Documentation Overview

The following diagrams and notes are my understanding of part of the ServiceMix architecture based on a study of the source code [See Also: NMR Flows ]

– PS

Contents

• NMR flow types
  • st
  • seda
  • jms
  • jca

NMR Flow types

The flow type determines the mechanism by which the Normalized Message Router (NMR) Broker sends messages from one BC/SE to another.

Flow implementation classes

• JBIContainer "flowName" attribute determines the flow type used

• There is only 1 flow per Broker (and 1 Broker per JBIContainer)

• Flow name/class mappings are in the ServiceMix JAR. See META-INF/services/org/servicemix/jbi/nmr/flow

• There are a number of flow implementations as shown in the following table
  

  Flow Name	Flow implementation Class
  st	org.servicemix.jbi.nmr.flow.st.STFlow
  seda	org.servicemix.jbi.nmr.flow.seda.SedaFlow
  cluster	org.servicemix.jbi.nmr.flow.jms.JMSFlow
  jms	org.servicemix.jbi.nmr.flow.jms.JMSFlow
  jca	org.servicemix.jbi.nmr.flow.jca.JCAFlow

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Broker send sequence diagram

• The NMR Broker calls sendExchangePacket to deliver a message

• The flow implementation of abstract doSend Method determines how the message sending mechanism works

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STFlow

STFlow = "Straight Through" Flow. This is the simplest mechanism.

There is no staging or buffering.

sequence diagram

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SedaFlow

SEDA = "Staged Event Driven Architecture" Flow.

SEDA decomposes a complex, event-driven application into a set of stages connected by queues.

SedaFlow / SedaQueue classes

• There is 1 SedaFlow instance and a number of SedaQueue instances (1 per component)

• The SedaFlow "enqueues" an ME to send a message

• The SedaQueue instance "dequeues" the ME and processes it

• Each SedaQueue holds a concurrent HashMap of MessageExchanges (MEs) to the component. Enqueue/Dequeue is simply put/get of this HashMap

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sequence diagram

• SedaQueue instances are lazily created as needed and referenced in a queueMap

• Each SedaQueue instance runs as JCA1.5 asynchronous Work thread polling the HashMap at fixed intervals

• Having enqueued the ME, the SedaFlow doSend Method may return

• When the SedaQueue Worker (run Method) finds (dequeues) an ME, it processes it in another JCA Worker thread created solely for that purpose

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JMSFlow

Uses JMS for message routing among a network of remote containers.

JMSFlow classes and JMS Destinations

• There is one single Topic across all containers.
  • This Topic is created during JMSFlow init.
  • A ConsumerAdvisor configured for this Topic allows container to be "aware" of each other.
  • Special messages sent to this Topic broadcasting awareness of your components to other containers in the network.

• There is one Queue per container.
  • This is created during JMSFlow init.
  • This Queue is for sending response MEs to.

• There is one Queue per unique destination component.
  • This is created when a component is activated.
  • These Queues is for sending request MEs to.

• Outbound (request) messages get routed to a Queue for a named component (so are load balanced) and responses get sent back to the Queue for the originating container.

• The JMSFlow is a JMS MessageListener (ie it implements onMessage Method) for the Topic and all Queues

• The JMSFlow is also an ActiveMQ ConsumerAdvisoryEventListener for the Topic.
  • This means all JMSFlow instances will be aware of remote container startup/shutdown

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Notification of remote component state changes

• The diagram shows a "local" and "remote" JMSFlow instance for clarity although they may be the same instance

• A container needs to be made aware when the state of a remote container's components changes.
  • JMSFlow uses an ActiveMQ ConsumerAdvisoryEvent to detect a change in status of a remote Consumer of the Topic
  • If remote Topic Consumer is activated - eg container started - information of all (local) components are re-broadcast to the Topic so the new container can learn about them
  • If remote Topic Consumer is deactivated - eg container shutdown - all (local) knowledge of the remote container's components is removed

• Conversely, a remote container needs to be made aware if there is some state change with any component of the local container.
  • The JMSFlow instance is a JMS MessageListener on the Topic
  • If a component state changes, a ComponentPacketEvent (which container component state information) is serialized and sent as a JMS ObjectMessage to the Topic.
  • All remote JMSFlows receive this message and adjust their knowledge of our component accordingly
  • If the component is becoming activated, then a Queue is created (for remote containers to send request MEs to)

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JMSFlow send ME sequence diagram

• The diagram shows a "local" and "remote" JMSFLow instance for clarity although they may be the same instance

• The ME is serialized and sent as a JMS ObjectMessage

• Requests are sent to a component Queue on some remote container
  • They are load balanced

• Responses are sent back to the container Queue of the conatiner that originated the request (because the sender may have done a synchronous send and is awaiting a response)

• The JMSFlow instance is a MessageListener for both Queues

• When the MessageListener's onMessage is triggered, the ObjectMessage content is deserialized. If the deserialized Object is a ME then it is routed to the appropriate component.

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JCAFlow

The JCAFlow uses a JCA1.5 inbound resource adapters for message routing among a network of remote containers.

The resource adapters encapsulate JMS functionality.

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