//条件变量
https://www.cnblogs.com/harlanc/p/8596211.html
https://www.cnblogs.com/hesper/p/10738996.html
https://www.cnblogs.com/feng9exe/p/6803611.html
https://blog.csdn.net/sunmenggmail/article/details/8105279
https://www.cnblogs.com/zgq0/p/8780893.html
原文：https://www.cnblogs.com/retry/p/11712642.html