[cdi-dev] Async events. We need ideas to improve CDI-499

Mon Feb 9 12:43:55 EST 2015

Guys I'm not sure to fully get the jira description now. Can you try
to rephrase it a bit?

Here what I see:

1) fireAsync (+1) is clear
2) (part I dont fully get) asyncSupported: is it mandatory? If yes I
think this API is not usable (=user friendly) and I would just suggest
it is on by default and to remove this flag

Can it break apps? Yes as mentionned by Mark. Will it break apps? No
since it is not yet used and this is surely what we want. I fully
understand all the mentionned pitfalls - but let me say @RequestScoped
is by definition as broken as this today since you can't associate it
with a request for the exact same reason. What I mean is: if you
choose async then you assume it so I think we shouldn't protect the
user from pitfalls then...in particular since we can't protect him
from other as vicious issues.

Romain Manni-Bucau
@rmannibucau
http://www.tomitribe.com
http://rmannibucau.wordpress.com
https://github.com/rmannibucau

2015-02-09 18:28 GMT+01:00 Antoine Sabot-Durand <antoine at sabot-durand.net>:
> Mark I understand your concern, now can you understand the one we discussed about the fact of having to enable async at both ends is a source of confusion for end users and will give a bad perception of the spec.
>
> So could we figure something user friendly to enable async event?
>
> Antoine
>
>
>> Le 9 févr. 2015 à 12:00, Mark Struberg <struberg at yahoo.de> a écrit :
>>
>> But that might defeat pluggabilgity. Basically no framework can use fireAsync in that case.
>>
>> Imagine a UserLoggedIn event. For most observers it is perfectly fine to observe this in a new thread. But some might need to access the session -> boom. Which means that all frameworks have to fall back to the 'safe' fire() instead of fireAsync()...
>>
>> That will leave us half-broken as it totally defeats the usage of this cool feature...
>>
>> LieGrue,
>> strub
>>
>>
>>
>>
>>
>>> On Monday, 9 February 2015, 11:51, Antoine Sabot-Durand <antoine at sabot-durand.net> wrote:
>>>> Mark,
>>>
>>>
>>> During last meeting we didn’t say there wasn’t use case that would break
>>> existing observer, we said that since we keep the current fire() method there is
>>> backward compatibility. User trying to send fireAsync() and experiencing error
>>> with legacy observer will have to fall back to fire().
>>>
>>> Antoine
>>>
>>>
>>>
>>>> Le 9 févr. 2015 à 11:12, Mark Struberg <struberg at yahoo.de> a écrit :
>>>>
>>>> Hi Jozef, here we go!
>>>>
>>>>
>>>> 1.) accessing @RequestScoped beans in your Observer
>>>>
>>>> 2.) accessing @SessionScoped beans in your Observer
>>>> 3.) accessing/relying on any transactional behaviour. This is really a
>>> boomer. Basically you break transactions that way.
>>>>
>>>> 4.) accessing @TransactionScoped beans in your Observer
>>>>
>>>> 5.) access/relying on any ThreadLocal in your Observer
>>>> 6.) accessing attached entities in your Observers (they must only get
>>> accessed from a very single Thread according to the JPA spec)
>>>> 7.) using an EntityManager in a parallel thread might give you unexpected
>>> results.
>>>>
>>>>
>>>> There might be quite a few more. E.g. we need to specify that EJBs and
>>> other EE features need to work in such a new Thread, etc
>>>>
>>>>
>>>> LieGrue,
>>>> strub
>>>>
>>>>
>>>> On Tuesday, 3 February 2015, 9:40, Jozef Hartinger
>>> <jharting at redhat.com> wrote:
>>>>
>>>>
>>>>>
>>>>>
>>>>> We should enumerate all the arguments supporting async flag on an
>>> observer. So far I have only seen one:
>>>>>
>>>>> - an observer accessing @RequestScoped state would no longer be able
>>>>    to do so since it would be run in a worker thread
>>>>>
>>>>> I am eager to hear more arguments as this single one may not be
>>>>    enough to justify the observer-async-flag design decision.
>>>>>
>>>>> Remember that introducing fireAsync() itself does not break any
>>>>    existing application because existing applications are using fire().
>>>>    It's when an existing application / library is modified to use
>>>>    fireAsync() when the problem may occur. Such change should not be
>>>>    done blindly. As with any other change, an author should consider
>>>>    possible consequences of the change. Clearly documenting the fact
>>>>    that fireAsync() processing is done in a different thread with a
>>>>    different @RequestScoped state may be sufficient.
>>>>>
>>>>> Jozef
>>>>>
>>>>>
>>>>> On 02/02/2015 03:43 PM, Antoine Sabot-Durand wrote:
>>>>>
>>>>> Hi all,
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> https://issues.jboss.org/browse/CDI-499 comes after a lot of
>>> discussion about async events.
>>>>>>
>>>>>>
>>>>>> I think the solution exposed here is quite satisfying, yet the idea
>>> to need to activate async behaviour on the observer side doesn’t please a lot of
>>> us. It’ll be confusing for users to have to activate async from the firing end
>>> and consuming end to see it work :-(.
>>>>>>
>>>>>>
>>>>>> I’d like to see alternative proposal to have this new feature as
>>> user friendly as possible and keep the retro-compatibility aspect.  We should
>>> find a better solution on our next meeting on wednesday.
>>>>>>
>>>>>>
>>>>>> Antoine
>>>>>>
>>>>>>
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