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https://issues.apache.org/jira/browse/LUCENE-3588?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Uwe Schindler updated LUCENE-3588:
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Attachment: LUCENE-3588-simpler.patch
Here a much simplier patch than the one yesterday (including Robert's test):
The added complexity by ConcurrentHashMap with WeakReference and ReferenceQueue
is nonsense, as CHM is optimized for many clients getting entries from the map.
In our use-case the only one who gets entries from the map is our close()
method. When cloning, we only call put() so its always synchronized by CHM and
no difference to a standard synchronized WhateverMap.
This patch uses the simple apprach: Use a native WeakHashMap where we have a
synchronization on the put()/close() cleanups. This removes all Reference
handling and simplifies code a lot.
I think this is ready to commit.
> Try harder to prevent SIGSEGV on cloned MMapIndexInputs
> -------------------------------------------------------
>
> Key: LUCENE-3588
> URL: https://issues.apache.org/jira/browse/LUCENE-3588
> Project: Lucene - Java
> Issue Type: Improvement
> Components: core/store
> Affects Versions: 3.4, 3.5
> Reporter: Uwe Schindler
> Assignee: Uwe Schindler
> Fix For: 3.6, 4.0
>
> Attachments: LUCENE-3588-simpler.patch, LUCENE-3588.patch,
> LUCENE-3588.patch
>
>
> We are unmapping mmapped byte buffers which is disallowed by the JDK, because
> it has the risk of SIGSEGV when you access the mapped byte buffer after
> unmapping.
> We currently prevent this for the main IndexInput by setting its buffer to
> null, so we NPE if somebody tries to access the underlying buffer. I recently
> fixed also the stupid curBuf (LUCENE-3200) by setting to null.
> The big problem are cloned IndexInputs which are generally not closed. Those
> still contain references to the unmapped ByteBuffer, which lead to SIGSEGV
> easily. The patch from Mike in LUCENE-3439 prevents most of this in Lucene
> 3.5, but its still not 100% safe (as it uses non-volatiles).
> This patch will fix the remaining issues by also setting the buffers of
> clones to null when the original is closed. The trick is to record weak
> references of all clones created and close them together with the original.
> This uses a ConcurrentHashMap<WeakReference<MMapIndexInput>,?> as store with
> the logic borrowed from WeakHashMap to cleanup the GCed references (using
> ReferenceQueue).
> If we respin 3.5, we should maybe also get this in.
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