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

Wed Apr 1 04:08:35 EDT 2015

Hello Antoine,

Romain Manni-Bucau
@rmannibucau <https://twitter.com/rmannibucau> |  Blog
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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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