https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/Multithreading/RunLoopManagement/RunLoopManagement.html#//apple_ref/doc/uid/10000057i-CH16-SW23runloop
https://github.com/DevTalking/CustomRunloopInputSourceSample
https://blog.ibireme.com/2015/05/18/runloop/深入理解RunLoop
https://blog.csdn.net/wzzvictory/article/details/9237973 Objective-C之run loop详解
https://blog.csdn.net/biyuhuaping/article/details/78503272 runloop面试必备
https://mp.weixin.qq.com/s/FpyIj7vVzjpDxUyYuCkmXQ RunLoop解决卡顿问题
http://www.mamicode.com/info-detail-1807382.html 深入理解Runloop，看我一篇就够了
https://www.cnblogs.com/kenshincui/p/6823841.html iOS刨根问底-深入理解RunLoop
https://blog.ibireme.com/2015/05/18/runloop/ 深入理解RunLoop
https://bestswifter.com/runloop-and-thread/深入研究 Runloop 与线程保活
https://github.com/bestswifter/blog/blob/master/articles/ios-runloop.md