[ http://issues.apache.org/jira/browse/XERCESJ-727?page=comments#action_60298 ] Michael Glavassevich commented on XERCESJ-727: ----------------------------------------------
Xerces' DOM implementation is not thread safe [1]. There's no requirement that a DOM be thread safe, so applications need to make sure that threads are properly synchronized for concurrent access to the DOM. This is true even if you're just invoking read operations. [1] http://xml.apache.org/xerces2-j/faq-dom.html#faq-1 > cloneNode(true) Element are still linked to original Element > ------------------------------------------------------------ > > Key: XERCESJ-727 > URL: http://issues.apache.org/jira/browse/XERCESJ-727 > Project: Xerces2-J > Type: Bug > Components: DOM > Versions: 2.4.0 > Environment: Operating System: Windows NT/2K > Platform: PC > Reporter: Francois Abot > Assignee: Xerces-J Developers Mailing List > > 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(); > } > } > } -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://issues.apache.org/jira/secure/Administrators.jspa - If you want more information on JIRA, or have a bug to report see: http://www.atlassian.com/software/jira --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
