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1
2
Pete Goodliffe
                         pete@goodliffe.net
               http://www.goodliffe.net
Who is Pete?




      ...
Specific

              The
impact
of

                                   design

              design
on
a

             ...
Learning
lessions
                      Design
Town
                              The
Messy

                             ...
Our roadmap




               So
what?


           3




6
So
what?



           7
So what?




8
So what?




9
What has design done for us?
                                   Ease of modification
                               ●



 ...
Effects within software
                 ●


                         Software quality
                     –

           ...
So
what?
Our roadmap




                         3




                             12
The
Messy

                         Metropolis

              So
what?
Our roadmap




                                   ...
These are comparable systems
                        ●



                            Similar size
                       ...
The
Messy

Metropolis



             15
A project well under way when I joined
                ●



                    “Modern” C++ codebase, a few years old
   ...
Micro-level problems:
                ●


                        Messy, inconsistent code, with no style
                ...
Macro-level problems:
                ●


                        Control flew around the system in
                    –
...
No one had a complete picture of system
                ●



                    No one actually knew how it worked!
     ...
The map




20
The map




21
The map




22
Design problems went directly to the top
                      ●


                              Development process
     ...
Hard to comprehend system
                       ●



                           Practically impossible to modify
        ...
Functionality and data in the wrong place
                         ●


                                 “Core services” no...
Design problems fed into code problems
                     ●


                             Like no one bothered with des...
Problems spilled out beyond development
                     ●


                         team
                           ...
It headed in a downward spiral
                   ●



                       Very uneconomical to maintain
              ...
Low quality product
                           ●
The upshot of bad design
                               Inflexible system...
The
Messy

                         Metropolis

              So
what?
Our roadmap




                                   ...
Design
Town
                             The
Messy

                             Metropolis

              So
what?
Our ro...
Design
Town



              32
Involved from very start
                ●



                    New team of capable programmers
                ●


    ...
XP and design?
                      ●




                          YAGNI
                      ●
eXtreme Programming

  ...
Started with design!
              ●



                  Not a big up-front design
              ●



                  I...
Audio path as sub-architecture
                ●



                    Pipe and filter
                ●



             ...
Other early choices:
              ●


                      Supporting libraries
                  –

                   ...
Helped to locate new functionality
                    ●


                            With clear system overview...
     ...
Entire system was consistent
                    ●


                            Every decision was taken in the context o...
Elegance at top level fed down to the
                    ●


                        lower levels
                       ...
New areas of functionality appeared
                    ●


                            Not a problem
                    ...
(Unit) test everything
                    ●


                            Change sections of software without breaking
  ...
Quality control
                    ●


                            Pair programming
                        –

          ...
Pragmatic approach to design
                    ●


                            Deadlines lead to corner-cutting
        ...
Team dynamics followed code design
                    ●


                            No one “owned” code
               ...
New team members could enter project
                    ●


                        easily


                        Code...
User Interface


                                                Control Components
                                      ...
Still in use
                   ●



                       Still being developed
                   ●



                ...
Design
Town
                             The
Messy

                             Metropolis

              So
what?
Our ro...
Learning
lessions
                      Design
Town
                              The
Messy

                             ...
Design matters
                         ●


                                 It can go spectacularly wrong
               ...
Good design comes from:
                         ●


                                 Actually doing up-front design (as m...
Fin


      53
Your turn




54
What's the best system you've ever seen?
            ●


                    What have you learnt from it?
               ...
Epilogue




56
“Its useful and fun and it'll
                     make       you     a     better
                     programmer.” Jez H...
Any questions?




58
© 2008 Pete Goodliffe. All rights reserved. No part of this document may be reproduced without the author's prior permissi...
Version info:


Slides version:   0.5
Last updated:     2008-03-12
Copyright:        © 2008 Pete Goodliffe




           ...
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A Tale Of Two Systems

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A Tale Of Two Systems

  1. 1. 1
  2. 2. 2
  3. 3. Pete Goodliffe pete@goodliffe.net http://www.goodliffe.net Who is Pete? 3
  4. 4. Specific
 The
impact
of
 design
 design
on
a
 techniques system An
entire
 Learn
some software
 ways
to
 Our roadmap design
 improve
our
 course software
 1 designs 4
  5. 5. Learning
lessions Design
Town The
Messy
 Metropolis So
what? Our roadmap 2 5
  6. 6. Our roadmap So
what? 3 6
  7. 7. So
what? 7
  8. 8. So what? 8
  9. 9. So what? 9
  10. 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. 11. Effects within software ● Software quality – Developer sanity – Influences outside software ● Success of project – Team structure – Design matters Morale – Company success – 11
  12. 12. So
what? Our roadmap 3 12
  13. 13. The
Messy
 Metropolis So
what? Our roadmap 4 13
  14. 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
  15. 15. The
Messy
 Metropolis 15
  16. 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. 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. 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. 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
  20. 20. The map 20
  21. 21. The map 21
  22. 22. The map 22
  23. 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. 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. 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. 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. 27. Problems spilled out beyond development ● team Slow development cycle – Support engineers – Consequences: Team External protocol – Intra-company politics (marketing, sales, – manufacturing) 27
  28. 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. 29. Low quality product ● The upshot of bad design 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. 30. The
Messy
 Metropolis So
what? Our roadmap 4 30
  31. 31. Design
Town The
Messy
 Metropolis So
what? Our roadmap 5 31
  32. 32. Design
Town 32
  33. 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. 34. XP and design? ● YAGNI ● eXtreme Programming Spikes ● 34
  35. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 47. User Interface Control Components User Interface One We Made Earlier External Audio Path controllers Control OS/Audio Codecs Storage Audio path management A B C D E F OS/Audio codecs Audio file Audio hardware 47
  48. 48. Still in use ● Still being developed ● Still changing ● Not perfect ● Where is it now? 48
  49. 49. Design
Town The
Messy
 Metropolis So
what? Our roadmap 5 49
  50. 50. Learning
lessions Design
Town The
Messy
 Metropolis So
what? Our roadmap 6 50
  51. 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. 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
  53. 53. Fin 53
  54. 54. Your turn 54
  55. 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
  56. 56. Epilogue 56
  57. 57. “Its useful and fun and it'll make you a better programmer.” Jez Higgins “A goldmine of information that every professional software developer should be aware of.” Tim Penhey “A terrific resource for developers wanting to learn or teach good coding practices ... . . . buy it now! deserves a place on the bookshelf.” Frazzled Dad blog “A unique and practical guide to being a professional programmer in the modern workplace.” Andrew Burrows “Readable, engaging, and even funny ... It's the book I 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 raw recruits.” Jon Jagger 57
  58. 58. Any questions? 58
  59. 59. © 2008 Pete Goodliffe. All rights reserved. No part of this document may be reproduced without the author's prior permission. 59
  60. 60. Version info: Slides version: 0.5 Last updated: 2008-03-12 Copyright: © 2008 Pete Goodliffe 60

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