[cdi-dev] async: back to completion future?

Romain Manni-Bucau rmannibucau at gmail.com
Mon Mar 7 17:26:06 EST 2016 

You can give CompletionStage a pool too. So it helps the other thread bit
not this one if we dont make any hazardeous hypothesis.

Le 7 mars 2016 23:19, "Reza Rahman" <reza_rahman at lycos.com> a écrit :
>
> What is still true for CompletionStage? As I've indicated, it's largely
an SPI rather than an end user API like CompletableFuture. For that reason
it will never have the level of familiarity that CompletableFuture already
does.
>
> Let's kindly not argue in circles or repeat ourselves needlessly. It
accomplishes nothing productive.
>
> On Mar 7, 2016, at 5:07 PM, Romain Manni-Bucau <rmannibucau at gmail.com>
wrote:
>
>> Side note: this is still true for CompletionStage.
>>
>> Le 7 mars 2016 22:48, "Reza Rahman" <reza_rahman at lycos.com> a écrit :
>>>
>>> Not sure how alias works, so resending directly. Responses inline.
>>>
>>> The bottom line is that we should think about the usability of the most
common end user. If anyone needs custom executor service control in the
worst case it's still just a matter of one extra parameter as opposed to
introducing an obscure alternative to CompletableFuture.
>>>
>>> On Mar 7, 2016, at 4:38 PM, Reza Rahman <reza_rahman at lycos.com> wrote:
>>>
>>>> Responses in-line.
>>>>
>>>> Sent from my iPhone
>>>>
>>>> On Mar 7, 2016, at 4:24 PM, Romain Manni-Bucau <rmannibucau at gmail.com>
wrote:
>>>>
>>>>>
>>>>> 2016-03-07 22:09 GMT+01:00 Reza Rahman <reza_rahman at lycos.com>:
>>>>>>
>>>>>> Responses in-line.
>>>>>>
>>>>>> On Mar 7, 2016, at 3:35 PM, Romain Manni-Bucau <rmannibucau at gmail.com>
wrote:
>>>>>>
>>>>>>>
>>>>>>> 2016-03-07 20:53 GMT+01:00 Reza Rahman <reza_rahman at lycos.com>:
>>>>>>>>
>>>>>>>> Yes, this can be done with a CompletableFuture that has already
been constructed - just take a look at the API.
>>>>>>>>
>>>>>>>
>>>>>>> so - just to try to ensure we speak about the same thing:
>>>>>>>
>>>>>>> asyncEvent.fireAsync(...).thenRunAsync(() -> ..., eePool); ?
>>>>>>
>>>>>>
>>>>>> Correct.
>>>>>>
>>>>>>>
>>>>>>> This works but has the drawback to not reuse the observer thread
>>>>>>
>>>>>>
>>>>>> Why would this matter to the average business code developer? All
this would run from managed executors of some kind or the other anyway...
>>>>>>
>>>>>>> and keep the original issue: the observer doesn't inherit from the
caller context so it would likely be:
>>>>>>>
>>>>>>> asyncEvent.fireAsync(..., eePool).thenRunAsync(() -> ..., eePool);
>>>>>>
>>>>>>
>>>>>> Again, why does it matter really?  The observer threads themselves
should be running from a managed pool that is smart enough to preserve
context anyway? If the business developer cares about preserving context in
their code, they can use a managed executor themselves on the returned
CompletableFuture.
>>>>>>
>>>>>
>>>>> Cause it is important to state which thread context is there to keep
the integration with other frameworks - think to security ones in
particualr - smooth and doable.
>>>>
>>>>
>>>> For framework developers usability is hardly a concern. If they need
to preserve their own context they can simply pass in their own managed
executor to both the observer thread and the CompletableFuture.
>>>>
>>>> In the end, the primary focus should be the masses that we hope will
adopt CDI into their applications. Making things harder for them to achieve
some limited SPI goal is pretty dangerous.
>>>>
>>>>>>>
>>>>>>> which looks weird since you trigger 2 tasks where you actually want
just one in another thread originally?
>>>>>>
>>>>>>
>>>>>> I don't follow. Whichever executor service you would use, ultimately
there are at least three different threads associated here in all cases.
>>>>>>
>>>>>>>
>>>>>>> asyncEvent.fireAsync(..., eePool).thenRunAsync(() -> ...); // in
the fire async thread
>>>>>>
>>>>>>
>>>>>> You mean using the same executor? Why does this matter really? They
are all managed executors anyway. At best it's reducing one method
parameter.
>>>>>>
>>>>>
>>>>> Cause very few apps are 100% EE in practise, probably never will be
and even if so JavaEE security is not integrated (yet?) at this level.
>>>>
>>>>
>>>> There is no such thing as context propagation outside of EE managed
executors. In SE land, the only thing you have is manually writing your own
executor to do the same things. These folks will have to pass around their
own executors anyway, even to the observer thread.
>>>>
>>>>>>> Are
>>>>>>> This last proposal works not that bad if context propagation would
work but since there are cases it would be expected to work and other it
shouldn't  - from a user point of view auto inheritance can break thread
safety - I wonder if it shouldn't be spec-ed. Can be the new API I proposed
or even just a new scope close to request scoped but inheritable by design.
>>>>>>>
>>>>>>>>
>>>>>>>> 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>
>>>>>>>>>>>>>>  >>
>>>>>>>>>>>>>>  >>
>>>>>>>>>>>>>>  >>
>>>>>>>>>>>>>>  >> _______________________________________________
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>>>>>>>>>>>>>>  >> https://lists.jboss.org/mailman/listinfo/cdi-dev
>>>>>>>>>>>>>>  >>
>>>>>>>>>>>>>>  >> Note that for all code provided on this list, the
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>>>>>>>>>>>>>>  >>
>>>>>>>>>>>>>>  >
>>>>>>>>>>>>>>  > --
>>>>>>>>>>>>>>  > Martin Kouba
>>>>>>>>>>>>>>  > Software Engineer
>>>>>>>>>>>>>>  > Red Hat, Czech Republic
>>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> --
>>>>>>>>>>>>> Martin Kouba
>>>>>>>>>>>>> Software Engineer
>>>>>>>>>>>>> Red Hat, Czech Republic
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> _______________________________________________
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>>>>>>>>>>
>>>>>>>>>>
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>>>>>>>>>
>>>>>>>>>
>>>>>>>>
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>>>>>>>
>>>>>>>
>>>>>>
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>>>>>
>>>>>
>>>
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