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<meta property="og:description" content="前面已经讲过一次多人会话聊天室的实现C++实战——多人会话聊天室（一），只不过上一篇是用最简单的方式，服务端每接收一个连接就起一个线程，而且是阻塞模式的，也就是说服务端每次调用accept函数时会一直等待有客户端连接上才会返回。今天介绍一种基于epoll模型的非阻塞方式的实现。 === 阻塞与非阻塞¶ 顾名思义，阻塞就是当你调用一个函数后它会一直等在那里，知道某个信号叫醒它，最典型的例子就是read之类的函数，当你调用时它会等待标准输入，直到你在屏幕上输完敲下回车，它才会继续执行。Linux默认IO都是阻塞模型的 非阻塞就是当你调用函数之后它会立马返回，同样还是拿read举例，它不会阻塞在屏幕上等待你输入，而是立马返回，如果返回错误，那就代表没有数据可读。下面的例子可以大致说明一下差别 #include <unistd.h> #include <stdio.h> #include <fcntl.h> #include <stdlib.h> int main(int argc, char *argv[]) { int res; res = fcntl(0, F_GETFL ..." />
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<meta name="twitter:description" content="前面已经讲过一次多人会话聊天室的实现C++实战——多人会话聊天室（一），只不过上一篇是用最简单的方式，服务端每接收一个连接就起一个线程，而且是阻塞模式的，也就是说服务端每次调用accept函数时会一直等待有客户端连接上才会返回。今天介绍一种基于epoll模型的非阻塞方式的实现。 === 阻塞与非阻塞¶ 顾名思义，阻塞就是当你调用一个函数后它会一直等在那里，知道某个信号叫醒它，最典型的例子就是read之类的函数，当你调用时它会等待标准输入，直到你在屏幕上输完敲下回车，它才会继续执行。Linux默认IO都是阻塞模型的 非阻塞就是当你调用函数之后它会立马返回，同样还是拿read举例，它不会阻塞在屏幕上等待你输入，而是立马返回，如果返回错误，那就代表没有数据可读。下面的例子可以大致说明一下差别 #include <unistd.h> #include <stdio.h> #include <fcntl.h> #include <stdlib.h> int main(int argc, char *argv[]) { int res; res = fcntl(0, F_GETFL ...">
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<h1><a href="https://chukeer.github.io/c++实战——多人会话聊天室2.html"> c++实战——多人会话聊天室2 </a></h1>
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<h4>Contents</h4>
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<li><a href="#_1">阻塞与非阻塞</a></li>
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<p>前面已经讲过一次多人会话聊天室的实现<a href="http://littlewhite.us/archives/109">C++实战——多人会话聊天室（一）</a>，只不过上一篇是用最简单的方式，服务端每接收一个连接就起一个线程，而且是阻塞模式的，也就是说服务端每次调用accept函数时会一直等待有客户端连接上才会返回。今天介绍一种基于epoll模型的非阻塞方式的实现。</p>
<p>===</p>
<h4 id="_1">阻塞与非阻塞<a class="headerlink" href="#_1" title="Permanent link">¶</a></h4>
<p>顾名思义，阻塞就是当你调用一个函数后它会一直等在那里，知道某个信号叫醒它，最典型的例子就是read之类的函数，当你调用时它会等待标准输入，直到你在屏幕上输完敲下回车，它才会继续执行。Linux默认IO都是阻塞模型的<br/>
非阻塞就是当你调用函数之后它会立马返回，同样还是拿read举例，它不会阻塞在屏幕上等待你输入，而是立马返回，如果返回错误，那就代表没有数据可读。下面的例子可以大致说明一下差别</p>
<div class="highlight"><pre><span></span><span class="cp">#include</span> <span class="cpf"><unistd.h></span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf"><stdio.h></span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf"><fcntl.h></span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf"><stdlib.h></span><span class="cp"></span>
<span class="kt">int</span> <span class="nf">main</span><span class="p">(</span><span class="kt">int</span> <span class="n">argc</span><span class="p">,</span> <span class="kt">char</span> <span class="o">*</span><span class="n">argv</span><span class="p">[])</span>
<span class="p">{</span>
<span class="kt">int</span> <span class="n">res</span><span class="p">;</span>
<span class="n">res</span> <span class="o">=</span> <span class="n">fcntl</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">F_GETFL</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">res</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">perror</span><span class="p">(</span><span class="s">"fcntl error!"</span><span class="p">);</span>
<span class="n">exit</span><span class="p">(</span><span class="mi">1</span><span class="p">);</span>
<span class="p">}</span>
<span class="cp">#ifdef NONBLOCK</span>
<span class="n">res</span> <span class="o">|=</span> <span class="n">O_NONBLOCK</span><span class="p">;</span>
<span class="k">if</span> <span class="p">(</span><span class="n">fcntl</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">F_SETFL</span><span class="p">,</span> <span class="n">res</span><span class="p">)</span> <span class="o">==</span> <span class="o">-</span><span class="mi">1</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">perror</span><span class="p">(</span><span class="s">"error"</span><span class="p">);</span>
<span class="n">exit</span><span class="p">(</span><span class="mi">1</span><span class="p">);</span>
<span class="p">}</span>
<span class="cp">#endif</span>
<span class="kt">char</span> <span class="n">buf</span><span class="p">[</span><span class="mi">100</span><span class="p">];</span>
<span class="kt">int</span> <span class="n">n</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
<span class="n">n</span> <span class="o">=</span> <span class="n">read</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">buf</span><span class="p">,</span> <span class="mi">100</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">n</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">perror</span><span class="p">(</span><span class="s">"read error"</span><span class="p">);</span>
<span class="n">exit</span><span class="p">(</span><span class="mi">1</span><span class="p">);</span>
<span class="p">}</span>
<span class="k">else</span>
<span class="p">{</span>
<span class="n">printf</span><span class="p">(</span><span class="s">"read %d characters</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">n</span><span class="p">);</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>代码的意思很好理解，我们从标准输入读取数据，并打印出读取了多少字节，但是我们做了个测试，当定义了宏NONBLOCK后，我们会将标准输入句柄改变成非阻塞的，宏可以通过编译时的-D参数指定，我们分别按如下指令编译，假设文件名为test.cpp</p>
<div class="highlight"><pre><span></span>g++ test.cpp -o test_block
g++ test.cpp -D NONBLOCK -o test_nonblock
</pre></div>
<p>然后我们运行./test_block，程序会阻塞在屏幕上等待输入，输入hello world并回车，程序运行结束<br/>
但是当我们运行./test_nonblock时，程序报错<em>read error: Resource temporarily unavailable</em>，这是因为此时的标准输入是非阻塞模式，当调用read后它会立马返回，而此时并没有数据可读取，就会返回错误，但是我们按如下方式就可运行成功</p>
<div class="highlight"><pre><span></span>echo "hello world" | ./test_nonblock
</pre></div>
<p>因为在read调用之前，管道里已经有了数据，所以它会去读取管道里的数据而不会出错。</p>
<p>to be continued...</p>
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