> "...that was just referring to the fact that when the message is sent by VM transport the same reference is used..."
That answers my question #1. Thanks. > "...changes to the original message after sending would also affect the message that was already sent since they are the same object still..." Thanks. My experiments show that is true only if ActiveMQObjectMessage.setObject(new Object()) is done in the producer after the original send. The same change when done in consumers has no effect. In both cases I set ActiveMQObjectMessage.setReadOnlyBody(false) beforehand, by the way. If you have running code that implements what you're describing, I'd be grateful if you could share it. Please? TIA. > "...See: .../org/apache/activemq/ActiveMQSession.java#L1955..." Forgive me if I sound ungrateful. But I had already seen that. Thanks just the same though. I've also seen the unit test for it [1]. And I've seen where it's used with objectMessageSerializationDefered [2]. ActiveMQObjectMessage.setObject() also uses objectMessageSerializationDefered [3]. Another test I've seen is one that verifies that an ObjectMessage's body is serialized over TCP transport but not serialized over VM transport when objectMessageSerializationDefered is true [4]. > "...a copy of the message is still sent even with the VM transport by default..." That might explain why I haven't had any luck producing pass-by-reference behavior (as I understand it [5]) in my experiments. Starting with this ActiveMQ-supplied example code [6] as a base, I tried every combination of values for objectMessageSerializationDefered and copyMessageOnSend I could think of. That documentation I linked to in my first post claims "Messages are passed by reference when objectMessageSerializationDefered is false" and "Messages are passed by value when objectMessageSerializationDefered is true". I would love to find a test that either verifies either of those claims or disproves either of them. Until I do though, I will still have these unanswered questions... 1. ... 2. Where can I find existing unit tests that exercise and verify ActiveMQ's expected pass-by-reference/pass-by-value behavior? 3. Is that ActiveMQ documentation even relevant for ActiveMQ 5+? Or only for 3x and 4x? ---- [1] https://bit.ly/testAMQcopy [2] https://bit.ly/AMQcopy [3] https://bit.ly/setObject [4] https://bit.ly/MsgNotSerTest [5] https://bit.ly/JavaDudePbV [6] https://bit.ly/HelloAMQApp ---- On Thu, Apr 1, 2021 at 2:39 PM Christopher Shannon < [email protected]> wrote: > I forgot to add that your experiment probably didn't show changes because I > believe by default the ActiveMQConnection has the flag "copyMessageOnSend" > set to true. So the message would have been copied anyways into a new > object which means the whole copy by reference wording is even less > relevant and more wrong since a copy of the message is still sent even with > the VM transport by default. > > See: > https://activemq.apache.org/connection-configuration-uri > > https://github.com/apache/activemq/blob/activemq-5.16.1/activemq-client/src/main/java/org/apache/activemq/ActiveMQSession.java#L1955 > > On Thu, Apr 1, 2021 at 8:28 AM Christopher Shannon < > [email protected]> wrote: > > > Yes, Java is pass by value but the value is a copy of the reference and > > not an independent copy of the message (unlike C or C++). The > documentation > > wording should be fixed as it is wrong as you pointed out but I assume > > whoever wrote that was just referring to the fact that when the message > is > > sent by VM transport the same reference is used so you need to be careful > > as changes to the original message after sending would also affect the > > message that was already sent since they are the same object still. The > > messages are just stored in a data structure in the JVM (I think a > > LinkedBlockingQueue). So this is just (poorly) trying to convey the fact > > that the messages are not independent copies of the message like they > > would be if sent over TCP or another protocol. > > >
