how to manage software complexity with osgi
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How to Manage Software Complexity
with OSGiPeter Kriens & David Savage
donderdag 24 maart 2011
What is Complexity?
donderdag 24 maart 2011
Complex?
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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.
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Complex?
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Worlds Largest Jigsaw Puzzle24.000 pieces
(4.28m x 1.57m)
Complex?
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The Eye Of The Beholder
• Complexity of a task is the energy you use to complete that task
c = √E/m
donderdag 24 maart 2011
The Eye Of The Beholder
• Complexity of a task is the energy you use to complete that task
c = √E/m
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Energy?
• Understanding the problem
• Learning the solution
• Accidental complexity
• Size matters!
donderdag 24 maart 2011
Energy?
• Understanding the problem
• Learning the solution
• Accidental complexity
• Size matters!
Subjective Complexity
donderdag 24 maart 2011
Energy?
• Understanding the problem
• Learning the solution
• Accidental complexity
• Size matters!
Subjective Complexity
Absolute Complexitysize related
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What’s Modularity Got to do With Size???
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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
donderdag 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 DABCD
donderdag 24 maart 2011
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
donderdag 24 maart 2011
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
Pub
donderdag 24 maart 2011
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
Pub
donderdag 24 maart 2011
EntropyE
func
tiona
lity
Emodularizationdonderdag 24 maart 2011
EntropyE
func
tiona
lity
Emodularizationdonderdag 24 maart 2011
EntropyE
func
tiona
lity
Emodularizationdonderdag 24 maart 2011
EntropyE
func
tiona
lity
Emodularizationdonderdag 24 maart 2011
EntropyE
func
tiona
lity
Emodularizationdonderdag 24 maart 2011
EntropyE
func
tiona
lity
Emodularizationdonderdag 24 maart 2011
#1 OSGi Complaint:Class Loaders!
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Classloaders & Modularity
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Class Loading Revisited
• Class.forName
• Class path Scanning
• Service Loader
• Thread Context Class Loaders
• Factory, and FactoryBuilders
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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
Class Loading Revisited
Pub
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A B
Class Loading Revisited
Public
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A B
Class Loading Revisited
Public
C
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A B
Class Loading Revisited
Public
IC
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A B
Class Loading Revisited
Public
IC X
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A B
Class Loading Revisited
Public
I
C P
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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?
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#2 OSGi Complaint: Dependency Hell
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Metadata Hell?
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Transitive Hell?
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A B
C D
• Modules require other modules
• Dependencies are transitive
• A → C → D
Coupling
Pub
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A B
C D
• Modules require other modules
• Dependencies are transitive
• A → C → D
Coupling
Pub
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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
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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
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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
donderdag 24 maart 2011
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
donderdag 24 maart 2011
Metadata Heaven?
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Requires Tools
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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
donderdag 24 maart 2011
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
donderdag 24 maart 2011
OSGiBuild Tools
OSGiRuntime Tools
OSGiCloud Tools
...
donderdag 24 maart 2011
OSGiBuild Tools
OSGiRuntime Tools
OSGiCloud 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
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