AppPerfect Java Profiler

Tutorial : Memory Leak Detection

This tutorial provides instructions on how to use AppPerfect Java Profiler product for detecting memory leak in a java application. This tutorial assumes you have successfully downloaded and installed AppPerfect DevTest4J on your machine with the default options.

This document is divided into following sections

Creating Common Project
AppPerfect Java Profiler

Within each section, multiple exercises are listed. All exercises assume you have installed the product in C:\AppPerfect\DevTest folder and will be referred as DEVTEST_HOME henceforth in tutorial. If you have installed the product in some other folder, modify the instructions below appropriately.

For this tutorial, create a java file called 'MemoryLeak.java' copy-pasting the code shown below and compile it.

import java.io.*;

public class MemoryLeak
{
    private static final int CAPACITY = 50;
    private static final int HALF_CAPACITY = CAPACITY/2;

    public static void main(String[] args) throws IOException
    {
        System.out.print("Press any key to start memory leak scenario... ");
        InputStreamReader reader = new InputStreamReader(System.in);
        reader.read();
        System.out.println();
        Stack stack = new Stack(CAPACITY);
        for (int i = 0; i < CAPACITY; ++i)
        {
            stack.push(new Object());
        }
        for (int i = 0; i < HALF_CAPACITY; ++i)
        {
            stack.pop();
        }
        System.out.print("Press any key to stop memory leak scenario... ");
        reader.read();
        reader.read();
    }
}

class Stack
{
    private Object[] elements;
    private int size = 0;
    public Stack(int initialCapacity)
    {
        this.elements = new Object[initialCapacity];
    }

    public void push(Object e)
    {
        ensureCapacity();
        elements[size++] = e;
    }

    public Object pop()
    {
        if (size > 0)
        {
            return elements[--size]; // MEMORY LEAK
        }
        return null;
    }

    /**
    * Ensure space for at least one more element, roughly
    * doubling the capacity each time the array needs to grow.
    */
    private void ensureCapacity()
    {
        if (elements.length == size)
        {
            Object[] oldElements = elements;
            elements = new Object[2 * elements.length + 1];
            System.arraycopy(oldElements, 0, elements, 0, size);
        }
    }
}

If a stack grows and then shrinks, the objects that were popped off the stack will not be garbage collected, even if the program using the stack has no more references to them. This is because the stack maintains obsolete references to these objects. An obsolete reference is simply a reference that will never be dereferenced again. In this case, any references outside of the “active portion” of the element array are obsolete. The active portion consists of the elements whose index is less than size.

- Source: Effective Java: Programming Language Guide by Joshua Bloch

Creating Common Project

Exercise 1: Launch AppPerfect DevTest4J

Action:

Click on Start -> Programs ->AppPerfect DevTest4J x.x.x -> AppPerfect DevTest4J
On launching AppPerfect DevTest4J a Welcome page will be displayed. Go through the brief description given for each product and click on the product icon to view its perspective.
NB: Welcome page is displayed only when DevTest4J x.x.x is launched and last time no project was opened.
To switch between different product perspectives click on corresponding project button in toolsbar.

Exercise 2: Creating a Common Project

Action:

Launch the Common Project Wizard by clicking File ->New... menu option. The New Project wizard will be launched.
Go through the instruction provided on top of the General tab.
Keep the default project name and location for the purpose of this exercise. We don't have to provide "Notification" settings or "Remote Application/AppServer" settings for this exercise. Click on the Next button.
In the Source tab provide the location of source file "MemoryLeak.java". Click the Next button.
Use the default JDK which is bundled with AppPerfect DevTest4J and click on the Next button.
In the "Environment" tab provide the location of "MemoryLeak.class" file.
Click on "Verify Classpath" button to validate the classpath.
Classpath validation dialog will be launched and the classpath will be verified. A message saying that the classpath specified is correct should be displayed. Click on the "OK" button. Click on the Next button.
In the "Target" tab select project type as "LOCAL".
For working folder provide the path to the folder containing the the "MemoryLeak.class" file.
Specify the Main Class as "MemoryLeak".
Select the "Launch target application automatically" checkbox. Click on the Finish button.
A confirmation message saying that the project is saved will be displayed. Click on the OK button.