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https://issues.apache.org/jira/browse/KAFKA-1008?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13740611#comment-13740611
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Jay Kreps commented on KAFKA-1008:
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But my understanding is that these copies are just copies of pointer object
(i.e. a position, limit, mark, etc) so if you unmap the underlying mmap while
reads are occurring something bad will happen.
Another way to say this is what happens in the following code execution:
MappedByteBuffer orig = // map file
MappedByteBuffer copy = orig.duplicate()
(orig.asInstanceOf[sun.nio.ch.DirectBuffer]).cleaner().clean()
copy.get()
My suspicion is that something terrible will happen, but I could be wrong.
> Unmap before resizing
> ---------------------
>
> Key: KAFKA-1008
> URL: https://issues.apache.org/jira/browse/KAFKA-1008
> Project: Kafka
> Issue Type: Bug
> Components: core, log
> Affects Versions: 0.8
> Environment: Windows, Linux, Mac OS
> Reporter: Elizabeth Wei
> Assignee: Jay Kreps
> Labels: patch
> Fix For: 0.8
>
> Attachments: unmap-v4.patch
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> While I was studying how MappedByteBuffer works, I saw a sharing runtime
> exception on Windows. I applied what I learned to generate a patch which uses
> an internal open JDK API to solve this problem.
> Following Jay's advice, I made a helper method called tryUnmap().
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