针对Tor的wallclock子系统的源码分析

<h1 id="tor">Tor子系统——时钟模块</h1>
<p><a href="/post/note_tor_index"><strong>Tor笔记目录索引</strong></a></p>
<p>Tor报错模块位于<code>src/lib/wallclock/</code>文件夹，用于替代原本的获取时间模块</p>
<p><a href="/post/note_wallclock_monotime">关于墙上时钟(wall clock)和递增时间(monotonic time)的更多解释</a></p>
<h2 id="heading">子系统结构</h2>
<p><a href="/post/note_tor_subsystem_winprocess#tor">子系统结构定义解释</a></p>
<pre style="background-color:#fff"><span style="font-weight:bold">const</span> subsys_fns_t sys_wallclock <span style="font-weight:bold">=</span> {
  .name <span style="font-weight:bold">=</span> <span style="color:#b84">&#34;wallclock&#34;</span>,
  .supported <span style="font-weight:bold">=</span> <span style="color:#999">true</span>,
  <span style="color:#998;font-style:italic">/* Approximate time is a diagnostic feature, we want it to init right after
</span><span style="color:#998;font-style:italic">   * low-level error handling. */</span>
  .level <span style="font-weight:bold">=</span> <span style="font-weight:bold">-</span><span style="color:#099">98</span>,
  .initialize <span style="font-weight:bold">=</span> subsys_wallclock_initialize,
};
</pre><h2 id="heading-1">初始化子系统</h2>
<p>在初始化后，会将当前时间赋值给<code>cached_approx_time</code></p>
<h2 id="heading-2">模块逻辑</h2>
<p>在<code>TIME_IS_FAST</code>未被设置时，会使用<code>cached_approx_time</code>来缓存时间值，在每次tor循环或者信号回调时，会使用<code>void update_approx_time(time_t now)</code>来重新设置缓存的时间值，从而在短时间内多次获取时间时，不需要多次调用相应的系统操作，节省时间</p>
