Mulgara

We have a shutdown handler on the client that closes open sessions;
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however, this shutdown handler is run is separate thread of its own.
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So an abort of the client while it's doing a db operation can generate
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the following sequence of events which leads to a deadlock:
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{noformat}
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&nbsp;&nbsp;Thread-1                Thread-2
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&nbsp;&nbsp;set autocommit off
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&nbsp;&nbsp;...
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&nbsp;&nbsp;insert ...              close()
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{noformat}
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(i.e. the insert and the close happen almost simultaneously). The
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resulting stack traces are roughly:
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{noformat}
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&nbsp;&nbsp;Thread-1:
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&nbsp;&nbsp;DatabaseSession.insert()
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&nbsp;&nbsp;&nbsp;&nbsp;DatabaseSession.execute()
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;MulgaraTransaxction.execute()
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;MulgaraTransaction.deactivate()                  &lt;---- monitor held
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;MulgaraTransaction.commitTransation()
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;MulgaraTransactionManager.transacactionComplete()
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;MulgaraTransactionManager.acquireMutex()   &lt;--- blocked
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&nbsp;&nbsp;Thread-2:
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&nbsp;&nbsp;DatabaseSession.close()
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&nbsp;&nbsp;&nbsp;&nbsp;MulgaraTransactionManager.rollbackCurrentTransactions()
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;MulgaraTransactionManager.acquireMutex()           &lt;--- mutex held
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;MulgaraTransaction.execute()
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;MulgaraTransaction.activate()                    &lt;--- blocked
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{noformat}
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