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https://issues.apache.org/jira/browse/DERBY-3909?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12638774#action_12638774
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Knut Anders Hatlen commented on DERBY-3909:
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The problem could be solved by obtaining the synchronization lock earlier and
releasing it later, or by checking for object identity instead of the ignoreMe_
flag when removing an object. I would prefer checking the object identity, as I
think the code will be clearer that way. We could then also remove the
ignoreMe_ field from the class.
> Race condition in NetXAResource.removeXaresFromSameRMchain()
> ------------------------------------------------------------
>
> Key: DERBY-3909
> URL: https://issues.apache.org/jira/browse/DERBY-3909
> Project: Derby
> Issue Type: Bug
> Components: Network Client
> Affects Versions: 10.5.0.0
> Reporter: Knut Anders Hatlen
> Assignee: Knut Anders Hatlen
>
> NetXAResource.removeXaresFromSameRMchain() does the following to remove a
> NetXAResource from what's logically a singly-linked list:
> 1) Mark the NetXAResource to remove with a flag (a field called ignoreMe_)
> 2) Synchronize on an object that protects the linked list
> 3) Follow the chain of next pointers in the linked list and remove the first
> flagged object
> 4) Release synchronization lock obtained in (2)
> 5) Clear the flag set in (1)
> Now, say that two threads (T1 and T2) perform step 1 in parallel. T1 is
> granted the synchronization lock in (2), and T2 must wait. T1 traverses the
> linked list, finds the object flagged by T2 and removes it. Further T1
> releases the synchronization lock and clears the flag on the object it had
> flagged. This is not the same object that it removed, so when T2 is granted
> the synchronization lock, there is no object flagged for removal. As a
> result, only the object T2 attempted to remove was in fact removed. The
> object that T1 flagged for removal is still in the linked list.
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