Duplication de code: un défi pour l assurance qualité des logiciels?

Transcription

1 Duplication de code: un défi pour l assurance qualité des logiciels? Foutse Khomh S.W.A.T

2 2

3 JHotDraw 3

4 Code duplication can be 4

5 Example of code duplication Duplication to experiment without risking the stability of the system 5

6 8 General cloning patterns 6

7 Hardware variations 7

8 Platform variations 8

9 Experimental variations 9

10 Boiler-plating 10

11 API/Library protocols 11

12 Language idioms 12

13 Bug workarounds 13

14 Replicate & Specialize 14

15 Types of Code Clone Clone Types Clone A Clone B Type-1 Type-2 Type-3 for( int j = 0; j < 5; j ++ ){ sum = sum + a[j]; } for( int j = 0; j < 5; j ++ ){ sum = sum + a[j]; } for( int j = 0; j < 5; j ++ ){ sum = sum + a[j]; } for( int j = 0; j < 5; j ++ ){ sum = sum + a[j]; } for( int id = 0; id < 5; id ++ ){ sum = sum + a[id]; } for( int id = 0; id < 5; id ++ ){ sum = sum + a[id]; d = sum * c; } 15

16 Is cloning a good practice? 16

17 Cloning can introduce bugs Cloning increase maintenance effort 17

18 Late Propagation in Software Clones 18

19 Clone Evolution Clone Genealogies The change history of a clone pair Consistent Change One or both of the clones changes, but the clone pair is preserved Inconsistent Change One or both of the clones changes independently, destroying the clone pair Consistent Change Inconsistent Change Clone Genealogy Clone A Clone B 19

20 Late Propagation (LP) Two Steps: 1. An inconsistent change that diverges the clone pair Diverging Change Clone A Clone B 2. A consistent change that re-synchronizes the clone pair Re-synchronizing Change 20

21 Why is Late Propagation Risky? Late Propagation can be risky because failure to propagate changes between clones in a clone pair can lead to faults Diverging Change Clone A Clone B 8-21% of genealogies contain a Late Propagation Re-synchronizing Change 21

22 Late Propagation With Propagation Example from ArgoUML Revision Clone A Clone B 595 add Field(new UMLComboBox(typeModel), 1,0,0); add Field(new UMLComboBox(classifierModel), 2,0,0); add Field(new UMLComboBoxNavigator (this, NavClass, new UMLComboBox(typeModel)), 1,0,0); add Field(new UMLComboBoxNavigator (this, NavClass, new UMLComboBox(classifierModel)), 2,0,0); 22

23 Late Propagation Without Propagation Example from ArgoUML Revision Clone A Clone B if( destfile == null ) { destfile = new File(destDir,file.getName()); } if ( m_destfile == null ) { m_destfile = new File(m_destDir,m_file.getName() ); } if (destfile == null ) { destfile = new File(destDir,file.getName()); } if ( destfile == null ) { destfile = new File(destDir,file.getName()); } 23

24 Types of Late Propagation Propagation Category Propagation Always Occurs Propagation May or May Not Occur Propagation Never Occurs LP Type Modified During Diverging Change Modified During the Period of Divergence Modified During Re-synchronizing Change LP1 A A B LP2 A A and B B LP3 A A A and B LP4 A A and B A LP5 A A and B A and B LP6 A and B A and B A or B LP7 A and B A and B A and B LP8 A A A 24

25 Research Questions RQ1: Are there different types of Late Propagation? RQ2: Are some types of Late Propagation more faultprone than others? RQ3: Which type of Late Propagation experiences the highest proportion of faults? 25

26 Subject Systems System # LOC # Revisions # Gen CCFinder # LP CCFinder # Gen Simian # LP Simian ArgoUML 3.1M 18k 14k 1.1k Ant 2.3M 1.0M 30k 4.7k

27 Our Approach 27

28 Mining the SVN Use J-Rex to mine the SVN Heuristics used to identify the reason for a commit (Mockus et al., 2000) Snapshots of all revisions to each Java file are stored in an XML file Test files are removed 28

29 Detecting Clones Contents of each method revision extracted into individual files Perform clone detection once on all snapshots Two existing clone detection tools are used Simian (text-based) and CCFinder (token-based) 29

30 Building Clone Genealogies Build clone genealogies using the existing clone list Query the SVN using diff to track changes to each clone in a clone pair over time If a change modifies one of the clones in a clone pair, query the clone list for a matching clone 30

31 RQ1: Are there different types of Late Propagation? 31

32 RQ1: Are there different types of Late Percentage of All LP Occurrences 80% 70% 60% 50% 40% 30% 20% 10% 0% Propagation? Breakdown of LP Type by System LP1 LP2 LP3 LP4 LP5 LP6 LP7 LP8 LP Types ArgoUML - Simian ArgoUML - CCFinder Ant - Simian Ant - CCFinder There is representation from multiple types of Late Propagation and across all categories of Late Propagation 32

33 RQ2: Are some types of Late Propagation more fault-prone than others? Part 1: Is Late Propagation fault-prone? Part 2: Are specific types of Late Propagation more fault-prone? 33

34 Fisher's exact test Analysis Method Odds Ratio (OR) OR = p q /(1 /(1 p) q) 34

35 Part 1: Is Late Propagation Fault-prone? Odds Ratio LP vs. Non-LP Odds Ratios Ant - Simian ArgoUML - CCFinder Ant - CCFinder ArgoUML Simian is omitted because it is not statistically significant In all significant cases, the odds ratio is greater than 1. Therefore, Late Propagation genealogies are more fault prone than non-late Propagation genealogies 35

36 Part 2: Are specific types of Late Propagation more fault-prone? Odds Ratio Odds Ratios Between Each LP Type and Non-LP Genealogies LP1 LP2 LP3 LP4 LP5 LP6 LP7 LP8 LP Type Ant - Simian ArgoUML - CCFinder Ant - CCFinder Note: ArgoUML Simian is omitted because it is not statistically significant 36

37 RQ2 Observations In general, some Late Propagation types are not more fault-prone than non-late Propagation genealogies (i.e. odds ratio < 1) Some types that make up a small proportion of Late Propagation instances have a very high odds ratio LP7 and LP8 occur frequently but have low odds ratios Each type of Late Propagation has a different level of fault-proneness 37

38 RQ3: Which type of Late Propagation experiences the highest proportion of faults? 38

39 RQ3: Which type of Late Propagation experiences the highest proportion of Percentage of Fault Occurrences 80% 60% 40% 20% 0% faults? Percentage of Fault Occurrences Broken Down by LP Type LP1 LP2 LP3 LP4 LP5 LP6 LP7 LP8 LP Type Ant - Simian ArgoUML - CCFinder Ant - CCFinder Note: ArgoUML Simian is omitted because it is not statistically significant 39

40 RQ3 Observations LP7 and LP8 contribute a large proportion of the faults but have lower odds ratios (RQ2) When faults occur, they occur in large numbers Overall, LP7 and LP8 are the most dangerous, with the other types being system dependent in their fault-proneness The proportion of faults is different for each Late Propagation type 40

41 Discussion In general, Late Propagation genealogies are more fault-prone than non-late Propagation genealogies LP7 and LP8 are the riskiest, in terms of their faultproneness and magnitude of faults LP8 contains no propagation of changes LP7 may or may not contain any propagation of changes The fault-proneness and fault-occurrence is dependent on the Late Propagation type and is system-dependent 41

42 Mutation and Migration occur during Clone Evolution Clone mutation Clone migration These two phenomena further increase the risk of bugs in Late propagation genealogies 42

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44 Acknowledgment Cloning patterns illustrations are from Nicolas Bettenburg, Cloning Considered Harmful Considered Harmful? 44