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Posted to dev@lucene.apache.org by "Uwe Schindler (JIRA)" <ji...@apache.org> on 2016/11/13 08:33:58 UTC
[jira] [Comment Edited] (LUCENE-6989) Implement MMapDirectory
unmapping for coming Java 9 changes
[ https://issues.apache.org/jira/browse/LUCENE-6989?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15661100#comment-15661100 ]
Uwe Schindler edited comment on LUCENE-6989 at 11/13/16 8:33 AM:
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The problem with backporting is usage of Java 8 APIs: To allow backporting to 5.5, we must change the unmapper bytecode, because {{Objects.nonNull(Object)}} does not exist in Java 7. We have to work around that with a hack (I had some in mind), I have to find the records.
UPDATE: The Java 7 workaround is a change to the nonNull check to use Objects.equals with bound {{code}} as 1st arg:
{code:java}
final MethodHandle nonNullTest = lookup.findStatic(Objects.class, "equals", methodType(boolean.class, Object.class, Object.class))
.bindTo(null)
.asType(methodType(boolean.class, cleanerClass));
{code}
I did not test / compile this code, was just hacked into this issue :-)
was (Author: thetaphi):
The problem with backporting is usage of Java 8 APIs: To allow backporting to 5.5, we must change the unmapper bytecode, because {{Objects.nonNull(Object)}} does not exist in Java 7. We have to work around that with a hack (I had some in mind), I have to find the records.
> 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-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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