title: Is epoll thread-safe?
body: <p>There are two functions in epoll:</p>
  
  <ol>
  <li>epoll_ctl</li>
  <li>epoll_wait</li>
  </ol>
  
  <p>Are they <strong>thread-safe</strong> when I use the same epoll_fd?
  <br/>What will happen if one thread calls epoll_wait and others call epoll_ctl at the same time? </p>