mjiderhamn / classloader-leak-quiz

Workshop for practicing on finding ClassLoader leaks

ClassLoader leak quiz

Use the ClassLoader Leak Test Framework and the process detailed in the first parts of this blog series to solve the following quiz.

Note, if you choose to run your tests with Maven, make sure to fork for each test case, or you'll aggregate leaked ClassLoaders for each test run.

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>2.19</version>
        <configuration>
          <forkCount>1</forkCount>
          <reuseForks>false</reuseForks>
        </configuration>
      </plugin>
    </plugins>
  </build>

Feel free to clone this repo to get a head start!

Goals

For each question in the quiz, you will need to find a specific letter. All letters, in the order of the questions, will form a word. Your goal is to find that word. Note that classname always refers to the simple/unqualified name of a class, i.e. ignore the package name.

In order to make sure you have not simply guessed missing letters, you need to note, for each question, the type of leak caused.

• System class reference
• Unstopped thread
• Uncleared ThreadLocal

Let's begin!

---

1. Axis

Find the first letter of the class causing the leak

<dependency>
  <groupId>org.apache.axis</groupId>
  <artifactId>axis</artifactId>
  <version>1.4</version>
  <scope>test</scope>
</dependency>

org.apache.axis.utils.XMLUtils.getDocumentBuilder();

2. Batik

Find the third letter of the Batik class causing the leak

<dependency>
  <groupId>org.apache.xmlgraphics</groupId>
  <artifactId>batik-svg-dom</artifactId>
  <version>1.7</version>
</dependency>

org.apache.batik.dom.GenericDocument document = (org.apache.batik.dom.GenericDocument) 
    org.apache.batik.dom.GenericDOMImplementation.getDOMImplementation()
      .createDocument("foo:bar", "foobar", 
        new org.apache.batik.dom.GenericDocumentType("foo", "bar", "baz"));
org.apache.batik.dom.GenericAttr attr = 
    (org.apache.batik.dom.GenericAttr) document.createAttribute("foo");
attr.setOwnerElement((org.apache.batik.dom.GenericElement) document.createElement("foo"));
attr.setIsId(true);
attr.setValue("bar");

3. Java Advanced Imaging (JAI)

Find the first letter of the class causing the leak. (As for the type, your dump may contain two references to this class, but only one of them has a single path to GC root.)

<repositories>
  <!-- Repo for JAI -->
  <repository>
    <id>jboss-thirdparty-releases</id>
    <url>https://repository.jboss.org/nexus/content/repositories/thirdparty-releases</url>
  </repository>
</repositories>

<dependency>
  <groupId>com.sun.media</groupId>
  <artifactId>jai-codec</artifactId>
  <version>1.1.3</version>
</dependency>

com.sun.media.jai.codec.SeekableStream.wrapInputStream(
  new java.io.ByteArrayInputStream(new byte[0]), true);

4. GeoTools

Find the second letter of the class causing the leak. (Ignore any references passing through JAI.)

<repositories>
  <!-- Repo for GeoTools -->
  <repository>
    <id>osgeo</id>
    <name>Open Source Geospatial Foundation Repository</name>
    <url>http://download.osgeo.org/webdav/geotools/</url>
  </repository>
</repositories>

<dependency>
  <groupId>org.geotools</groupId>
  <artifactId>gt-shapefile</artifactId>
  <version>13.2</version>
</dependency>

org.geotools.util.SoftValueHashMap m = new org.geotools.util.SoftValueHashMap(1);
m.put("foo", "bar");
m.put("foo2", "bar2");

5. JEditorPane

Find the second uppercase letter of the name of the class causing the leak

new javax.swing.JEditorPane("text/plain", "dummy");

6. JGroups

Find the second letter of the outer JGroups class causing one of the two leaks. You'll have to guess which of the two to get the letter from. Note the type of leaks for both!

<dependency>
  <groupId>org.jgroups</groupId>
  <artifactId>jgroups</artifactId>
  <version>3.0.0.Final</version>
</dependency>

org.jgroups.stack.GossipRouter gossipRouter = new org.jgroups.stack.GossipRouter();
gossipRouter.start();
gossipRouter.stop();

7. MVEL

Find the the letter occurring 3 times in the name of the class causing the leak

<dependency>
  <groupId>org.mvel</groupId>
  <artifactId>mvel2</artifactId>
  <version>2.0</version>
</dependency>

org.mvel2.MVEL.executeExpression(
    org.mvel2.MVEL.compileExpression("new Integer(1)"), Collections.emptyMap());

8. dom4j

Find the first letter of the attribute that holds the reference to the dom4j class

<dependency>
  <groupId>dom4j</groupId>
  <artifactId>dom4j</artifactId>
  <version>1.5</version>
</dependency>

org.dom4j.DocumentHelper.createDocument();

9. PIG

Find the second uppercase letter of outer class to the first non-PIG class in the GC path

<dependency>
  <groupId>org.apache.pig</groupId>
  <artifactId>pig</artifactId>
  <version>0.15.0</version>
</dependency>

org.apache.pig.impl.util.SpillableMemoryManager.getInstance();