title: What is the purpose of epoll's edge triggered option?
body: <p>From epoll's man page:</p>
  
  <pre><code>epoll is a variant of poll(2) that can be used either as an edge-triggered
  or a level-triggered interface
  </code></pre>
  
  <p>When would one use the edge triggered option? The man page gives an example that uses it, but I don't see why it is necessary in the example.</p>