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