Race condition in NetXAResource.removeXaresFromSameRMchain()
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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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