Understanding Source Code Differences by Separating Refactoring Effects

UNDERSTANDING SOURCE CODE DIFFERENCES BY SEPARATING REFACTORING EFFECTS

*Sirinut Thangthumachit, Shinpei Hayashi, Motoshi Saeki Tokyo Institute of Technology, Japan

Motivation • Source code differences

• Comparing and reading the differences of old and new versions of source code

• Refactoring complicates differences[1,2] • Refactoring: the technique to restructuring source code

that will not change program’s behavior •  makes large amount of differences •  shows same differences multiple times •  hides other changes’ differences

2

[1] K. Prete et al, “Template-based reconstruction of complex refactorings” , ICSM2010. [2] Weißgerber et al, “Identifying refactoring from source-code changes” , ASE2006.

Source Code Differences

3

public ThreadPoolRxTaskPool (int …

RED: deleted code BLUE: added code

Apache Tomcat 6.0.4 – 6.0.5

4 Example

public ThreadPool (int maxThreads, int minThreads, ThreadCreatorRxTaskPool (int maxTasks, int minTasks, TaskCreator creator) throws Exception { // fill up the pool with worker threads this.maxThreads = maxThreadsmaxTasks = maxTasks; this.minThreads = minThreadsminTasks = minTasks; this.creator = creator; //for (int i = 0; i < minThreads; i++) { for (int i = 0; i < maxThreads; i++) { //temporary fix for thread hand off problem WorkerThread thread = creator.getWorkerThread(); setupThread(thread); idle.add (thread); } } protected void setupThread(WorkerThread threadconfigureTask(AbstractRxTask task) { synchronized (threadtask) { thread.setPooltask.setTaskPool(this); thread.setName(thread// task.setName(task.getClass ().getName() + "[" + inc() + "]"); thread// task.setDaemon(true); thread// task.setPriority(Thread.MAX_PRIORITY); thread// task.start(); try {thread.wait(500); }catch ( InterruptedException x ) {} } }

5 Example

public ThreadPool (int maxThreads, int minThreads, ThreadCreatorRxTaskPool (int maxTasks, int minTasks, TaskCr eator creator) throws Exception { // fill up the pool with worker threads this.maxThreads = maxThreadsmaxTasks = maxTasks; this.minThreads = minThreadsminTasks = minTasks; this.creator = creator; //for (int i = 0; i < minThreads; i++) { for (int i = 0; i < maxThreads; i++) { //temporary fix for thread hand off problem WorkerThread thread = creator.getWorkerThread(); setupThread(thread); idle.add (thread); } }

6 Example


Delete ‘for-loop’

7 Example



Class ‘ThreadPool’　→　‘RxTaskPool’

8 Example



Class ‘ThreadPool’　→　‘RxTaskPool’ Parameter ‘maxThreads’　→　‘maxTasks’

9 Example



Class ‘ThreadPool’　→　‘RxTaskPool’ Parameter ‘maxThreads’　→　‘maxTasks’

4 more refactorings

10 Example


Delete ‘for-loop’ Refactorings

Apache Tomcat 6.0.4 – 6.0.5

11 Example

public ThreadPool (int maxThreads, int minThreads, ThreadCreatorRxTaskPool (int maxTasks, int minTasks, TaskCreator creator) throws Exception { // fill up the pool with worker threads this.maxThreads = maxThreadsmaxTasks = maxTasks; this.minThreads = minThreadsminTasks = minTasks; this.creator = creator; //for (int i = 0; i < minThreads; i++) { for (int i = 0; i < maxThreads; i++) { //temporary fix for thread hand off problem WorkerThread thread = creator.getWorkerThread(); setupThread(thread); idle.add (thread); } } protected void setupThread(WorkerThread threadconfigureTask(AbstractRxTask task) { synchronized (threadtask) { thread.setPooltask.setTaskPool(this); thread.setName(thread// task.setName(task.getClass ().getName() + "[" + inc() + "]"); thread// task.setDaemon(true); thread// task.setPriority(Thread.MAX_PRIORITY); thread// task.start(); try {thread.wait(500); }catch ( InterruptedException x ) {} } }

12 Example

protected void setupThread(WorkerThread threadconfigure Task(AbstractRxTask task) { synchronized (threadtask) { thread.setPooltask.setTaskPool(this); thread.setName(thread// task.setName(task. getClass().getName() + "[" + inc() + "]"); thread// task.setDaemon(true); thread// task.setPriority(Thread.MAX_PRIORITY); thread// task.start(); try {thread.wait(500); }catch ( InterruptedException x ) {} } }

13 Example


Comment Out

14 Example


Comment Out

Method ‘setupThread’　→　‘configureTask’

15 Example


Comment Out

Method ‘setupThread’　→　‘configureTask’ Parameter ‘thread’　→　‘task’

16 Example


Comment Out

Method ‘setupThread’　→　‘configureTask’ Parameter ‘thread’　→　‘task’

2 more refactorings

17 Example


Comment Out Refactorings

Basic Ideas

• Developer knows refactoring well •  ‘ThreadPool’ was renamed to ‘RxTaskPool’

• →　It is no need to read refactorings in source code differences •  ThreadPoolRxTaskPool

• →　Extract & Eliminate Refactorings • Source code differences without refactoring

• →　Show refactoring information to user

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Separating Refactorings 19

‘ThreadPool’　→　‘RxTaskPool’ ‘setupThread’　→　‘configureTask’ and 8 more.

public RxTaskPool (int maxTasks, int minTasks, TaskCreator creator) throws Exception { // fill up the pool with worker threads this.maxTasks = maxTasks; this.minTasks = minTasks; this.creator = creator; //for (int i = 0; i < minThreads; i++) { for (int i = 0; i < maxTasks; i++) { //temporary fix for thread hand off problem AbstractRxTask thread = creator.createRxTask(); configureTask(thread); idle.add (thread); } } protected void configureTask(AbstractRxTask task) { synchronized (task) { task.setTaskPool(this); // task.setName(task.getClass().getName() + "[" + inc() + "]"); // task.setDaemon(true); // task.setPriority(Thread.MAX_PRIORITY); // task.start(); try {Thread.wait(500); }catch ( InterruptedException x ) {} } }




public ThreadPool (int maxThreads, int minThreads, ThreadCreatorRxTaskPool (int maxTasks, int minTasks, TaskCreator creator) throws Exception { // fill up the pool with worker threads this.maxThreads = maxThreadsmaxTasks = maxTasks; this.minThreads = minThreadsminTasks = minTasks; this.creator = creator; //for (int i = 0; i < minThreads; i++) { for (int i = 0; i < maxThreads; i++) { //temporary fix for thread hand off problem WorkerThread thread = creator.getWorkerThread(); setupThread(thread); idle.add (thread); } } protected void setupThread(WorkerThread threadconfigureTask(AbstractRxTask task) { synchronized (threadtask) { thread.setPooltask.setTaskPool(this); thread.setName(thread// task.setName(task.getClass ().getName() + "[" + inc() + "]"); thread// task.setDaemon(true); thread// task.setPriority(Thread.MAX_PRIORITY); thread// task.start(); try {thread.wait(500); }catch ( InterruptedException x ) {} } } With Refactorings Without Refactorings




Delete 'for-loop'




Delete 'for-loop' Comment out




Delete 'for-loop' Comment out

Delete 'try&catch'

Approach

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Old New Modified

Old New

Old version of source code New version of source code Source code differences refactoring

New

Old

Overview of the proposed technique

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Comparing Source Code

Ordered Listof Refactorings


without Refactoring

Outputs

New Ver.

Old Ver.

Inputs

Separating Refactorings


26

Extracting Refactorings

Ordered List of Refactorings

Output 1

Applying "Refactorings

Output 2

Old Ver.

Input 1

New Ver. Input 2

ModifiedVer.


27

Comparing Source Code

Ordered Listof Refactorings


without Refactoring

Outputs

New

Old

Inputs

File Class Method"

Field Local Package

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Supporting tool

Extraction Application

Rename packages, files, classes, interfaces,

enums, methods all elements

Move files, methods files, methods

Extract - methods

• Refactoring Extraction • Automatical extraction • External Input

• Refactoring Application • Automatically apply by using Eclipse Refactoring

Browser

• Application on OSS • Can extracted refactorings be applied? • Can separating refactorings reduce the amount of source

code differences?

• Human Subject Study • With approach, can subjects understand more changes in

the same limited time? • Does the approach satisfy subjects?

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Evaluations

• Target projects • OW2 Carol 1.0.1-1.8.5 (30 pairs)

• Result •  Tool found refactorings in 5 pairs

•  1.0.1–1.3.0, 1.4.0–1.4.2, 1.5.2–1.5.3, 1.5.6–1.5.7, 1.5.8–1.6.

• Refactorings application

• → All real refactorings were applied successfully 30

Evaluation 1 (Application on OSS)

Found Successfully applied

Detected Refactorings 21 18

False 5 2

True 16 16

• The amount of source code differences

　→ Approach reduced more than 21% • Can extracted refactorings be applied?

•  →　Yes • Can separating refactorings reduce the amount of source

code differences? •  →　Yes

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Changed lines

WO: without approach 18,721 (100%) A: with approach 14,624 (78.12%) WO - A 4,097 (21.88%)

Evaluation 1

• Procedure •  Let subjects read the source code differences with and

without our approach. • Ask them to answer what was changed between the

versions • Evaluate by time and changes found

• Target Projects • OW2 Carol 1.5.6-1.5.7 • Apache Tomcat 6.0.4-6.0.5

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Evaluation 2 (Human Subject)

• Subjects

• Result

• → Approach made 32% higher efficiency

Changes found

Time (minute)

Efficiency (changes found/ time)

average w/o Approach 28.3 112.75 0.25 (100%)

Approach 39.25 120 0.33 (132%)

Evaluation 2

Subjects A B C D Carol Approach w/o Approach Approach w/o approach

Tomcat w/o Approach Approach w/o Approach Approach

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• Questionnaires • All subjects agreed that our approach is useful

•  Especially, renaming class.

• With approach, can subjects understand more changes in the same limited time? •  →　Yes

• Does the approach satisfy subjects? •  →　Yes

Evaluation 2

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• Understanding source code differences by separating refactorings effects •  Separating refactorings •  Implemented supporting tool

•  Rename + Move refactorings •  Evaluations

•  Approach is applicable to OSS •  Separating refactorings helps understanding differences

• Future Works • Better tool

•  Support more refactoring types 35

Conclusion