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From "Uwe Schindler (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-6989) Implement MMapDirectory unmapping for coming Java 9 changes
Date Fri, 09 Dec 2016 22:46:58 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-6989?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15736570#comment-15736570
] 

Uwe Schindler commented on LUCENE-6989:
---------------------------------------

I opened thread: http://mail.openjdk.java.net/pipermail/jigsaw-dev/2016-December/010454.html

> Implement MMapDirectory unmapping for coming Java 9 changes
> -----------------------------------------------------------
>
>                 Key: LUCENE-6989
>                 URL: https://issues.apache.org/jira/browse/LUCENE-6989
>             Project: Lucene - Core
>          Issue Type: Task
>          Components: core/store
>            Reporter: Uwe Schindler
>            Assignee: Uwe Schindler
>              Labels: Java9
>             Fix For: 6.0
>
>         Attachments: LUCENE-6989-disable5x.patch, LUCENE-6989-disable5x.patch, LUCENE-6989-fixbuild148.patch,
LUCENE-6989-v2.patch, LUCENE-6989.patch, LUCENE-6989.patch, LUCENE-6989.patch, LUCENE-6989.patch
>
>
> Originally, the sun.misc.Cleaner interface was declared as "critical API" in [JEP 260|http://openjdk.java.net/jeps/260
]
> Unfortunately the decission was changed in favor of a oficially supported {{java.lang.ref.Cleaner}}
API. A side effect of this change is to move all existing {{sun.misc.Cleaner}} APIs into a
non-exported package. This causes our forceful unmapping to no longer work, because we can
get the cleaner instance via reflection, but trying to invoke it will throw one of the new
Jigsaw RuntimeException because it is completely inaccessible. This will make our forceful
unmapping fail. There are also no changes in Garbage collector, the problem still exists.
> For more information see this [mailing list thread|http://mail.openjdk.java.net/pipermail/core-libs-dev/2016-January/thread.html#38243].
> This commit will likely be done, making our unmapping efforts no longer working. Alan
Bateman is aware of this issue and will open a new issue at OpenJDK to allow forceful unmapping
without using the now private sun.misc.Cleaner. The idea is to let the internal class sun.misc.Cleaner
implement the Runable interface, so we can simply cast to runable and call the run() method
to unmap. The code would then work. This will lead to minor changes in our unmapper in MMapDirectory:
An instanceof check and casting if possible.
> I opened this issue to keep track and implement the changes as soon as possible, so people
will have working unmapping when java 9 comes out. Current Lucene versions will no longer
work with Java 9.



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