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From "Matt Benson (JIRA)" <>
Subject [jira] Resolved: (JXPATH-76) CompiledExpression not completely thread-safe
Date Wed, 31 Jan 2007 16:28:05 GMT


Matt Benson resolved JXPATH-76.

       Resolution: Fixed
    Fix Version/s: 1.3

It takes less analysis on my part (as a self-appointed, but non-expert, custodian of JXPath)
to simply synchronize these methods, which I have done in SVN HEAD.  Thanks for the report!

> CompiledExpression not completely thread-safe
> ---------------------------------------------
>                 Key: JXPATH-76
>                 URL:
>             Project: Commons JXPath
>          Issue Type: Bug
>    Affects Versions: 1.2 Final
>            Reporter: Simon Raess
>             Fix For: 1.3
>         Attachments: jxpath.patch
> Some classes in compiled expressions are not thread-safe, because they lazily initialize
some information that should be initialized at object construction. The classes I've found
are Path and ExpressionPath. I've attached a path that fixes the problem. 
> When two threads tried to initialize such an object concurrently, it was possible that
the expression was evaluated as simple expression when it should have been evaluated as complex
expression. See the two stack traces below (using xpath expression //ExternalData/Order/@id).
The first stack trace shows the bug in action, the second how it should look:
> caused by java.lang.UnsupportedOperationException: Not supported node test for attributes:
> 	at org.apache.commons.jxpath.ri.axes.SimplePathInterpreter.getNodeIterator(
> 	at org.apache.commons.jxpath.ri.axes.SimplePathInterpreter.doStepNoPredicatesStandard(
> 	at org.apache.commons.jxpath.ri.axes.SimplePathInterpreter.doStep(
> 	at org.apache.commons.jxpath.ri.axes.SimplePathInterpreter.interpretSimpleLocationPath(
Compiled Code))
> 	at org.apache.commons.jxpath.ri.compiler.Path.getSingleNodePointerForSteps(
Compiled Code))
> 	at org.apache.commons.jxpath.ri.compiler.LocationPath.computeValue(
> 	at org.apache.commons.jxpath.ri.JXPathContextReferenceImpl.getPointer(
> 	at org.apache.commons.jxpath.ri.JXPathCompiledExpression.selectSingleNode(
Compiled Code))
> This replaces the lines starting at Path.getSingleNodePointerForSteps:
>         LocationPath(Path).searchForPath(EvalContext) line: 183	
>         LocationPath(Path).getSingleNodePointerForSteps(EvalContext) line: 159	

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