span><span class="p">,</span>
   <span class="kt">DispatchSource</span> <span class="k">is</span> <span class="n">used</span><span class="p">,</span> <span class="k">as</span> <span class="n">it</span> <span class="k">is</span> <span class="n">used</span> <span class="n">on</span> <span class="kt">OSX</span><span class="o">.</span>
</code></pre>
<h3 id='usage-example' class='heading'>Usage Example:</h3>
<pre class="highlight swift"><code> <span class="kd">func</span> <span class="nf">upgrade</span><span cla