Distributed OSGi and Possible
Future Enhancements
David Bosschaert Marc Schaaf
david.bosschaert@gmail.com marc@marc-schaaf.de
OSGi DevCon Europe 2009 - Zürich

About Us
● David Bosschaert
● Works at Progress Software in Dublin (previously IONA
Technologies)
● Member of the OSGi Enterprise Expert Group
● Coding Open Source projects
● Marc Schaaf
● Student of computer science at the University of Applied Science
in Hannover, Germany
● Currently writing his masters thesis on a possible integration of
asynchronous messaging into OSGi

Distributed OSGi
(Remote Services)

Remote Services
New OSGi Specifications, based on the Distributed OSGi RFC 119.
1. Remote Services, which specifies the standardized properties for
service remoting.
Will be released this summer as part of OSGi 4.2
2. Distribution Service Admin API’s. Contains standard API’s for
interacting with the Distribution Provider and Discovery Providers.
Will be released before the end of the year.

Demo of Remote Services
Client Side OSGi container Server Side OSGi container
(Felix) (Equinox)
Core OSGi Bundles Core OSGi Bundles
Library Bundles Library Bundles
DOSGi Bundles DOSGi Bundles
(Apache CXF) (Apache CXF)
My App Interfaces Bundle My App Interfaces Bundle
ook
My App Consumer Bundle My App Service Bundle
egistry H
Service R red by
invokes creates
provides
trigge
publishes
svc OSGi
proxy svc
remote
service
metadata
remote remote endpoint
publishes
Discovery invocation
service

Asynchronous Messaging
in OSGi
An integration approach

Project Lightsabre – Aims
OSGi Container
OSGi Container OSGi Container
OSGi Container
“Normal” Bundle “Normal” Bundle
Mediation Component Mediation Component
Queue
or
Messaging System
Messaging System Topic
Already existing / /Legacy
Already existing Legacy
Application
Application

The OSGi EventAdmin
● EventAdmin
● OSGi internal mechanism for (asynchronous) event based
communication with topic semantic
EventAdmin
Service
Push Events
SendingBundle
EventAdmin Impl.
Receive Events Deliver Events
ReceivingBundle
EventHandler
Service
● Events consist of a topic and an arbitrary number of key:value
pairs
● An EventHandler can provide a filter to select the events he
wants to receive

EventAdmin Based Integration
Idea: Introduce an “Event Distribution System” (EDS)
which mediates between the EventAdmin and the MoM
OSGi Container
OSGi Container
Events Messages
EventHandling
Service
EventAdmin Configuration
Receiving Bundle Service
EventAdmin EDS MoM
Sending Bundle
EventAdmin EventHandling
Service Service
Events Messages

EventAdmin Based Integration
● Basic messaging functionality with existing API
● Seamless integration
● Usage of MoM without any knowledge about it
●
Drawbacks
● No guaranteed delivery → No reliability
● No error handling, .....
●
Possible solutions
● Use another (new) API
● Extend the existing API (next slide)

“Extended” EventAdmin
● Idea: Introduce an extended EventAdmin API
● The additional API could provide guaranteed delivery and could
be implemented directly by the EDS
● The old API still enables legacy bundles to use messaging with
limited features
OSGi Container
OSGi Container Extended EventAdmin
Service
EventHandling
Service
EventAdmin
Service
Receiving Bundle
EventAdmin EDS MoM
Sending Bundle
EventAdmin EventHandling
Service Service

Demo
Sending OSGi Container
Sending OSGi Container Receiving OSGi Container
Receiving OSGi Container
Message Producing Bundle Message Consuming Bundle
EventAdmin Events EventAdmin
EDS EDS
ActiveMQWrapper ActiveMQWrapper
ActiveMQ Topic
ActiveMQ

How to Send Messages
ServiceTracker
st = new ServiceTracker(bctx, EventAdmin.class.getName(), null) {
@Override
public Object addingService(ServiceReference reference) {
eventAdmin = (EventAdmin) bctx.getService(reference);
jbSend.setEnabled(true);
return super.addingService(reference);
}
};
Sending an Event
Dictionary<String, Object> props = new Hashtable<String, Object>();
props.put("message", jtMessage.getText());
Event ev = new Event("demo", props);
eventAdmin.sendEvent(ev);
Configuration
org.fusesource.lightsabre.name=DemoActiveMqForwarding
org.fusesource.lightsabre.direction=send
org.fusesource.lightsabre.event.topic=demo
org.fusesource.lightsabre.messaging.binding=org.apache.activemq
org.fusesource.lightsabre.messaging.url=tcp://localhost:61616
org.fusesource.lightsabre.messaging.subject=DemoActivemqTopic
[...]

How to Receive Messages
Bundle Activator
public void start(BundleContext context) throws Exception {
Dictionary props = new Hashtable();
props.put(EventConstants.EVENT_TOPIC, "demo");
context.registerService(EventHandler.class.getName(),new DemoMessageReceiver(),
props);
}
Event Handler
public class DemoMessageReceiver implements EventHandler {
public void handleEvent(Event event) {
System.out.println("DemoMessageReceiver: " + event.getProperty("message"));
}
}
Configuration
org.fusesource.lightsabre.name=DemoActiveMqForwarding
org.fusesource.lightsabre.direction=receive
org.fusesource.lightsabre.messaging.binding=org.apache.activemq
org.fusesource.lightsabre.messaging.url=tcp://localhost:61616
org.fusesource.lightsabre.messaging.subject=DemoActivemqTopic
[...]

Conclusion
● Distributed OSGi
● A standardized way to use the OSGi Services model with Remote
Service Distribution
● Asynchronous Messaging
● Promising approach as a basis for further research found
● Lightsabre provides a first implementation

Thank you for your kind attention
OSGi Remote Services Project Lightsabre
OSGi Asynchronous Messaging
OSGi 4.2 Draft
➔ http://www.osgi.org/Specifications/Drafts ➔ http://lightsabre.fusesource.org
Reference Implementation
➔ http://cxf.apache.org/distributed-osgi.html