2015-04-01 21:46 GMT+02:00 José Paumard <jose.paumard@gmail.com>:
> What's your proposal? EJB API is quite nice to use and it integrates smoothly with Future<>, not sure I get what's your issue is here.
EJB has me to write this kind of code : 

return es.submit(myTask) ;


this looks wrong, return new AsyncFuture<String>("i did it"); is what you should have written otherwise you just didnt use EJB async feature.
 
Because this is a synchronous call, that has to return a Future. But on the other hand this is purely tehcnical code, that cant be put in the framework, since one can call directly an EJB method. So the return type has to be the one of the EJB method. 

With events the situation is different. On the calling side, I write

completableFuture = event.fireAsync(payload) ; // type is CompletionStage<probably void since there are many observers and an allOf call>

On the observing side I can write : 

public T observes(@Observes payload) { return t ; }

And the framework will take care of wrapping this t in a CompletableFuture.allOf(...) with all the other observers to return it. So I dont have to deal myself with the technical aspects of calling ES myself. IMHO it leads to easier to write patterns. 

Why T then? And actually your explanation is my proposal but a on purpose typing.
 

José



2015-04-01 19:54 GMT+02:00 Romain Manni-Bucau <rmannibucau@gmail.com>:


2015-04-01 19:43 GMT+02:00 José Paumard <jose.paumard@gmail.com>:
CompletionStage has a toCompletableFuture() method, that returns a CompletableFuture. So there is no limitation in returning CompletionStage. It could allow different implementation in the future than the only one we have so far : CompletableFuture, since one can build a CompletableFuture that wraps another implementation. 


+1, missed it
 
Problem with CF.allOf() and anyOf() is that they return resp. CF<Void> and CF<Object>, which is not very API friendly. 


it is enough in enough cases IMO
 
Having the observers writers to provide his own implementation of CompletableFuture is not that great imho. For the async EJB, all you can do is return executorService.submit(myTask). I understand why the API designers have chosen that, but I dont think it's that great. Correct me if I'm wrong, but I think that we have the opportunity to move that burden from the observers writers to the framework. And I think it would make the API easier to use. 


What's your proposal? EJB API is quite nice to use and it integrates smoothly with Future<>, not sure I get what's your issue is here.
 
José


2015-04-01 10:08 GMT+02:00 Romain Manni-Bucau <rmannibucau@gmail.com>:
Hello Antoine,


Romain Manni-Bucau
@rmannibucau |  Blog | Github | LinkedIn | Tomitriber

2015-04-01 9:55 GMT+02:00 Antoine Sabot-Durand <antoine@sabot-durand.net>:
Hi Romain,

Intersting proposal. As I felt reading you that we misse the CompletableFuture stuff in Java 8, I just repeat here that the agreed on fireAsync signatures 

<U extends T> CompletionStage<U> fireAsync(U event);
and
<U extends T> CompletionStage<U> fireAsync(U event, Executor executor);

Yeah it’s CompletionStage because Jozef preferred using interfaces in our API, but I guess implementation will use CompletableFuture under the hood to avoid reinventing the wheel.


This sounds "normal" but JVM doesn't follow it with its utility methods so basically today CompletionStage is super poor compared to CompletionFuture so I'm tempted to say the impl is preferred here. I didn't check what is the adoption of both in other framework, can validate or not my thought maybe.
 
With this approach your example:

event.fireAsync(new LetTheWorldKnow()).thenRun(() -> System.out.println("We did it!"));

will work without adding constraint on observer signature.

Regarding the observer part, we already discuss similar approach. In a former version of my async event doc I proposed using return type on observer to do discrimination between async and sync and Mark made a suggestion near yours during this meeting:


(search for the first “signature” in text)

The main drawback of this approach is to let end user generate the returned CompletableFuture. So each async observer should provide a way to construct this completableFuture. The second question is the type param of the returned CompletableFuture. Should we use raw type? Now we could imagine helped to do that but...


Exactly why I think this is a better solution. Cause it opens the door to asynchronism in a more elegant manner handling completion properly. I guess first impl will use allOf() combination but I see anyOf() - i fire to "notifiers" and I care only of 1 at least being called as a caller - and potentially other combinations other potentials needs we could cover in another spec (hopefully).

If async is just fire and forget we don't need fireAsync() but only fire() (void) and then observers are async or not which ensures compat at all levels since observers decide to be in the same context or not but I guess we don't want only fire and forget.

About creating a CompletableFuture we can do as in EJB spec and provide version to use by observer impl (javax.ejb.AsyncResult).
 
Don’t get me wrong, I’d love to find a solution based on this kind of idea, but I fear it will add more complexity than double activation.

Antoine


Le 1 avr. 2015 à 09:15, Romain Manni-Bucau <rmannibucau@gmail.com> a écrit :

No, fireAsync is still needed for all the reason we mzntionned - strongest one being the fact we need a return type and cant change fire - but using the return type we have the double activation without introducing a new API. Said otherwise API stays natural on both sides which was my main fear with a fireAsync and an @ObservesAsync (or any other new api we talked about). And we have the bonus to be aligned on SE async which sounds quite interesting for the future.

Le 1 avr. 2015 08:48, "Jozef Hartinger" <jharting@redhat.com> a écrit :
So instead of calling observers asynchronously you suggest turning observers into producers of CompletableFuture that will then be completed asynchronously?

On 03/31/2015 06:21 PM, Romain Manni-Bucau wrote:
// fire side
event.fireAsync(new LetTheWorldKnow()).thenRun(() -> System.out.println("We did it!"));

// observer side
CompletableFuture iWantToKnow(@Observes LetTheWorldKnow event) {}

// impl behavior would be like CompletableFuture.allOf(allObserverReturnedInstances) to be aligned on CompletableFuture behavior I think

Am I clearer?



Romain Manni-Bucau
@rmannibucau |  Blog | Github | LinkedIn | Tomitriber

2015-03-31 18:15 GMT+02:00 Sven Linstaedt <sven.linstaedt@gmail.com>:
Hi Romain,

I am not sure, I have fully understand how an observer with CompletableFuture could look like. Could you give us an example? 

Afair CompletableFuture was considered to be used in the "trigger" side in order to track async event invocation completion.

br, Sven

2015-03-31 18:00 GMT+02:00 Romain Manni-Bucau <rmannibucau@gmail.com>:
Hi guys,

on async topic if I followed we are at the point where we are looking for an activation on the observer side.

Since Java 8 has now CompletableFuture it would be great to use it. Today the spec doesnt use observer returned values so it is mainly a bad practise to have one even if not strictly forbidden - BTW never saw it in real applications - plus spec is not compatible - not specified at all - with CompletableFuture since it is a new API so we can use it as a marker.

This is quite interesting for few reasons:
1- we have our double activation
2- API is user friendly (observer is async and has an async signature)
3- open door for future async enhancements (hopefully not in CDI) with composition of these observers


Only point I'm not sure is should these observers support sync events. I don't see anything blocking to do it but can have missed something.


wdyt?


Romain Manni-Bucau
@rmannibucau |  Blog | Github | LinkedIn | Tomitriber

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