Transaction demarcation/transaction borders in Spring JMS

I have a chain of 3 Spring JMS listeners A, B and C implemented on DefaultMessageListenerContainer (DMLC). All DMLCs are deployed in one Java EE application.

A and C:

• have a transaction manager injected (the same one),
• they both receive and send messages in transacted sessions,开发者_运维技巧
• the same ConnectionFactory is injected in their DMLC (for receiving) and used for sending.

B:

• has no transaction manager,
• sends transactionless messages (Connection.createSession(false, AUTO_ACKNOWLEDGE)),
• has a different, non-XA ConnectionFactory

Question: are transaction borders as illustrated below, and transactions 1 and 2 are separate (ML = message listener)?

         |   transaction 1 |    ?   | no transaction |    ?   | transaction 2 |
 (broker) --> [ML A]   -->  (broker)  --> [ML B]  --> (broker) --> [ML C]     |

Or maybe transaction 1 and 2 are one, and the fact that the "ML B" is non-transactional has no effect on continuity?

Additional question: what happens to the active transaction in the places marked "?", when the message is in the broker?

I don't know how to access transaction manager logs, so I cannot really verify that.