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https://issues.apache.org/jira/browse/KAFKA-4901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15928347#comment-15928347
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Jun Rao commented on KAFKA-4901:
--------------------------------
Not sure why the PR didn't show up here. Merged
https://github.com/apache/kafka/pull/2689 to trunk (0.11.0.0).
> Make ProduceRequest thread-safe
> -------------------------------
>
> Key: KAFKA-4901
> URL: https://issues.apache.org/jira/browse/KAFKA-4901
> Project: Kafka
> Issue Type: Bug
> Reporter: Ismael Juma
> Assignee: Ismael Juma
> Fix For: 0.11.0.0, 0.10.2.1
>
>
> If request logging is enabled, ProduceRequest can be accessed
> and mutated concurrently from a network thread (which calls
> toString) and the request handler thread (which calls
> clearPartitionRecords()).
> That can lead to a ConcurrentModificationException when iterating
> the partitionRecords map.
> The underlying thread-safety issue has existed since the server
> started using the Java implementation of ProduceRequest in 0.10.0.
> However, we were incorrectly not clearing the underlying struct until
> 0.10.2, so toString itself was thread-safe until that change. In 0.10.2,
> toString is no longer thread-safe and we could potentially see a
> NullPointerException given the right set of interleavings between
> toString and clearPartitionRecords although we haven't seen that
> happen yet.
> In trunk, we changed the requests to have a toStruct method
> instead of creating a struct in the constructor and toString was
> no longer printing the contents of the Struct. This accidentally
> fixed the race condition, but it meant that request logging was less
> useful.
> A couple of days ago, AbstractRequest.toString was changed to
> print the contents of the request by calling toStruct().toString()
> and reintroduced the race condition. The impact is more visible
> because we iterate over a HashMap, which proactively
> checks for concurrent modification (unlike arrays).
> We will need a separate PR for 0.10.2.
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