[cdi-dev] CompletableFuture vs. CompletionStage

Reza Rahman reza_rahman at lycos.com
Mon Mar 7 21:15:29 EST 2016 

I have forwarded this issue to the Java EE platform EG for review. My inclination now is to simply leave this alone with a final earnest request to kindly think carefully about this before finalizing and getting this into the real world. Please keep in mind that the average developer is not that skilled and looks to resources on the web routinely for answers. All those resources are going to immediately point to CompletableFuture, not some obscure superclass.

All I am trying to do is help design an API that is not going to immediately become difficult for the average end developer to understand and use. It's rather unfortunate that I am already feeling fed up in that simple effort to provide feedback.

Anyway I am now basically done with this. Unfortunately I have far more urgent matters for Java EE 7 and Java EE 8 to deal with. If I have time I'll look at some more of the CDI 2 work and provide feedback if I can manage time.

> On Mar 7, 2016, at 2:53 PM, Reza Rahman <reza_rahman at lycos.com> wrote:
> Argue
> Yes, this can be done with a CompletableFuture that has already been constructed - just take a look at the API.
> 
> As far as not adding it to CDI, I can see either way. What was the original motivation for adding CompletableFutures?
> 
> Also, it's a good idea to run this by the platform expert group. I know at least JAX-RS is planning to use CompletableFutures for their client API.
> 
>> On Mar 7, 2016, at 2:39 PM, Romain Manni-Bucau <rmannibucau at gmail.com> wrote:
>> 
>> 
>> 2016-03-07 20:35 GMT+01:00 Reza Rahman <reza_rahman at lycos.com>:
>>> Talking with a colleague about this he reminded me of an important fact I almost forgot. The CompletableFuture API can actually be used with custom executors. That means users concerned about managed threads in a Java EE environment can use it with existing EE 7 concurrency executors.
>>> 
>>> Basically this means CompletableFutures are already pretty Java EE ready.
>>> 
>>> If this is the main cited reason for using CompletionStage, is it really that valid of an argument to justify yet another custom subclass specific only to CDI instead of what's likely to be far more familiar and expected?
>> 
>> Did he mention it is true for *created* comlpetion future which is not the case for async events? But this is a good point to not add anything to CDI: the feature is a one liner *already*.
>>  
>>>> On Mar 7, 2016, at 8:11 AM, Reza Rahman <reza_rahman at lycos.com> wrote:
>>>> 
>>>> I think this is a very bad idea. It's better not to use either API and wait to sort out how CompletableFuture can be used in EE consistently. Because of backwards compatibility rules, it is better to have no API than a bad API.
>>>> 
>>>>> On Mar 7, 2016, at 3:45 AM, Romain Manni-Bucau <rmannibucau at gmail.com> wrote:
>>>>> 
>>>>> 2016-03-07 9:07 GMT+01:00 Martin Kouba <mkouba at redhat.com>:
>>>>>> 
>>>>>> Dne 7.3.2016 v 09:03 Romain Manni-Bucau napsal(a):
>>>>>>> 
>>>>>>> Le 7 mars 2016 08:35, "Martin Kouba" <mkouba at redhat.com
>>>>>>> <mailto:mkouba at redhat.com>> a écrit :
>>>>>>>  >
>>>>>>>  > Dne 6.3.2016 v 15:39 Romain Manni-Bucau napsal(a):
>>>>>>>  >
>>>>>>>  >> Hi guys,
>>>>>>>  >>
>>>>>>>  >> as a user having a ComlpetionStage makes me loose some JDK utilities,
>>>>>>>  >> can we move back to CompletionFuture?
>>>>>>>  >>
>>>>>>>  >> It would allow for instance:
>>>>>>>  >>
>>>>>>>  >> // doesn't work with CompletionStage
>>>>>>>  >> CompletionFuture.allOf(event1.fireAsync(...), event2.fireAsync(...))
>>>>>>>  >>        .then(...)
>>>>>>>  >
>>>>>>>  >
>>>>>>>  > Well, this should work if the underlying CompletionStage impl
>>>>>>> supports toCompletableFuture(), i.e. in Weld 3:
>>>>>>>  >
>>>>>>> 
>>>>>>> Yes but it is not natural to convert it IMO = we can do better
>>>>>>> 
>>>>>>>  > CompletableFuture.allOf(event1.fireAsync(...).toCompletableFuture(),
>>>>>>> event2.fireAsync(...).toCompletableFuture())
>>>>>>>  >
>>>>>>>  > AFAIK the default async execution facility of CompletableFuture is
>>>>>>> ForkJoinPool.commonPool() which is not a good fit for Java EE. Using the
>>>>>>> CompletionStage interface allows us to wrap the async calls without the
>>>>>>> specified executor (e.g. CompletionStage.thenApplyAsync(Function<? super
>>>>>>> T, ? extends U>)) and supply a default one provided by the impl.
>>>>>>>  >
>>>>>>> 
>>>>>>> Should use the pool in which the evznt is fired then "then step" is
>>>>>>> synchronous is my sample so all is decided at fire time
>>>>>> 
>>>>>> I don't talk about your particular example - I understand that it's not using async exec (although the "then()" method does not exist).
>>>>> 
>>>>> was supposed to represent the different flavours (thenRun, thenCompose, ...) ;).
>>>>> 
>>>>> That said I agree on the state switching the pool is better but with these 2 notes:
>>>>> 
>>>>> - could be better to hide these poorly designed methods then -> don't use CompletionXXX but a CDI API with a bridge to CompletionX to let the user go back on SE tools
>>>>> - we still don't have a *standard* config for the pool(s) underlying CDI features so it sounds as poor as SE solution IMO (at least a core/max/ttl config in beans.xml)
>>>>>  
>>>>>>> 
>>>>>>>  >
>>>>>>>  >>
>>>>>>>  >> 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>
>>>>>>>  >>
>>>>>>>  >>
>>>>>>>  >>
>>>>>>>  >> _______________________________________________
>>>>>>>  >> cdi-dev mailing list
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>>>>>>>  >> https://lists.jboss.org/mailman/listinfo/cdi-dev
>>>>>>>  >>
>>>>>>>  >> Note that for all code provided on this list, the provider licenses
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>>>>>>>  >>
>>>>>>>  >
>>>>>>>  > --
>>>>>>>  > Martin Kouba
>>>>>>>  > Software Engineer
>>>>>>>  > Red Hat, Czech Republic
>>>>>> 
>>>>>> -- 
>>>>>> Martin Kouba
>>>>>> Software Engineer
>>>>>> Red Hat, Czech Republic
>>>>> 
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