Message listener service on z/OS
On the z/OS platform, the message listener service implementation uses the scalable server architecture to divide the listener port functions between the controller and servant processes.
A single message listener is registered in the controller portion of the ListenerPort, whereas application dispatch (that is, dispatch of the user application onMessage(Message) EJB method) is spread across the various servants comprising the server. This implementation is referred to as "listening in the controller" for the message-driven bean messages.
The WebSphere Application Server for z/OS message listener service implementation does not use the "listening in the controller" internal configuration in all cases, but only when the message-driven bean is mapped to a queue (that is, listening on a queue) or mapped (listening) to a topic through a durable subscription.
If the message-driven bean is listening to a topic through a non-durable subscription, the listener port registers a listener in each servant, rather than registering a single listener in the controller. In this case, a single message published to that topic is dispatched once for each servant comprising the server. If a message-driven bean is listening on a queue, or to a topic through a durable subscription, a single message sent is dispatched once only, to a single servant, for the entire server.
The configuration of the listener port, in the "listening in the controller" case, is administered externally through the controls described in
For a non-durable subscription message-driven bean that is listening in each servant as described above, the listener ports are configured in the same manner as they are on distributed platforms. In this case, the single set of settings configured for the listener port are applied identically to each servant.
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