[ http://issues.apache.org/jira/browse/XALANJ-2101?page=all ]
Brian Minchau updated XALANJ-2101:
----------------------------------
Fix Version: 2.7
> DTM Usage in a multithreaded environment
> ----------------------------------------
>
> Key: XALANJ-2101
> URL: http://issues.apache.org/jira/browse/XALANJ-2101
> Project: XalanJ2
> Type: Bug
> Components: DTM
> Versions: 2.5
> Environment: All platforms, JDK1.4.2_05, xalan with xerces 2.5
> Reporter: Rony Zoghby
> Assignee: Henry Zongaro
> Priority: Critical
> Fix For: 2.7
>
> Hi,
> We have a multi-threaded memory intensive application with extensive use of
> xsl processing.
> Performance is critical so we're using a caching mechanism of xalan DTM
> structures
> so not to build the DTM everytime.
> Based on the code below, we would like to know if our usage is thread safe,
> as the DTM
> structure is an internal xalan structure.
> The code we're using (a structure of the code rather than the actual code) is
> the following:
> /*
> get the xsl stylesheet templates object from our templates cache using the
> templatesKey
> The templates key is for us the content of the stylesheet
> */
> Templates templates=null;
> synchronized(templatesCache){
> templates=cache.getTemplates(templatesKey);
> if(templates==null){
> synchronized(transformerFactory){
> templates=transformerFactory.newTemplates(...);
> }
> cache.addTemplates(templatesKey, templates);
> }
> }
>
> /*
> Each xsl stylesheet templates object has a pool of xsl transformers, so not
> to create
> a transformer each time.
> */
> TransformerImpl
> transformerImpl=templates.getTransformerPool().getTransfomer();
> try{
> transformerImpl.setURIResolver(...);
>
> /*
> Get the DTM structure from our dtmCache, if not in cache create it and
> put it in cache
> We have a DTM cache so that we don't create the DTM each time and we
> didn't want to use a DOM
> object because the xalan library transforms it internally to DTM. The
> dtmKey is the content
> of the XML document that we want to execute the XSL formula on.
> */
> DTM dtm=null;
> synchronized(dtmCache){
> dtm=(org.apache.xml.dtm.DTM)dtmCache.getDTM(dtmKey);
> if(dtm==null){
> /*
> We also have a DOMParser cache so that we don't create one each
> time.
> Here we're building the DTM for the first time and adding it to
> our DTM cache
> */
> DOMParser domParser=(DOMParser)domParserPool.getDomParser();
> try{
> domParser.setEntityResolver(...);
> InputSource inputSource=new InputSource(new StringReader(...));
> domParser.parse(inputSource);
> Node node=domParser.getDocument();
> DOMSource domSource=new DOMSource(node);
> dtm=transformerImpl.getXPathContext().getDTM(domSource, false,
> transformerImpl, true, true);
> dtmCache.addDTM(dtmKey, dtm);
> }finally{
> domParserPool.release(domParser);
> }
> }else{
> /*
> We found the DTM in our DTM cache, so we're setting it in the
> manager to be able to use that
> DTM for our execution
> */
>
> DTMManagerDefault
> dtmManagerDefault=(DTMManagerDefault)transformerImpl.getXPathContext().getDTMManager();
> dtmManagerDefault.addDTM(dtm,
> dtmManagerDefault.getFirstFreeDTMID());
> }
> }
> transformerImpl.setQuietConflictWarnings(true);
> /*
> We set the parameters for xsl:param
> */
> transformerImpl.setParameter(strParameterKey, strParameterValue);
> /*
> We execute the XSL stylesheet using the DTM from our DTM cache
> */
> transformerImpl.transformNode(dtm.getDocument(), new
> SAXResult(xslQueryHandler));
> }finally{
> /* We reset the objects for next execution*/
> transformerImpl.clearParameters();
> transformerImpl.reset();
> templates.getTransformerPool().release(transformerImpl);
> }
> Using this code, we faced a problem where two same XMLs executed a foreach
> xsl command
> at the same time on the same DTM and we had the xalan library hanging (kill
> -QUIT
> on the java process) in:
> at
> org.apache.xml.dtm.ref.DTMDefaultBaseTraversers$IndexedDTMAxisTraverser.getNextIndexed(Unknown
> Source)
> at
> org.apache.xml.dtm.ref.DTMDefaultBaseTraversers$DescendantTraverser.first(Unknown
> Source)
> at org.apache.xpath.axes.DescendantIterator.nextNode(Unknown Source)
> at org.apache.xpath.axes.LocPathIterator.asNode(Unknown Source)
> at org.apache.xpath.axes.DescendantIterator.asNode(Unknown Source)
> at org.apache.xpath.axes.LocPathIterator.bool(Unknown Source)
> at org.apache.xpath.XPath.bool(Unknown Source)
> at org.apache.xalan.templates.ElemChoose.execute(Unknown Source)
> at
> org.apache.xalan.transformer.TransformerImpl.executeChildTemplates(Unknown
> Source)
> at org.apache.xalan.templates.ElemIf.execute(Unknown Source)
> at
> org.apache.xalan.templates.ElemForEach.transformSelectedNodes(Unknown Source)
> at org.apache.xalan.templates.ElemForEach.execute(Unknown Source)
> So we guessed that the DTM cannot be shared by two threads, and we're
> thinking of adding
> a synchronized(dtm) just before doing the transformNode. Is this safe?
> - Can we also use this code to sequentially execute different XSL stylesheets
> on the same DTM?
> - Is there another safe way of using XML documents caching, DomParser
> pooling, etc ...?
> Thank you.
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