OSGi Subsystemsfrom theory to practiceGlyn NormingtonEclipse Virgo Project LeadSpringSource/VMware

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@glynnormingtonOSGi Subsystems

Software rots

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modularity helps

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but ...

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A clean design

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without enforcement

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works fine for a while

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then starts to decay

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and soon

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the rot sets in

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and spreads

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and worsens

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until the original design

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has gone.

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OSGi Subsystems to the rescue

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Subsystem: identified manageable optionally scopedgroup of bundles

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subsystemsspec

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subsystemsreference

implementation

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subsystemsreference

implementation

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@glynnormingtonOSGi Subsystems

Now some theory

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and practice

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followed by

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•getting started• the future

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TheorySubsystem Types

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@glynnormingtonOSGi Subsystems

Feature Subsystems

Feature

bundle

bundle bundle

bundle

Scoping:•None

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@glynnormingtonOSGi Subsystems

Feature Subsystems

Feature

bundle

bundle bundle

bundle

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A depends on B

bundle Bbundle A

• bundle• package• capability• service

Notation

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Feature Subsystems

Feature

bundle

bundle bundle

bundle

Scoping:•None

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@glynnormingtonOSGi Subsystems

Application Subsystems

int x;{ int y;}

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Application Subsystems

Application

bundle

bundle

bundle

bundle

Scoping:•No exports•Automatic

imports

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{ }

@glynnormingtonOSGi Subsystems

Composite Subsystems

Composite

bundle

bundle bundle

bundle

Configurablescoping

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@glynnormingtonOSGi Subsystems

PracticeSubsystem Types

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@glynnormingtonOSGi Subsystems

Feature Subsystems

Useful for:

• Grouping dependencies

• Sharing infrastructure

• Avoiding uses constraint failures

Feature

bundle

bundle bundle

bundle

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@glynnormingtonOSGi Subsystems

Application Subsystems

Useful for top layer of the system

Avoid duplicating contents

• Reduces sharing

• Complicates update

• Leads to resolution errors

Application

bundlebundle

Feature

bundlebundle

Application

bundlebundle

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@glynnormingtonOSGi Subsystems

Composite SubsystemsUseful for special infrastructure

Not for general use

• Complex

• Can duplicate infrastructure

• extenders

• management bundles

Composite

bundle

bundle bundle

bundle

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bundlespackages

capabilitiesservices

services

kernel

user region compositesubsystem

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TheorySubsystem Content and

Dependencies

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@glynnormingtonOSGi Subsystems

Subsystem Content• By value in a subsystem archive

or

• By reference to a repository

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@glynnormingtonOSGi Subsystems

Dependencies

• Subsystem content dependencies

• Installed from repository

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@glynnormingtonOSGi Subsystems

PracticeSubsystem Content and

Dependencies

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@glynnormingtonOSGi Subsystems

Subsystem Content (by value)

• Easy to deploy

• Limits sharing

• Harder to update

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Repository Content

• Convenient during development

• Avoids bloat

• Generally preferable

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TheoryNested

Subsystems

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@glynnormingtonOSGi Subsystems

Nested Subsystems• So far all subsystems have been

children of the ‘root’ subsystem

Root

Application

bundlebundle

Feature

bundlebundle

Application

bundlebundle

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Nested Subsystems

• Unlimited nesting

• Sharing determined by the child

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PracticeNested Subsystems

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Nested Subsystems• Features useful for grouping other subsystems

Root

Feature

Application

bundle

bundle

bundle

Application

bundle

bundle

bundle

bundle

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@glynnormingtonOSGi Subsystems

Nested Subsystems• Nested features useful for logical grouping

Root

Application

bundlebundle

Feature

bundlebundle

Root

Feature

bundlebundle

Feature

bundlebundle

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@glynnormingtonOSGi Subsystems

Nested Subsystems• Nested applications useful for scoping

Root

Application

bundlebundle

Application

bundlebundle

bundle

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@glynnormingtonOSGi Subsystems

More Theory

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Subsystem States

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installing

installed uninstalling

resolving resolved

starting stopping

active

uninstalled

install failed

install

start

start

stop

uninstall

uninstall

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RegionsRegion, group of bundles:

• scoped subsystems

• root subsystem

Directed graph; arcs are filters

Region context bundle

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Getting Started

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Aries Subsystems

on Virgo kernel

https://github.com/glyn

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Feature

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Subsystem-SymbolicName: hello.feature.subsystem

Subsystem-Type: osgi.subsystem.feature

Subsystem-Content: hello

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Application

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Subsystem-SymbolicName: hello.application.subsystem

Subsystem-Type: osgi.subsystem.application

Subsystem-Content: hello

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Composite

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Subsystem-SymbolicName: hello.composite.subsystem

Subsystem-Type: osgi.subsystem.composite

Subsystem-Content: hello;version="[1,1]"

Import-Package: org.osgi.framework

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Nested Subsystem

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Subsystem-SymbolicName: hello.nested.composite.subsystem

Subsystem-Type: osgi.subsystem.composite

Subsystem-Content: hello;version="[1,1]",

hello.application.subsystem;

type="osgi.subsystem.application";

version="[0,0]"

Import-Package: org.osgi.framework

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Region Digraph

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kernel

user region

application composite nested composite

application

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Alternatives

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Technology Stack

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Equinox region bundle

Aries Subsystems Virgo Kernel

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VirgoStandard Virgo Equivalent

Feature Unscoped plan

Application Scoped plan or PAR

Composite User region

Nesting Nested plans

Repository Repository

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Equinox Region Support• org.eclipse.equinox.region

• RegionDigraph service

• Persistence

• JMX mxbeans

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Back to software rot

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Subsystems

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guide evolution

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and discourage rot.

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The Future

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Future Work Items

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Spec topics

•Extenders•Weaving and dynamic imports•Service dependency determination•Thread context class loaders•Config Admin

Tooling support

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ThanksJohn Ross - Aries SubsystemsGraham Charters - Subsystems spec

@glynnormingtonOSGi Subsystems

OSGi R5 Enterprise Specificationhttp://www.osgi.org/Download/Release5

Arieshttp://aries.apache.org/

Aries Subsystems on Virgo Kernelhttps://github.com/glyn

Virgohttp://www.eclipse.org/virgo

Equinox Region Bundlegit://git.eclipse.org/gitroot/equinox/rt.equinox.bundles.git

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@glynnormingtonOSGi Subsystems

Questions?

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