[ 
https://issues.apache.org/jira/browse/YARN-3878?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14611245#comment-14611245
 ] 

Varun Saxena commented on YARN-3878:
------------------------------------

The reason for this issue is as under :
* On call to {{GenericEventHandler#handle}} we make the flag drained as false 
even before putting the event in queue. If {{InterruptedException}} occurs, 
this flag is never reset.
{code}
public void handle(Event event) {
      if (blockNewEvents) {
        return;
      }
      drained = false;
     .......
      try {
        eventQueue.put(event);
      } catch (InterruptedException e) {
        if (!stopped) {
          LOG.warn("AsyncDispatcher thread interrupted", e);
        }
        throw new YarnRuntimeException(e);
      }
{code}

* In {{AsyncDispatcher#serviceStop}}, code is as under. As can be seen we wait 
for drained flag to become true
{code}
 protected void serviceStop() throws Exception {
    if (drainEventsOnStop) {
      blockNewEvents = true;
      LOG.info("AsyncDispatcher is draining to stop, igonring any new events.");
      synchronized (waitForDrained) {
        while (!drained && eventHandlingThread.isAlive()) {
          waitForDrained.wait(1000);
          LOG.info("Waiting for AsyncDispatcher to drain. Thread state is :" +
              eventHandlingThread.getState());
        }
      }
    }
{code}

* In event queue thread's run method though, we make a call to 
{{LinkedBlockingQueue#take}} which is a blocking call till it finds elements in 
the queue. So if queue is already empty and as nothing is posting elements to 
this queue, the drained flag would never become true. 
{code}
  Runnable createThread() {
    return new Runnable() {
      @Override
      public void run() {
        while (!stopped && !Thread.currentThread().isInterrupted()) {
          drained = eventQueue.isEmpty();
          ......
          try {
            event = eventQueue.take();
          } catch(InterruptedException ie) {
            ....
          }
          if (event != null) {
            dispatch(event);
          }
{code}

> AsyncDispatcher can hang while stopping if it is configured for draining 
> events on stop
> ---------------------------------------------------------------------------------------
>
>                 Key: YARN-3878
>                 URL: https://issues.apache.org/jira/browse/YARN-3878
>             Project: Hadoop YARN
>          Issue Type: Bug
>    Affects Versions: 2.7.0
>            Reporter: Varun Saxena
>            Assignee: Varun Saxena
>            Priority: Critical
>
> The sequence of events is as under :
> # RM is stopped while putting a RMStateStore Event to RMStateStore's 
> AsyncDispatcher. This leads to an Interrupted Exception being thrown.
> # As RM is being stopped, RMStateStore's AsyncDispatcher is also stopped. On 
> {{serviceStop}}, we will check if all events have been drained and wait for 
> event queue to drain(as RM State Store dispatcher is configured for queue to 
> drain on stop). 
> # This condition never becomes true and AsyncDispatcher keeps on waiting 
> incessantly for dispatcher event queue to drain till JVM exits.
> *Initial exception while posting RM State store event to queue*
> {noformat}
> 2015-06-27 20:08:35,922 DEBUG [main] service.AbstractService 
> (AbstractService.java:enterState(452)) - Service: Dispatcher entered state 
> STOPPED
> 2015-06-27 20:08:35,923 WARN  [AsyncDispatcher event handler] 
> event.AsyncDispatcher (AsyncDispatcher.java:handle(247)) - AsyncDispatcher 
> thread interrupted
> java.lang.InterruptedException
>       at 
> java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(AbstractQueuedSynchronizer.java:1219)
>       at 
> java.util.concurrent.locks.ReentrantLock.lockInterruptibly(ReentrantLock.java:340)
>       at 
> java.util.concurrent.LinkedBlockingQueue.put(LinkedBlockingQueue.java:338)
>       at 
> org.apache.hadoop.yarn.event.AsyncDispatcher$GenericEventHandler.handle(AsyncDispatcher.java:244)
>       at 
> org.apache.hadoop.yarn.server.resourcemanager.recovery.RMStateStore.updateApplicationAttemptState(RMStateStore.java:652)
>       at 
> org.apache.hadoop.yarn.server.resourcemanager.rmapp.attempt.RMAppAttemptImpl.rememberTargetTransitionsAndStoreState(RMAppAttemptImpl.java:1173)
>       at 
> org.apache.hadoop.yarn.server.resourcemanager.rmapp.attempt.RMAppAttemptImpl.access$3300(RMAppAttemptImpl.java:109)
>       at 
> org.apache.hadoop.yarn.server.resourcemanager.rmapp.attempt.RMAppAttemptImpl$ContainerFinishedTransition.transition(RMAppAttemptImpl.java:1650)
>       at 
> org.apache.hadoop.yarn.server.resourcemanager.rmapp.attempt.RMAppAttemptImpl$ContainerFinishedTransition.transition(RMAppAttemptImpl.java:1619)
>       at 
> org.apache.hadoop.yarn.state.StateMachineFactory$MultipleInternalArc.doTransition(StateMachineFactory.java:385)
>       at 
> org.apache.hadoop.yarn.state.StateMachineFactory.doTransition(StateMachineFactory.java:302)
>       at 
> org.apache.hadoop.yarn.state.StateMachineFactory.access$300(StateMachineFactory.java:46)
>       at 
> org.apache.hadoop.yarn.state.StateMachineFactory$InternalStateMachine.doTransition(StateMachineFactory.java:448)
>       at 
> org.apache.hadoop.yarn.server.resourcemanager.rmapp.attempt.RMAppAttemptImpl.handle(RMAppAttemptImpl.java:786)
>       at 
> org.apache.hadoop.yarn.server.resourcemanager.rmapp.attempt.RMAppAttemptImpl.handle(RMAppAttemptImpl.java:108)
>       at 
> org.apache.hadoop.yarn.server.resourcemanager.ResourceManager$ApplicationAttemptEventDispatcher.handle(ResourceManager.java:838)
> {noformat}
> *JStack of AsyncDispatcher hanging on stop*
> {noformat}
> "AsyncDispatcher event handler" prio=10 tid=0x00007fb980222800 nid=0x4b1e 
> waiting on condition [0x00007fb9654e9000]
>    java.lang.Thread.State: WAITING (parking)
>         at sun.misc.Unsafe.park(Native Method)
>         - parking to wait for  <0x0000000700b79250> (a 
> java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
>         at java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
>         at 
> java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2043)
>         at 
> java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
>         at 
> org.apache.hadoop.yarn.event.AsyncDispatcher$1.run(AsyncDispatcher.java:113)
>         at java.lang.Thread.run(Thread.java:744)
> "main" prio=10 tid=0x00007fb98000a800 nid=0x49c3 in Object.wait() 
> [0x00007fb989851000]
>    java.lang.Thread.State: TIMED_WAITING (on object monitor)
>       at java.lang.Object.wait(Native Method)
>       - waiting on <0x0000000700b79430> (a java.lang.Object)
>       at 
> org.apache.hadoop.yarn.event.AsyncDispatcher.serviceStop(AsyncDispatcher.java:156)
>       - locked <0x0000000700b79430> (a java.lang.Object)
>       at 
> org.apache.hadoop.service.AbstractService.stop(AbstractService.java:221)
>       - locked <0x0000000700b79420> (a java.lang.Object)
>       at 
> org.apache.hadoop.yarn.server.resourcemanager.recovery.RMStateStore.serviceStop(RMStateStore.java:515)
>       at 
> org.apache.hadoop.service.AbstractService.stop(AbstractService.java:221)
>       - locked <0x0000000700b79630> (a java.lang.Object)
>       at 
> org.apache.hadoop.service.AbstractService.close(AbstractService.java:250)
>       at 
> org.apache.hadoop.yarn.server.resourcemanager.ResourceManager$RMActiveServices.serviceStop(ResourceManager.java:599)
> {noformat}
> We keep on getting below logs
> {noformat}
> 2015-06-27 20:08:35,926 INFO  [main] event.AsyncDispatcher 
> (AsyncDispatcher.java:serviceStop(140)) - AsyncDispatcher is draining to 
> stop, igonring any new events.
> 2015-06-27 20:08:36,926 INFO  [main] event.AsyncDispatcher 
> (AsyncDispatcher.java:serviceStop(144)) - Waiting for AsyncDispatcher to 
> drain. Thread state is :WAITING
> 2015-06-27 20:08:37,927 INFO  [main] event.AsyncDispatcher 
> (AsyncDispatcher.java:serviceStop(144)) - Waiting for AsyncDispatcher to 
> drain. Thread state is :WAITING
> 2015-06-27 20:08:38,927 INFO  [main] event.AsyncDispatcher 
> (AsyncDispatcher.java:serviceStop(144)) - Waiting for AsyncDispatcher to 
> drain. Thread state is :WAITING
> 2015-06-27 20:08:39,928 INFO  [main] event.AsyncDispatcher 
> (AsyncDispatcher.java:serviceStop(144)) - Waiting for AsyncDispatcher to 
> drain. Thread state is :WAITING
> 2015-06-27 20:08:40,929 INFO  [main] event.AsyncDispatcher 
> (AsyncDispatcher.java:serviceStop(144)) - Waiting for AsyncDispatcher to 
> drain. Thread state is :WAITING
> 2015-06-27 20:08:41,929 INFO  [main] event.AsyncDispatcher 
> (AsyncDispatcher.java:serviceStop(144)) - Waiting for AsyncDispatcher to 
> drain. Thread state is :WAITING
> 2015-06-27 20:08:42,930 INFO  [main] event.AsyncDispatcher 
> (AsyncDispatcher.java:serviceStop(144)) - Waiting for AsyncDispatcher to 
> drain. Thread state is :WAITING
> 2015-06-27 20:08:43,930 INFO  [main] event.AsyncDispatcher 
> (AsyncDispatcher.java:serviceStop(144)) - Waiting for AsyncDispatcher to 
> drain. Thread state is :WAITING
> 2015-06-27 20:08:44,931 INFO  [main] event.AsyncDispatcher 
> (AsyncDispatcher.java:serviceStop(144)) - Waiting for AsyncDispatcher to 
> drain. Thread state is :WAITING
> 2015-06-27 20:08:45,931 INFO  [main] event.AsyncDispatcher 
> (AsyncDispatcher.java:serviceStop(144)) - Waiting for AsyncDispatcher to 
> drain. Thread state is :WAITING
> 2015-06-27 20:08:46,932 INFO  [main] event.AsyncDispatcher 
> (AsyncDispatcher.java:serviceStop(144)) - Waiting for AsyncDispatcher to 
> drain. Thread state is :WAITING
> {noformat}



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