+1
Make me recall managed beans ...
JLouis
2012/9/20 Antonio Goncalves <antonio.goncalves_at_gmail.com>
> 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
> > 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>|
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>