非阻塞IO

http://www.cnblogs.com/littlejohnny/archive/2010/12/29/1921069.html

http://www.ibm.com/developerworks/cn/linux/l-async/

http://www.zhihu.com/question/19732473

http://www.cnblogs.com/Anker/p/3254269.html

http://blog.csdn.net/historyasamirror/article/details/5778378