https://developer.ibm.com/articles/l-async/
https://gist.github.com/staltz/868e7e9bc2a7b8c1f754
https://dzone.com/articles/5-things-to-know-about-reactive-programming
https://www.baeldung.com/java-9-reactive-streams
https://dzone.com/articles/reactive-programming-with-spring-webflux
https://webtide.com/servlet-3-1-async-io-and-jetty/
https://projectreactor.io/docs/core/release/reference/index.html#_blocking_can_be_wasteful
