https://buvidk1234.github.io/tags/syscall/Recent content in Syscall on 我的技术博客Hugozh-cnTue, 18 Aug 2026 00:15:00 +0800https://buvidk1234.github.io/posts/go-runtime-06-netpoll-syscall/Tue, 18 Aug 2026 00:15:00 +0800https://buvidk1234.github.io/posts/go-runtime-06-netpoll-syscall/<blockquote> <p>本文源码基线为 <strong>Go 1.26.2、Linux/amd64</strong>。尤其注意：Go 1.26.2 已不再使用历史上的 <code>_Psyscall</code> 状态；旧文章基于 <code>_Psyscall</code> 描述的状态机不能直接套用到当前源码。</p> </blockquote> <p>网络等待和阻塞系统调用都会让当前 goroutine 暂时无法继续，但 runtime 的处理方式不同：</p> <details class="code-fold" open> <summary>TEXT</summary><div class="highlight"><pre tabindex="0" class="chroma"><code class="language-text" data-lang="text"><span class="line"><span class="cl">非阻塞 fd + netpoll </span></span><span class="line"><span class="cl"> G 等在 runtime 中，M/P 可以继续调度 </span></span><span class="line"><span class="cl"> </span></span><span class="line"><span class="cl">阻塞 syscall </span></span><span class="line"><span class="cl"> M 等在内核中，runtime 设法把 P 交给其他 M</span></span></code></pre></div></details> <p>理解这一区别，就能解释 Go 为什么能用同步风格编写高并发网络服务，以及为什么某些 syscall 仍会增加线程数量。</p> <h2 id="从netconnread到runtime">从net.Conn.Read到runtime</h2> <p>以 Unix 上 TCP 读取为例，调用链可简化为：</p> <details class="code-fold" open> <summary>TEXT</summary><div class="highlight"><pre tabindex="0" class="chroma"><code class="language-text" data-lang="text"><span class="line"><span class="cl">net.(*TCPConn).Read </span></span><span class="line"><span class="cl"> -&gt; netFD.Read </span></span><span class="line"><span class="cl"> -&gt; internal/poll.(*FD).Read </span></span><span class="line"><span class="cl"> -&gt; syscall.Read </span></span><span class="line"><span class="cl"> -&gt; 数据就绪：直接返回 </span></span><span class="line"><span class="cl"> -&gt; EAGAIN：pollDesc.waitRead </span></span><span class="line"><span class="cl"> -&gt; runtime_pollWait </span></span><span class="line"><span class="cl"> -&gt; runtime.netpollblock </span></span><span class="line"><span class="cl"> -&gt; gopark</span></span></code></pre></div></details> <p>socket 被设置为非阻塞。第一次 <code>read</code> 仍然是真实系统调用；只有内核返回 <code>EAGAIN</code>/<code>EWOULDBLOCK</code> 时，当前 G 才进入 netpoll 等待。</p>