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https://issues.apache.org/jira/browse/LUCENE-10158?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17426191#comment-17426191
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Uwe Schindler commented on LUCENE-10158:
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For discussion about this interface see:
https://github.com/apache/lucene/pull/173#pullrequestreview-677347736
> Add a new interface Unwrappable to the utils package to ease migration to new
> MMAPDirectory and its testing
> -----------------------------------------------------------------------------------------------------------
>
> Key: LUCENE-10158
> URL: https://issues.apache.org/jira/browse/LUCENE-10158
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/other, general/test
> Affects Versions: main (9.0)
> Reporter: Uwe Schindler
> Assignee: Uwe Schindler
> Priority: Major
> Fix For: main (9.0)
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> While creating the new MMapDirectory using Project Panama in the recent
> OpenJDK versions (not yet released, incubation only), I stumbled on our
> testing framework, which wraps many objects with AssertingXY. The problem
> with that is, mmap in project panama only works when the java.nio.files.Path
> is owned by the default file system provider. During testing we wrap it often
> with custom implementations emulating Windows or track open file handles.
> If you pass such a wrapped Path to the NIO2 Panama APIs, it will fail with
> exception, because it can't refer to file channel internal methods from it.
> In the final version of Panama this may go away and we can provide our own
> wrapper for memory mapping, but this is problematic with current testing.
> My plan is to release versions of MMapDirectory version 2 with different
> implementations of the Panama APIs for easy pluggin into Lucene, Solr,
> Elasticsearch by just adding a JAR file that fits your JDK version. To run
> tests, unfortunately the MMapDir impl must "unrwap" the Path wrappers added
> by the test system.
> To help with that and to make it more general, in my pull requests (e.g.
> https://github.com/apache/lucene/pull/177), I added a new interface
> {{org.apache.lucene.util.Unwrappable}} that allows to unwrap external code to
> get the "original" Path implementation. The same interface could be applied
> to many other Lucene/Test classes that needs unwrapping sometimes (e.g.
> around Directory or Queries), but for now it is only implemented for Test's
> FilterPath. The interface is part of Lucene core and just used by the test to
> supply unwrapping.
> MMapDirectory version 2 uses it to get the original Path to be passed to
> MemorySegment.mapFile().
> I'd like to get this into Lucene 9.0. It does not hurt, it is just an
> interface, which is implemented by test classes, ready for extension to other
> classes. It also provides the unwrapper method, which is generic.
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