Overview

JBossMQ is made up of multiple layers and plugins.

Front End

At the front end there is the javax.jms implementation which can be found in org.jboss.mq..

Some of the work is handled at this layer, but most of the work is handed off to the server using a simplified

API called the IL (invocation layer).

Invocation Layer

The invocation layer is made up of two interfaces.

• ServerIL - the requests are handled by the ServerILService on the server

• ClientIL - allows the server to invoke back on the client's ClientILService (mainly to push messages to the client as they arrive)

There are a number of implementations of these interfaces which depends upon your choice of ConnectionFactory

Invoker/Interceptors

The ServerILService targets the JMSServerInvoker whose responsibilty is to pass the request through a series of

interceptors.

The standard interceptors are:

• TraceInterceptor - For debugging requests

• SecurityInterceptor - To authenticate and authorise requests

• JMSDestinationManager - The main server

Destination Manager

The JMSDestinationManager is the main broker for requests. It performs three main operations

• Passing subscription related requests to the StateManager

• Passing message send requests to the JMSDestination

• Passing message receive requests to the ClientConsumer

Destinations

The JMSDestination provides different behaviour depending upon the type of destination, either

• JMSQueue - queues

• JMSTopic - topics

Client Consumer

The ClientConsumer is reponsible for keeping track of client subscriptions.

It also pushes messages back to the client over the ClientIL as messages arrive.

BasicQueue

The JMSDestination and ClientConsumer target BasicQueue implementations. There are a number

of different types:

• BasicQueue - a simple queue used for temporary queues

• PersistentQueue - a queue that persists messages used for permenant queues and durable topic subscriptions

• ExclusiveQueue - an optimization of BasicQueue for non durable subscriptions

• SelectorPersistentQueue - an optimization of PersistentQueue for topic subscriptions that have selectors

Security Manager

The SecurityManager is used by the SecurityInterceptor.

The default implementation delegates to a JAAS login module for authentication and uses configuration from the

JMSDestination for authorization.

State Manager

The StateManager is responsible for maintaining durable subscription information.

It can also be used to maintain users and roles.

Persistence

The PersistenceManager handles the saving and restoring of persistent messages.

It also maintains a transaction log for transactional sessions.

Message Cache

The MessageCache is used to avoid too many messages causing an OutOfMemoryError.

Instead of holding direct references to the messages the server holds a MessageReference.

The MessageReference either holds a direct reference to the message or a pointer to the message in an

offline store. This allows the server to move messages in and out of memory.

An Example Send

QueueSender -> ServerIL -> network -> ServerILService -> JMSServerInvoker -> TracingInterceptor ->

SecurityInterceptor -> JMSDestinationManager -> JMSQueue -> PersistentQueue

An Example Receive

QueueReceiver -> ServerIL -> network -> ServerILService -> JMSServerInvoker -> TracingInterceptor ->

SecurityInterceptor -> JMSDestinationManager -> ClientConsumer -> JMSQueue -> PersistentQueue

If no message is available the call returns, then when a message arrives:

PersistentQueue -> ClientConsumer -> ClientIL -> network -> ClientILService -> QueueReceiver