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https://issues.apache.org/jira/browse/JCR-2865?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12985597#action_12985597
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Jukka Zitting commented on JCR-2865:
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Here's the best quick solution I came up with: We'll copy the DefaultISMLocking
class into a VersioningLock class for use only by the version manager code.
This way we can keep the DefaultISMLocking class clean and focused to just one
use case, while still leveraging the code and your fix in the version manager.
Would you mind preparing a patch like that?
> a dead lock in DefaultISMLocking
> --------------------------------
>
> Key: JCR-2865
> URL: https://issues.apache.org/jira/browse/JCR-2865
> Project: Jackrabbit Content Repository
> Issue Type: Bug
> Components: jackrabbit-core
> Affects Versions: 2.2.0
> Environment: winXP/JDK1.6
> Reporter: codeparser
> Attachments: trackReader.diff
>
>
> The jackrabbit 2.2 's org.apache.jackrabbit.core.state.DefaultISMLocking has
> a defect which will cause a dead lock in concurrent use cases.
> The use case is as follows:
> 1. Thread A apply a read lock, now there is an active reader hold the read
> lock.
> 2. Thread B apply a write lock, and then thread B will wait for thread A's
> reading end. You could see below code snippet from the Jackrabbit source.
> readerCount is the current active reader.
> writersWaiting++;
> while (writerId != null? !isSameThreadId(writerId, currentId) : readerCount >
> 0) {
> wait();
> }
> 3. Thread A apply another read lock, then it will wait too, since there is
> a writer is waiting. Then a dead lock happens.
> while (writerId != null? (writerCount > 0 && !isSameThreadId(writerId,
> currentId)): writersWaiting > 0) {
> wait();
> }
> Since the lock in DefaultISMLocking is global lock, so I think if a thread
> has already hold a reader lock, it could get the reader lock again. I create
> a fix with this idea.
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