socket阻塞与非阻塞，同步与异步、I/O模型，select与poll、epoll比较

socket阻塞与非阻塞，同步与异步、I/O模型，select与poll、epoll比较

http://www.cnblogs.com/wujing-hubei/p/6111347.html
https://www.cnblogs.com/bw13/p/6410877.html