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https://issues.apache.org/jira/browse/LUCENE-6989?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15750785#comment-15750785
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Dawid Weiss commented on LUCENE-6989:
-------------------------------------

bq. There are still a few special cases (like retrieving sun.misc.Unsafe, but 
thats unsupported API anyways). This is a separate issue and requires, that 
RAMUsageEstimator in Lucene's tests and RandomizedRunner needs to be disabled.

Hmm... There are no Unsafe references in RR, are there? As for setAccessible, 
they could be present in certain rules but should be guarded with try-catch 
blocks. Let me know what's not working, I'll fix.

> 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, 6.4
>
>         Attachments: LUCENE-6989-disable5x.patch, 
> LUCENE-6989-disable5x.patch, LUCENE-6989-fixbuild148.patch, 
> LUCENE-6989-v2.patch, LUCENE-6989-v3-post-b148.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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