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Debugging Effectively
Colin O’Dell
@colinodell
Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
Colin O’Dell
• Lead Web Developer at Unleashed Technologies
• Primary language is PHP
• PHP developer for 15 years
• PHP League Leadership Team
• Author/maintainer of PHP CommonMark library
• PHP 7 Upgrade Guide e-book author
• Also experienced in JavaScript, Java, C#, and Python
@colinodell
Overview
I. Importance of debugging
II. Debugging process
III. Tools & Techniques
IV. Q&A
Photo by Roman Boed // cc by 2.0 // https://flic.kr/p/ngwcf1
@colinodell
Debugging is...
Photo by Ewan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
(adjective)
@colinodell
Debugging is...
Photo by Ewan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m
important
@colinodell
Debugging is...
Photo by Ewan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m
the single most
important skill in
programming.
@colinodell
Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
PlanningCoding
@colinodell
Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
Planning
Testing &
Debugging
Coding
@colinodell
Debugging is the process of finding and resolving bugs
or defects that prevent correct operation of computer
software or a system.
– Wikipedia
Photo by Stephen Dyrgas // cc by-nc-nd 2.0 // https://flic.kr/p/3eTfWU
Process is the foundation of effective debugging
Process
Photo by Matthew Paulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa
Photo by Matthew Paulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa
Gain experience with code and tools
Experience
Process
Photo by Matthew Paulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa
Develop your intuition
Intuition
Experience
Process
Junior Developers
• Try the “usual” steps
• Clear caches
• Re-install dependencies
• chmod –R 777 *
• Ask somebody else
• Co-worker
• Google
• StackOverflow post
Photo by Yoel Ben-Avraham, with changes // cc by--nd 2.0 // https://flic.kr/p/6pmtQL
@colinodell
XY Problem
Photo by Yoel Ben-Avraham, with changes // cc by--nd 2.0 // https://flic.kr/p/6pmtQL
•I want to solve problem X
•How do I solve X?
@colinodell
XY Problem
Photo by Yoel Ben-Avraham, with changes // cc by--nd 2.0 // https://flic.kr/p/6pmtQL
•I want to solve problem X
•How do I solve X?
•Solution Y might work
•How can I do Y?
@colinodell
Photo by quattrostagioni // cc by 2.0 // https://flic.kr/p/aGjVq8
1.Don’t parse HTML with regex
2.Solve problems the right way @colinodell
“I don’t know why”
“For some reason”
“Doesn’t make sense”
Photo by Stanley Yuu // cc by-nc-nd 2.0 // https://flic.kr/p/pMnfNu
@colinodell
Bugs are logical
Photo by Photofest
@colinodell
“The bug is not moving around in your code,
trying to trick or evade you. It is just siting in
one place, doing the wrong thing in the same
way every time.” – Nick Parlante, Debugging Zen
Photo by GrahamC57 // cc by-nc-nd 2.0 // https://flic.kr/p/cwJi9Q
@colinodell
Assume your
code is the
problem
Photo by Sergio Flores Rosales // cc by-nc-nd 2.0 // https://flic.kr/p/5UHkaW
@colinodell
Systematic Approach
1. Gather information
2. Replicate the issue
3. Identify the culprit
4. Fix it & re-test
5. Mitigate future occurrences
Photo from EduSpiral // cc by-nc-nd 3.0
@colinodell
1. Gather information
• Expected behavior vs.
actual behavior
• Error messages
• Stack traces
Photo from youmustdesireit.wordpress.com
•Screenshots
•Browser & OS
•Date & time
•Log entries
@colinodell
2. Replicate the Issue
Be able to replicate with 100% certainty
Photo by Nick Royer // cc by-sa // https://flic.kr/p/d41ASC
@colinodell
3. Identify the Culprit
Photo by U.S. Navy // cc 2.0 // https://flic.kr/p/n6Wgks
• Be methodical
• Make no assumptions
• Understand the bug @colinodell
4. Fix it & Re-test
• Attempt to replicate again
• Avoid XY problem
• No temporary workarounds!
• Add technical debt
• May introduce other issues
• Never get replaced with true solutions
Photo by Jeff Eaton // cc by-sa 2.0 // https://flic.kr/p/b33rSx
@colinodell
5. Mitigate Future Occurrences
• Add an automated test
• Share your new knowledge
• Project documentation
• Blog post
• StackOverflow
• Submit patch upstream
Photo by marcokalmann // cc by-nc-nd 2.0 // https://flic.kr/p/4CqLMQ
@colinodell
Recap
1. Gather information
2. Replicate the issue
3. Identify the culprit
4. Fix it & re-test
5. Mitigate future occurrences
Photo from EduSpiral // cc by-nc-nd 3.0
@colinodell
Long-Term Results
• Gain experience
• Learn how the system works
• Build heuristics
• Boost confidence
Photo by Glenn Beltz // cc by 2.0 // https://flic.kr/p/i7Csdx
@colinodell
Tools & Techniques
Photo by Alan // cc by-nc-sa 2.0 // https://flic.kr/p/9azLii
@colinodell
Two essential tools
• Integrated development
environment (IDE)
• Interactive debugger
Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
@colinodell
Integrated Development Environment
•Minimum features:
•Syntax highlighting
•Auto-completion
•Fast code navigation
•Debugger
Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
@colinodell
Interactive Debugger
•Pause code execution
•Step through execution
•Examine variables
•Explore call stack
Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
@colinodell
Techniques
1. Trace backwards from known issue
2. Trace forwards from start
3. Binary search
4. Use tools
5. Get help
6. Take a break
Photo by Massmo Relsig // cc by-nc-nd 2.0 // https://flic.kr/p/pFrJCe
@colinodell
1. Trace backwards
•Error is thrown from known location
•Use a debugger
•Establish context
•Work backwards
Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
@colinodell
1. Trace backwards
•Error is thrown from known location
•Use a debugger
•Establish context
•Work backwards
a()
b()
c()
d()
Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
1. Trace backwards
•Error is thrown from known location
•Use a debugger
•Establish context
•Work backwards
a()
b()
c()
d()
Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
1. Trace backwards
•Error is thrown from known location
•Use a debugger
•Establish context
•Work backwards
a()
b()
c()
d()
Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
1. Trace backwards
•Error is thrown from known location
•Use a debugger
•Establish context
•Work backwards
a()
b()
c()
d()
Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
1. Trace backwards
•Error is thrown from known location
•Use a debugger
•Establish context
•Work backwards
a()
b()
c()
d()
Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
2. Trace forwards
•Opposite direction
•Problematic line
isn’t known
•Use debugger or logging
a()
b()
c()
d()
Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
2. Trace forwards
•Opposite direction
•Problematic line
isn’t known
•Use debugger or logging
a()
b()
c()
d()
Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
2. Trace forwards
•Opposite direction
•Problematic line
isn’t known
•Use debugger or logging
a()
b()
c()
d()
Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
2. Trace forwards
•Opposite direction
•Problematic line
isn’t known
•Use debugger or logging
a()
b()
c()
d()
Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
3. Divide & Conquer
• Identify different code sections
• Set breakpoints at the boundaries
• Isolate issue to one particular area
• Focus efforts on that area
@colinodell
@colinodell
@colinodell
@colinodell
✓
X
@colinodell
@colinodell
4. Use tools
•Variable dumps
•Debug toolbars
•Console utility
•Profilers
•git bisect
•netcat
•curl
•strace
•etc.
Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
@colinodell
Variable dumps
Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
•Print to output:
•var_dump()
•pprint()
•puts()
•Log to file
•file_put_contents()
•Logger.debug()
@colinodell
Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
Debug toolbars
@colinodell
Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
Console Utility
Symfony: bin/console
Laravel: artisan
Drupal: drush
Drupal Console
Magento: n98-magerun
@colinodell
Performance Profiling
Identify slowness:
• Bottlenecks
• Resource hogs
• Inefficient code
Photo by Alan Stark // cc by-sa 2.0 // https://flic.kr/p/dn3qjx
Tools:
• Blackfire (freemium)
• New Relic (freemium)
• xhprof (open-source)
@colinodell
git bisect
v1.7 ? ? ? ? ? ? ? HEAD
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
@colinodell
git bisect
v1.7 ? ? ? ? ? ? ? HEAD
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
@colinodell
git bisect
v1.7 ? ? ? BAD ? ? ? HEAD
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
@colinodell
git bisect
v1.7 ? ? ? BAD BAD BAD BAD HEAD
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
@colinodell
git bisect
v1.7 ? GOOD ? BAD BAD BAD BAD HEAD
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
@colinodell
git bisect
v1.7 GOOD GOOD ? BAD BAD BAD BAD HEAD
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
@colinodell
git bisect
v1.7 GOOD GOOD
X BAD BAD BAD BAD HEAD
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
abcd123 is the first bad commit
@colinodell
git bisect
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
@colinodell
# of Commits # of Tests
9 4
90 8
900 16
Scales logarithmically – runs in O(log N)
Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
netcat
@colinodell
Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
strace
@colinodell
5. Get help
• RTFM / RTFD
• Project forums or issue queue
• StackOverflow, IRC, etc.
• Ask a colleague
• Expert in that area
• Senior developer
• Rubber ducking
Photo by Hiromitsu Morimoto // cc by-sa 2.0 // https://flic.kr/p/6Vzzaa
@colinodell
6. Take a break
Photo by Kristina Alexadnerson // cc by-nc-nd 2.0 // https://flic.kr/p/cFEcDC
• Clear your mind; start fresh
• Forget invalid assumptions
• Recharge your batteries
• Let your subconscious work on it
@colinodell
Four things to walk away with
1. Computers aren’t random,
and neither are bugs
2. Persistence will always pay off
3. Don’t be afraid to dive deep
4. Don’t make assumptions or
take things for granted
Photo by Kristina Alexadnerson // cc by-nc-nd 2.0 // https://flic.kr/p/dvEpfY
@colinodell
Questions?
Photo by Marcello Maria Perongini // cc by-nc-nd 2.0 // https://flic.kr/p/6KDtm
@colinodell
Learn More
• https://web.duke.edu/cps001/notes/Debugging.pdf
• http://www.fiveminutegeekshow.com/20
• http://blog.codeunion.io/2014/09/03/teaching-novices-how-to-debug-
code/
• https://www.jetbrains.com/phpstorm/help/debugging.html
• http://www.sitepoint.com/debugging-git-blame-bisect/
• http://unix.stackexchange.com/a/50099/80744
• http://codeception.com/docs/01-Introduction
• http://chadfowler.com/blog/2014/01/26/the-magic-of-strace/
• http://c2.com/cgi/wiki?RubberDucking
Photo by Samantha Marx // cc by 2.0 // https://flic.kr/p/8KrU1R
@colinodell
Thanks!
@colinodell / colinodell@gmail.com
Photo by Steve Rotman // cc by-nc-nd 2.0 // https://flic.kr/p/xiBK

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Debugging Effectively: Techniques and Tools

  • 2. Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe Colin O’Dell • Lead Web Developer at Unleashed Technologies • Primary language is PHP • PHP developer for 15 years • PHP League Leadership Team • Author/maintainer of PHP CommonMark library • PHP 7 Upgrade Guide e-book author • Also experienced in JavaScript, Java, C#, and Python @colinodell
  • 3. Overview I. Importance of debugging II. Debugging process III. Tools & Techniques IV. Q&A Photo by Roman Boed // cc by 2.0 // https://flic.kr/p/ngwcf1 @colinodell
  • 4. Debugging is... Photo by Ewan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ (adjective) @colinodell
  • 5. Debugging is... Photo by Ewan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m important @colinodell
  • 6. Debugging is... Photo by Ewan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m the single most important skill in programming. @colinodell
  • 7. Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC PlanningCoding @colinodell
  • 8. Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC Planning Testing & Debugging Coding @colinodell
  • 9. Debugging is the process of finding and resolving bugs or defects that prevent correct operation of computer software or a system. – Wikipedia Photo by Stephen Dyrgas // cc by-nc-nd 2.0 // https://flic.kr/p/3eTfWU
  • 10. Process is the foundation of effective debugging Process Photo by Matthew Paulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa
  • 11. Photo by Matthew Paulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa Gain experience with code and tools Experience Process
  • 12. Photo by Matthew Paulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa Develop your intuition Intuition Experience Process
  • 13. Junior Developers • Try the “usual” steps • Clear caches • Re-install dependencies • chmod –R 777 * • Ask somebody else • Co-worker • Google • StackOverflow post Photo by Yoel Ben-Avraham, with changes // cc by--nd 2.0 // https://flic.kr/p/6pmtQL @colinodell
  • 14. XY Problem Photo by Yoel Ben-Avraham, with changes // cc by--nd 2.0 // https://flic.kr/p/6pmtQL •I want to solve problem X •How do I solve X? @colinodell
  • 15. XY Problem Photo by Yoel Ben-Avraham, with changes // cc by--nd 2.0 // https://flic.kr/p/6pmtQL •I want to solve problem X •How do I solve X? •Solution Y might work •How can I do Y? @colinodell
  • 16. Photo by quattrostagioni // cc by 2.0 // https://flic.kr/p/aGjVq8 1.Don’t parse HTML with regex 2.Solve problems the right way @colinodell
  • 17. “I don’t know why” “For some reason” “Doesn’t make sense” Photo by Stanley Yuu // cc by-nc-nd 2.0 // https://flic.kr/p/pMnfNu @colinodell
  • 18. Bugs are logical Photo by Photofest @colinodell
  • 19. “The bug is not moving around in your code, trying to trick or evade you. It is just siting in one place, doing the wrong thing in the same way every time.” – Nick Parlante, Debugging Zen Photo by GrahamC57 // cc by-nc-nd 2.0 // https://flic.kr/p/cwJi9Q @colinodell
  • 20. Assume your code is the problem Photo by Sergio Flores Rosales // cc by-nc-nd 2.0 // https://flic.kr/p/5UHkaW @colinodell
  • 21. Systematic Approach 1. Gather information 2. Replicate the issue 3. Identify the culprit 4. Fix it & re-test 5. Mitigate future occurrences Photo from EduSpiral // cc by-nc-nd 3.0 @colinodell
  • 22. 1. Gather information • Expected behavior vs. actual behavior • Error messages • Stack traces Photo from youmustdesireit.wordpress.com •Screenshots •Browser & OS •Date & time •Log entries @colinodell
  • 23. 2. Replicate the Issue Be able to replicate with 100% certainty Photo by Nick Royer // cc by-sa // https://flic.kr/p/d41ASC @colinodell
  • 24. 3. Identify the Culprit Photo by U.S. Navy // cc 2.0 // https://flic.kr/p/n6Wgks • Be methodical • Make no assumptions • Understand the bug @colinodell
  • 25. 4. Fix it & Re-test • Attempt to replicate again • Avoid XY problem • No temporary workarounds! • Add technical debt • May introduce other issues • Never get replaced with true solutions Photo by Jeff Eaton // cc by-sa 2.0 // https://flic.kr/p/b33rSx @colinodell
  • 26. 5. Mitigate Future Occurrences • Add an automated test • Share your new knowledge • Project documentation • Blog post • StackOverflow • Submit patch upstream Photo by marcokalmann // cc by-nc-nd 2.0 // https://flic.kr/p/4CqLMQ @colinodell
  • 27. Recap 1. Gather information 2. Replicate the issue 3. Identify the culprit 4. Fix it & re-test 5. Mitigate future occurrences Photo from EduSpiral // cc by-nc-nd 3.0 @colinodell
  • 28. Long-Term Results • Gain experience • Learn how the system works • Build heuristics • Boost confidence Photo by Glenn Beltz // cc by 2.0 // https://flic.kr/p/i7Csdx @colinodell
  • 29. Tools & Techniques Photo by Alan // cc by-nc-sa 2.0 // https://flic.kr/p/9azLii @colinodell
  • 30. Two essential tools • Integrated development environment (IDE) • Interactive debugger Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC @colinodell
  • 31. Integrated Development Environment •Minimum features: •Syntax highlighting •Auto-completion •Fast code navigation •Debugger Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC @colinodell
  • 32. Interactive Debugger •Pause code execution •Step through execution •Examine variables •Explore call stack Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC @colinodell
  • 33. Techniques 1. Trace backwards from known issue 2. Trace forwards from start 3. Binary search 4. Use tools 5. Get help 6. Take a break Photo by Massmo Relsig // cc by-nc-nd 2.0 // https://flic.kr/p/pFrJCe @colinodell
  • 34. 1. Trace backwards •Error is thrown from known location •Use a debugger •Establish context •Work backwards Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw @colinodell
  • 35. 1. Trace backwards •Error is thrown from known location •Use a debugger •Establish context •Work backwards a() b() c() d() Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
  • 36. 1. Trace backwards •Error is thrown from known location •Use a debugger •Establish context •Work backwards a() b() c() d() Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
  • 37. 1. Trace backwards •Error is thrown from known location •Use a debugger •Establish context •Work backwards a() b() c() d() Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
  • 38. 1. Trace backwards •Error is thrown from known location •Use a debugger •Establish context •Work backwards a() b() c() d() Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
  • 39. 1. Trace backwards •Error is thrown from known location •Use a debugger •Establish context •Work backwards a() b() c() d() Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
  • 40. 2. Trace forwards •Opposite direction •Problematic line isn’t known •Use debugger or logging a() b() c() d() Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
  • 41. 2. Trace forwards •Opposite direction •Problematic line isn’t known •Use debugger or logging a() b() c() d() Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
  • 42. 2. Trace forwards •Opposite direction •Problematic line isn’t known •Use debugger or logging a() b() c() d() Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
  • 43. 2. Trace forwards •Opposite direction •Problematic line isn’t known •Use debugger or logging a() b() c() d() Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
  • 44. 3. Divide & Conquer • Identify different code sections • Set breakpoints at the boundaries • Isolate issue to one particular area • Focus efforts on that area @colinodell
  • 50. 4. Use tools •Variable dumps •Debug toolbars •Console utility •Profilers •git bisect •netcat •curl •strace •etc. Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC @colinodell
  • 51. Variable dumps Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe •Print to output: •var_dump() •pprint() •puts() •Log to file •file_put_contents() •Logger.debug() @colinodell
  • 52. Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe Debug toolbars @colinodell
  • 53. Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe Console Utility Symfony: bin/console Laravel: artisan Drupal: drush Drupal Console Magento: n98-magerun @colinodell
  • 54. Performance Profiling Identify slowness: • Bottlenecks • Resource hogs • Inefficient code Photo by Alan Stark // cc by-sa 2.0 // https://flic.kr/p/dn3qjx Tools: • Blackfire (freemium) • New Relic (freemium) • xhprof (open-source) @colinodell
  • 55. git bisect v1.7 ? ? ? ? ? ? ? HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm @colinodell
  • 56. git bisect v1.7 ? ? ? ? ? ? ? HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm @colinodell
  • 57. git bisect v1.7 ? ? ? BAD ? ? ? HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm @colinodell
  • 58. git bisect v1.7 ? ? ? BAD BAD BAD BAD HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm @colinodell
  • 59. git bisect v1.7 ? GOOD ? BAD BAD BAD BAD HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm @colinodell
  • 60. git bisect v1.7 GOOD GOOD ? BAD BAD BAD BAD HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm @colinodell
  • 61. git bisect v1.7 GOOD GOOD X BAD BAD BAD BAD HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm abcd123 is the first bad commit @colinodell
  • 62. git bisect Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm @colinodell # of Commits # of Tests 9 4 90 8 900 16 Scales logarithmically – runs in O(log N)
  • 63. Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe netcat @colinodell
  • 64. Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe strace @colinodell
  • 65. 5. Get help • RTFM / RTFD • Project forums or issue queue • StackOverflow, IRC, etc. • Ask a colleague • Expert in that area • Senior developer • Rubber ducking Photo by Hiromitsu Morimoto // cc by-sa 2.0 // https://flic.kr/p/6Vzzaa @colinodell
  • 66. 6. Take a break Photo by Kristina Alexadnerson // cc by-nc-nd 2.0 // https://flic.kr/p/cFEcDC • Clear your mind; start fresh • Forget invalid assumptions • Recharge your batteries • Let your subconscious work on it @colinodell
  • 67. Four things to walk away with 1. Computers aren’t random, and neither are bugs 2. Persistence will always pay off 3. Don’t be afraid to dive deep 4. Don’t make assumptions or take things for granted Photo by Kristina Alexadnerson // cc by-nc-nd 2.0 // https://flic.kr/p/dvEpfY @colinodell
  • 68. Questions? Photo by Marcello Maria Perongini // cc by-nc-nd 2.0 // https://flic.kr/p/6KDtm @colinodell
  • 69. Learn More • https://web.duke.edu/cps001/notes/Debugging.pdf • http://www.fiveminutegeekshow.com/20 • http://blog.codeunion.io/2014/09/03/teaching-novices-how-to-debug- code/ • https://www.jetbrains.com/phpstorm/help/debugging.html • http://www.sitepoint.com/debugging-git-blame-bisect/ • http://unix.stackexchange.com/a/50099/80744 • http://codeception.com/docs/01-Introduction • http://chadfowler.com/blog/2014/01/26/the-magic-of-strace/ • http://c2.com/cgi/wiki?RubberDucking Photo by Samantha Marx // cc by 2.0 // https://flic.kr/p/8KrU1R @colinodell
  • 70. Thanks! @colinodell / colinodell@gmail.com Photo by Steve Rotman // cc by-nc-nd 2.0 // https://flic.kr/p/xiBK

Editor's Notes

  1. PHP developer 15 years JS, Java, C#, Python
  2. What are some words For me: fun challenge
  3. Take this one step further Why is that?
  4. How much time coding? 2/3rds
  5. According to the Mythical Man Month, 1/6th ½ is testing/debugging How much - actually writing code vs getting it working Area where it’s worthwhile to become efficient
  6. READ SLOWLY Shouldn’t be done haphazardly
  7. Like intuition, but not Understanding without proof Clarity; accuracy; precision -- Focus on the process Experience and “sixth sense” will come with time NEXT: Debugging process
  8. BE NICE / CONSTRUCTIVE
  9. TODO ADD NOTES
  10. When you give up on the proper approach Apply workaround instead Improper solutions will cause issues later NEXT - EXAMPLE
  11. Base85-encoded Don’t be clever TRANSITION NEEDED!!
  12. Magical thinking
  13. Article sneaky
  14. Bugs are almost always based on faulty assumptions 95% in your code If helping others, assume their code is problem Challenge their assumptions Take with grain of salt
  15. Define the symptoms Collect everything you can
  16. Automated tests preferred, but manual is okay too LEGOS
  17. Understand the fundamental nature Exactly why
  18. Other nice-to-haves: File syncing Git integration Run tools PhpStorm, Sublime Text, vim NOT Notepad++ or Dreamweaver
  19. Debuggers are awesome tool … Better than primitive approaches Examine in real time Xdebug Chrome developer tools
  20. Click 4 times Dive in Look at call stack
  21. Advanced breakpoints Grouping Conditions
  22. Stack trace Grep for error message Set breakpoint For example
  23. Examine variables How did I get here? – call stack
  24. Log/output results at different steps Identify where things start going wrong
  25. Log/output results at different steps Identify where things start going wrong
  26. Log/output results at different steps Identify where things start going wrong
  27. Log/output results at different steps Identify where things start going wrong
  28. Debugger is critical Not only tool Tools are not a substitute for thinking
  29. Scales logarithmically – runs in O(log N) 9 commits - 4 tests 10x: 90 commits – 8 tests 100x: 900 commits - 16 tests
  30. Scales logarithmically – runs in O(log N) 9 commits - 4 tests 10x: 90 commits – 8 tests 100x: 900 commits - 16 tests
  31. END TOOLS SECTION
  32. Fifth technique
  33. 1. There is ALWAYS a logical explanation 3. Great learning opportunity 4. Challenge everything
  34. ? Other Questions? Talk afterwards or contact me
  35. Thank you guys I’d appreciate feedback