Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.
Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
Debugging Effectively
Colin O’Dell
Colin O’Dell
• Lead Web Developer at Unleashed Technologies
• PHP developer since 2002
• Certifications: Symfony and Magen...
Overview
I. Importance of debugging
II. Debugging process
III. Tools & Techniques
IV. Q&A
Photo by Roman Boed // cc by 2.0...
Debugging is...
Photo by Ewan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _...
Debugging is...
important
Photo by Ewan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m
Debugging is...
the single most
important skill in
programming.
Photo by Ewan Cross // cc by-nc-nd 2.0 // https://flic.kr/...
PlanningCoding
Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
Planning
Testing &
Debugging
Coding
Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
Debugging is the process of finding and
resolving bugs or defects that prevent correct
operation of computer software or a...
Process is the foundation of effective
debugging
Process
Photo by Matthew Paulson // cc by-nc-nd 2.0 // https://flic.kr/p/...
Photo by Matthew Paulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa
Gain experience with tools and code
Experience
Pro...
Photo by Matthew Paulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa
Develop a “sixth sense”
“Sixth Sense”
Experience
P...
Junior Developers
• Try the “usual” steps
• app/console cache:clear
• composer install
• chmod –R 777 *
• Google the error...
XY Problem
•I want to solve problem X
•How do I solve X?
Photo by Yoel Ben-Avraham, with changes // cc by--nd 2.0 // https...
XY Problem
•I want to solve problem X
•How do I solve X?
•Solution Y might work
•How can I do Y?
Photo by Yoel Ben-Avraham...
Photo by quattrostagioni // cc by 2.0 // https://flic.kr/p/aGjVq8
1.Don’t parse HTML with regex
2.Solve problems the right...
“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/pMn...
Bugs are
logical
Photo by Photofest
“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 ...
Assume your
code is the
problem
Photo by Sergio Flores Rosales // cc by-nc-nd 2.0 // https://flic.kr/p/5UHkaW
Systematic Approach
1. Gather information
2. Replicate the issue
3. Identify the culprit
4. Fix it & re-test
5. Mitigate f...
•Expected behavior
vs. actual behavior
•Error messages
•Stack traces
Photo from youmustdesireit.wordpress.com
• Screenshot...
2. Replicate the Issue
Be able to replicate with 100% certainty
Photo by Nick Royer // cc by-sa // https://flic.kr/p/d41ASC
• Be methodical
• Make no assumptions
• Understand the bug
Photo by U.S. Navy // cc 2.0 // https://flic.kr/p/n6Wgks
3. Ide...
• Attempt to replicate again
• Avoid XY problem
• No temporary workarounds!
• Add technical debt
• May introduce other iss...
5. Mitigate Future Occurrences
•Add an automated test
•Share your new knowledge
• Project documentation
• Blog post
• Stac...
Recap
1. Gather information
2. Replicate the issue
3. Identify the culprit
4. Fix it & re-test
5. Mitigate future occurren...
Long-Term Results
• Gain experience
• Learn how the system works
• Build heuristics
• Boost confidence
Photo by Glenn Belt...
Tools &Techniques
Photo by Alan // cc by-nc-sa 2.0 // https://flic.kr/p/9azLii
Two essential tools
• Integrated development
environment (IDE)
• Interactive debugger
Photo by florianric // cc by 2.0 // ...
Integrated Development
Environment
• Minimum features:
• Syntax highlighting
• Auto-completion
• Fast code navigation
• De...
Interactive Debugger
• Pause code execution
• Breakpoints
• Conditional breakpoints
• Step through execution
• Examine var...
Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
Techniques
1. Trace backwards from known issue
2. Divide & conquer
3. Use tools
4. Get help
5. Take a break
Photo by Massm...
1. Trace backwards
•Use a debugger
•Identify source of error
•Establish context
•Work backwards
Photo by Shawn Harquail //...
1. Trace backwards
a()
b()
c()
d()
Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
1. Trace backwards
a()
b()
c()
d()
Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
2. Divide & Conquer
• Identify different code sections
• Set breakpoints at the boundaries
• Isolate issue to one particul...
✓
X
3. Use tools
• VarDumper
• Debug toolbars
• Console utility
• Profilers
• git bisect
Photo by florianric // cc by 2.0 // h...
VarDumper
Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
Twig:
{{ dump(foo) }}
{% dump foo %}
PHP:
dump(...
Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
Debug toolbars
Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
Console Utility
Symfony: app/console
Drupal: drush
Magent...
Performance Profiling
Identify slowness:
• Bottlenecks
• Resource hogs
• Inefficient code
Photo by Alan Stark // cc by-sa ...
git bisect
v1.7 ? ? ? ? ? HEAD
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
git bisect
v1.7 ? ? BAD ? ? HEAD
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
git bisect
v1.7 ? ? BAD BAD BAD HEAD
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
git bisect
v1.7 GOOD ? BAD BAD BAD HEAD
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
git bisect
v1.7 GOOD
X BAD BAD BAD HEAD
Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
abcd123 is the firs...
netcat
Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
4. Get help
•RTFM / RTFD
•Project forums or issue queue
•StackOverflow, IRC, etc.
•Ask a colleague
• Expert in that area
•...
5. Take a break
• Clear your mind; start fresh
• Forget invalid assumptions
• Recharge your batteries
• Let your subconsci...
Four things to walk away with
1. Computers aren’t random,
and neither are bugs
2. Persistence will always pay off
3. Don’t...
Questions?
Photo by Marcello Maria Perongini // cc by-nc-nd 2.0 // https://flic.kr/p/6KDtm
Learn More
• https://web.duke.edu/cps001/notes/Debugging.pdf
• http://www.fiveminutegeekshow.com/20
• http://blog.codeunio...
Thanks!
Feedback?
• https://joind.in/16056
• @colinodell
Photo by Steve Rotman // cc by-nc-nd 2.0 // https://flic.kr/p/xiBK
Debugging Effectively - SymfonyLive San Francisco 2015
Debugging Effectively - SymfonyLive San Francisco 2015
Debugging Effectively - SymfonyLive San Francisco 2015
Debugging Effectively - SymfonyLive San Francisco 2015
Debugging Effectively - SymfonyLive San Francisco 2015
Upcoming SlideShare
Loading in …5
×

Debugging Effectively - SymfonyLive San Francisco 2015

1,144 views

Published on

Software bugs are inevitable - it doesn't matter how experienced you are or how well you follow best-practices. Some bugs are especially difficult to track down, causing you to waste countless hours before throwing your hands up in defeat. It doesn't have to be this way though! The mental fatigue and wasted time can be avoided by implementing effective debugging strategies like: identifying & using the most-appropriate tool; taking a logical & objective approach; challenging assumptions; listening to variables; isolating the code path; rubber ducking; and reinforcing code with automated tests. Attendees will learn how to combine these techniques with the right mindset and attitude in order to debug their code effectively.

Published in: Software
  • Be the first to comment

Debugging Effectively - SymfonyLive San Francisco 2015

  1. 1. Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe Debugging Effectively Colin O’Dell
  2. 2. Colin O’Dell • Lead Web Developer at Unleashed Technologies • PHP developer since 2002 • Certifications: Symfony and Magento • PHP League Member • league/commonmark • league/html-to-markdown • What’s New in PHP 7 e-book • @colinodell / www.colinodell.com Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
  3. 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
  4. 4. Debugging is... Photo by Ewan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ (adjective)
  5. 5. Debugging is... important Photo by Ewan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m
  6. 6. Debugging is... the single most important skill in programming. Photo by Ewan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m
  7. 7. PlanningCoding Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
  8. 8. Planning Testing & Debugging Coding Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
  9. 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. 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. 11. Photo by Matthew Paulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa Gain experience with tools and code Experience Process
  12. 12. Photo by Matthew Paulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa Develop a “sixth sense” “Sixth Sense” Experience Process
  13. 13. Junior Developers • Try the “usual” steps • app/console cache:clear • composer install • chmod –R 777 * • Google the error • Try every solution • Ask somebody else • Co-worker • StackOverflow post • Give up Photo by Yoel Ben-Avraham, with changes // cc by--nd 2.0 // https://flic.kr/p/6pmtQL
  14. 14. XY Problem •I want to solve problem X •How do I solve X? Photo by Yoel Ben-Avraham, with changes // cc by--nd 2.0 // https://flic.kr/p/6pmtQL
  15. 15. XY Problem •I want to solve problem X •How do I solve X? •Solution Y might work •How can I do Y? Photo by Yoel Ben-Avraham, with changes // cc by--nd 2.0 // https://flic.kr/p/6pmtQL
  16. 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
  17. 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
  18. 18. Bugs are logical Photo by Photofest
  19. 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
  20. 20. Assume your code is the problem Photo by Sergio Flores Rosales // cc by-nc-nd 2.0 // https://flic.kr/p/5UHkaW
  21. 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
  22. 22. •Expected behavior vs. actual behavior •Error messages •Stack traces Photo from youmustdesireit.wordpress.com • Screenshots • Browser & OS • Date & time • Log entries 1. Gather Information
  23. 23. 2. Replicate the Issue Be able to replicate with 100% certainty Photo by Nick Royer // cc by-sa // https://flic.kr/p/d41ASC
  24. 24. • Be methodical • Make no assumptions • Understand the bug Photo by U.S. Navy // cc 2.0 // https://flic.kr/p/n6Wgks 3. Identify the Culprit
  25. 25. • 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 4. Fix & Re-test
  26. 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
  27. 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
  28. 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
  29. 29. Tools &Techniques Photo by Alan // cc by-nc-sa 2.0 // https://flic.kr/p/9azLii
  30. 30. Two essential tools • Integrated development environment (IDE) • Interactive debugger Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
  31. 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
  32. 32. Interactive Debugger • Pause code execution • Breakpoints • Conditional breakpoints • Step through execution • Examine variables • Explore call stack Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
  33. 33. Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC
  34. 34. Techniques 1. Trace backwards from known issue 2. Divide & conquer 3. Use tools 4. Get help 5. Take a break Photo by Massmo Relsig // cc by-nc-nd 2.0 // https://flic.kr/p/pFrJCe
  35. 35. 1. Trace backwards •Use a debugger •Identify source of error •Establish context •Work backwards Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
  36. 36. 1. Trace backwards a() b() c() d() Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
  37. 37. 1. Trace backwards a() b() c() d() Photo by Shawn Harquail // cc by-nc 2.0 // https://flic.kr/p/npxFVw
  38. 38. 2. Divide & Conquer • Identify different code sections • Set breakpoints at the boundaries • Isolate issue to one particular area • Focus efforts on that area
  39. 39. ✓ X
  40. 40. 3. Use tools • VarDumper • Debug toolbars • Console utility • Profilers • git bisect Photo by florianric // cc by 2.0 // https://flic.kr/p/c4QJzC •netcat •curl •strace •etc.
  41. 41. VarDumper Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe Twig: {{ dump(foo) }} {% dump foo %} PHP: dump($somevar);
  42. 42. Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe Debug toolbars
  43. 43. Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe Console Utility Symfony: app/console Drupal: drush Magento: n98-magerun.phar Laravel: artisan
  44. 44. 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)
  45. 45. git bisect v1.7 ? ? ? ? ? HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
  46. 46. git bisect v1.7 ? ? BAD ? ? HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
  47. 47. git bisect v1.7 ? ? BAD BAD BAD HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
  48. 48. git bisect v1.7 GOOD ? BAD BAD BAD HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm
  49. 49. git bisect v1.7 GOOD X BAD BAD BAD HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm abcd123 is the first bad commit
  50. 50. netcat Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe
  51. 51. 4. 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
  52. 52. 5. Take a break • Clear your mind; start fresh • Forget invalid assumptions • Recharge your batteries • Let your subconscious work on it Photo by Kristina Alexadnerson // cc by-nc-nd 2.0 // https://flic.kr/p/cFEcDC
  53. 53. 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
  54. 54. Questions? Photo by Marcello Maria Perongini // cc by-nc-nd 2.0 // https://flic.kr/p/6KDtm
  55. 55. 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://symfony.com/doc/current/components/var_dumper/introducti on.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
  56. 56. Thanks! Feedback? • https://joind.in/16056 • @colinodell Photo by Steve Rotman // cc by-nc-nd 2.0 // https://flic.kr/p/xiBK

×