Future promise、observe pattern、callback

三种都能够用于notification、通知。

1、future promise 通过判断future的状态来进行判断，它是较高的封装、抽象

2、observe pattern、callback 通过执行对应的callback来进行通知

observer pattern允许开放式的注册、注销

TODO

stackoverflow Java executors: how to be notified, without blocking, when a task completes?

jayconrod Futures are better than callbacks

hackernoon From Callback to Future -> Functor -> Monad

callback vs promise vs observer pattern

https://itnext.io/javascript-promises-vs-rxjs-observables-de5309583ca2

https://scotch.io/courses/10-need-to-know-javascript-concepts/callbacks-promises-and-async