Support Asynchronous Callbacks with RxJava Integration

[benjchristensen]

Add an observe() method that returns an Observable (https://github.com/Netflix/RxJava) to allow callbacks and composition.

This will be in addition to the existing execute() and queue() methods.

Thus the 3 invocation methods will be:

T execute()
Future<T> queue()
Observable<T> observe()

(This has been planned for a while - just documenting it. I had hoped to have this in when RxJava was released but have had other competing priorities. It is near the top of my list.)

[johngmyers]

This begs the question of when T is an Iterable<A> how one could get an Observable<A>.

[benjchristensen]

Here's one way of doing it:

observableOfIterable.mapMany({ iterable -> Observable.from(iterable)});

Full context to show where that statement fits:

// simulate an Observable of Iterable<String>
ArrayList<String> s = new ArrayList<String>();
s.add("one")
s.add("two")
s.add("three")
Observable<Iterable<String>> o = Observable.from(s);

// transform it into Observable<String>
Observable<String> os = o.mapMany({ iterable -> Observable.from(iterable)});
os.subscribe({stringValue -> println(stringValue)})

If this was being done with a HystrixCommand it could look like this:

Observable<Iterable<Data>> o = new HystrixCommandToFetchListOfData(args);
Observable<Data> d = o.mapMany({ iterable -> Observable.from(iterable)});
d.subscribe({data -> println(data)})

[johngmyers]

The idea would be to be able to consume the items as they are produced, not to have to collect the entire iteration before consuming any of it. This would require a streaming counterpart to HystrixCommand with a different interface. This is a separate issue with lower priority.

[benjchristensen]

Agreed. I too want a progressive/streaming model like that and it will likely evolve out of work on this issue and #11.

[rore]

+1 (subscribing)

[benjchristensen]

Schedulers (ReactiveX/RxJava#19) are almost ready which will unblock progression on this.

[benjchristensen]

I am working on this at https://github.com/benjchristensen/Hystrix/tree/observe-rxjava

Unit tests are passing for changing HystrixCommand, now I'm doing performance testing and will put it through canary and production traffic at Netflix before merging this into the main project and releasing since it is non-trival change. Once I'm happy with that then I'll do HystrixCollapser, go through similar testing and then release.

[samhendley]

Is this still on the roadmap?

[benjchristensen]

Yes, in fact I got all unit tests passing on it today and am canary
testing in our Netflix environments. I found a bug I'm trying to track
down.

[benjchristensen]

I think I've found and fixed the bug. I have version 1.3 running in production canaries again.