Small window in wakeup logic for PooledTaskRunner - task can get executed in
parallell
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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
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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