title: When to use the POLLOUT event of the poll C function?
body: <p>I wrote a small TCP servers with <code>socket()</code> + <strong>POLLIN</strong> <code>poll()</code> + <code>recv()</code> + <code>send()</code>, but I don't know when to use <strong>POLLOUT</strong> poll or select <code>writefds</code> to poll on writable event.</p>
  
  <p>Can anyone give me an example of the real usage of <strong>POLLOUT</strong>?</p>