ConcurrentModificationException during mvn test

[i3wangyi]

@narendly reported the stack trace of a problematic exception

22723 [ZkClient-EventThread-752-localhost:2183] ERROR org.apache.helix.manager.zk.ZKExceptionHandler - exception in handling data-change. path: /TestHelixAdminCli_grand/INSTANCES/controller_9000/CURRENTSTATES/10014b003960037/TestHelixAdminCli, listener: org.apache.helix.controller.GenericHelixController@64b7b07
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1442)
at java.util.HashMap$KeyIterator.next(HashMap.java:1466)
at org.apache.helix.controller.stages.ClusterEvent.clone(ClusterEvent.java:119)
at org.apache.helix.controller.GenericHelixController.pushToEventQueues(GenericHelixController.java:1010)
at org.apache.helix.controller.GenericHelixController.onStateChange(GenericHelixController.java:826)
at org.apache.helix.manager.zk.CallbackHandler.invoke(CallbackHandler.java:418)
at org.apache.helix.manager.zk.CallbackHandler.enqueueTask(CallbackHandler.java:341)
at org.apache.helix.manager.zk.CallbackHandler.handleDataChange(CallbackHandler.java:625)
at org.apache.helix.zookeeper.zkclient.ZkClient$6.run(ZkClient.java:1305)
at org.apache.helix.zookeeper.zkclient.ZkEventThread.run(ZkEventThread.java:90)
true: wait 426ms, ClusterStateVerifier$BestPossAndExtViewZkVerifier(TestHelixAdminCli@localhost:2183)
true: wait 250ms, ClusterStateVerifier$BestPossAndExtViewZkVerifier(TestHelixAdminCli@localhost:2183)
END testDropAddResource at Thu Feb 13 14:50:12 PST 2020, took: 3075ms.
START testInstanceOperations at Thu Feb 13 14:50:12 PST 2020

The root cause is: In ClusterEvent.java, the hashmap is updated in another thread while clone is still in the for-loop

for (String attributeName : _eventAttributeMap.keySet()) {
  newEvent.addAttribute(attributeName, _eventAttributeMap.get(attributeName));
}


public void addAttribute(String attrName, Object attrValue) {
  if (logger.isTraceEnabled()) {
    logger.trace("Adding attribute:" + attrName);
    logger.trace(" attribute value:" + attrValue);
  }

  _eventAttributeMap.put(attrName, attrValue);
}