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https://issues.apache.org/jira/browse/LUCENE-4259?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Uwe Schindler resolved LUCENE-4259.
-----------------------------------
Resolution: Fixed
Committed trunk revision: 1366115
Committed 4.x revision: 1366116
> Allow reloading of codec/postings format list when classpath changes
> --------------------------------------------------------------------
>
> Key: LUCENE-4259
> URL: https://issues.apache.org/jira/browse/LUCENE-4259
> Project: Lucene - Core
> Issue Type: Improvement
> Affects Versions: 4.0-ALPHA
> Reporter: Uwe Schindler
> Assignee: Uwe Schindler
> Fix For: 4.0, 5.0
>
> Attachments: LUCENE-4259.patch, LUCENE-4259.patch, LUCENE-4259.patch,
> LUCENE-4259.patch
>
>
> While implementing the SPI for analysis factories, Robert and me found out
> that Solr does not see codecs/postingsformats or analysis factories outside
> it's webapp/lib folder. The reason is simple: SPI uses by default the context
> classloader of the thread calling the codec API for the first time (which is
> Jetty's webapp classpath).
> We solved the problem for analysis factories, because those are loaded with
> the help of SolrResourceLoader, which exports the ClassLoader it uses, so it
> can return all analysis compoenst visible to the ResourceLoader. This is
> cool, because you can drop the analysis/smartchinese or analysis/icu module
> JAR into your plugin folder and Solr will automatically use it.
> For Codecs and PostingsFormats this is a little bit more complicated: The
> list of codecs is loaded on clinit of Codecs.class or PostingsFormat.class,
> which can be very early in Solr's startup. When Solr changes his classpath in
> ResourceLoader, the new Codecs are never seen, so you cannot drop new codecs
> into the plugin folder. Similar problems may happen with other webapps,
> because Tomcat & Jetty have crazy classloader delegations (there were
> although reports that Lucene did not find their codecs at all - Simon
> Willnauer told me!)
> This patch will change NamedSPILoader to provide similar support like
> java.util.ServiceLoader does in JDK: You can tell NamedSPILoader to reload
> (means again list the classpath's JAR files and look for new
> META-INF/services files). This API is statically exported to
> Codec.reloadCodecs() and PostingsFormat.reploadPostingsFormats(), which takes
> a ClassLoader. This Classloader will then be checked only for *new* codecs,
> old ones or those already visible are not removed/replaced.
> SolrResourceLoader can then call this static method on each change of its
> classloader on startup.
> The implementation presented here is threadsafe, the SPI map is updated in a
> copy-on-write way and assigned to a volatile field.
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