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https://issues.apache.org/jira/browse/SOLR-409?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12541771
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Henri Biestro commented on SOLR-409:
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Sorry about the non-regular patch, my bad, I should've documented that.
I like the idea of being able to specify a default shared lib directory for all
cores in the multicore configuration.
I've thus modified Config.java to allow overriding how to solve the default
shared library (I'm producing the patch the same way as the first one, so to
apply it on a trunk, you may want to 'cd src/java/org/.apache/solr/core' first).
>From a solr-350 base, I've updated MultiCore to look for a 'libDir' attribute
>that serves as the default shared library.
To ease testing, I'm thus also uploading the solr-350 + solr-409 patch here.
> Allow configurable class loader sharing between cores
> -----------------------------------------------------
>
> Key: SOLR-409
> URL: https://issues.apache.org/jira/browse/SOLR-409
> Project: Solr
> Issue Type: Sub-task
> Affects Versions: 1.3
> Reporter: Henri Biestro
> Priority: Minor
> Fix For: 1.3
>
> Attachments: solr-409.patch
>
>
> WHAT:
> This patch allows to configure in the solrconfig.xml the library directory
> and associated class loader used to dynamically create instances.
> The solr config XML can now specify a libDir element (the same way the
> dataDir can be specified).
> That element can also specify through the 'shared' attribute whether the
> library is shared.
> By default, the shared attribute is true; if you specify a libDir, its class
> loader is made shareable.
> Syntax:
> <libDir shared='true*|false'>/path/to/shareable/dir</libDir>
> WHY:
> Current behavior allocates one class loader per config & thus per core.
> However, there are cases where one would like different cores to share some
> objects that are dynamically instantiated (ie, where the class name is used
> to find the class through the class loader and instantiate). In the current
> form; since each core possesses its own class loader, static members are
> indeed different objects. For instance, there is no way of implementing a
> singleton shared between 2 request handlers.
> Originally from
> http://www.nabble.com/Post-SOLR215-SOLR350-singleton-issue-tf4776980.html
> HOW:
> The libDir element is extracted from the XML configuration file and parsed in
> the Config constructor.
> A static map of weak reference to classloaders keyed by library path is used
> to keep track of already built shareable class loaders.
> The weak reference is here to allow class eviction by the GC, avoiding
> leakage that would result by keeping hard reference to class loaders.
> STATUS:
> initial code drop
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