[NIFI-1333] FlowController fails to shut down gracefully even though there is nothing going on in the flow

• Type: Bug
• Status: Resolved
• Priority: Trivial
• Resolution: Fixed
• Affects Version/s: 0.4.1
• Fix Version/s: 0.5.0
• Component/s: Core Framework
• Assignee: Oleg Zhurakousky
• Reporter: Oleg Zhurakousky
• Created: 23/Dec/15 20:33
• Updated: 28/Jan/16 13:34
• Resolved: 28/Jan/16 13:34

Description

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 . . .

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.

What actually happens is deadlock during the shutdown.
Below are the relevant jstack:

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)

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