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https://issues.apache.org/jira/browse/LUCENE-2779?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12964570#action_12964570
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Shai Erera commented on LUCENE-2779:
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I checked CHM iterators and they are safe w.r.t the map being modified after
the iterator was obtained. It's easily testable: I added 3 items to CHM and
called keySet.iterator(). I then called next() once, removed an item, called
next() again and added an item. The changes were no visible to the iterator and
it returned 3 items only (those that I added first). So I think we're safe on
that.
About remove I'll have to look in the code (not near the comp now) - but I had
a feeling that it is safe too, b/c the file is first removed, which is a
blocking 'write' operation and only if it isn't null then the AtomicLong is
updated. But I'll Check the code again, and maybe even add a concurrent test
case.
Thanks for the review. If in the end this change will smell bad, I'll close the
issue - introducing concurrency bugs is the last thing we need :).
> Use ConcurrentHashMap in RAMDirectory
> -------------------------------------
>
> Key: LUCENE-2779
> URL: https://issues.apache.org/jira/browse/LUCENE-2779
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Store
> Reporter: Shai Erera
> Assignee: Shai Erera
> Priority: Minor
> Fix For: 3.1, 4.0
>
> Attachments: LUCENE-2779.patch
>
>
> RAMDirectory synchronizes on its instance in many places to protect access to
> map of RAMFiles, in addition to updating the sizeInBytes member. In many
> places the sync is done for 'read' purposes, while only in few places we need
> 'write' access. This looks like a perfect use case for ConcurrentHashMap
> Also, syncing around sizeInBytes is unnecessary IMO, since it's an AtomicLong
> ...
> I'll post a patch shortly.
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