[cdi-dev] async activation on observers, why not CompletableFuture

Wed Apr 1 16:04:50 EDT 2015

2015-04-01 21:46 GMT+02:00 José Paumard <jose.paumard at 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 at gmail.com>:
>
>>
>>
>> 2015-04-01 19:43 GMT+02:00 José Paumard <jose.paumard at 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 at gmail.com>:
>>>
>>>> Hello Antoine,
>>>>
>>>>
>>>> Romain Manni-Bucau
>>>> @rmannibucau <https://twitter.com/rmannibucau> |  Blog
>>>> <http://rmannibucau.wordpress.com> | Github
>>>> <https://github.com/rmannibucau> | LinkedIn
>>>> <https://www.linkedin.com/in/rmannibucau> | Tomitriber
>>>> <http://www.tomitribe.com>
>>>>
>>>> 2015-04-01 9:55 GMT+02:00 Antoine Sabot-Durand <
>>>> antoine at 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:
>>>>>
>>>>>
>>>>> http://transcripts.jboss.org/meeting/irc.freenode.org/cdi-dev/2015/cdi-dev.2015-02-25-17.06.log.html
>>>>>
>>>>> (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 at 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 at 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 <https://twitter.com/rmannibucau> |  Blog
>>>>>> <http://rmannibucau.wordpress.com/> | Github
>>>>>> <https://github.com/rmannibucau> | LinkedIn
>>>>>> <https://www.linkedin.com/in/rmannibucau> | Tomitriber
>>>>>> <http://www.tomitribe.com/>
>>>>>>
>>>>>> 2015-03-31 18:15 GMT+02:00 Sven Linstaedt <sven.linstaedt at 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 at 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 <https://twitter.com/rmannibucau> |  Blog
>>>>>>>> <http://rmannibucau.wordpress.com/> | Github
>>>>>>>> <https://github.com/rmannibucau> | LinkedIn
>>>>>>>> <https://www.linkedin.com/in/rmannibucau> | Tomitriber
>>>>>>>> <http://www.tomitribe.com/>
>>>>>>>>
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>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
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>
>
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