Hi Stephan,
I like the idea of CDI interceptor solution you're proposing in your
blogpost [1]. However, concurrency is a difficult topic. First of all,
this only solves concurrent access to the bean instance (i.e.
method-level locking) - the bean state is always up to the user. Also
I'm not so sure it's a good idea to only apply @Lock at the method level
(some methods are guarded some not - AFAIK EJB does not allow this either).
I agree that conversation concurrentAccessTimeout in Weld should be
configurable. In fact, it should be possible to change this timeout even
now using Weld API and org.jboss.weld.context.ConversationContext. But
it should be definitely more straightforward [2].
To sum it up - I wouldn't add concurrency control to the spec provided
it's implementable using interceptors. This is a similar situation as to
javax.transaction.Transactional and JTA. The best place to specify this
is IMHO "Concurrency Utilities for Java EE".
Martin
[1]
I just want to bring this to everyone attention one more time.
The conversation scope concurrency control mechanism seems to be a
frequent point of pain in many projects.
Especially when working with browser triggered asynchronous requests,
you can not rely on client-sided request synchronization.
Weld, unlike OWB, grants a 1 second timeout prior to throwing a (the
specified) BusyConversationException mitigating the effect a bit.
This is a rather strict un-configurable type of CC. Also its
completely out of alignment with the other build-in scopes, offering no
CC what so ever.
In the cases of Session- and Application-Scope, thread handling is left
entirely to the developer, even so they are just as vulnerable in AJAX
environments.
We should really consider introducing a common configurable mechanism,
that is aligned across all scopes (obviously accounting for backwards
compatibility in the case of conversation scope).
Would really appreciate some feedback.
Kind regards,
Stephan
On Mon, 22 Feb 2016 at 23:10 Reza Rahman <Reza.Rahman(a)oracle.com
<mailto:Reza.Rahman@oracle.com>> wrote:
We've discussed this issue before. I definitely still think @Lock
belongs in a modular CDI specification. It would be highly useful to
both @Singleton and @ApplicationScoped. Today if I need to use
declarative concurrency control for a shared component I am
essentially forced to use EJB singleton - which shouldn't be the
case and perhaps should not have been the case past Java EE 6.
On 2/19/2016 5:27 AM, Stephan Knitelius wrote:
> Hi all,
>
> CDI spec does not define a common concurrency control mechanism.
> The time any type of concurrency control is mentioned is in
> conjunction with EJB and a rather restrictive one for conversation
> context.
>
> CDI Spec:
> The container ensures that a long-running conversation may be
> associated with at most one request at a time, by blocking or
> rejecting concurrent requests. If the container rejects a request,
> it must associate the request with a new transient conversation
> and throw an exception of
> type|javax.enterprise.context.BusyConversationException|.
>
>
> It would be helpful if a common configurable concurrency mechanism
> (EJB Singleton style locking?) could be established for all normal
> scopes.
>
> What are your thoughts on this?
>
> Regards,
>
> Stephan
>
>
>
>
>
>
>
>
>
>
> ______________________________________
> *Stephan Knitelius*
> Alteburger Str. 274
> 50968 Köln / Cologne
> Deutschland / Germany
> stephan(a)knitelius.com <mailto:stephan@knitelius.com>
>
>
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