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

[Antoine Sabot-Durand]

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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