Late Propagation in Software Clones

Liliane Barbour, Foutse Khomh, and Ying Zou

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Late Propagation (LP)

• Definition: An inconsistent change that diverges a clone pair, later followed by a consistent, re-synchronizing change.

• It can be risky because failure to propagate changes between clones in a clone pair can lead to faults

• In our work, we found that 8-21% of genealogies contain a late propagation

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LP With Propagation Example from ArgoUML

//Clone A, Revision 595add Field(new UMLComboBox(typeModel),1,0,0);

//Clone B, Revision 595add Field(new UMLComboBox(classifierModel),2,0,0);

//Diverging Change: Clone A, Revision 602add Field(new UMLComboBoxNavigator(this,”NavClass”,

new UMLComboBox(typeModel)),1,0,0);

//Re-synchronizing Change: Clone B, Revision 604add Field(new UMLComboBoxNavigator (this,”NavClass”,

new UMLComboBox(classifierModel)),2,0,0);Clone A Clone B

Diverging Change

Re-synchronizing Change

Revision 595

Revision 602

Revision 604

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LP Without Propagation Example from Ant

//Clone A, Revision 270250if( destFile == null ){ destFile = new File(destDir,file.getName());}

//Clone B, Revision 270250if (destFile == null ) {

destFile = new File(destDir,file.getName());}

// Diverging Change: Clone A, Revision 270264if ( m_destFile == null ){

m_destFile = new File(m_destDir,m_file.getName());}

//Re-synchronizing Change: Clone A, Revision 271109if ( destFile == null ) {

destFile = new File(destDir,file.getName());}

Clone A Clone B

Diverging Change

Re-synchronizing Change

Revision 270250

Revision 270264

Revision 271109

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Types of Late PropagationPropagation Category

LP Type

Modified During Diverging Change

Modified During the Period of Divergence

Modified During Re-synchronizing Change

Propagation Always Occurs

LP1 A A B

LP2 A A and B B

LP3 A A A and B

Propagation May or May Not Occur

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

Propagation Never Occurs

LP8 A A A

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Research Questions

RQ1: Are there different types of LP?

RQ2: Are some types of LP more fault-prone than others?

RQ3: Which type of LP experiences the highest proportion of faults?

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Subject Systems

System # LOC # Revisions# Gen CCFinder

# LP CCFinder

# Gen Simian

# LP Simian

ArgoUML 3.1M 18k 14k 1.1k 111 23Ant 2.3M 1.0M 30k 4.7k 461 80

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Our Approach

Mining the SVN

• Use J-Rex to mine the SVN• Heuristics used to identify reason for commit

(Mockus et al., 2000)• Snapshots of all revisions to each Java file are stored

in an XML file• Test files are removed

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Clone Detection

• 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)

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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

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RQ1: Are there different types of LP?

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RQ1: Are there different types of LP?

There is representation from multiple types of LP and across all categories of LP.

LP1 LP2 LP3 LP4 LP5 LP6 LP7 LP8 0%

10%20%30%40%50%60%70%80%

Breakdown of LP Type by System

ArgoUML - Simian ArgoUML - CCFinder Ant - Simian Ant - CCFinderLP Types

Perc

enta

ge o

f All

LP O

ccur

renc

es

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Part 1: Is Late Propagation fault-prone?

Part 2: Are specific types of late propagation more fault-prone?

RQ2: Are some types of LP more fault-prone than others?

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In all significant cases, the odds ratio is greater than 1. Therefore, LP genealogies are more fault prone than

non-LP genealogies.

ArgoUML – Simian is omitted because it is not statistically

significant

00.5

11.5

22.5

33.5

LP vs. Non-LP Odds Ratios

Ant - Simian ArgoUML - CCFinder Ant - CCFinder

Odd

s Ra

tio

Part 1: Is Late Propagation Fault-prone?

16Note: ArgoUML – Simian is omitted because it is not statistically significant

Part 2: Are specific types of late propagation more fault-prone?

LP1 LP2 LP3 LP4 LP5 LP6 LP7 LP8 02468

10121416

Odds Ratios Between Each LP Type and Non-LP Genealogies

Ant - Simian ArgoUML - CCFinder Ant - CCFinder

LP Type

Odd

s Ra

tio

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RQ2 Observations

• In general, some LP types are not more fault-prone than non-LP genealogies (i.e. odds ratio < 1)

• Some types that make up a small proportion of LP instances have a very high odds ratio

• LP7 and LP8 occur frequently but have low odds ratios.

Each type of LP has a different level of fault-proneness.

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RQ3: Which type of LP experiences the highest proportion of faults?

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RQ3: Which type of LP experiences the highest proportion of faults?

Note: ArgoUML – Simian is omitted because it is not statistically significant

LP1 LP2 LP3 LP4 LP5 LP6 LP7 LP8 0%

10%20%30%40%50%60%70%80%

Percentage of Fault Occurrences Broken Down by LP Type

Ant - Simian ArgoUML - CCFinder Ant - CCFinder

LP Type

Perc

enta

ge o

f Fau

lt O

ccur

renc

es

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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 LP type.

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Conclusion

• In general, LP genealogies are more fault-prone than non-LP genealogies

• LP7 and LP8 are the riskiest, in terms of their fault-proneness 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 LP type and is system-dependent.

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