[infinispan-issues] [JBoss JIRA] (ISPN-4497) Race condition in LocalLockMergingSegmentReadLocker results in file content being deleted

[Sanne Grinovero (JIRA)]

    [ https://issues.jboss.org/browse/ISPN-4497?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12984075#comment-12984075 ] 

Sanne Grinovero commented on ISPN-4497:
---------------------------------------

[~chp-anujs] thanks! your very detailed analysis is extremely helpful.

> Race condition in LocalLockMergingSegmentReadLocker results in file content being deleted
> -----------------------------------------------------------------------------------------
>
>                 Key: ISPN-4497
>                 URL: https://issues.jboss.org/browse/ISPN-4497
>             Project: Infinispan
>          Issue Type: Bug
>      Security Level: Public(Everyone can see) 
>          Components: Lucene Directory
>    Affects Versions: 5.2.6.Final
>            Reporter: Anuj Shah
>            Assignee: Sanne Grinovero
>
> There is a race condition in LocalLockMergingSegmentReadLocker which can lead to more calls delete on the underlying DistributedSegmentReadLocker which results in the file being removed from the caches. 
> This happens with three or more threads acquiring and releasing locks on the same file simultaneously:
> # Thread 1 (T1) acquires a lock and creates a {{LocalReadLock}}, call it L1 - the underlying lock is acquired
> # T2 starts to acquire and holds a reference to L1
> # T3 starts to acquire and holds a reference to L1
> # T1 releases - L1 at this stage only has value of 1 - so the underlying lock is released, and L1 is removed from the map
> # T2 continues - finds L1 with value 0 and acquires the underlying lock
> # T3 continues - increments L1 value to 2
> # T2 releases - creates a new {{LocalReadLock}}, L2 - this has zero value so the underlying lock is released, and L2 is removed from the map
> # T3 releases - creates a new {{LocalReadLock}}, L3 - this has zero value so the underlying lock is released, and L3 is removed from the map
> # The final step triggers a real file delete as underlying lock is released one too many times



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