How to manage software complexity with OSGi

How to Manage Software Complexity

with OSGiPeter Kriens & David Savage

donderdag 24 maart 2011

What is Complexity?


Complex?


The puzzle looks very simple, contrary to many other wire puzzles, that look scary and complex right from the start. Nevertheless, its looks are

deceiving, as it can prove to be frustratingly difficult to

solve.


Complex?


Worlds Largest Jigsaw Puzzle24.000 pieces

(4.28m x 1.57m)

Complex?


The Eye Of The Beholder

• Complexity of a task is the energy you use to complete that task

c = √E/m


The Eye Of The Beholder

• Complexity of a task is the energy you use to complete that task

c = √E/m


Energy?

• Understanding the problem

• Learning the solution

• Accidental complexity

• Size matters!


Energy?




• Size matters!

Subjective Complexity


Energy?




• Size matters!

Subjective Complexity

Absolute Complexitysize related


What’s Modularity Got to do With Size???


Modularity• Functions

• local variables

• Object Oriented

• fields, methods, inheritance,polymorphism

• instances

• Bundles

• implementations, services

• componentsdonderdag 24 maart 2011

Modularity• Functions

• local variables

• Object Oriented

• fields, methods, inheritance,polymorphism

• instances

• Bundles

• implementations, services

• componentsdonderdag 24 maart 2011

Modularity• Modularity is about

creating a difference between an inside and an outside

• Chunking - having an anchor for an aggregation

• Visibility - is reduced, reducing the scope to attend for changes

A B

C D

ABCD


Modularity• Modularity is about

creating a difference between an inside and an outside

• Chunking - having an anchor for an aggregation

• Visibility - is reduced, reducing the scope to attend for changes

A B

C DABCD


A B

C D

• modules have a private space and share a public space

• modules limit their visibility and exposure

• Reduces geometric to linear complexity

Modularity


A B

C D




Modularity

Pub


A B

C D




Modularity

Pub


EntropyE

func

tiona

lity

Emodularizationdonderdag 24 maart 2011

EntropyE

func

tiona

lity


EntropyE

func

tiona

lity


EntropyE

func

tiona

lity


EntropyE

func

tiona

lity


EntropyE

func

tiona

lity


#1 OSGi Complaint:Class Loaders!


Classloaders & Modularity


Class Loading Revisited

• Class.forName

• Class path Scanning

• Service Loader

• Thread Context Class Loaders

• Factory, and FactoryBuilders


A B

C D

• Class loaders are used to provide extensibility and decoupling

• They were not designed for this purpose,

• And class loaders break module boundaries


Pub


A B


Public


A B


Public

C


A B


Public

IC


A B


Public

IC X


A B


Public

I

C P


µServicesWould be nice to mentionhow µServices reduce surface area of design

efficiency of packet based approaches?

but cost of packet based system is congestion - leads into dependency hell?


#2 OSGi Complaint: Dependency Hell


Metadata Hell?


Transitive Hell?


A B

C D

• Modules require other modules

• Dependencies are transitive

• A → C → D

Coupling

Pub


A B

C D

• Modules require other modules

• Dependencies are transitive

• A → C → D

Coupling

Pub


C

A

D

• Fan out is a problem

• A does not transitively depend on D!

• The dependency is caused by (unnecessarily) packing 1 and 2 in the same module

Cohesion

B


C

A

D

• Fan out is a problem

• A does not transitively depend on D!

• The dependency is caused by (unnecessarily) packing 1 and 2 in the same module

Cohesion

B

2

A

1


C CC D

• Refactoring can increase the cohesion and reduce coupling

• But now A depends on C1 and B depends on C2

• Package dependencies are more robust to changes

Cohesion

B

2

A

1


C C D

• Refactoring can increase the cohesion and reduce coupling

• But now A depends on C1 and B depends on C2

• Package dependencies are more robust to changes

Cohesion

B

2

A

1


Metadata Heaven?


Requires Tools


Tools

Refer to

Application

Policy Resolver

Request deployment of a

component, e.g. a Bundle,

WAR, WAB or EAR

App

Policy

Repository

Resolve

Dependencies

according to

Policy

Provision

component and

dependencies

1

3

4

Nimble

2


Tools

Refer to

Application

Policy Resolver

Request deployment of a

component, e.g. a Bundle,

WAR, WAB or EAR

App

Policy

Repository

Resolve

Dependencies

according to

Policy

Provision

component and

dependencies

1

3

4

Nimble

2


OSGiBuild Tools

OSGiRuntime Tools

OSGiCloud Tools

...


OSGiBuild Tools

OSGiRuntime Tools

OSGiCloud Tools

...


How to Manage Complexity?

• Prepare to spend energy!

• Architecture = µservice model

• Use tools to manage Metadata and Dependencies

• Small increments

• One test is worth a thousand opinions.


Technology

How to manage software complexity with OSGi