Major Description
TopicCount uses scala.util.parsing.json.JSON, which isn't thread-safe https://issues.scala-lang.org/browse/SI-4929
If you have multiple consumers within the same JVM, and they all rebalance at the same time, you can get errors like the following:
[...] kafka.consumer.TopicCount$.constructTopicCount:39] ERROR: error parsing consumer json string [...]
java.lang.NullPointerException
at scala.util.parsing.combinator.Parsers$NoSuccess.<init>(Parsers.scala:131)
at scala.util.parsing.combinator.Parsers$Failure.<init>(Parsers.scala:158)
at scala.util.parsing.combinator.Parsers$$anonfun$acceptIf$1.apply(Parsers.scala:489)
...
at scala.util.parsing.combinator.Parsers$$anon$2.apply(Parsers.scala:742)
at scala.util.parsing.json.JSON$.parseRaw(JSON.scala:71)
at scala.util.parsing.json.JSON$.parseFull(JSON.scala:85)
at kafka.consumer.TopicCount$.constructTopicCount(TopicCount.scala:32)
at kafka.consumer.ZookeeperConsumerConnector$ZKRebalancerListener.kafka$consumer$ZookeeperConsumerConnector$ZKRebalancerListener$$getTopicCount(ZookeeperConsumerConnector.scala:422)
at kafka.consumer.ZookeeperConsumerConnector$ZKRebalancerListener.kafka$consumer$ZookeeperConsumerConnector$ZKRebalancerListener$$rebalance(ZookeeperConsumerConnector.scala:460)
at kafka.consumer.ZookeeperConsumerConnector$ZKRebalancerListener$$anonfun$syncedRebalance$1.apply$mcVI$sp(ZookeeperConsumerConnector.scala:437)
at scala.collection.immutable.Range$ByOne$class.foreach$mVc$sp(Range.scala:282)
at scala.collection.immutable.Range$$anon$2.foreach$mVc$sp(Range.scala:265)
at kafka.consumer.ZookeeperConsumerConnector$ZKRebalancerListener.syncedRebalance(ZookeeperConsumerConnector.scala:433)
at kafka.consumer.ZookeeperConsumerConnector$ZKRebalancerListener.handleChildChange(ZookeeperConsumerConnector.scala:375)
at org.I0Itec.zkclient.ZkClient$7.run(ZkClient.java:568)
at org.I0Itec.zkclient.ZkEventThread.run(ZkEventThread.java:71)
I ran into this on 0.7.0, but the code in trunk appears to be vulnerable to the same issue.