消息队列，广播模式

https://www.cnblogs.com/kerwinC/p/5967584.html

https://www.cnblogs.com/daliangtou/p/5147730.html

http://www.jb51.net/article/75647.htm         (有注释，讲的详细)

https://blog.csdn.net/fgf00/article/details/52872730    (wanmei)