https://ask.csdn.net/questions/664596
https://www.cnblogs.com/mengdd/archive/2013/02/16/2913659.html
多线程while(!state){}有问题，volatile优化，sleep睡着之后唤醒，刷新变量缓存
原文：https://www.cnblogs.com/CreatorKou/p/11361186.html
