Debugging- for rigtige programmører

1. Quality Up Front
How to spend less time debugging
Lars Jarnbo Pedersen
Co-founder Switch-Gears ApS

2. About me
Partner at Switch-Gears ApS
● Transitioning companies from old
development tools to modern Open Source
ones
Been working for Nokia 2001-2012
● Release manager for S40 software for many
years
● Part of a small team that introduced Git,
Gerrit and Jenkins to S40 development
resulting in BIG productivity gains

3. Pain in SW Development
50%
COST OF BUGS
of developer time is spent
finding and fixing bugs*
*http://www.businessweekly.co.uk/hi-tech/14898-software-bugs-cost-more-than-double-eurozone-bailout

4. Why?
Programming is hard…
● you have to map the problem domain to
the programming language in use
● its usually a collaborative effort
● time pressure
● best practises are not shared
Bugs are discovered late…
● context is lost
● often it is not the programmer who
introduced the bug, who is fixing it

5. Luckily
90%
COST OF BUGS
of the bugs can be
caught during
development*
*http://www.codinghorror.com/blog/2006/01/code-reviews-just-do-it.html

6. Because
Average defect detection rate is 25 percent for
unit testing, 35 percent for function testing, and
45 percent for integration testing. [McConnell93]
Furthermore, the average effectiveness of
design and code inspections are 55 and 60
percent. [McConnell93]

7. How?

8. Peer Code Review
● Beneficial for “quality of review” if the author
pre-reviews and leaves comments for
subsequent reviewers [Cohen2006]
● The longer a reviewer spends on the initial
read-through, the more defects will ultimately
be found [Uwano2006]
● Defect detection drops dramatically after ~60
minutes, to zero after ~90 minutes [Dunsmore2000]

9. Peer Code Review
● Long methods and loops are very time
consuming to understand [Uwano2006]
● Review 100 to 300 LOC at a time, in 30-60
minutes chunks, with a break between each
sitting [Cohen2006]
● Spend at least 5 minutes reviewing a single
line of code [Cohen2006]
● Limit reviewing to 1 hour per day [Ganssle2009]

10. Mental Model
Platform Knowledge
+
Development Process
=
Platform Quality

11. Increase Platform Knowledge
Write Readable Code!!!
● You spend much more time reading code than
writing it - so make it nice to read!
● Refactor if necessary
● Include test-code
Commit changes in logical units
● Always commit working code
● Never mix error-fixes and feature implementations
Write descriptive commit messages
● Make sure the reason for the change is clearly
explained

12. Optimize Development Process
Make it simple on the developers,
● allow multiple workflows at the developers
desk
● don’t let the release/integration process
stop the development flow
● minimize manual process steps
while keeping a strict process
● automatically build and test all commits
● require code-review of all commits

13. This is NOT rocket science!
So why don’t we do it already?
● Waterfall development
● Code Reviews are perceived expensive
● Last generation of tools do not support
this easily
What is enabling it now?
● Agile development
● New breed of Open Source tools

14. Git / Gerrit / Jenkins

15. Git (DVCS) changes everything!
Git is NOT subversion++
● all operations except for push/pull are
local => well suited for continuous
integration
● allows for multiple workflows
○ development
○ integration / releasing
● is a first class citizen during development
AND debugging!
○ gitk for code analysis
○ git bisect for debugging

16. Gerrit
A developer codes - and asks for feedback

17. Peer Code Review
Another developer reviews and comments

18. Continuous Integration
Actually you saw it in action already!
Good tools help you without getting in the way

19. Our experiences - Low Gain Example
[Anonymized and obscured]

20. Our experiences - High Gain Example
[Anonymized and obscured]

21. References
Books
●
●
Code Complete: A Practical Handbook of Software Construction, Second
Edition by Steve McConnell (Jun 16, 2004)
Clean Code: A Handbook of Agile Software Craftsmanship by Robert C.
Martin (Aug 11, 2008)
Articles
●
●
●
●
●
SCM Ranking (Switch-Gears)
CI Ranking (Switch-Gears)
Best Kept Secrets of Peer Code Review (Smartbear)
The Cost of Software Bugs (Business Weekly)
Code Review - Just Do It (Coding Horror)
Videos
●
●
Linus Torvalds on Git (Google TechTalk)
Development at the Speed and Scale of Google (InfoQ)