3. Pete Goodliffe
pete@goodliffe.net
http://www.goodliffe.net
Who is Pete?
3
4. The impact of Specific
design on a design
system techniques
Learn some An entire
ways to software
Our roadmap
improve our design
software course
designs 1
4
5. Learning lessions
Design Town
The Messy
Metropolis
So what?
Our roadmap
2
5
10. What has design done for us?
● Ease of modification
● Ease of extension
●
Fit for purpose
● Ease of documentation
● Design quality is a sink or swim issue for
software projects
● Some people/teams are inherently
better at design than others
10
11. ● Effects within software
– Software quality
– Developer sanity
● Influences outside software
– Success of project
– Team structure
Design matters
– Morale
– Company success
11
13. The Messy
Metropolis
So what?
Our roadmap
4
13
14. ● These are comparable systems
● Similar size
●
Both Linux-based
“Embedded” applications
A tale of two systems
●
● Audio products
● C++
● Developed by “experienced”
programmers
● Programmers were designers
● Names have been changed to protect the
innocent/guilty
14
16. ● A project well under way when I joined
● “Modern” C++ codebase, a few years old
●
Ouch!
● Warning signs:
– Code took a fantastically long time to learn
– No obvious routes into the system
– It was (broadly) clear what the product did,
First contact
but no one explained how it did it
– Actually getting the code, and getting it to
build was a rite of passage
16
17. ● Micro-level problems:
– Messy, inconsistent code, with no style
– Badly put together
– No unifying concepts
– Far to many bad code smells
Warning signs
17
18. ● Macro-level problems:
– Control flew around the system in
unfathomable ways
– Data rarely kept near where it was used
– Many baroque caching layers to mitigate this
Warning signs
18
19. ● No one had a complete picture of system
● No one actually knew how it worked!
– A combination of luck and heroic
maintenance programmers
● People only knew their own small areas
● Naturally there was no documentation
Warning signs
● Town planning disaster!
●
We needed a map
19
23. ● Design problems went directly to the top
– Development process
– Company culture
● Code grown “organically” over time
Software archeology
●
Had been given no architectural design
●
A system never has no design
● Understandable given company history
23
24. ● Hard to comprehend system
● Practically impossible to modify
●
Bad design encouraged further bad design
Consequences: Design
– Paths of least resistance
● New recruits stunned by complexity
– Very high staff turnover
●
System components not cohesive
– Grab-bags of unrelated functionality
– Hard to determine why a component existed
– Hard to work out where particular
functionality was implemented
●
Bugfixing nightmare!
24
25. ● Functionality and data in the wrong place
– “Core services” not in the core
Consequences: Layering
– Why? Team dynamics! (Empire building)
● No clear layering
– Bidirectional coupling
– No “bottom” or “hub” or the system
● tight coupling
●
Low-level testing impossible
– No class unit tests
– No component tests
25
26. ● Design problems fed into code problems
– Like no one bothered with design, no one
bothered with code standard
– Duplication
Consequences: Code
– No common libraries
– No common idioms
– No naming conventions
– No common build system
● Why?
– More software archeology...
– An accidental conurbation
– Know what you're designing
26
27. ● Problems spilled out beyond development
team
– Slow development cycle
– Support engineers
Consequences: Team
– External protocol
– Intra-company politics (marketing, sales,
manufacturing)
27
28. ● It headed in a downward spiral
● Very uneconomical to maintain
●
Did not fulfil business objectives
● Thrown away
● Rewritten in C# on Windows
Where is it now?
28
29. The upshot of bad design ●
Low quality product
● Inflexible system
– Can't accommodate change
– Can't add new functionality
● Pervasive code problems
● Infrequent releases
● Staffing problems
● Messy internal politics
●
Lack of success
●
Many painful headaches and late nights
29
30. The Messy
Metropolis
So what?
Our roadmap
4
30
31. Design Town
The Messy
Metropolis
So what?
Our roadmap
5
31
33. ● Involved from very start
● New team of capable programmers
– Small team
– Flat structure
– No rivalry
● Clear roadmap
– Initial product
First contact
– Future functionality
● XP development
33
34. ● XP and design?
●
YAGNI
eXtreme Programming
● Spikes
34
35. ● Started with design!
● Not a big up-front design
●
Identified main areas of functionality
● Initial architecture
● Core threading models
User Interface
First steps
Control Components
Audio Path
OS/Audio Codecs
35
36. ● Audio path as sub-architecture
● Pipe and filter
●
Product configuration determines
individual audio path
User Interface
A B C D E F
First steps
Control Components
Audio file Audio hardware
Audio Path
OS/Audio Codecs
36
37. ● Other early choices:
– Supporting libraries
– Top-level file structure
– Naming
– “House” presentation style
– Coding idioms
– Choice of unit test framework
– Infrastructure
First steps
●
Source control
● Build system
●
Continuous integration
●
These influenced design decisions
37
38. ● Helped to locate new functionality
– With clear system overview...
– New units of functionality consistently added
the the right place
– Easy to find where existing functionality
implemented
The story unfolds
– Easy to locate/fix bugs
– Not always convenient
●
Made programmers work harder
●
Payoff: easier life later
38
39. ● Entire system was consistent
– Every decision was taken in the context of
the whole design
– Done intentionally
– Design always in view:
All code produced fitted the design
The story unfolds
●
– Over entire life of system, things followed
original design
39
40. ● Elegance at top level fed down to the
lower levels
– At lowest level, code uniform and neat
– Helped by
●
Pair programming
●
Code reviews
The story unfolds
● Code standards
– No unusual surprises
40
41. ● New areas of functionality appeared
– Not a problem
– Design (like code) malleable
– Nothing is set in stone
– Design must be changed when required
The story unfolds
– Encouraged simple design
– Consequence:
●
Code could grow rapidly
●
Code could maintain good internal structure
41
42. ● (Unit) test everything
– Change sections of software without breaking
everything else
●
Design town had major design changes
– Shaping of the code design
●
Enforce good code structure
The story unfolds
● Loosely coupled: construct in a test harness
● Cohesive
– Encouraged good APIs
42
43. ● Quality control
– Pair programming
– Code reviews
– Reviews ensured changes did not sully design
The story unfolds
● Programmers took responsibility for
the design
43
44. ● Pragmatic approach to design
– Deadlines lead to corner-cutting
– Technical debt
– Scheduled for later revision
The story unfolds
● Timescales worked in favour
– Not too long
– Not too short
44
45. ● Team dynamics followed code design
– No one “owned” code
– Everyone expected to write high-quality code
– Closely co-operating colleagues
– Conway's Law
The story unfolds
● Design was sufficiently well documented
– Architecture overview
– Code as documentation
● Naming conventions
● Structure (namespaces, nested classes,
enums, etc)
– Doxygen
45
46. ● New team members could enter project
easily
● Code still enjoyable to work with
– Low turnover of members
The story unfolds
– Programmers taking ownership
46
47. User Interface
Control Components
User Interface
One We Made Earlier
External
Audio Path
Control controllers
OS/Audio Codecs
Storage
Audio path
management
A B C D E F
OS/Audio codecs
Audio file Audio hardware
47
48. ● Still in use
● Still being developed
●
Still changing
● Not perfect
Where is it now?
48
49. Design Town
The Messy
Metropolis
So what?
Our roadmap
5
49
50. Learning lessions
Design Town
The Messy
Metropolis
So what?
Our roadmap
6
50
51. ● Design matters
– It can go spectacularly wrong
– It can go spectacularly right
You've got to design on purpose
The moral of the story
●
– This does not mean a big up-front design
●
Good design
– Leads to better code
– Leads to better teams
– Leads to success
51
52. ● Good design comes from:
– Actually doing up-front design (as much as
required)
– Quality and experience of designers
The moral of the story
– Keeping design in view at all times
– Team being given/talking responsibility
– Not being afraid of changing design
– Team:
●
Having the right people on the team
●
Size of the team
● Health of working relationships
– Making decisions at the right time
– Good project management
52
55. ● What's the best system you've ever seen?
– What have you learnt from it?
– What were the consequences of this design:
● Inside code
● Outside code
● What's the worst system you've ever seen
Your turn
– What have you learnt from it?
– What were the consequences of this design:
● Inside code
●
Outside code
55
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“A unique and practical
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“Readable, engaging, and
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wish I'd had when I started
work as a programmer.quot; Steve
Love “A 'must read' for any
The book
programmer who wants to be
a better programmer” Linux
Tutorial “This is exactly the
kind of book you should give
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57
