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https://issues.apache.org/jira/browse/OAK-3234?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15163065#comment-15163065
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Alex Parvulescu commented on OAK-3234:
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FWIW we don't usually apply backported patches on branches, we do {{svn merge}}
on the trunk commits so the svn history is clearer.
> LIRS cache: possible deadlock while loading an entry
> ----------------------------------------------------
>
> Key: OAK-3234
> URL: https://issues.apache.org/jira/browse/OAK-3234
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: core
> Reporter: Thomas Mueller
> Assignee: Thomas Mueller
> Labels: candidate_oak_1_0, candidate_oak_1_2
> Fix For: 1.3.4
>
> Attachments: OAK-3234-backported.patch
>
>
> If multiple threads concurrently load entries while they are already loading
> entries (using a cache loader or callable), then it is possible to get into a
> deadlock. For example:
> * Thread 1 loads entry A, so it is calling the loader...
> * Thread 2 loads entry B, so it is calling the loader...
> * Thread 1 (within the loader) tries to load entry B, so it waits for thread
> 2...
> * Thread 2 (within the loader) tries to load entry A, so it waits for thread
> 1...
> One solution is to detect the case that the current thread is already loading
> an entry, and then instead of waiting for the other thread, it can also load
> the entry. A small optimization for that is to only load the entry (not
> waiting for the other thread) if the hash code of the key is smaller or equal
> the entry that this thread is loading. So that there is a clear order.
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