OSGi For Eclipse Developers

OSGi for Eclipse Developers

Chris Aniszczyk (EclipseSource)
zx@eclipsesource.com
http://twitter.com/caniszczyk

Bernd Kolb (SAP)
bernd.kolb@sap.com
http://twitter.com/berndkolb

Martin Lippert (it-agile)
lippert@acm.org

© 2009 by C. Aniszczyk, B. Kolb | OSGi for Eclipse Developers | April 23rd, 2009

Overview
• Introduction
• Topics
Frameworks
o
Import-Package vs. Require-Bundle
o
Dynamic Bundles
o
Versioning
o
Extensions and Services
o
Compendium Services
o
OSGi Tooling
o
• Conclusion


Introduction
• OSGi Alliance
Worldwide consortium of technology innovators that advances
o
OSGi technology

• OSGi Technology
Set of specifications that define a dynamic component system for
o
Java

OSGi is a lot more than Eclipse

• Many Eclipse developers oblivious to OSGi topics

• How about starting with a history lesson?


A Blast from the Past...
• Eclipse had it's own non-standard plug-in model
• OSGi and old Eclipse plug-in model were similar


Eclipse + OSGi FTW
• Eclipse went to OSGi in 3.0 with Equinox*
The transition went “smoothly”
o

*http://portal.acm.org/citation.cfm?id=1086616


Eclipse
folks

Plug-In

Eclipse
OSGi
folks
guys

Bundle
Plug-In

Frameworks
• There’s a world outside of Eclipse and Equinox


Be aware of special headers…
• Forget about:
Eclipse-BuddyPolicy
o
Eclipse-PatchFragment
o
Eclipse-SourceBundle
o
Eclipse-…
o
Otherwise you are tied to Equinox

• Tip: PAX Runner to test against multiple frameworks
http://wiki.ops4j.org/display/ops4j/Pax+Runner
o


The Alien called “Import-Package”
• Eclipse
Dependencies are declared using Require-Bundle
o
Never heard of Import-Package, sounds strange
o

Plug-in

• OSGi
Uuuha, no, please don’t use Require-Bundle at all
o
o Instead, define dependencies using Import-Package

Bundle


What is the difference?
• Require-Bundle
Imports all exported packages of the bundle, including re-
o
exported and split bundle packages

p-1.0.1 p-1.0.1
q-1.0 q-1.0
t
u
Require
Bundle

• Import-Package
Import just the package you need
o

p-1.0 p-1.0.1
q-1.0 q-1.0
t
u
Import
Package


When to use what?
• Prefer using Import-Package
Lighter coupling between bundles
o
Less visibilities
o
Eases refactoring p-1.0.1
o

p-1.0
q-1.0
t
u

q-1.0

• Require-Bundle, when necessary
Higher coupling between bundles
o
Use only for very specific situations:
o
 split packages (same package in different bundles)


Bundles are dynamic? You're kidding…


Dynamics with OSGi
• OSGi allows you to manage bundles at runtime
Install
o
Update
o
Uninstall
o

• But there is no magic behind the scenes
nothing is changed automatically
o
objects stay the same
o
references remain valid
o

• This means you need to cleanup after yourself so the
GC can help you!


Updating a bundle at runtime means...
• Dependent bundles (with wires to the updated bundle
via Require-Bundle or Import-Package) are
stopped and re-started

• The consequence:
updating a bundle might cause the system to “restart”
o
this is not what I associate with “cool dynamics”
o

 When programming anticipate OSGi’s dynamics


Think about dependencies
• Less is more!
Less dependencies
o
Dependency Inversion Principle (DIP)
o

• Think more about APIs
API in separate bundle
o
depend only on API bundle
o
implementation can change
o


Versioning Guidelines
• Bundle-Version: 3.4.2.qualifier
 3 - major version
 4 - minor version
 2 - micro version
• From the OSGi specification...

• Eclipse Versioning Guidelines
 http://wiki.eclipse.org/Version_Numbering


Versioning Bundles
• On Bundle level
Each Bundle has a version
o
You should set a version range when using require-bundle
o

• On Package level
Packages should also have a version when exported
o
o Remember: Import-Package
o Package imports should have version ranges as well!

• Summary
Version everything!
o
A version isn’t a marketing number!
o


Versioning Tools
• PDE API Tools
 http://www.eclipse.org/pde/pde-api-tools/

• Assists with the mechanics of API evolution
Binary compatibility (breaking) issues

API leaks

API freeze issues

Suggestions bundle versions

Runs headless and in your workspace



OSGi Services – another alien…
• Services? SOA? Oh no... please no buzzwords!!!

• Something like Extension Points?

• Hey, wait!
o OSGi Services are the key feature to build
modular and dynamic apps


OSGi Services – your best friend
OSGi Service providers: OSGi Service consumers:
implement an interface and register lookup a service via the interface
an implementation


Versioned Contracts
• the service interface is the contract
many consumers possible
o
many producers possible
o

• this contract is versioned
multiple versions of service might be available
o
you get only those that matches your dependencies
o

You cannot get that with extension points
singleton bundles
−
You always get the latest version
−


“You come and go”
• A bundle is started:
services are registered
o
and available from that on
o

• A bundle is stopped:
services are unregistered
o
no longer available
o

• OSGi services are dynamic by definition!
+ dozens of techniques to deal with these dynamics
o


Life Cycle Differences
• Services are bound to the ACTIVE state

• Extensions are available in RESOLVED state


Declarative and lazy
• OSGi services are bound to the active state
they need class loading to happen
o
they need objects to be created
o

• There are declarative approaches for OSGi services
OSGi Declarative Services
o
OSGi Blueprint
o
Spring Dynamic Modules
o
iPOJO
o


When to use what?
• OSGi Services:
Dependencies between bundles
o
Dynamics
o
Looser coupling
o
quot;I provide a service for anybody out therequot;
o
quot;I need a service and don't care who delivers itquot;
o

• Extension-Registry:
UI contributions (too small for OSGi services)
o
Non-code contributions
o
quot;I open up myself for extensions that I don't know upfrontquot;
o
If you have tons of thousand of extensions
o


Compendium Services
• OSGi has spec’d 20+ services

• LogService
• EventAdmin
• HttpService
• Declarative Services
• Configuration Admin


LogService
• A general purpose message logger (20kb)

• LogService
Log message, level, exception, service ref, bundle
o

• LogReaderService
Retrieve current or previous log entries
o

• Note: ExtendedLogService (bug 260672)
named loggers
o
extended log entry (e.g., thread id)
o
filters for log listeners
o


EventAdmin
• An inter-bundle pub-sub system (30kb)

• EventAdmin
publish events synchronously and asynchronously
o
 postEvent(new Event(quot;com/acme/timerquot;, time ));
 sendEvent(new Event(quot;com/acme/timerquot;, time ));

• EventHandler
handle events based on topics
o
 handleEvent(Event event)

• Event
has topic and properties as attributes
o


HttpService
• A way to register servlets and resources

• HttpService
Register servlets and resources
o

• Http Registry (org.eclipse.equinox.http.registry)


Declarative Services
• A declarative model for publishing, finding and
binding to OSGi services (150kb)

• ServiceTracker's – the programmatic way to get a
service – suck


Declarative Services Tooling
Graphical Editor
•
Validation
•
Source Editing
•


ConfigAdmin
• A service to configure components (bundles)
o A configuration is a list of key-value pairs

• The configuration admin service persists and
distributes these configurations to interested parties

• Components to be configured register a
ManagedService

• To apply several configurations of the same kind you
could use a ManagedServiceFactory


PDE
• Eclipse has been tooling OSGi forever with PDE
Plug-ins == Bundles! Blugins?
o

• PDE Tools:
Bundles
o
Fragments
o
Declarative Services
o

• New Plug-in Project wizard has OSGi love


BND
• Bundle Tool (BND)
creates and diagnoses OSGi bundles
o
Maven, Eclipse and Ant integration
o
http://www.aqute.biz/Code/Bnd
o

• Relies on specification (.bnd file) + classpath

• Generates bundle artifacts like manifests

• Useful for converting third party libs to bundles


Sigil
• Provides OSGi Tooling
• http://sigil.codecauldron.org/
• driven by sigil.properties file
• BND used under the covers

• bundles fetched from repositories
 based on your Import-Package statements


Thank you for your attention!

• Questions and feedback welcome!

C. Aniszczyk
zx@eclipsesource.com
http://twitter.com/caniszczyk

B. Kolb
bernd.kolb@sap.com
http://twitter.com/berndkolb

M. Lippert (it-agile)
lippert@acm.org


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