Nigel,
Yes, the calls to acknowledge each message (coming from the same
session) would be serialized. I will update the JIRA ticket to make that
clear. But your question has made me start wondering if that is
sufficient to respect the rules about Session being a single threaded
object. Section "2.8 multi-threading" of the spec does not mention the
Message object in its table of JMS objects that (do or do not) support
concurrent use. So it's not very clear what the rules are for calling
acknowledge() on a Message. If there are message listeners on a Session,
is it valid to call <Message>.acknowledge at all outside of the message
listeners? In practice those JMS providers I have worked with do seem to
allow this.
thanks,
Chris
On 6/29/2012 2:30 AM, Nigel Deakin wrote:
> Chris,
>
> Thanks. That's great. I've added an approriate tag to help me track it
> and added it to the "new issues" list at
> http://java.net/projects/jms-spec/pages/JSR343Planning#Priority_3:_New_issues
>
> Since we already have a backlog of unfinished issues I'd like to defer
> formal consideration of this until later, but if anyone has any
> immediate comments on this please use the reply button or add them to
> the JIRA issue. It's likely we won't have time to consider this
> properly for JMS 2.0, which is why I want to make sure it is captured
> properly in JIRA.
>
> You refer to dispatching received messages to other threads for
> processing. Were you envisaging that the calls to acknowledge each
> message would be serialised (since this counts as "using the resources
> of the session")?
>
> Nigel
>
>
> On 28/06/2012 18:51, Chris Barrow wrote:
>> Hi Nigel,
>>
>> I have filed it as JMS_SPEC-95
>> <http://java.net/jira/browse/JMS_SPEC-95>. I clarified about the
>> threading in the wording of the issue. but to summarize, I meant that
>> there is a single thread receiving messages (as required by the spec)
>> but they are then dispatched to other threads or even other processes
>> across the network for asynchronous processing. The order in which
>> the messages will be processed and therefore acknowledged is
>> unpredictable, hence the need to acknowledge them individually.
>> Certain messages may fail to be processed and need to be redelivered
>> ("NACKed") by closing or resetting the Session.
>>
>> Chris
>>
>> On 6/28/2012 3:22 AM, Nigel Deakin wrote:
>>> Chris,
>>>
>>> Thanks for the interesting suggestions. Could you please open a new
>>> issue in the JMS spec JIRA for this?
>>> http://java.net/jira/browse/JMS_SPEC
>>>
>>> I'd like to clear the existing backlog of started-but-incomplete
>>> features before we consider new ones, but I don't want to lose this
>>> idea. More comments below...
>>>
>>> (N.B. Anyone else reading this is very welcome to join in)
>>>
>>> On 28/06/2012 06:36, Chris Barrow wrote:
>>>> Hi all,
>>>>
>>>> Currently the JMS 1.1 and 2.0 specifications only allow for one
>>>> mode of operation for applications which wish to do their own
>>>> message acknowledgment. This is CLIENT_ACKNOWLEDGE mode. This mode
>>>> has the following characteristic, as defined in the spec:
>>>> "Acknowledging a consumed message automatically acknowledges the
>>>> receipt of all messages that have been delivered by its session.".
>>>>
>>>> This Implicit acknowledgment of all messages is not only confusing,
>>>> it is highly inconvenient in cases where message processing is
>>>> being done by multiple threads asynchronously.
>>>
>>> Hmm. If the application is consuming messages in different threads
>>> at the same time then shouldn't it be using different sessions?
>>>
>>>> I realise this can be overcome to some degree by using multiple
>>>> MessageConsumers on separate Sessions, but that imposes more of an
>>>> overhead on the JMS provider. A better alternative, which is
>>>> already offered by certain JMS providers (including Tibco EMS and
>>>> ActiveMQ), is INDIVIDUAL_ACKNOWLEDGE mode, where acknowledging a
>>>> message /acknowledges only that message/. This makes multithreaded
>>>> or asynchronous processing of messages much easier to implement.
>>>
>>> This sounds reasonable, but I think we would need to explore that
>>> you mean by multi-threaded processing of messages so we can be sure
>>> that the use case you have in mind can be supported without breaking
>>> the threading restrictions on a session.
>>>
>>> Over in Java EE, where messages from a destination are being
>>> processed by a pool of MDB instances, then we do have multi-threaded
>>> processing of messages. If the MDB is configured to use
>>> container-managed transactions then a transaction commit covers an
>>> individual message only, which sounds a bit like what you have in
>>> mind. Interestingly, though, the EJB spec doesn't allow client
>>> acknowledgement in MDBs. I wonder why.
>>>
>>>>
>>>> One can imagine other acknowledge modes that could be useful too,
>>>> for example: CONSUMER_ACKNOWLEDGE where Message.acknowledge() would
>>>> acknowledge only messages received up on a particular
>>>> MessageConsumer, or CONSUMER_CHECKPOINT_ACKNOWLEDGE where
>>>> Message.acknowledge() would acknowledge only messages received up
>>>> to and including the Message instance on which the method was called.
>>>>
>>>> Without embarking on all these various different possibilities,
>>>> would it be possible to consider just adding INDIVIDUAL_ACKNOWLEDGE
>>>> mode? This alone would make it possible for multithreaded
>>>> applications to achieve whatever behaviors they need.
>>>>
>>>> thanks,
>>>> Chris Barrow
>>>
>>> Nigel
>>
>>