Review your code
and all your wildest dreams
will come true
(vote for Pedro)
http://smartbear.com
Jason Cohen
@ASmartBear
StackOverflow Rep: 11,723. Booyah.
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smartbear.com
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Code Collaborator
codecollaborator.com
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Peer Code Review != Suck
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Act I
What’s the Point?
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Requirements
Discussion
Design
Review
Architecture
Review
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Requirements
Discussion
Design
Review
Architecture
Review
Code
(void)0
Where most of the bugs come from
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COUNT(editors)
>
COUNT(writers)
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9 errors/page
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Spell Czech:
Good, butt knot enough
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Common Sense
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The Experiment
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Before Code Review
Bugs Remaining in the Application
500
What if we had Peer Review?
Bugs Remaining
463
400
Bugs Remaining
321
Rule of Bug:
300
Bugs Remaining
194
200
?
Earlier == Cheaper
?
100
?
0
After
Development
After
QA/Test
($200/fix)
+
After
Customer
($1000/fix)
Cost of fixing bugs: $174k
Cost of 194 latent bugs: $194k
Total Cost: $368k
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Bugs Remaining in the Application
After Code Review
500
Bugs Remaining
463
400
300
Bugs Remaining
180
200
32, down
from 194
Bugs Remaining
113
100
Bugs Remaining
32
0
After
Development
After
Code Review
($25/fix)
After
QA/Test
($200/fix)
+
After
Customer
($1000/fix)
Cost of fixing bugs: $120k
Cost of 32 latent bugs: $ 32k
Total Cost: $152k
$152k, down from $368k
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It’s made of people
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The Ego Effect
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Team building
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Team building, for reals
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Go faster!
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“The problem is, they suck.”
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“Those guys are pretty cool.”
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Specifications
Meetings
Talking about code
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if(“integrate”.equals( s ))
if( 0 == ptr )
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I’m thiiiiinking of a number…
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if ( youLikeItSoMuch() )
{
marryIt();
}
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Hapless
Developer
Version
Control
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Reviewers
Peer Code Review != Suck
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Lots of techniques
Look over shoulder
Auto-email from version control after check-in
Walk-through meeting
Formal inspection
Pair programming
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Act II
Best Practices
How to not waste time
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Cisco® MeetingPlace® Case Study
3,200,000 lines of code
2,500 reviews
50 developers
10 months
San Diego, Bangalore, Budapest
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CodeReviewBook.com
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Defects Found
60-90 minutes max
Time (minutes)
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Go slow: 200-500 LOC/hour
Defect Density vs. Inspection Rate
Defect Density (defects/kLOC)
150
125
100
75
50
25
0
0
200
400
600
800
1000
Review Inspection Rate (LOC/hour)
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1200
1400
Not too much: 200-400 LOC
Defect Density vs. LOC
Defect Density (defects/kLOC)
200
150
100
50
0
0
200
400
600
LOC under Review
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800
1000
Author Preparation is Good!
???
Average Defect Density (Defects/kLOC)
Effect of Author Preparation on Defect Density
90
85
80
70
60
50
48
40
30
20
10
0
Without Preparation
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With Prepration
Meetings
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Meetings are required.
—Michael Fagan, ‘76
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Fagan Phases
1. Planning
2. Intro
3. Reading
6. Verify
5. Rework
4. Inspect
7. Complete
8. Improve
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= Meeting
Meetings are required.
—Gilb, Fagan, Wiegers
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You didn’t check for null.
—The Phantom Inspector
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Are meetings worth it?
—Lawrence Votta, ‘93
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Defects Found By Inspection Phase
Defects from Reading
100
4%
Percentage of Total Defects
90
80
70
60
50
40
30
20
10
0
13 Inspection Trials
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Defects from Meeting
Checklists
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Checklist for Checklists
7  2 (George Miller, ’52)
No obvious stuff
Nothing that can be automated
Stuff that’s easy to forget
EXAMPLE:
Errors handled properly everywhere in method
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(Re)building a checklist
The Week of Pain
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Act III
Just do it.
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Selected Code
Stable branch
Core module
Top 10 scariest files
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Unit tests only
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During feature-freeze
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You know what to do,
and you know when to do it.
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Gotta
Wanna
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Jason Cohen
jason@asmartbear.com
http://blog.ASmartBear.com
Twit: @asmartbear
Code Collaborator
http://codecollab.com
(Visit our table on your
way out!)
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