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https://issues.apache.org/jira/browse/NIFI-1333?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15105971#comment-15105971
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Joseph Witt commented on NIFI-1333:
-----------------------------------
[~tkurc] [~markap14] [~ozhurakousky] How much additional time would it take to
get that JStack? I mean ultimately it doesn't seem to me to make much
difference whether we're super nice to the locking of the flow controller we're
about to kill anyway but it would be good to understand what condition could
hold the write lock and not release it in a timely fashion. But, we should
certainly understand that logic enough such that we know why a readLock is
insufficient.
> FlowController fails to shut down gracefully even though there is nothing
> going on in the flow
> ----------------------------------------------------------------------------------------------
>
> Key: NIFI-1333
> URL: https://issues.apache.org/jira/browse/NIFI-1333
> Project: Apache NiFi
> Issue Type: Bug
> Components: Core Framework
> Affects Versions: 0.4.1
> Reporter: Oleg Zhurakousky
> Assignee: Oleg Zhurakousky
> Priority: Trivial
> Fix For: 0.5.0
>
>
> Basically the following test fails:
> https://github.com/olegz/nifi/blob/int-test/nifi-integration-tests/src/test/java/org/apache/nifi/test/flowcontroll/FlowControllerTests.java#L50
> even though there is no compelling reason for it to fail based on what's in
> the flow.
> Also, the message in logs is confusing . . .
> {code}
> Initiated graceful shutdown of flow controller...waiting up to 10 seconds
> 2015-12-23 15:19:11,977 WARN [main] o.apache.nifi.controller.FlowController
> Controller hasn't terminated properly. There exists an uninterruptable
> thread that will take an indeterminate amount of time to stop. Might need to
> kill the program manually.
> {code}
> What actually happens is deadlock during the shutdown.
> Below are the relevant jstack:
> {code}
> java.lang.Thread.State: TIMED_WAITING (parking)
> at sun.misc.Unsafe.park(Native Method)
> - parking to wait for <0x00000007aeb20988> (a
> java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
> at
> java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:226)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2082)
> at
> java.util.concurrent.ThreadPoolExecutor.awaitTermination(ThreadPoolExecutor.java:1468)
> at
> org.apache.nifi.controller.FlowController.shutdown(FlowController.java:1124)
> at org.apache.nifi.test.s2s.SiteToSiteTests.bar(SiteToSiteTests.java:75)
> . . .
> "Framework Task Thread Thread-1" prio=5 tid=0x00007fc8a2064800 nid=0x6a03
> waiting on condition [0x0000700001ded000]
> java.lang.Thread.State: WAITING (parking)
> at sun.misc.Unsafe.park(Native Method)
> - parking to wait for <0x00000007aeb20288> (a
> java.util.concurrent.locks.ReentrantReadWriteLock$NonfairSync)
> at java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:834)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireShared(AbstractQueuedSynchronizer.java:964)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireShared(AbstractQueuedSynchronizer.java:1282)
> at
> java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock.lock(ReentrantReadWriteLock.java:731)
> at
> org.apache.nifi.controller.FlowController.getRootGroupId(FlowController.java:1262)
> at
> org.apache.nifi.controller.tasks.ExpireFlowFiles.run(ExpireFlowFiles.java:54)
> . . .
> "Timer-Driven Process Thread-1" prio=5 tid=0x00007fc8a3146800 nid=0x6c03
> waiting on condition [0x0000700001ef0000]
> java.lang.Thread.State: WAITING (parking)
> at sun.misc.Unsafe.park(Native Method)
> - parking to wait for <0x00000007aeb20288> (a
> java.util.concurrent.locks.ReentrantReadWriteLock$NonfairSync)
> at java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:834)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireShared(AbstractQueuedSynchronizer.java:964)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireShared(AbstractQueuedSynchronizer.java:1282)
> at
> java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock.lock(ReentrantReadWriteLock.java:731)
> at
> org.apache.nifi.controller.FlowController.isClustered(FlowController.java:2984)
> at
> org.apache.nifi.controller.FlowController.heartbeat(FlowController.java:3444)
> {code}
> The issue the way I see it is that FlowController's _shutdown_ routine is
> synchronized under the same lock as most of the FlowController callbacks made
> by other threads, hence those threads can't be shutdown since they are in
> dead-lock.
> I don't think there is any reason to synchronize the the shutdown routine
> since all we are trying to do is shut down the very same threads that are
> blocking. Removing synchronization resolves the issue.
> Will submit a patch in a few
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