Published on March 16, 2008
Pete Goodliffe firstname.lastname@example.org 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
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
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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
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