Marina and all,
Just another thought.
Regarding David's proposal (modernize connector), does singleton still make
sense?
I mean, do we have a JMS only use case in mind or does it really fit all
connector potential usages as per David's proposal for example?
Jean-Louis
2013/1/3 Marina Vatkina <marina.vatkina_at_oracle.com>
> Jean-Louis,
>
> I'm all for it, but if we add it, we need to do so very quickly.
>
> The problem with @Singleton reuse (even though it maps very nicely in
> general and into the rules and rules of concurrency in particular), is that
> @Singleton is a component-defining annotation for the "singleton session
> beans". If we are to reuse it, the rule will become "unless it is an MDB",
> which is a bit odd...
>
> Carlo, Antonio, others, WDYT?
>
> thanks,
> -marina
>
>
> On 1/2/13 2:39 AM, Jean-Louis MONTEIRO wrote:
>
> Marina,
>
> time to reactivate the discussion on Single MessageDrivenBean instance.
> FYI, a similar issue has been created.
>
> http://java.net/jira/browse/EJB_SPEC-80
>
> As for Stateless versus Singleton, I think it could be fine to be able
> to only have one instance.
>
> Jean-Louis
>
>
>
>
> 2012/9/20 Marina Vatkina <marina.vatkina_at_oracle.com>
>
>> I understand your concern, though it is a question of what is more
>> confusing...
>>
>> Experts,
>>
>> Before we decide on *how* to specify a single MDB instance, do you think
>> it *is* useful to be able to have one?
>>
>> thanks,
>> -marina
>>
>> Antonio Goncalves wrote:
>>
>>> Like Carlo I was thinking of reusing @Singleton. The EE platform
>>> already has 3 (javax.ejb.Singleton & javax.inject.Singleton &
>>> @ApplicationScoped) which already confuses people. I understand the
>>> technical issues that you express Marina, I'm just a bit disapointed to
>>> think that we have another way to have singletons.
>>>
>>> Antonio
>>>
>>> On Wed, Sep 19, 2012 at 1:05 AM, Marina Vatkina <
>>> marina.vatkina_at_oracle.com <mailto:marina.vatkina_at_oracle.com>> wrote:
>>>
>>>
>>> Carlo de Wolf wrote:
>>>
>>> Thinking out loud I would find it counter-intuitive, rather I
>>> would think @Singleton @MessageDriven. Taking it a bit farther
>>> @MessageDriven can actually be construed to be a view instead
>>> of a component type. The component type would, by default, be
>>> like a stateless session bean.
>>>
>>>
>>> Let's not go too far from the current MDB setup ;) As we discussed
>>> it before, any major changes to MDBs would require substantial
>>> changes in the JCA spec, which is not possible in the MR release
>>> (i.e. without a JCA EG).
>>>
>>>
>>> Even without going over that hurdle, the question also raises
>>> thinking about locking. Sooner or later somebody is going to
>>> make that leap.
>>>
>>>
>>> Right. This is why I was suggesting an attribute on a
>>> @MessageDriven. It can have a simpler requirements and no
>>> confusion with a singleton *session* bean (that a @Singleton
>>> defines).
>>>
>>> Theoretically speaking, even now (see the example in David's
>>> proposal), a connector impl gets a hold of the proxy and use it
>>> however it sees it fit (in David's example it uses it as a
>>> singleton), and cause a deadlock or any non-thread-safe behavior.
>>> So if the single-instance MDB is defined as only a responsibility
>>> of the MDB container not to create a new instance and serialize
>>> access to it, it will solve the ordering problem without bringing
>>> in additional features.
>>>
>>> Does it make sense?
>>>
>>> thanks,
>>> -marina
>>>
>>>
>>> Carlo
>>>
>>> On 09/15/2012 02:18 AM, Marina Vatkina wrote:
>>>
>>> Experts,
>>>
>>> While you are thinking about David's proposal (as I hope
>>> you all do ;) ), here is another question: do we need to
>>> provide a standard way to guarantee a single MDB instance
>>> running in a server instance? I do not propose support for
>>> all other features available to the singleton session
>>> beans, just a guarantee of a single MDB instance.
>>>
>>> In GlassFish (RI) we had this request to support message
>>> ordering processed by the MDB.
>>>
>>> If you think that it is useful, we can add an attribute
>>> (e.g. 'isSingleton') to the @MessageDriven annotation that
>>> would default to false for backward compatibility.
>>>
>>> thanks,
>>> -marina
>>>
>>>
>>>
>>>
>>>
>>>
>>> --
>>> Antonio Goncalves
>>> Software architect and Java Champion
>>>
>>> Web site <http://www.antoniogoncalves.org> | Twitter <
>>> http://twitter.com/agoncal> | LinkedIn <
>>> http://www.linkedin.com/in/agoncal> | Paris JUG <http://www.parisjug.org>
>>> | Devoxx France <http://www.devoxx.fr>
>>>
>>
>
>
> --
> Jean-Louis
>
>
>
--
Jean-Louis