scala modules

ScalaModulesScala and OSGi

OSGi Services

• The key to modularity

• Arguably, the key to OOP itself?

Dr Alan Kay

Dr Alan Kay

“Dude I invented friggin’ OOP. Have you heard of it?”

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.”

Late Binding with Services

• Services answer the question:where do I get an implementation of this interface?

• The registry decentralises the architecture.

Consuming Services

Harder than Expected!

Why...?

Slippery

Dynamics

• A service can come and go

• At any time

• On any thread

• Yes... even while you’re using it

Result

•Service usage code can be very complex

Service Consumption in Java

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()); }

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

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()); } }

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

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()); } } }

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

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); } }

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

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); } } }

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

An Answer:Stop Writing Code!

Declarative Services (DS)

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

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>

Problem

• These frameworks provide abstractions

• Abstraction hide detail

• Sometimes we need the detail

Example: Cardinality?

Component

Service

Service

Service

Service

Single

Component

Service

Service

Service

Service

Multiple

Component

Service

Service

Service

Service

???

Component

Service

Service

Service

Service

Component

Component

Component

Not supported by DS

♥IDeclarative

Services(and Blueprint)

The “80%” Solution

“Normal” Users


“Normal” UsersDS support


“Normal” UsersDS support“Power” Users


“Normal” UsersDS support“Power” UsersEasy in Java


“Normal” UsersDS support“Power” UsersEasy in JavaEasy in Scala

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???

What is ScalaModules?

NOT Another Module System (phew!)

“A Scala internal DSL to ease OSGi development”

• Now:

• Services

• Future:

• Extender Pattern?

• Resources?

An Eclipse Project!

Examples

ScalaModules

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

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

Get Involved

http://www.eclipse.org/forums/eclipse.scalamodules





scala modules

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