API Design Review: Async & Future

[benjchristensen]

We have started collecting functionality related to Async.java, Observable.start, and similar such as in #645 and #622.

These do not directly apply to the goals of rxjava-core in enabling async Observable behavior but are valuable utilities for converting to and from Observable and executing work asynchronously.

Having them in the core however has the following drawbacks:

• they increase API surface area, code and byte size
• they complicate the mental model by mixing multiple different concepts
• they are tied to the java.util.concurrent model
• different Java libraries such as Guava and Akka have different models
• each JVM language has different concurrency models and libraries
• work can be executed asynchronous in many ways such as actors, event-loops or thread pools and rxjava-core is purposefully non-opinionated about the source of concurrency or asynchronocity

For these reasons it is felt that this functionality should be removed and/or not accepted into rxjava-core but instead placed in a contrib module. This is similar to how rxjava-android and rxjava-swing add additional functionality.

https://github.com/Netflix/RxJava/tree/master/rxjava-contrib

/cc @headinthebox and @jhusain

[benjchristensen]

The Async class and related operators has been moved into rxjava-async-util: https://github.com/Netflix/RxJava/tree/master/rxjava-contrib/rxjava-async-util