Pete Goodliffe A Tale Of Two Systems
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Pete Goodliffe A Tale Of Two Systems

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Pete Goodliffe A Tale Of Two Systems Pete Goodliffe A Tale Of Two Systems Presentation Transcript

  • 1
  • 2
  • Pete Goodliffe pete@goodliffe.net http://www.goodliffe.net Who is Pete? 3
  • 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
  • Learning
lessions Design
Town The
Messy
 Metropolis So
what? Our roadmap 2 5
  • Our roadmap So
what? 3 6
  • So
what? 7
  • So what? 8
  • So what? 9
  • 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
  • ● Effects within software – Software quality – Developer sanity ● Influences outside software – Success of project – Team structure Design matters – Morale – Company success 11
  • So
what? Our roadmap 3 12
  • The
Messy
 Metropolis So
what? Our roadmap 4 13
  • ● 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
  • The
Messy
 Metropolis 15
  • ● 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
  • ● Micro-level problems: – Messy, inconsistent code, with no style – Badly put together – No unifying concepts – Far to many bad code smells Warning signs 17
  • ● 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
  • ● 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
  • The map 20
  • The map 21
  • The map 22
  • ● 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
  • ● 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
  • ● 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
  • ● 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
  • ● Problems spilled out beyond development team – Slow development cycle – Support engineers Consequences: Team – External protocol – Intra-company politics (marketing, sales, manufacturing) 27
  • ● 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
  • 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
  • The
Messy
 Metropolis So
what? Our roadmap 4 30
  • Design
Town The
Messy
 Metropolis So
what? Our roadmap 5 31
  • Design
Town 32
  • ● 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
  • ● XP and design? ● YAGNI eXtreme Programming ● Spikes 34
  • ● 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
  • ● 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
  • ● 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
  • ● 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
  • ● 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
  • ● 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
  • ● 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
  • ● (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
  • ● Quality control – Pair programming – Code reviews – Reviews ensured changes did not sully design The story unfolds ● Programmers took responsibility for the design 43
  • ● 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
  • ● 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
  • ● New team members could enter project easily ● Code still enjoyable to work with – Low turnover of members The story unfolds – Programmers taking ownership 46
  • 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
  • ● Still in use ● Still being developed ● Still changing ● Not perfect Where is it now? 48
  • Design
Town The
Messy
 Metropolis So
what? Our roadmap 5 49
  • Learning
lessions Design
Town The
Messy
 Metropolis So
what? Our roadmap 6 50
  • ● 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
  • ● 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
  • Fin 53
  • Your turn 54
  • ● 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
  • Epilogue 56
  • “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
  • Any questions? 58
  • © 2008 Pete Goodliffe. All rights reserved. No part of this document may be reproduced without the author's prior permission. 59
  • Version info: Slides version: 0.5 Last updated: 2008-03-12 Copyright: © 2008 Pete Goodliffe 60