Need Scheduler Shutdown

[blesa]

Use of Schedulers.io() or Schedulers.computation() creates several executors (thread pools) which are never shutted down. Threads stay in memory until the whole JVM finishes. This causes memory leak warnings on Tomcat aplication server (while reloading web app). Maybe it also violates section 4.3 of Rx Design Guidelines (not sure about that).
There should be a method to gracefully terminate all schedulers and their executors (thread pools). I'd propose something like Schedulers.reset() (or .shutdown or .shutdownNow).
All default schedulers are now created in Schedulers class constructor and referenced from its final member variables. I think it should be changed and sequence like this should be possible:
Schedulers.io(); // singleton referencing schedulers is created, threads are running
Schedulers.reset(); // all executors are shutted down, threads are gone
...
Schedulers.io(); // a fresh new set of executors is initialized

[benjchristensen]

A reset of some kind would be okay.

This never comes up in the Netflix environment as we never reload containers.

This is not related to design guideline 4.3. Each Observable is cleaning up after itself (shutting down scheduled work it used, etc). Threadpools are system level, otherwise new threads would be created on every subscription which would be far worse.

[daschl]

Hm I wonder, aren't those scheduler threads daemonized anyway? So they should go down silently once the app is reloaded?

[benjchristensen]

They are daemon threads, but the pools themselves would not clean themselves up.

https://github.com/ReactiveX/RxJava/blob/1.x/src/main/java/rx/internal/util/RxThreadFactory.java#L34

[davidmoten]

This relates to #1624 inasmuch as the Schedulers.shutdown suggestion above would enable proper isolation of unit tests of asynchronous functionality.

[benjchristensen]

Does Schedulers.reset() work? Or is it awkward to exist on the factory class where all other methods are for creating Schedulers? If not there where should it live?

[benjchristensen]

I prefer reset() over shutdown() as reset() implies it can be reused whereas shutdown() suggests it can't.