ScalaModules is an elegant and intuitive domain specific language for OSGi development written in the Scala programming language. In this podcast, Neil Bartlett examines the differences between java and scala osgi implementations. He also shared his views on the advantages of scalamodules for osgi.

1. ScalaModules
Scala and OSGi

2. OSGi Services
• The key to modularity
• Arguably, the key to OOP itself?

3. Dr Alan Kay

4. Dr Alan Kay
“Dude I
invented
friggin’ OOP.
Have you
heard of it?”

5. Dr Alan Kay
“OOP to me means only
messaging, local
retention and protection
and hiding of state-
process, and extreme
late-binding of all things.”

6. Late Binding with
Services
• Services answer the question:where do I
get an implementation of this interface?
• The registry decentralises the architecture.

7. Consuming Services

8. Harder than Expected!

9. Why...?

11. Slippery

12. Dynamics
• A service can come and go
• At any time
• On any thread
• Yes... even while you’re using it

13. Result
• Service usage code can be
very complex

14. Service Consumption
in Java

15. Consuming a Service
public void consumeService(BundleContext context) {
ServiceReference ref = context.getServiceReference(Greeting.class.getName());
Greeting greeting = (Greeting) context.getService(ref);
System.out.println(greeting.getMessage());
}

16. Consuming a Service
public void consumeService(BundleContext context) {
ServiceReference ref = context.getServiceReference(Greeting.class.getName());
Greeting greeting = (Greeting) context.getService(ref);
System.out.println(greeting.getMessage());
}
WRONG

17. Consuming a Service
public void consumeService(BundleContext context) {
ServiceReference ref = context.getServiceReference(Greeting.class.getName());
if(ref != null) {
Greeting greeting = (Greeting) context.getService(ref);
System.out.println(greeting.getMessage());
}
}

18. Consuming a Service
public void consumeService(BundleContext context) {
ServiceReference ref = context.getServiceReference(Greeting.class.getName());
if(ref != null) {
Greeting greeting = (Greeting) context.getService(ref);
System.out.println(greeting.getMessage());
}
}
WRONG

19. Consuming a Service
public void consumeService(BundleContext context) {
ServiceReference ref = context.getServiceReference(Greeting.class.getName());
if(ref != null) {
Greeting greeting = (Greeting) context.getService(ref);
if(greeting != null) {
System.out.println(greeting.getMessage());
}
}
}

20. Consuming a Service
public void consumeService(BundleContext context) {
ServiceReference ref = context.getServiceReference(Greeting.class.getName());
if(ref != null) {
Greeting greeting = (Greeting) context.getService(ref);
if(greeting != null) {
System.out.println(greeting.getMessage());
}
}
}
WRONG

21. Consuming a Service
public void consumeService(BundleContext context) {
ServiceReference ref = context.getServiceReference(Greeting.class.getName());
if(ref != null) {
Greeting greeting = (Greeting) context.getService(ref);
if(greeting != null) {
System.out.println(greeting.getMessage());
}
context.ungetService(ref);
}
}

22. Consuming a Service
public void consumeService(BundleContext context) {
ServiceReference ref = context.getServiceReference(Greeting.class.getName());
if(ref != null) {
Greeting greeting = (Greeting) context.getService(ref);
if(greeting != null) {
System.out.println(greeting.getMessage());
}
context.ungetService(ref);
}
}
WRONG

23. Consuming a Service
public void consumeService(BundleContext context) {
ServiceReference ref = context.getServiceReference(Greeting.class.getName());
if(ref != null) {
try {
Greeting greeting = (Greeting) context.getService(ref);
if(greeting != null) {
System.out.println(greeting.getMessage());
}
} finally {
context.ungetService(ref);
}
}
}

24. Consuming a Service
public void consumeService(BundleContext context) {
ServiceReference ref = context.getServiceReference(Greeting.class.getName());
if(ref != null) {
try {
Greeting greeting = (Greeting) context.getService(ref);
if(greeting != null) {
System.out.println(greeting.getMessage());
}
} finally {
context.ungetService(ref);
}
}
}
NOT TYPE SAFE

25. Consuming a Service
public void consumeService(BundleContext context) {
ServiceReference ref = context.getServiceReference(Greeting.class.getName());
if(ref != null) {
try {
Greeting greeting = (Greeting) context.getService(ref);
if(greeting != null) {
System.out.println(greeting.getMessage());
}
} finally {
context.ungetService(ref);
}
}
}
NOT TYPE SAFE

26. An Answer:
Stop Writing Code!

27. Declarative Services
(DS)
@Reference
public void setGreeting(Greeting greeting) {
this.greeting = greeting;
}
public void consumeService() {
System.out.println(greeting.getMessage());
}

28. Blueprint
public void setGreeting(Greeting greeting) {
this.greeting = greeting;
}
public void consumeService() {
System.out.println(greeting.getMessage());
}
<blueprint>
<reference id="greeting" interface="org.example.Greeting"/>
<bean id="foo" class="com.foo.Foo"/>
<property name="greeting" ref="greeting"/>
</bean>
</blueprint>

29. Problem
• These frameworks provide abstractions
• Abstraction hide detail
• Sometimes we need the detail

30. Example: Cardinality?
Service
Service
Component
Service
Service

31. Single
Service
Service
Component
Service
Service

32. Multiple
Service
Service
Component
Service
Service

33. ???
Component Service
Component Service
Component Service
Component Service
Not supported by DS

34. Declarative
I Services
(and Blueprint)

35. Declarative
I Services
(and Blueprint)

36. The “80%” Solution
“Normal” Users

37. The “80%” Solution
“Normal” Users
DS support

38. The “80%” Solution
“Normal” Users
DS support

39. The “80%” Solution
“Normal” Users
DS support
“Power” Users

40. The “80%” Solution
“Normal” Users
DS support
“Power” Users

41. The “80%” Solution
“Normal” Users
DS support
“Power” Users
Easy in Java

42. The “80%” Solution
“Normal” Users
DS support
“Power” Users
Easy in Java

43. The “80%” Solution
“Normal” Users
DS support
“Power” Users
Easy in Java
Easy in Scala

44. The “80%” Solution
“Normal” Users
DS support
“Power” Users
Easy in Java
Easy in Scala

45. Java
ServiceTracker tracker = new ServiceTracker(context, Greeting.class.getName(),
new ServiceTrackerCustomizer() {
public Object addingService(ServiceReference reference) {
Greeting greeting = (Greeting) context.getService(reference);
ServiceRegistration reg = context.registerService(IFoo.class.getName(),
new Foo(greeting), null);
return reg;
}
public void modifiedService(ServiceReference reference, Object service) {
}
public void removedService(ServiceReference reference, Object service) {
ServiceRegistration reg = (ServiceRegistration) service;
reg.unregister();
}
});

46. Java
ServiceTracker tracker = new ServiceTracker(context, Greeting.class.getName(),
new ServiceTrackerCustomizer() {
public Object addingService(ServiceReference reference) {
Greeting greeting = (Greeting) context.getService(reference);
ServiceRegistration reg = context.registerService(IFoo.class.getName(),
new Foo(greeting), null);
return reg;
}
public void modifiedService(ServiceReference reference, Object service) {
}
public void removedService(ServiceReference reference, Object service) {
ServiceRegistration reg = (ServiceRegistration) service;
reg.unregister();
}
});
Type Safety???

47. What is ScalaModules?

48. NOT Another Module
System (phew!)

51. “A Scala internal DSL to ease
OSGi development”

52. • Now:
• Services
• Future:
• Extender Pattern?
• Resources?

53. An Eclipse Project!

54. Examples

55. Java
ServiceTracker tracker = new ServiceTracker(context, Greeting.class.getName(),
new ServiceTrackerCustomizer() {
public Object addingService(ServiceReference reference) {
Greeting greeting = (Greeting) context.getService(reference);
ServiceRegistration reg = context.registerService(IFoo.class.getName(),
new Foo(greeting), null);
return reg;
}
public void modifiedService(ServiceReference reference, Object service) {
}
public void removedService(ServiceReference reference, Object service) {
ServiceRegistration reg = (ServiceRegistration) service;
reg.unregister();
}
});

56. ScalaModules
val greetingTrack = context track classOf[Greeting] on {
case Adding(greeting) => context createService (classOf[IFoo],
new Foo(greeting))
case Removed(_, reg) => reg unregister
}

57. Plan
• Started moving the code & docs to Eclipse
• 19 March: M1
• 7 May: M2
• 28 May: RC1
• 11 June: RC2
• 23 June: ScalaModules 2.0 Release &
Graduation

58. Get Involved
http://www.eclipse.org/forums/
eclipse.scalamodules