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https://issues.apache.org/jira/browse/LUCENE-4713?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13599891#comment-13599891
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Uwe Schindler edited comment on LUCENE-4713 at 3/12/13 10:22 AM:
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Hi Christian,
another patch, with some optimization. The clazz's classloader is only scanned,
if its not a parent or the same. If the Lucene's clazz' classloader is a parent
of the context one, it does not need to scan it.
This also works around the problems with "hiding" classes. To override the
Lucene core codecs, e.g. Tomcat's classloader (J2EE) will use parent-last
semantics, and in that case the precedence goes to the webapp.
Only if the lucene classloader is not at all related to the context one, it is
scanned.
Can you try this, too? Unfortunately its hard to write a good testcase without
some fake classes in separate compilation units which complicates the Lucene
build :-)
was (Author: thetaphi):
Hi Christian,
another patch, with some optimization. The clazz's classloader is only scanned,
if its not a parent or the same. If the Lucene's clazz' classloader is a parent
of the context one, it does not need to scan it.
This also works around the problems with "hiding" classes. To override the
Lucene core codecs, e.g. Tomcat's classloader (J2EE) will use parent-last
semantics, and in that case the precedence goes to the webapp.
Only if the lucene classloader is not at all related to the context one, it is
scanned.
> SPI: Allow fallback to default ClassLoader if Thread#getContextClassLoader
> fails
> --------------------------------------------------------------------------------
>
> Key: LUCENE-4713
> URL: https://issues.apache.org/jira/browse/LUCENE-4713
> Project: Lucene - Core
> Issue Type: Improvement
> Affects Versions: 4.0, 4.1, 4.2
> Reporter: Christian Kohlschütter
> Priority: Minor
> Labels: ClassLoader, Thread
> Fix For: 4.3
>
> Attachments: LUCENE-4713.patch, LUCENE-4713.patch, LUCENE-4713.patch,
> LuceneContextClassLoader.patch
>
>
> NOTE: This issue has been renamed from:
> "Replace calls to Thread#getContextClassLoader with the ClassLoader of the
> current class"
> because the revised patch provides a clean fallback path.
> I am not sure whether it is a design decision or if we can indeed consider
> this a bug:
> In core and analysis-common some classes provide on-demand class loading
> using SPI. In NamedSPILoader, SPIClassIterator, ClasspathResourceLoader and
> AnalysisSPILoader there are constructors that use the Thread's context
> ClassLoader by default whenever no particular other ClassLoader was specified.
> Unfortunately this does not work as expected when the Thread's ClassLoader
> can't see the required classes that are instantiated downstream with the help
> of Class.forName (e.g., Codecs, Analyzers, etc.).
> That's what happened to us here. We currently experiment with running Lucene
> 2.9 and 4.x in one JVM, both being separated by custom ClassLoaders, each
> seeing only the corresponding Lucene version and the upstream classpath.
> While NamedSPILoader and company get successfully loaded by our custom
> ClassLoader, their instantiation fails because our Thread's
> Context-ClassLoader cannot find the additionally required classes.
> We could probably work-around this by using Thread#setContextClassLoader at
> construction time (and quickly reverting back afterwards), but I have the
> impression this might just hide the actual problem and cause further trouble
> when lazy-loading classes later on, and potentially from another Thread.
> Removing the call to Thread#getContextClassLoader would also align with the
> behavior of AttributeSource.DEFAULT_ATTRIBUTE_FACTORY, which in fact uses
> Attribute#getClass().getClassLoader() instead.
> A simple patch is attached. All tests pass.
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