A Tale Of Two Systems

Pete Goodliffe pete@goodliffe.net http://www.goodliffe.net Who is Pete? 3

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

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

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

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 controllers Control 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

A Tale Of Two Systems

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