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CSE3010: (Software Pattern Theory and Practice) Yann-Gal Guhneuc The Be a Debugger process pattern This work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 3.0 Unported

  1. CSE3010: 소프트웨어패턴 이론및실험 (Software Pattern Theory and Practice) Yann-Gaël Guéhéneuc The Be a Debugger process pattern This work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 3.0 Unported License

  2. Bug 2/40

  3. Bug 3/40

  4. Outline  Definition  Method  Tools – Logging – Debugger  Conclusion 4/40

  5. Outline  Definition  Method  Tools – Logging – Debugger  Conclusion 5/40

  6. Definition A software bug is an error, flaw, failure, or fault in a computer program or system that produces an incorrect or unexpected result, or causes it to behave in unintended ways.  —Wikipedia 6/40

  7. Including “non-functional” behaviour, e.g., consume too much memory or Definition perform to many method calls A software bug is an error, flaw, failure, or fault in a computer program or system that produces an incorrect or unexpected result, or causes it to behave in unintended ways or to have unexpected non-functional characteristics  —Wikipedia with additions 7/40

  8. Definition  Error, aka crash, exception… – A difference between a computed result and the correct (expected) result  Failure – The (incorrect) result of a fault  Fault, aka defect, flaw – An incorrect step, process, or data definition includes also non-functional (design) defects  Mistake – A human action that produces an incorrect result 8/40

  9. Definition A mistake may lead to a fault, which may lead to a failure, which may lead to an error 9/40

  10. Definition A mistake may lead to a fault, which may lead to a failure, which may lead to an error 10/40

  11. Outline  Definition  Method  Tools – Logging – Debugger  Conclusion 11/40

  12. How to Fix a Bug? “Installed Firefox and it does not work at all” —https://support.mozilla.org/en- US/questions/977001 12/40

  13. How to Fix a Bug?  Method – Process to collect, analyse, understand, and fix the bug (error, failure, fault, mistake)  Tools – To concretely apply the process 13/40

  14. Method “Installed Firefox and it does not work at all”  Descriptive  NOT informative  Essentially useless… 14/40

  15. Method  Minimum – Crash report  Better – Steps to reproduce  Even better – Short, Self Contained, Correct Example 15/40

  16. Method  Minimum – Crash report  Better – Steps to reproduce  Even better – Short, Self Contained, Correct Example 16/40

  17. Method  Short, Self Contained, Correct Example http://sscce.org/ – Actually a (simple) test case – Descriptive – Informative – Can be use repeatedly until fixed – Can be used as regression test too 17/40

  18. Method  Short, Self Contained, Correct Example – Ockham's razor is “a principle of parsimony, economy, or succinctness used in logic and problem-solving” [Wikipedia] c. 1287 – 1347 – Why use more when you can use less? 18/40

  19. Method  To build the SSCCE and to solve the error (or fault or failure) illustrated by the SSCCE, follow the scientific method 19/40

  20. Method  To build the SSCCE and to solve the error (or fault or failure) illustrated by the SSCCE, follow the scientific method 20/40

  21. Method  To build the SSCCE and to solve the error (or fault or failure) illustrated by the SSCCE, follow the scientific method A method or procedure consisting in the systematic observation, measurement, and experiment, and the formulation, testing, and modification of hypotheses —Oxford English Dictionary 21/40

  22. Method  Scientific method – Daniel ( לאֵיִּנָדּ ), 7th century BCE – Thales ( Θαλῆς ), 6th BCE – Plato ( Πλάτων ), 4th BCE – Aristotle ( Ἀριστοτέλης ), 3th BCE – … – al- Ḥ asan ( مﺛﯾﮭﻟا نﺑ نﺳﺣﻟا نﺑ نﺳﺣﻟا ،ﻲﻠﻋ وﺑأ ), 8th c. CE – … 22/40

  23. Method  Scientific method – … – Roger Bacon, 13th century CE – Francis Bacon, 17th CE – Descartes, 17th CE – … – Charles Sanders Peirce, 19 th CE – Popper, 20th CE 23/40

  24. Method  Scientific method Sir Karl Raimund Popper 28 July 1902–17 Septembre 1994 – Falsifiability http://karl-popper.over-blog.com “Are all swans white?” “Do mermaids exist?” 24/40

  25. Method Yes? Next bug No? Continue Analyse whether you can fix Hypothesise where the the failure / fault / mistake can Failure / fault / mistake is Test your hypothesis, From your hypothesis, i.e., debug the SSCCE set breakpoints 25/40

  26. Outline  Definition  Method  Tools – Logging – Debugger  Conclusion 26/40

  27. Tools  Poor man’s debugger – System.out.println(…);  Better – Logging (e.g., Log4J) logger.debug(…);  (Even) better – Use the debugger 27/40

  28. Tools  System.out.println(…); – Not scalable – Clutter the output  Logging – Scalable, levels – Off-line, remote  Debugger – On-line (interactive) – SSCCE 28/40

  29. Tools  System.out.println(…); – Not scalable – Clutter the output  Logging – Scalable, levels – Off-line, remote  Debugger – On-line (interactive) – SSCCE 29/40

  30. Outline  Definition  Method  Tools – Logging – Debugger  Conclusion 30/40

  31. Tools  Logging, e.g., Log4J // Get a logger instance named "com.foo" Logger logger = Logger.getLogger( "com.foo" ); // Normally you do not set the level of a logger in code. logger .setLevel( Level.INFO ); // This request is enabled, because WARN >= INFO . logger. warn ("Low fuel level."); // This request is disabled, because DEBUG < INFO . logger. debug ("Starting search for nearest gas station."); // The logger instance barlogger inherits its level from // the logger named "com.foo". This request is enabled // because INFO >= INFO . Logger barlogger = Logger.getLogger( "com.foo.Bar" ); barlogger. info ("Located gas station."); // This request is disabled, because DEBUG < INFO . barlogger. debug ("Exiting gas station search"); 31/40

  32. Tools DEBUG | 2008-09-06 10:51:44,817 | DefaultBeanDefinitionDocumentReader.java | 86 | Loading bean DEBUG | 2008-09-06 10:51:44,848 | AbstractBeanDefinitionReader.java | 185 | Loaded 5 bean defini INFO | 2008-09-06 10:51:44,848 | XmlBeanDefinitionReader.java | 323 | Loading XML bean definition DEBUG | 2008-09-06 10:51:44,848 | DefaultDocumentLoader.java | 72 | Using JAXP provider [com.su DEBUG | 2008-09-06 10:51:44,848 | BeansDtdResolver.java | 72 | Found beans DTD [http://www.spr DEBUG | 2008-09-06 10:51:44,864 | DefaultBeanDefinitionDocumentReader.java | 86 | Loading bean … DEBUG | 2008-09-06 10:51:45,473 | AbstractAutowireCapableBeanFactory.java | 383 | Creating insta DEBUG | 2008-09-06 10:51:45,473 | AbstractAutowireCapableBeanFactory.java | 459 | Eagerly cachi 10:51:45,473 | AbstractAutowireCapableBeanFactory.java | 411 | Finished creating instance of bean ' INFO | 2008-09-06 10:51:45,473 | SQLErrorCodesFactory.java | 128 | SQLErrorCodes loaded: [DB2, … 32/40

  33. Tools  Logging, e.g., Log4J – DEBUG: low level things, e.g., cache hit, cache miss, opening database connection… – INFO: events that have business meaning, e.g., creating a customer, charging a card… – WARN: any problem that does not stop the program, e.g., email address not found… – ERROR: unexpected problem that could prevent the program to work, e.g., failed to open a database connection... 33/40

  34. Outline  Definition  Method  Tools – Logging – Debugger  Conclusion 34/40

  35. Tools  Debugger – “Usual” features • Query processor • Symbol resolver • Expression interpreter • Step-by-step execution • Stopping (breaking) execution • Tracking the values of variables – Reverse debugging • Omniscient debugger 35/40

  36. Tools  Debugger – Hardware support for single-stepping a program • Popek and Goldberg’s virtualization requirements • In-System Programming • Test access ports – Instruction set simulator – Virtual machine • Smalltalk again  36/40

  37. Tools 37/40

  38. Tools DEMO! 38/40

  39. Outline  Definition  Method  Tools – Logging – Debugger  Conclusion 39/40

  40. Conclusion  Beware of the ubiquitous term “bug”  Debug with (scientific) method – Use SSCCE!  Use the tools to your advantage 40/40

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