[XALANJ-1198] Xalan's DOMSource is not thread-safe

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Won't Fix
• Affects Version/s: 2.3Dx
• Component/s: JAXP
• Security Level: No security risk; visible to anyone (Ordinary problems in Xalan projects. Anybody can view the issue.)
• Environment: Operating System: Windows NT/2K; Platform: PC
• Bugzilla Id: 13039
• Assignee: Unassigned
• Reporter: Vlad Mamut
• Created: 26/Sep/02 23:54
• Updated: 02/Apr/05 06:46
• Resolved: 02/Apr/05 06:46

Description

When using Xalan in a multi-threaded environment and DOMSource is used for
transformations, occasional java.lang.NullPointerException are thrown.
A program running multiple printing threads accesses the same DOM document. The
printing uses transformation to serialize the document content into an output
stream. An exception is thrown when Transformer.transform() is called. Replacing
DOMSource with StreamSource seems to alleviate the problem.

Attached are the test results and the source used to reproduce the problem.

Similar results (NullPointerExceptions in
org.apache.xml.utils.TreeWalker.dispatachChars) are produced when using
Serializer in multi-threaded environment. It might be a separate issue deserving
it 'own' bug.

Case 1 (exception in 2 threads)
*******************************
C:\CitiFile\PrintException>java TestSerializer C:\Citifile\PrintException\data.x
ml
Classpath: .;xalan.jar;xml-apis.jar
Starting processing Thread ID: 0
Enter Print Thread ID: 0
Starting processing Thread ID: 1
Enter Print Thread ID: 1
Starting processing Thread ID: 2
Enter Print Thread ID: 2
Exception in Thread ID: 1
java.lang.NullPointerException
at org.apache.xml.utils.TreeWalker.dispatachChars(TreeWalker.java:275)
at org.apache.xml.utils.TreeWalker.startNode(TreeWalker.java:419)
at org.apache.xml.utils.TreeWalker.traverse(TreeWalker.java:183)
at org.apache.xalan.transformer.TransformerIdentityImpl.transform(Transf
ormerIdentityImpl.java:325)
at SerializerThread.printXMLdocument(SerializerThread.java:46)
at SerializerThread.run(SerializerThread.java:26)
Exception in Thread ID: 0
java.lang.NullPointerException
at org.apache.xml.utils.TreeWalker.dispatachChars(TreeWalker.java:275)
at org.apache.xml.utils.TreeWalker.startNode(TreeWalker.java:419)
at org.apache.xml.utils.TreeWalker.traverse(TreeWalker.java:183)
at org.apache.xalan.transformer.TransformerIdentityImpl.transform(Transf
ormerIdentityImpl.java:325)
at SerializerThread.printXMLdocument(SerializerThread.java:46)
at SerializerThread.run(SerializerThread.java:26)
Exit Print Thread ID: 2
Completed Thread ID: 2

Case 2 (exception in 1 thread)
******************************
C:\CitiFile\PrintException>java TestSerializer C:\Citifile\PrintException\data.x
ml
Classpath: .;xalan.jar;xml-apis.jar
Starting processing Thread ID: 0
Enter Print Thread ID: 0
Starting processing Thread ID: 1
Enter Print Thread ID: 1
Starting processing Thread ID: 2
Enter Print Thread ID: 2
Exception in Thread ID: 1
java.lang.NullPointerException
at org.apache.xml.utils.TreeWalker.dispatachChars(TreeWalker.java:275)
at org.apache.xml.utils.TreeWalker.startNode(TreeWalker.java:419)
at org.apache.xml.utils.TreeWalker.traverse(TreeWalker.java:183)
at org.apache.xalan.transformer.TransformerIdentityImpl.transform(Transf
ormerIdentityImpl.java:325)
at SerializerThread.printXMLdocument(SerializerThread.java:46)
at SerializerThread.run(SerializerThread.java:26)
Exit Print Thread ID: 0
Completed Thread ID: 0
Exit Print Thread ID: 2
Completed Thread ID: 2

Case 3 (no exceptions, successful processing)
*********************************************
C:\CitiFile\PrintException>java TestSerializer C:\Citifile\PrintException\data.x
ml
Classpath: .;xalan.jar;xml-apis.jar
Starting processing Thread ID: 0
Enter Print Thread ID: 0
Starting processing Thread ID: 1
Enter Print Thread ID: 1
Starting processing Thread ID: 2
Enter Print Thread ID: 2
Exit Print Thread ID: 0
Completed Thread ID: 0
Exit Print Thread ID: 1
Completed Thread ID: 1
Exit Print Thread ID: 2
Completed Thread ID: 2

*****************************************************************************
import org.w3c.dom.Document;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import java.io.FileInputStream;

public class TestSerializer {
public static void main (String[] args) {
try {
System.out.println("Classpath: " +
System.getProperty("java.class.path"));
DocumentBuilderFactory dbFactory =
DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder =
dbFactory.newDocumentBuilder();
Document xmlDocument = dBuilder.parse(new
FileInputStream("data.xml"));
for (int i=0; i < 3; i++)

{ new SerializerThread(xmlDocument, i).start(); }

}
catch (Exception ex)

{ ex.printStackTrace(); }

}
}
*****************************************************************************

import org.w3c.dom.Document;

import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.Transformer;

import java.io.FileInputStream;
import java.io.FileOutputStream;

public class SerializerThread extends Thread {

private Document xmlDocument;
private int threadId;

public SerializerThread(Document xmlDocument, int threadId)

{ this.xmlDocument = xmlDocument; this.threadId = threadId; }

public void run() {
try

{ System.out.println("Starting processing Thread ID: " + this.threadId); printXMLdocument(this.xmlDocument); System.out.println("Completed Thread ID: " + this.threadId); }

catch (Exception ex)

{ System.out.println("Exception in Thread ID: " + this.threadId); ex.printStackTrace(); }

}

private void printXMLdocument(Document xmlDocument) throws Exception

{ System.out.println("Enter Print Thread ID: " + this.threadId); StreamResult result = new StreamResult(new FileOutputStream("out" + this.threadId + ".xml")); /*** replacing DOMSource with StreamSource works *******/ DOMSource source = new DOMSource(xmlDocument); // StreamSource source = new StreamSource(new FileInputStream("data.xml")); /*******************************************************/ TransformerFactory transformerFactory = TransformerFactory.newInstance(); Transformer transformer = transformerFactory.newTransformer(); transformer.transform(source, result); System.out.println("Exit Print Thread ID: " + this.threadId); }

}

*****************************************************************************

I use:
Sun JVM (java version "1.3.1_02", Java(TM) 2 Runtime Environment, Standard
Edition (build 1.3.1_02-b02), Java HotSpot(TM) Client VM (build 1.3.1_02-b02,
mixed mode))
Xalan J 2.3.1