On 19 September 2017 at 13:10, Clemens Vasters
<[email protected]> wrote:
> This may be my ignorance of JMS details, but why does a Qpid JMS consumer go
> off and happily prefetch messages when its associated Session/Connection
> hasn't even been start()'ed yet?
>
Mainly its just 'because it does', i.e. it doesn't have any specific
smarts in there to delay it. There are actually some advantages to
doing that, and some downsides.
As Rob said, JMS doesnt speak to this at all, prefetching isn't
something it addresses, so its just an implementation detail as far as
thats concerned.
> I just got misled by the trace output into believing that my app code's
> receive/callback usage was wrong.
Assuming you wanted to received messages with the Consumer you
created, it was actually wrong in that you had any such usage without
calling start(), but I can see what you are saying, the logging is
speaking to details of its internal operation but if you thought it
was really describing handing messages to the application it could
mislead.
>
> Here:
>
> Connection connection = cf.createConnection(csb.getSasKeyName(),
> csb.getSasKey());
> // Create Session, no transaction, client ack
> Session session = connection.createSession(false, Session.CLIENT_ACKNOWLEDGE);
> // Create consumer
> MessageConsumer consumer = session.createConsumer(queue);
> consumer.setMessageListener(message -> {
> try {
> // receives message is passed to callback
> logger.info(String.format("Received message %d with sq#: %s",
> totalReceived.incrementAndGet(), message.getJMSMessageID()));
> message.acknowledge();
> } catch (Exception e) {
> logger.error(e);
> }
> });
> //connection.start();
> If I just let the app spin after this, it'll start logging prefetch events
>
> ...
> 2017-09-19 14:04:42,515 [windows.net:-1]] - TRACE AmqpProvider
> - New Proton Event: DELIVERY
> 2017-09-19 14:04:42,515 [windows.net:-1]] - TRACE AmqpConsumer
> - AmqpConsumer { ID:fce87003-90ac-4fb9-8e83-fdb4cd975a6a:2:1:1 } has
> incoming Message(s).
> 2017-09-19 14:04:42,517 [windows.net:-1]] - DEBUG AmqpConsumer
> - Dispatching received message: JmsInboundMessageDispatch { sequence = 1,
> messageId = ID:21a39efc-8501-45e8-8c67-d3483ca03874:1:1:1-5, consumerId =
> ID:fce87003-90ac-4fb9-8e83-fdb4cd975a6a:2:1:1 }
> ...
>
> But my callback is never invoked.
>
> Once I call start() on the connection (which I now do right after creating
> the connection in my code), the callback does get invoked.
>
> That is quite confusing.
To be fair, that would happen regardless as it is behaviour JMS does
dictate, you just wouldnt have seen any logging in the alternative
case, and with more familiarity of the protocol spec would perhaps
have figured it out a little easier. Most folks won't understand the
spec enough to get that, or maybe turn up the logging at all, and will
just be left with the silly JMS behaviour and resort to
google/stackoverflow for the age old 'you need to start the
connection' answer. JMSContext from JMS 2.0 auto-starts things by
default to avoid such issues.
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