good article

NGINX TIME_OUT

http://www.cnblogs.com/QLeelulu/p/3601499.html

About TCP connection － how to detect if tcp client is closed

http://stackoverflow.com/questions/283375/detecting-tcp-client-disconnect

http://blog.stephencleary.com/2009/05/detection-of-half-open-dropped.html

http://stackoverflow.com/questions/13085676/tcp-socket-no-connection-timeout

http://stackoverflow.com/questions/5907527/application-control-of-tcp-retransmission-on-linux

TCP state

http://blog.chinaunix.net/uid-25018796-id-94900.html

SO_REUSEADDRESS

http://blog.sina.com.cn/s/blog_53a2ecbf010095db.html

select/epoll 区别

http://www.cnblogs.com/Anker/p/3265058.html