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https://issues.apache.org/jira/browse/SOLR-5526?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13837937#comment-13837937
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Hoss Man commented on SOLR-5526:
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Ouch!
Nikolay: Nice diagnoses! thanks for digging into this.
Maybe i'm missing something, but isn't the root level bug really that the
standard parsers should all be declaring the static NAME as final? ... even
with your proposed change, it seems dangerous to me that those NAME variables
are mutable.
If we fix them all to be "final" then the problem goes away w/o needing the
rest of your patch, correct?
We should also be able to whip up a simple test using reflection to fail the
build if anyone ever adds a class to QParserPlugin.standardPlugins w/o static
final NAME.
You mentioned discovering this problem because you have custom query parsers
extending some standard one where NAME isn't final --
Is there an aspect of this bug that you're seeing with your custom parser that
wouldn't be fixed with the solution i'm suggesting?
> Query parser extends standard cause NPE on Solr startup
> -------------------------------------------------------
>
> Key: SOLR-5526
> URL: https://issues.apache.org/jira/browse/SOLR-5526
> Project: Solr
> Issue Type: Bug
> Components: query parsers
> Affects Versions: 4.5.1, 4.6, 5.0
> Environment: Linux, Java 1.7.0_45
> Reporter: Nikolay Khitrin
> Priority: Blocker
> Attachments: SOLR-5526.patch
>
>
> Adding any custom query parser extending standard one with non-final field
> {{NAME}} lead to messy {{NullPointerException}} during Solr startup.
> Definition of standard parsers is located in
> {{QParserPlugin.standardPlugins}} static array. The array contains names from
> static {{NAME}} fields and classes for each plugin.
> But all of listed parsers are derived from {{QParserPlugin}}, so we have
> circular dependency of static fields.
> Normally, class loader start initializing {{QParserPlugin}} before all listed
> plugins in {{SolrCore.initQParsers}}, and array elements referenced to
> {{NAME}} plugins' fields are filled properly.
> Custom parsers are instantiated before standard parsers. And when we subclass
> plugin with non-final {{NAME}} field and add it to Solr via
> {{solrconfig.xml}}, class loader start loading our class before
> {{QParserPlugin}}. Because {{QParserPlugin}} is a superclass for plugin, it
> must be initialized before subclasses, and static dereferencing cause null
> elements in {{standardPlugins}} array because it filled before {{NAME}} field
> of loading plugin's superclass.
> How to reproduce:
> # Checkout Solr (trunk or stable)
> # Add the following line to solr/example/solr/collection1/conf/solrconfig.xml
> {{<queryParser name="fail" class="solr.search.LuceneQParserPlugin"/>}}
> # Call ant run-example in solr folder
> Possible workarounds:
> * dev-workaround: add {{int workaround =
> QParserPlugin.standardPlugins.length;}} as a first line to
> {{SolrCore.initQParsers}}
> * user-workaround: add plugin with final {{NAME}} field (edismax) to
> solrconfig.xml before subclasses of standard plugins.
> {{<queryParser name="workaround"
> class="solr.search.ExtendedDismaxQParserPlugin"/>}}
>
> Possible fix:
> Move {{standardPlugins}} to new final class to break circular dependency.
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