DO NOT REPLY [Bug 19982] New: - cloneNode(true) Element are still linked to original Element

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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=19982

cloneNode(true) Element are still linked to original Element

           Summary: cloneNode(true) Element are still linked to original
                    Element
           Product: Xerces2-J
           Version: 2.4.0
          Platform: PC
        OS/Version: Windows NT/2K
            Status: NEW
          Severity: Major
          Priority: Other
         Component: DOM
        AssignedTo: xerces-j-dev@xml.apache.org
        ReportedBy: fabot@lucent.com


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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