====== Epoll ======
  * [[http://man7.org/linux/man-pages/man7/epoll.7.html|man epoll]]
  * [[https://banu.com/blog/2/how-to-use-epoll-a-complete-example-in-c/|How to use epoll? A complete example in C]]
  * [[https://zh.wikipedia.org/wiki/Epoll|zh.wiki]]
    * 使用红黑树