Eric Lee. Who am I?. Not a professional presenter – be patient!. 16 years at Microsoft. 6 years in Office building automated testing systems. 9 years in Microsoft Game Studios making games testable. ID: 308706 Download Presentation
Eric Lee. Who am I?. Not a professional presenter – be patient!. 16 years at Microsoft. 6 years in Office building automated testing systems. 9 years in Microsoft Game Studios making games testable.
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Presentation on theme: "Misadventures In Legacy Code"— Presentation transcript:
Slide1
Misadventures In Legacy Code
Eric Lee
Slide2
Who am I?
Not a professional presenter – be patient!
16 years at Microsoft
6 years in Office building automated testing systems
9 years in Microsoft Game Studios making games testable
1 year in Engineering Excellence building a secure source code portal
Enthusiastic Agile practitioner
I’ve inherited at least three “legacy” systems during my career
Slide3
The plan
Part 1: What is a legacy system?
Part 2: How do I survive a legacy system?
Part 3: How do I avoid creating more legacy systems?
Slide4
Part 1: What is a legacy system?
Slide5
What does legacy mean?
Slide6
What the dictionary says…
leg·a·cy
[
léggəssee
]
noun (
plural
leg·a·cies
)
Definition:
1.
bequest made in will:
money or property that is left to somebody in a will
2.
something from past:
something that is handed down or remains from a previous generation or time
Encarta® World English Dictionary
Slide7
What developers really mean…
Bob
Jagendorf
Slide8
Zombies vs. Legacy apps
Zombies:
Legacy apps:
Walking undead corpsesExtremely hideous and disgustingOverwhelm you with numbersInfect anything they touchConsume your brain and destroy your willVery hard to eradicateCampy fiction
Walking undead corpses
Extremely hideous and disgusting
Overwhelm you with numbers
Infect anything they touch
Consume your brain and destroy your will
Very hard to eradicate
Horrifyingly real
Slide9
Stuart Halloway says…
“Legacy” is the degree to which code:
fails to capture essence
fails to communicate essence
captures irrelevant detail (ceremony)
Slide10
Michael Feathers says…
“Legacy code is code without tests.”
Slide11
Practical Considerations
Legacy apps are often (but not always) old
Sometimes no original developers remain
Extremely difficult to make changes without breaking things
Critical infrastructure has often been lost
Source code is archaic, bewildering, and way too complex for what it does
Documentation is nonexistent or wrong
No automated test suite
Slide12
Part 2: How do I survive a legacy system?
Slide13
"I say we take off and nuke the entire site from orbit. It's the only way to be sure."
Slide14
Should we start over?
Sure, if you have unlimited resources
Otherwise, probably not!
The legacy code base holds valuable, hard-won knowledge
Legacy code base continues to accumulate new features and bug fixes
Feature parity is a moving target
Users want to see regular evidence of progress
Slide15
Then what do we do?
First, take a deep breath - this is
gonna
hurt
Take inventory
Eliminate friction
Build a safety net
Divide and conquer
Practice software archeology
Build for the future
Have boat-loads of patience
Slide16
Take inventory
Understand the environment:
History of the project
Problem space
Stakeholders
Target audience
Future goals
Capture initial code metrics
Inspect and prune all documentation
Slide17
Eliminate friction
FRICTION
Slide18
Eliminate friction
Make lists of annoyances
After three months problems become invisible
Always ask the five whys
Get
everything
under source control
Enable local builds, local execution
Repeatable build process
Build scripts
Dedicated build machine for official builds
Repeatable deployment
Slide19
Build a safety net
You need tests!
Automated if you can, manual if you can’t
Let you change the code with less terror
Baby steps
Start with integration tests
Don’t try to write unit tests for everything all at once
Michael Feathers,
Working Effectively With Legacy Code
Slide20
Divide and conquer
Don’t start with sweeping architectural changes
Focus on one small area at a time
Refactor
/rewrite as you go
Build firewalls to protect new code from old code
Practice the Boy Scout rule
Have patience and a long-term plan
Slide21
Software archeology
Slide22
Software archeology
Legacy code is like an archeological dig site
Layer upon layer of history
Lots of rubble from previous times
Before changing code, try to understand:
The historical purpose of the code
The desired purpose of the code today
Be suspicious and paranoid
Any mysterious behavior will bite you later
Always look for root causes
Slide23
Break the cycle
Clear away the rubble
Source code is a liability, not an asset
Delete dead code
Delete redundant comments
Simplify, simplify, simplify!
I reduced one component from 4000 to 400 ELOC, another from 6800 to 3200
Write unit tests for all new code
Slide24
Break the cycle
Focus on
today’s
requirements, not ancient history
Rethink all assumptions
Bad code is often a symptom of squishy problem definition
Get really crisp on the fundamental concepts
Slide25
Forensic development
The code lies, don’t trust it
Dig until you understand the whole story
Collect evidence and build a case
Refactor
the code until it tells the truth
Slide26
How do I avoid creating more legacy systems?
Slide27
Do the right thing!
“
Always code as if the person who ends up maintaining your code is a violent psychopath who knows where you live.
