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From "Carsten Ziegeler" <>
Subject Strange problems with concurrent access of Xalan-2.0.0
Date Thu, 15 Feb 2001 15:47:32 GMT

since the switch from the Xalan2D07 to the Xalan-2.0.0 version in Cocoon2 we get sometimes
very strange problems.

We are using frames which all four use the same stylesheets. The xalan is driven by the cocoon

If we turn on the storing (formerly known as caching) of the TraxTransformer we get from time
to time a NPE in one frame. Sometimes its even worse: One frame contains part of the content
of another frame and the other frame is totally broken. Reloading the whole page brings up
all frames correctly.

However if we turn off the storing we never did see this phenomenen. So we assume that this
problems have something to do with the storing.

The store stores the Templates. Is it possible, that this problem can occure, when several
threads use the same Template (as delivered by the store). A thread might finish first, resetting
the template and the other thread still try to use it. 

This is only a guess - has someone else had these problems? 

As they only occur occasionally it his very hard to reproduce them...

Perhaps someone of you has a guess whats going on.

The exception we get is the following:

        at org.apache.xalan.templates.ElemCopy.execute(
        at org.apache.xalan.templates.ElemForEach.transformSelectedNodes(ElemFor
        at org.apache.xalan.templates.ElemApplyTemplates.execute(ElemApplyTempla
        at org.apache.xalan.transformer.TransformerImpl.executeChildTemplates(Tr
        at org.apache.xalan.transformer.TransformerImpl.executeChildTemplates(Tr
        at org.apache.xalan.transformer.TransformerImpl.applyTemplateToNode(Tran
        at org.apache.xalan.transformer.TransformerImpl.transformNode(Transforme

This indicates that the ResultTreeHandler is not available (set to null). 

As most times everything is working fine it must have to do with the parallel usage of the

Carsten Ziegeler

Open Source Group              sunShine - Lighting up e:Business
Carsten Ziegeler, S&N AG, Klingenderstrasse 5, D-33100 Paderborn                  

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