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https://issues.apache.org/jira/browse/JXPATH-76?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12469179
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Simon Raess commented on JXPATH-76:
-----------------------------------
I've thought about that solution too, but the change without synchronized is
pretty straightforward. Instead of lazy initialization, the initialization is
simply moved to the constructor. There are no side-effects and the need of
synchronization is completely removed. The cost of synchronization has to be
paid for each expression evaluation. It is needed only on the first time. How
else can I convince you? ;-)
> CompiledExpression not completely thread-safe
> ---------------------------------------------
>
> Key: JXPATH-76
> URL: https://issues.apache.org/jira/browse/JXPATH-76
> 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: node()
> at
> org.apache.commons.jxpath.ri.axes.SimplePathInterpreter.getNodeIterator(SimplePathInterpreter.java(Compiled
> Code))
> at
> org.apache.commons.jxpath.ri.axes.SimplePathInterpreter.doStepNoPredicatesStandard(SimplePathInterpreter.java(Compiled
> Code))
> at
> org.apache.commons.jxpath.ri.axes.SimplePathInterpreter.doStep(SimplePathInterpreter.java(Compiled
> Code))
> at
> org.apache.commons.jxpath.ri.axes.SimplePathInterpreter.interpretSimpleLocationPath(SimplePathInterpreter.java(Inlined
> Compiled Code))
> at
> org.apache.commons.jxpath.ri.compiler.Path.getSingleNodePointerForSteps(Path.java(Inlined
> Compiled Code))
> at
> org.apache.commons.jxpath.ri.compiler.LocationPath.computeValue(LocationPath.java(Compiled
> Code))
> at
> org.apache.commons.jxpath.ri.JXPathContextReferenceImpl.getPointer(JXPathContextReferenceImpl.java(Compiled
> Code))
> at
> org.apache.commons.jxpath.ri.JXPathCompiledExpression.selectSingleNode(JXPathCompiledExpression.java(Inlined
> 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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