How to manage software complexity with OSGi

How to Manage Software Complexity with OSGi Peter Kriens & David Savagedonderdag 24 maart 2011

What is Complexity?donderdag 24 maart 2011

Complex?donderdag 24 maart 2011

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.donderdag 24 maart 2011

Complex?donderdag 24 maart 2011

Complex? Worlds Largest Jigsaw Puzzle 24.000 pieces (4.28m x 1.57m)donderdag 24 maart 2011

The Eye Of The Beholder • Complexity of a task is the energy you use to complete that task c = √E/mdonderdag 24 maart 2011

Energy? • Understanding the problem • Learning the solution • Accidental complexity • Size matters!donderdag 24 maart 2011

Energy? Subjective Complexity • Understanding the problem • Learning the solution • Accidental complexity • Size matters!donderdag 24 maart 2011

Energy? Subjective Complexity • Understanding the problem • Learning the solution • Accidental complexity • Size matters! Absolute Complexity size relateddonderdag 24 maart 2011

What’s Modularity Got to do With Size???donderdag 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 A B outside AB CD • Chunking - having an anchor for an aggregation C D • Visibility - is reduced, reducing the scope to attend for changesdonderdag 24 maart 2011

Modularity • Modularity is about creating a difference between an inside and an A B outside • Chunking - having an anchor for an aggregation C AB CD D • Visibility - is reduced, reducing the scope to attend for changesdonderdag 24 maart 2011

Modularity • modules have a private space and share a public space A B • modules limit their visibility and exposure C D • Reduces geometric to linear complexitydonderdag 24 maart 2011

Modularity • modules have a private space and share a public space A B • modules limit their Pub visibility and exposure C D • Reduces geometric to linear complexitydonderdag 24 maart 2011

Entropy E functionality Emodularizationdonderdag 24 maart 2011

#1 OSGi Complaint: Class Loaders!donderdag 24 maart 2011

Classloaders & Modularitydonderdag 24 maart 2011

Class Loading Revisited • Class.forName • Class path Scanning • Service Loader • Thread Context Class Loaders • Factory, and FactoryBuildersdonderdag 24 maart 2011

Class Loading Revisited • Class loaders are used to provide extensibility and decoupling A B • They were not Pub designed for this purpose, C D • And class loaders break module boundariesdonderdag 24 maart 2011

Class Loading Revisited A B Publicdonderdag 24 maart 2011

Class Loading Revisited A B C Publicdonderdag 24 maart 2011

Class Loading Revisited A B C I Publicdonderdag 24 maart 2011

Class Loading Revisited A B C X I Publicdonderdag 24 maart 2011

Class Loading Revisited A B C P I Publicdonderdag 24 maart 2011

Would be nice to mention how µServices reduce surface area of design µServices efficiency of packet based approaches? but cost of packet based system is congestion - leads into dependency hell?donderdag 24 maart 2011

#2 OSGi Complaint: Dependency Helldonderdag 24 maart 2011

Metadata Hell?donderdag 24 maart 2011

Transitive Hell?donderdag 24 maart 2011

Coupling • Modules require other modules • Dependencies are A B transitive Pub • A→C→D C Ddonderdag 24 maart 2011

Cohesion • Fan out is a problem • A does not transitively depend on D! A B • The dependency is caused by C D (unnecessarily) packing 1 and 2 in the same moduledonderdag 24 maart 2011

Cohesion • Fan out is a problem • A does not transitively depend on D! A A B • The dependency is caused by 1 2 D (unnecessarily) packing C 1 and 2 in the same moduledonderdag 24 maart 2011

Cohesion • Refactoring can increase the cohesion and reduce coupling A B • But now A depends on C1 and B depends on C2 C 1 C 2 D • Package dependencies C are more robust to changesdonderdag 24 maart 2011

Cohesion • Refactoring can increase the cohesion and reduce coupling A B • But now A depends on C1 and B depends on C2 C 1 C 2 D • Package dependencies are more robust to changesdonderdag 24 maart 2011

Metadata Heaven?donderdag 24 maart 2011

Requires Toolsdonderdag 24 maart 2011

Tools 1 Request deployment of a component, e.g. a Bundle, WAR, WAB or EAR 2 Refer to Application Policy Resolver App Policy 3 Resolve Dependencies 4 Provision according to component and Policy dependencies Repository Nimbledonderdag 24 maart 2011

OSGi OSGi OSGi Build Tools Runtime Tools Cloud Tools ...donderdag 24 maart 2011

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.donderdag 24 maart 2011

How to manage software complexity with OSGi

by Peter Kriens

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