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https://issues.apache.org/jira/browse/SOLR-17297?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17848000#comment-17848000
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David Smiley commented on SOLR-17297:
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I believe it's only one classloader across modules & shardLib. On the other
hand, "packages" are isolated.
If one day modules get classloader isolation, then I think we would have to
invoke the Lucene SPI stuff for each separate classloader.
> Classloading issue with plugin and modules
> ------------------------------------------
>
> Key: SOLR-17297
> URL: https://issues.apache.org/jira/browse/SOLR-17297
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Components: SolrCloud
> Affects Versions: 9.3
> Reporter: Patson Luk
> Priority: Critical
>
> h2. Summary
> Using plugin jar and enabling any modules could trigger
> {{java.lang.ClassNotFoundException}}
> h2. Description
> 1. An implementation of {{org.apache.lucene.codecs.PostingsFormat}} with the
> jar within the <solr install dir>/lib
> 2. Enable modules in solr.xml for example <str
> name="modules">opentelemetry</str>
> 3. Now on startup. As a part of {{NodeConfig#setupSharedLib}}, it would load
> all the SPIs, it locates our jar and loads the class with a
> {{FactoryURLClassLoader}} with the classpaths point at the jar of the lib,
> which is correct
> 4. After {{NodeConfig#setupSharedLib}}, {{NodeConfig#initModules}} is
> invoked, which eventually calls {{SolrResourceLoader#addURLsToClassLoader}}
> that closes the previous class loader, which is the one used in 3.
> 5. Now a core is loaded with that codec, it runs the <init> code which
> references other classes within our plugin jar, but unfortunately it would
> use the Classloader that loads our class in step 3., and such loader is
> marked as "closed" hence no longer load the correct resource/class. This
> triggers ClassNotFoundException.
> I have tried several things, the only thing that seems to work so far is
> commenting out {{IOUtils.closeWhileHandlingException(oldLoader);}} in
> {{SolrResourceLoader#addURLsToClassLoader}}, which is likely not the right
> workaround as the {{closeWhileHandlingException}} should be there for a
> reason ;)
> Switching {{setupSharedLib}} and {{initModules}} might work too (haven't
> tested), but I don't want to try any weird changes since I don't really know
> the ordering significance.
> Would appreciate some helps from the Solr experts! :)
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