallback、WriteCallback。</p>
<p>每个Channel自始至终只属于一个EventLoop，所以每个Channel只属于一个<code>IO线程</code></p>
<p>Channel处理事件（其中revents_代表事件类型，由poller负责填写）：</p>
<div class="highlight"><pre><span></span><span class="kt">void</span> <span class="n">Channel</span><span class="o">::</span><span class="n">handleEvent</span><span class="p">(</span><span class="n">Timestamp</span> <span class="n">receiveTime</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">eventHandling_</span> <span class="o">=</span> <span class="nb">true</span><span class="p">;</span>
<span class="n">LOG_TRACE</span> <span class="o"><<</span> <span class="n">reventsToString</span><span class="p">();</span>
<span class="k">if</span> <span class="p">((</span><span class="n">revents_</span> <span class="o">&</span> <span class="n">POLLHUP</span><span class="p">)</span> <span class="o">&&</span> <span class="o">!</span><span class="p">(</span><span class="n">revents_</span> <span class="o">&</span> <span class="n">POLLIN</span><span class="p">))</span>
<span class="p">{</span>
<span class="k">if</span> <span class="p">(</span><span class="n">logHup_</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">LOG_WARN</span> <span class="o"><<</span> <span class="s">"fd = "</span> <span class="o"><<</span> <span class="n">fd_</span> <span class="o"><<</span> <span class="s">" Channel::handle_event() POLLHUP"</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">if</span> <span class="p">(</span><span class="n">closeCallback_</span><span class="p">)</span> <span class="n">closeCallback_</span><span class="p">();</span>
<span class="p">}</span>
<span class="k">if</span> <span class="p">(</span><span class="n">revents_</span> <span class="o">&</span> <span class="n">POLLNVAL</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">LOG_WARN</span> <span class="o"><<</span> <span class="s">"fd = "</span> <span class="o"><<</span> <span class="n">fd_</span> <span class="o"><<</span> <span class="s">" Channel::handle_event() POLLNVAL"</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">if</span> <span class="p">(</span><span class="n">revents_</span> <span class="o">&</span> <span class="p">(</span><span class="n">POLLERR</span> <span class="o">|</span> <span class="n">POLLNVAL</span><span class="p">))</span>
<span class="p">{</span>
<span class="k">if</span> <span class="p">(</span><span class="n">errorCallback_</span><span class="p">)</span> <span class="n">errorCallback_</span><span class="p">();</span>
<span class="p">}</span>
<span class="k">if</span> <span class="p">(</span><span class="n">revents_</span> <span class="o">&</span> <span class="p">(</span><span class="n">POLLIN</span> <span class="o">|</span> <span class="n">POLLPRI</span> <span class="o">|</span> <span class="n">POLLRDHUP</span><span class="p">))</span>
<span class="p">{</span>
<span class="k">if</span> <span class="p">(</span><span class="n">readCallback_</span><span class="p">)</span> <span class="n">readCallback_</span><span class="p">(</span><span class="n">receiveTime</span><span class="p">);</span>
<span class="p">}</span>
<span class="k">if</span> <span class="p">(</span><span class="n">revents_</span> <span class="o">&</span> <span class="n">POLLOUT</span><span class="p">)</span>
<span class="p">{</span>
<span class="k">if</span> <span class="p">(</span><span class="n">writeCallback_</span><span class="p">)</span> <span class="n">writeCallback_</span><span class="p">();</span>
<span class="p">}</span>
<span class="n">eventHandling_</span> <span class="o">=</span> <span class="nb">false</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
<h1>Poller</h1>
<p>Poller是对IO Multiplexing的封装（可用select、poll、epoll），它属于某个EventLoop，生命周期与EventLoop相同，使用时无需加锁。Poller并不拥有Channel，只是持有Channel的裸指针（<code>map<int,Channel*></code>,一个fd对应一个channel），因此Channel在析构之前，需要自己unregister，即调用<code>EventLoop::removeChannel--->Poller::removeChannel</code>，将自己从Poller的channels中删除，避免空悬指针。</p>
<p>EPollPoller继承了Poller，主要的事件轮询poll实现如下，通过<code>epoll_wait</code>获取就绪的channel，放到activeChannels中，供EventLoop使用。</p>
<div class="highlight"><pre><span></span><span class="n">Timestamp</span> <span class="n">EPollPoller</span><span class="o">::</span><span class="n">poll</span><span class="p">(</span><span class="kt">int</span> <span class="n">timeoutMs</span><span class="p">,</span> <span class="n">ChannelList</span><span class="o">*</span> <span class="n">activeChannels</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">LOG_TRACE</span> <span class="o"><<</span> <span class="s">"fd total count "</span> <span class="o"><<</span> <span class="n">channels_</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="c1">// channels是一个map<fd, Channel*>,保存了fd对应的channel</span>
<span class="c1">// 查询发生了哪些事件，存放在events_中</span>
<span class="kt">int</span> <span class="n">numEvents</span> <span class="o">=</span> <span class="o">::</span><span class="n">epoll_wait</span><span class="p">(</span><span class="n">epollfd_</span><span class="p">,</span>
<span class="o">&*</span><span class="n">events_</span><span class="p">.</span><span class="n">begin</span><span class="p">(),</span>
<span class="n">static_cast</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="n">events_</span><span class="p">.</span><span class="n">size</span><span class="p">()),</span>
<span class="n">timeoutMs</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="n">numEvents</span> <span class="o">></span> <span class="mi">0</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">fillActiveChannels</span><span class="p">(</span><span class="n">numEvents</span><span class="p">,</span> <span class="n">activeChannels</span><span class="p">);</span> <span class="c1">// 将就绪的channel放到activeChannels，供EventLoop使用</span>
<span class="k">if</span> <span class="p">(</span><span class="n">implicit_cast</span><span class="o"><</span><span class="kt">size_t</span><span class="o">></span><span class="p">(</span><span class="n">numEvents</span><span class="p">)</span> <span class="o">==</span> <span class="n">events_</span><span class="p">.</span><span class="n">size</span><span class="p">())</span>
<span class="p">{</span>
<span class="n">events_</span><span class="p">.</span><span class="n">resize</span><span class="p">(</span><span class="n">events_</span><span class="p">.</span><span class="n">size</span><span class="p">()</span><span class="o">*</span><span class="mi">2</span><span class="p">);</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">numEvents</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">LOG_TRACE</span> <span class="o"><<</span> <span class="s">"nothing happended"</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">else</span>
<span class="p">{</span>
<span class="c1">// error happens, log uncommon ones</span>
<span class="k">if</span> <span class="p">(</span><span class="n">savedErrno</span> <span class="o">!=</span> <span class="n">EINTR</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">errno</span> <span class="o">=</span> <span class="n">savedErrno</span><span class="p">;</span>
<span class="n">LOG_SYSERR</span> <span class="o"><<</span> <span class="s">"EPollPoller::poll()"</span><span class="p">;</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="c1">//...</span>
<span class="p">}</span>
<span class="kt">void</span> <span class="n">EPollPoller</span><span class="o">::</span><span class="n">fillActiveChannels</span><span class="p">(</span><span class="kt">int</span> <span class="n">numEvents</span><span class="p">,</span>
<span class="n">ChannelList</span><span class="o">*</span> <span class="n">activeChannels</span><span class="p">)</span> <span class="k">const</span>
<span class="p">{</span>
<span class="n">assert</span><span class="p">(</span><span class="n">implicit_cast</span><span class="o"><</span><span class="kt">size_t</span><span class="o">></span><span class="p">(</span><span class="n">numEvents</span><span class="p">)</span> <span class="o"><=</span> <span class="n">events_</span><span class="p">.</span><span class="n">size</span><span class="p">());</span>
<span class="k">for</span> <span class="p">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">numEvents</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span>
<span class="p">{</span>
<span class="c1">// epoll_event.data.ptr存放的是Channel的指针</span>
<span class="n">Channel</span><span class="o">*</span> <span class="n">channel</span> <span class="o">=</span> <span class="n">static_cast</span><span class="o"><</span><span class="n">Channel</span><span class="o">*></span><span class="p">(</span><span class="n">events_</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">data</span><span class="p">.</span><span class="n">ptr</span><span class="p">);</span>
<span class="n">channel</span><span class="o">-></span><span class="n">set_revents</span><span class="p">(</span><span class="n">events_</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">events</span><span class="p">);</span> <span class="c1">// 设置发生的事件到Channel::revents_</span>
<span class="n">activeChannels</span><span class="o">-></span><span class="n">push_back</span><span class="p">(</span><span class="n">channel</span><span class="p">);</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
<p>channel注册事件通过<code>Poller::updateChannel</code>实现。其中channel有几个状态<code>kNew、kDeleted、kAdded</code>，分别表示<code>新的、已删除、已被添加到Poller</code>。在updateChannel时会根据Channel的状态执行不同的操作。可以看到底层操作使用的是<code>epoll_ctl</code></p>
<div class="highlight"><pre><span></span><span class="kt">void</span> <span class="n">EPollPoller</span><span class="o">::</span><span class="n">updateChannel</span><span class="p">(</span><span class="n">Channel</span><span class="o">*</span> <span class="n">channel</span><span class="p">)</span>
<span class="p">{</span>
<span class="k">const</span> <span class="kt">int</span> <span class="n">index</span> <span class="o">=</span> <span class="n">channel</span><span class="o">-></span><span class="n">index</span><span class="p">();</span>
<span class="k">if</span> <span class="p">(</span><span class="n">index</span> <span class="o">==</span> <span class="n">kNew</span> <span class="o">||</span> <span class="n">index</span> <span class="o">==</span> <span class="n">kDeleted</span><span class="p">)</span>
<span class="p">{</span>
<span class="c1">// a new one, add with EPOLL_CTL_ADD</span>
<span class="kt">int</span> <span class="n">fd</span> <span class="o">=</span> <span class="n">channel</span><span class="o">-></span><span class="n">fd</span><span class="p">();</span>
<span class="k">if</span> <span class="p">(</span><span class="n">index</span> <span class="o">==</span> <span class="n">kNew</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">assert</span><span class="p">(</span><span class="n">channels_</span><span class="p">.</span><span class="n">find</span><span class="p">(</span><span class="n">fd</span><span class="p">)</span> <span class="o">==</span> <span class="n">channels_</span><span class="p">.</span><span class="n">end</span><span class="p">());</span>
<span class="n">channels_</span><span class="p">[</span><span class="n">fd</span><span class="p">]</span> <span class="o">=</span> <span class="n">channel</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">else</span> <span class="c1">// index == kDeleted</span>
<span class="p">{</span>
<span class="n">assert</span><span class="p">(</span><span class="n">channels_</span><span class="p">.</span><span class="n">find</span><span class="p">(</span><span class="n">fd</span><span class="p">)</span> <span class="o">!=</span> <span class="n">channels_</span><span class="p">.</span><span class="n">end</span><span class="p">());</span>
<span class="n">assert</span><span class="p">(</span><span class="n">channels_</span><span class="p">[</span><span class="n">fd</span><span class="p">]</span> <span class="o">==</span> <span class="n">channel</span><span class="p">);</span>
<span class="p">}</span>
<span class="n">channel</span><span class="o">-></span><span class="n">set_index</span><span class="p">(</span><span class="n">kAdded</span><span class="p">);</span>
<span class="n">update</span><span class="p">(</span><span class="n">EPOLL_CTL_ADD</span><span class="p">,</span> <span class="n">channel</span><span class="p">);</span>
<span class="p">}</span>
<span class="k">else</span>
<span class="p">{</span>
<span class="c1">// update existing one with EPOLL_CTL_MOD/DEL</span>
<span class="kt">int</span> <span class="n">fd</span> <span class="o">=</span> <span class="n">channel</span><span class="o">-></span><span class="n">fd</span><span class="p">();</span>
<span class="p">(</span><span class="kt">void</span><span class="p">)</span><span class="n">fd</span><span class="p">;</span>
<span class="n">assert</span><span class="p">(</span><span class="n">channels_</span><span class="p">.</span><span class="n">find</span><span class="p">(</span><span class="n">fd</span><span class="p">)</span> <span class="o">!=</span> <span class="n">channels_</span><span class="p">.</span><span class="n">end</span><span class="p">());</span>
<span class="n">assert</span><span class="p">(</span><span class="n">channels_</span><span class="p">[</span><span class="n">fd</span><span class="p">]</span> <span class="o">==</span> <span class="n">channel</span><span class="p">);</span>
<span class="n">assert</span><span class="p">(</span><span class="n">index</span> <span class="o">==</span> <span class="n">kAdded</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="n">channel</span><span class="o">-></span><span class="n">isNoneEvent</span><span class="p">())</span>
<span class="p">{</span>
<span class="n">update</span><span class="p">(</span><span class="n">EPOLL_CTL_DEL</span><span class="p">,</span> <span class="n">channel</span><span class="p">);</span>
<span class="n">channel</span><span class="o">-></span><span class="n">set_index</span><span class="p">(</span><span class="n">kDeleted</span><span class="p">);</span>
<span class="p">}</span>
<span class="k">else</span>
<span class="p">{</span>
<span class="n">update</span><span class="p">(</span><span class="n">EPOLL_CTL_MOD</span><span class="p">,</span> <span class="n">channel</span><span class="p">);</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="kt">void</span> <span class="n">EPollPoller</span><span class="o">::</span><span class="n">update</span><span class="p">(</span><span class="kt">int</span> <span class="n">operation</span><span class="p">,</span> <span class="n">Channel</span><span class="o">*</span> <span class="n">channel</span><span class="p">)</span>
<span class="p">{</span>
<span class="k">struct</span> <span class="n">epoll_event</span> <span class="n">event</span><span class="p">;</span>
<span class="n">bzero</span><span class="p">(</span><span class="o">&</span><span class="n">event</span><span class="p">,</span> <span class="k">sizeof</span> <span class="n">event</span><span class="p">);</span>
<span class="n">event</span><span class="p">.</span><span class="n">events</span> <span class="o">=</span> <span class="n">channel</span><span class="o">-></span><span class="n">events</span><span class="p">();</span>
<span class="n">event</span><span class="p">.</span><span class="n">data</span><span class="p">.</span><span class="n">ptr</span> <span class="o">=</span> <span class="n">channel</span><span class="p">;</span> <span class="c1">// 保存Channel的指针</span>
<span class="kt">int</span> <span class="n">fd</span> <span class="o">=</span> <span class="n">channel</span><span class="o">-></span><span class="n">fd</span><span class="p">();</span>
<span class="n">LOG_TRACE</span> <span class="o"><<</span> <span class="s">"epoll_ctl op = "</span> <span class="o"><<</span> <span class="n">operationToString</span><span class="p">(</span><span class="n">operation</span><span class="p">)</span>
<span class="o"><<</span> <span class="s">" fd = "</span> <span class="o"><<</span> <span class="n">fd</span> <span class="o"><<</span> <span class="s">" event = { "</span> <span class="o"><<</span> <span class="n">channel</span><span class="o">-></span><span class="n">eventsToString</span><span class="p">()</span> <span class="o"><<</span> <span class="s">" }"</span><span class="p">;</span>
<span class="k">if</span> <span class="p">(</span><span class="o">::</span><span class="n">epoll_ctl</span><span class="p">(</span><span class="n">epollfd_</span><span class="p">,</span> <span class="n">operation</span><span class="p">,</span> <span class="n">fd</span><span class="p">,</span> <span class="o">&</span><span class="n">event</span><span class="p">)</span> <span class="o"><</span> <span class="mi">0</span><span class="p">)</span>
<span class="p">{</span>
<span class="k">if</span> <span class="p">(</span><span class="n">operation</span> <span class="o">==</span> <span class="n">EPOLL_CTL_DEL</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">LOG_SYSERR</span> <span class="o"><<</span> <span class="s">"epoll_ctl op ="</span> <span class="o"><<</span> <span class="n">operationToString</span><span class="p">(</span><span class="n">operation</span><span class="p">)</span> <span class="o"><<</span> <span class="s">" fd ="</span> <span class="o"><<</span> <span class="n">fd</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">else</span>
<span class="p">{</span>
<span class="n">LOG_SYSFATAL</span> <span class="o"><<</span> <span class="s">"epoll_ctl op ="</span> <span class="o"><<</span> <span class="n">operationToString</span><span class="p">(</span><span class="n">operation</span><span class="p">)</span> <span class="o"><<</span> <span class="s">" fd ="</span> <span class="o"><<</span> <span class="n">fd</span><span class="p">;</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
<p>可以看到<code>epoll_event.data.ptr</code>存放的是Channel的指针，这样在相应的fd变得active时，可以从<code>epoll_event.data.ptr</code>找到对应的Channel。可以看到指针的重要性，它连接了“两个世界”。</p>
<h1>Example</h1>
<p>这是书上的使用示例，展示了EventLoop、Channel、Poller的使用方法：</p>
<div class="highlight"><pre><span></span><span class="n">muduo</span><span class="o">::</span><span class="n">net</span><span class="o">::</span><span class="n">EventLoop</span><span class="o">*</span> <span class="n">g_loop</span><span class="p">;</span>
<span class="kt">void</span> <span class="nf">timeout</span><span class="p">()</span>
<span class="p">{</span>
<span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o"><<</span> <span class="s">"Timeout!"</span> <span class="o"><<</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
<span class="n">g_loop</span><span class="o">-></span><span class="n">quit</span><span class="p">();</span>
<span class="p">}</span>
<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<span class="n">muduo</span><span class="o">::</span><span class="n">net</span><span class="o">::</span><span class="n">EventLoop</span> <span class="n">loop</span><span class="p">;</span>
<span class="n">g_loop</span> <span class="o">=</span> <span class="o">&</span><span class="n">loop</span><span class="p">;</span>
<span class="kt">int</span> <span class="n">timerfd</span> <span class="o">=</span> <span class="o">::</span><span class="n">timerfd_create</span><span class="p">(</span><span class="n">CLOCK_MONOTONIC</span><span class="p">,</span> <span class="n">TFD_NONBLOCK</span> <span class="o">|</span> <span class="n">TFD_CLOEXEC</span><span class="p">);</span>
<span class="k">if</span><span class="p">(</span><span class="o">-</span><span class="mi">1</span> <span class="o">==</span> <span class="n">timerfd</span><span class="p">)</span> <span class="p">{</span>
<span class="n">std</span><span class="o">::</span><span class="n">cerr</span> <span class="o"><<</span> <span class="s">"timerfd_create faile"</span> <span class="o"><<</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
<span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
<span class="p">}</span>
<span class="c1">// 创建一个Channel</span>
<span class="n">muduo</span><span class="o">::</span><span class="n">net</span><span class="o">::</span><span class="n">Channel</span> <span class="n">channel</span><span class="p">(</span><span class="o">&</span><span class="n">loop</span><span class="p">,</span> <span class="n">timerfd</span><span class="p">);</span>
<span class="c1">// 设置读回调函数</span>
<span class="n">channel</span><span class="p">.</span><span class="n">setReadCallback</span><span class="p">(</span><span class="n">timeout</span><span class="p">);</span>
<span class="c1">// 注册读事件</span>
<span class="n">channel</span><span class="p">.</span><span class="n">enableReading</span><span class="p">();</span>
<span class="k">struct</span> <span class="n">itimerspec</span> <span class="n">howlong</span><span class="p">;</span>
<span class="n">howlong</span><span class="p">.</span><span class="n">it_value</span><span class="p">.</span><span class="n">tv_sec</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span>
<span class="o">::</span><span class="n">timerfd_settime</span><span class="p">(</span><span class="n">timerfd</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="o">&</span><span class="n">howlong</span><span class="p">,</span> <span class="nb">NULL</span><span class="p">);</span>
<span class="c1">// 进行事件循环，通过Poller获取就绪的Channel，调用Channel::handleEvent，根据事件类型调用相应的回调函数</span>
<span class="n">loop</span><span class="p">.</span><span class="n">loop</span><span class="p">();</span>
<span class="o">::</span><span class="n">close</span><span class="p">(</span><span class="n">timerfd</span><span class="p">);</span>
<span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
<p>可以发现muduo中类的设计比较有意思。Poller是EventLoop的成员变量，而Poller会持有EventLoop的指针，通过调用<code>EventLoop::assertInLoopThread</code>来保证某些操作只在所属的IO线程被调用。如Poller::updateChannel和Poller::removeChannel。</p>
<p>此外，Channel也持有EventLoop的指针，通过该指针间接地使用Poller的updateChannel和remvoeChannel。</p>
<h1>Source Code</h1>
<p>从muduo源码中提取的，仅供学习使用</p>
<blockquote>
<p>https://github.com/huntinux/muduo-learn/tree/v0.1</p>
</blockquote>
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