Nick Howard created KAFKA-379:
---------------------------------

             Summary: TopicCount.constructTopicCount isn't thread-safe
                 Key: KAFKA-379
                 URL: https://issues.apache.org/jira/browse/KAFKA-379
             Project: Kafka
          Issue Type: Bug
          Components: clients
    Affects Versions: 0.7, 0.8
            Reporter: Nick Howard


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.

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