Debugging Effectively - DrupalCon Nashville 2018
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Software bugs are inevitable; some 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! The mental fatigue and wasted time can be avoided by using strategies like identifying the most-appropriate tool, taking a logical & objective approach, challenging assumptions, listening to variables, isolating the code path, and reinforcing code with automated tests.
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Debugging Effectively - DrupalCon Nashville 2018
- 2. Photo by Joseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe Colin O’Dell / @colinodell • Lead Web Developer & DevOps Engineer at Unleashed Technologies • Primary language is PHP • PHP developer for 16 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
- 45. @colinodell
- 46. @colinodell
- 47. @colinodell
- 48. ✓ X @colinodell
- 49. @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 Drupal: drush Drupal Console Symfony: bin/console Laravel: artisan 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
- What are some words For me: fun challenge
- Take this one step further Why is that?
- How much time coding? 2/3rds
- 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
- READ SLOWLY Shouldn’t be done haphazardly
- 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
- BE NICE / CONSTRUCTIVE
- TODO ADD NOTES
- When you give up on the proper approach Apply workaround instead Improper solutions will cause issues later NEXT - EXAMPLE
- Base85-encoded Don’t be clever TRANSITION NEEDED!!
- Magical thinking
- Article sneaky
- 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
- Define the symptoms Collect everything you can
- Automated tests preferred, but manual is okay too LEGOS
- Understand the fundamental nature Exactly why
- Other nice-to-haves: File syncing Git integration Run tools PhpStorm, Sublime Text, vim NOT Notepad++ or Dreamweaver
- Debuggers are awesome tool … Better than primitive approaches Examine in real time Xdebug Chrome developer tools
- Click 4 times Dive in Look at call stack
- Advanced breakpoints Grouping Conditions
- Stack trace Grep for error message Set breakpoint For example
- Examine variables How did I get here? – call stack
- Log/output results at different steps Identify where things start going wrong
- Log/output results at different steps Identify where things start going wrong
- Log/output results at different steps Identify where things start going wrong
- Log/output results at different steps Identify where things start going wrong
- Debugger is critical Not only tool Tools are not a substitute for thinking
- Scales logarithmically – runs in O(log N) 9 commits - 4 tests 10x: 90 commits – 8 tests 100x: 900 commits - 16 tests
- Scales logarithmically – runs in O(log N) 9 commits - 4 tests 10x: 90 commits – 8 tests 100x: 900 commits - 16 tests
- END TOOLS SECTION
- Fifth technique
- 1. There is ALWAYS a logical explanation 3. Great learning opportunity 4. Challenge everything
- ? Other Questions? Talk afterwards or contact me
- Thank you guys I’d appreciate feedback