[jira] Closed: (AMQ-1686) Small window in wakeup logic for PooledTaskRunner - task can get executed in parallell

["Gary Tully (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/activemq/browse/AMQ-1686?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Gary Tully closed AMQ-1686.
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> Small window in wakeup logic for PooledTaskRunner - task can get executed in parallell
> --------------------------------------------------------------------------------------
>
>                 Key: AMQ-1686
>                 URL: https://issues.apache.org/activemq/browse/AMQ-1686
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Broker
>    Affects Versions: 5.0.0
>         Environment: windows XP
>            Reporter: Gary Tully
>            Assignee: Hiram Chirino
>             Fix For: 5.1.0
>
>         Attachments: AMQ-1689.patch
>
>
> org.apache.activemq.broker.region.cursors.CursorDurableTest fails on windows sometimes with the error:
> Exception in thread "Persistence Adaptor Task" java.lang.NullPointerException
>         at org.apache.activemq.store.amq.AMQMessageStore$4.execute(AMQMessageStore.java:381)
>         at org.apache.activemq.util.TransactionTemplate.run(TransactionTemplate.java:44)
>         at org.apache.activemq.store.amq.AMQMessageStore.doAsyncWrite(AMQMessageStore.java:374)
>         at org.apache.activemq.store.amq.AMQMessageStore.asyncWrite(AMQMessageStore.java:341)
>         at org.apache.activemq.store.amq.AMQMessageStore$1.iterate(AMQMessageStore.java:95)
>         at org.apache.activemq.thread.PooledTaskRunner.runTask(PooledTaskRunner.java:122)
>         at org.apache.activemq.thread.PooledTaskRunner$1.run(PooledTaskRunner.java:43)
>         at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650)
>         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675)
>         at java.lang.Thread.run(Thread.java:595)
> Tests run: 1, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 303.672 sec <<< FAILURE!
> The problem appears to be in the interaction between wakup and runTask in PooledTaskRunner
> iterating is set to false in a finally  and queued is checked in a separate sync block.
> if wakeup is called in this window, it can set queued and find iterating false so it will execute, and runTask will find queued true and it too will execute.
> the fix is to include the queued check in the finally block so that iterating and queued are checked at the same time. I will attach a patch with this fix.
> I attempted to reproduce this problem with a unit test but I did not have any real success. the window is quite small. I will include the unit test in case it can be improved upon.
> chirino merged a fix yesterday that addresses the symptom of this issue in a different way,
> http://svn.apache.org/viewvc?view=rev&revision=650956
> The added synchronisation means that parallel calls by the PooledTaskRunner.asyncWrite are serialised on the method access.
> This fix addresses the route cause and can negate the need for the synchronisation.
> fyi: In the test, the paralell calls can come from flush() and from the asyncWrite task.

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