The following comment has been added to this issue:
Author: Aaron Kardell
Created: Thu, 20 May 2004 6:29 PM
Body:
This issue may or may not be related to the issue reported by XERCESJ-525, of which
I just submitted test cases and a patch for.
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View this comment:
http://issues.apache.org/jira/browse/XERCESJ-727?page=comments#action_35660
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View the issue:
http://issues.apache.org/jira/browse/XERCESJ-727
Here is an overview of the issue:
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Key: XERCESJ-727
Summary: cloneNode(true) Element are still linked to original Element
Type: Bug
Status: Open
Project: Xerces2-J
Components:
DOM
Versions:
2.4.0
Assignee: Xerces-J Developers Mailing List
Reporter: Francois Abot
Created: Fri, 16 May 2003 9:35 AM
Updated: Thu, 20 May 2004 6:29 PM
Environment: Operating System: Windows NT/2K
Platform: PC
Description:
NB : tested only under Windows 2000/ jdk 1.4.1_02
-------
- Create a DOM Element.
- Create many threads, giving each of them a cloneNode(true) copy of the
Element.
- Start all the threads.
- Each thread just finds the Element's embedded sub-Elements.
The following Exceptions occur many times (but not always) :
java.lang.NullPointerException
at org.apache.xerces.dom.ParentNode.nodeListItem(Unknown Source)
at org.apache.xerces.dom.ParentNode.item(Unknown Source)
at Tst2Threads.run(Tst2Threads.java:40)
java.lang.NullPointerException
at org.apache.xerces.dom.ParentNode.nodeListItem(Unknown Source)
at org.apache.xerces.dom.ParentNode.item(Unknown Source)
at Tst2Threads.run(Tst2Threads.java:41)
where lines 40 and 41 are :
if ( lesNoeuds.item(i).getNodeType() != Element.ELEMENT_NODE ) continue;
noeud = (Element)(lesNoeuds.item( i ));
in the following example.
NB : if I create an different Element from file for each thread creation
(different Element instances, not created from cloneNode) then no Exception
occurs
This seems a wrong behaviour, keeping Xerces from being used in multi-threading
environment.
I understand that Xerces is not thread safe, but how can I use same data in
different threads if the cloning fails this way ?
How can I write correct thread safe code using DOM data ?
These symptoms seem close to bug #6885 but are NOT DUPLICATE at first sight :
there is no concurrent access on the same instance in my example.
Thanks to tell me if there is any error in my code. I am interested in any
workaround for that behaviour...
Francois.
***************************************
Here follows a code example (sorry for poor comments ;-).
Usage :
- just run it from command line,
- enter a XML file name, Element used will be the first one read from file (I
suggest a consequent Element),
- enter a number of threads,
==> with 200 threads the Exception occurs almost immediately.
***************************************
import org.w3c.dom.*;
public class Tst2Threads extends Thread
{
static protected Document readDOM( String nomFichier ) throws Exception
{
java.net.URL url= new java.net.URL( nomFichier );
java.io.InputStream inputXML = url.openStream();
javax.xml.parsers.DocumentBuilderFactory factory =
javax.xml.parsers.DocumentBuilderFactory.newInstance();
factory.setValidating( false );
factory.setNamespaceAware( false );
factory.setIgnoringComments( true );
javax.xml.parsers.DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse( inputXML );
return document;
}
/*******************************************************/
Element element = null;
public Tst2Threads(ThreadGroup gp, Element elt, String _nom)
{
super( gp, _nom);
element = elt;
}
public void run()
{
NodeList lesNoeuds = element.getChildNodes();
Element noeud;
while (true)
{
for (int i=0, max=lesNoeuds.getLength(); i<max ; i++)
{
if ( lesNoeuds.item(i).getNodeType() != Element.ELEMENT_NODE ) continue;
noeud = (Element)(lesNoeuds.item( i ));
}
}
}
// get first Element
static Element readElmt(String nomFic) throws Exception
{
Document doc = readDOM( "file://"+nomFic );
NodeList liste = doc.getChildNodes();
boolean done = false;
Element elmt = null;
if (liste != null)
{
for(int i=0, max=liste.getLength(); (i<max) && (! done); i++)
{
if ( liste.item(i).getNodeType() != Element.ELEMENT_NODE ) continue;
elmt = (Element)(liste.item( i ));
done = true ;
}
}
return elmt;
}
/*******************************************************/
public static void main( java.lang.String[] args)
{
try
{
java.io.BufferedReader br=new java.io.BufferedReader( new
java.io.InputStreamReader( System.in));
System.out.print("XML file name for Element description
[d:/tmp/menu.xml] :");
String nomFic= br.readLine();
if ("".equals(nomFic)) nomFic = "d:/tmp/menu.xml";
Element elmt = readElmt(nomFic);
System.out.print("Nb of threads [200] :");
String s= br.readLine();
if ("".equals(s)) s="200";
int nbThreads = Integer.valueOf(s).intValue() - 1;
System.out.println(" Starting for :\n file="+nomFic+"\n nb
threads="+nbThreads);
ThreadGroup groupe = new ThreadGroup("TEST");
Tst2Threads t;
for (int i=0; i<nbThreads; i++)
{
// Element cloned here (from main thread --v)
t = new Tst2Threads(groupe, (Element)(elmt.cloneNode(true)), "Th"+i);
t.start();
}
}
catch (Throwable t)
{
t.printStackTrace();
}
}
}
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