流的概念
https://zhuanlan.zhihu.com/p/25418336
http://blog.csdn.net/zzp_403184692/article/details/8057693
http://blog.csdn.net/wenzhi20102321/article/details/52582705
https://zhuanlan.zhihu.com/p/25418336
http://blog.csdn.net/zzp_403184692/article/details/8057693
http://blog.csdn.net/wenzhi20102321/article/details/52582705