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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-8409) Race condition in KafkaConsumerThread leads to potential NPE
Date Wed, 31 Jan 2018 12:55:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-8409?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16346767#comment-16346767
] 

ASF GitHub Bot commented on FLINK-8409:
---------------------------------------

Github user tzulitai commented on the issue:

    https://github.com/apache/flink/pull/5329
  
    Merging ...


> Race condition in KafkaConsumerThread leads to potential NPE
> ------------------------------------------------------------
>
>                 Key: FLINK-8409
>                 URL: https://issues.apache.org/jira/browse/FLINK-8409
>             Project: Flink
>          Issue Type: Bug
>          Components: Kafka Connector
>    Affects Versions: 1.4.0, 1.3.2, 1.5.0
>            Reporter: Tzu-Li (Gordon) Tai
>            Assignee: Tzu-Li (Gordon) Tai
>            Priority: Blocker
>             Fix For: 1.3.3, 1.5.0, 1.4.1
>
>
> The following lines in the {{KafkaConsumerThread::setOffsetsToCommit(...)}} suggests
a race condition with the asynchronous callback from committing offsets to Kafka:
> {code}
> // record the work to be committed by the main consumer thread and make sure the consumer
notices that
> if (nextOffsetsToCommit.getAndSet(offsetsToCommit) != null) {
>     log.warn("Committing offsets to Kafka takes longer than the checkpoint interval.
" +
>         "Skipping commit of previous offsets because newer complete checkpoint offsets
are available. " +
>         "This does not compromise Flink's checkpoint integrity.");
> }
> this.offsetCommitCallback = commitCallback;
> {code}
> In the main consumer thread's main loop, {{nextOffsetsToCommit}} will be checked if there
are any offsets to commit. If so, an asynchronous offset commit operation will be performed.
The NPE happens in the case when the commit completes, but {{this.offsetCommitCallback = commitCallback;}}
is not yet reached.
> A possible fix is to make setting the next offsets to commit along with the callback
instance a single atomic operation.



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