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Debugging Effectively - PHP UK 2017
This document, by Colin O'Dell, presents a comprehensive guide to effective debugging, emphasizing its importance as a critical programming skill. It outlines a systematic approach to debugging, which includes gathering information, replicating issues, identifying culprits, fixing problems, and preventing future occurrences, while also detailing essential tools and techniques. The document highlights the logical nature of bugs and encourages developers to adopt a methodical mindset in their debugging practices.
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Debugging Effectively - PHP UK 2017
- 1.
- 2. Photo by JosephB // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe Colin O’Dell • Lead Web Developer at Unleashed Technologies • PHP League Member • league/commonmark • league/html-to-markdown • PHP 7 Upgrade Guide e-book @colinodell
- 3. Overview I. Importance ofdebugging 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 byEwan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ (adjective) @colinodell
- 5. Debugging is... Photo byEwan Cross // cc by-nc-nd 2.0 // https://flic.kr/p/7MCt3m important @colinodell
- 6. Debugging is... Photo byEwan 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 theprocess 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 thefoundation of effective debugging Process Photo by Matthew Paulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa
- 11. Photo by MatthewPaulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa Gain experience with code and tools Experience Process
- 12. Photo by MatthewPaulson // cc by-nc-nd 2.0 // https://flic.kr/p/di35xa Develop your intuition Intuition Experience Process
- 13. Junior Developers • Trythe “usual” steps • bin/console cache:clear • composer install • 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 byYoel 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 byYoel 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 knowwhy” “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 Photoby Photofest @colinodell
- 19. “The bug isnot 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 isthe problem Photo by Sergio Flores Rosales // cc by-nc-nd 2.0 // https://flic.kr/p/5UHkaW @colinodell
- 21. Systematic Approach 1. Gatherinformation 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 theIssue Be able to replicate with 100% certainty Photo by Nick Royer // cc by-sa // https://flic.kr/p/d41ASC @colinodell
- 24. 3. Identify theCulprit 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 FutureOccurrences • 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 • Gainexperience • 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 Photoby 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 •Minimumfeatures: •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 codeexecution •Breakpoints •Conditional breakpoints •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 backwardsfrom 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 •Erroris 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 •Erroris 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 •Erroris 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 •Erroris 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 •Erroris 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 •Erroris 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 •Oppositedirection •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 •Oppositedirection •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 •Oppositedirection •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 •Oppositedirection •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.
- 46.
- 47.
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- 49.
- 50. 4. Use tools •Variabledumps •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 byJoseph B // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe •var_dump() •kint() •file_put_contents() •$logger->debug() @colinodell
- 52. Photo by JosephB // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe Debug toolbars @colinodell
- 53. Photo by JosephB // 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 GOODGOOD ? BAD BAD BAD BAD HEAD Photo by unbekannt270 // cc by 2.0 // https://flic.kr/p/oHReqm @colinodell
- 61. git bisect v1.7 GOODGOOD 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. Photo by JosephB // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe netcat @colinodell
- 63. Photo by JosephB // cc by-nc-nd 2.0 // https://flic.kr/p/7GAMBe curl @colinodell
- 64. Photo by JosephB // 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 abreak 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 towalk 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 MarcelloMaria 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! Feedback Appreciated! • https://joind.in/talk/549fd •@colinodell / colinodell@gmail.com Photo by Steve Rotman // cc by-nc-nd 2.0 // https://flic.kr/p/xiBK
Editor's Notes
- #3 PHP developer 14 years JS, Java, C#
- #5 What are some words For me: fun challenge
- #7 Take this one step further Why is that?
- #8 How much time coding? 2/3rds
- #9 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
- #10 READ SLOWLY Shouldn’t be done haphazardly
- #13 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
- #14 BE NICE / CONSTRUCTIVE
- #15 TODO ADD NOTES
- #16 When you give up on the proper approach Apply workaround instead Improper solutions will cause issues later NEXT - EXAMPLE
- #17 Base85-encoded Don’t be clever TRANSITION NEEDED!!
- #18 Magical thinking
- #20 Article sneaky
- #21 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
- #23 Define the symptoms Collect everything you can
- #24 Automated tests preferred, but manual is okay too LEGOS
- #25 Understand the fundamental nature Exactly why
- #32 Other nice-to-haves: File syncing Git integration Run tools PhpStorm, Sublime Text, vim NOT Notepad++ or Dreamweaver
- #33 Debuggers are awesome tool … Better than primitive approaches Examine in real time Xdebug Chrome developer tools
- #34 Click 4 times Dive in Look at call stack
- #35 Advanced breakpoints Grouping Conditions
- #37 Stack trace Grep for error message Set breakpoint For example
- #38 Examine variables How did I get here? – call stack
- #43 Log/output results at different steps Identify where things start going wrong
- #44 Log/output results at different steps Identify where things start going wrong
- #45 Log/output results at different steps Identify where things start going wrong
- #46 Log/output results at different steps Identify where things start going wrong
- #53 Debugger is critical Not only tool Tools are not a substitute for thinking
- #54 Phpunit Phpspec behat
- #64 Scales logarithmically – runs in O(log N) 9 commits - 4 tests 10x: 90 commits – 8 tests 100x: 900 commits - 16 tests
- #67 END TOOLS SECTION
- #68 Fifth technique
- #70 1. There is ALWAYS a logical explanation 3. Great learning opportunity 4. Challenge everything
- #71 ? Other Questions? Talk afterwards or contact me
- #73 Thank you guys I’d appreciate feedback