Java – JMS Message Driven Bean worker synchronization

javajboss-mdbjms

We are just starting to build our JMS architecture and have the following basic setup:

  1. GLassfish v2.1
  2. MDB listening on a Topic through a TopicConnectionFactory (all on local server)

Now, the MDB spawns a worker thread when a new message arrives and even though we have in order delivery of messages, we need a synchronization mechanism so that threads check for a certain condition before processing the request concurrently.

Is there a way for these threads to share data? Or are there any other mechanisms (except for database table/row locks) that we can use for synchronization?

Thanks in advance.

To clarify, I am not creating my own threads. As everyone rightly pointed out, the container does that for me. Let me help explain my dilemma with an example.

-Message A arrives at t=0 which 'creates' data id 1

-Message B arrives at t=0.1 which 'updates' data id 1

Now assuming the container spawns 2 workers to process A & B and that it takes much more time to 'create' data than update it, the update would process earlier and have no effect.

To be clearer,

-While processing Message B, I would look for data id 1 at t=1 (not find it and thus have finish without doing anything).

-Data id 1 would be created while processing Message A at t=2.

Best Answer

Pedant alert! I'm the kind of guy that reads the actual specs for technologies.

Reading the EJB spec version 3.0, section 21.1.2 (Programming Restrictions) disallows using threads in your code. Here's the language and the rationale ...

The enterprise bean must not attempt to manage threads. The enterprise bean must not attempt to start, stop, suspend, or resume a thread, or to change a thread’s priority or name. The enterprise bean must not attempt to manage thread groups.

These functions are reserved for the EJB container. Allowing the enterprise bean to manage threads would decrease the container’s ability to properly manage the runtime environment.

So if you do what you're saying, the EJB police will come knocking on your door in the middle of the night and take you away. Or your app might malfunction and the vendor will laugh when you complain. Or nothing bad at all will happen.

But, as duffymo says, why do this? If you want the scalability offered by lots of threads, can you configure that in for your MDB? The point of EJB's is to handle stuff like that for you.

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