https://www.zhihu.com/question/30297970
写的很详细，仔细阅读后有很大收获。
https://mp.weixin.qq.com/s?__biz=MzAwMjI2NjUxNQ==&mid=2656280262&idx=1&sn=f6fb0b5f4e13a2110cd7438f0500530e&chksm=816a3a3ab61db32cf9e3d78ed9fce847523dccb31688f43aa3d72feade511ab946658589b7b4&scene=21#wechat_redirect