[ 
https://issues.apache.org/jira/browse/FLINK-9349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16479355#comment-16479355
 ] 

ASF GitHub Bot commented on FLINK-9349:
---------------------------------------

GitHub user snuyanzin opened a pull request:

    https://github.com/apache/flink/pull/6040

    [FLINK-9349][Kafka Connector] KafkaConnector Exception while fetching from 
multiple kafka topics

    *Thank you very much for contributing to Apache Flink - we are happy that 
you want to help us improve Flink. To help the community review your 
contribution in the best possible way, please go through the checklist below, 
which will get the contribution into a shape in which it can be best reviewed.*
    
    *Please understand that we do not do this to make contributions to Flink a 
hassle. In order to uphold a high standard of quality for code contributions, 
while at the same time managing a large number of contributions, we need 
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contextual information for the review. Please also understand that 
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    ## Contribution Checklist
    
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issue](https://issues.apache.org/jira/projects/FLINK/issues). Exceptions are 
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    ## What is the purpose of the change
    
    *(For example: This pull request makes task deployment go through the blob 
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    ## Brief change log
    
    fix synchronization issue
    + test to verify it
    
    ## Verifying this change
    
    This change added tests and can be verified as follows:
    via 
org.apache.flink.streaming.connectors.kafka.internal.Flink9349Test#testConcurrentPartitionsDiscoveryAndLoopFetching
    
    ## Does this pull request potentially affect one of the following parts:
    
      - Dependencies (does it add or upgrade a dependency): (no)
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      - The runtime per-record code paths (performance sensitive): (no )
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components), Checkpointing, Yarn/Mesos, ZooKeeper: ( no )
      - The S3 file system connector: ( no)
    
    ## Documentation
    
      - Does this pull request introduce a new feature? ( no)
      - If yes, how is the feature documented? (not applicable)


You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/snuyanzin/flink 
FLINK-9349_KafkaConnector_Exception_while_fetching_from_multiple_kafka_topics

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/flink/pull/6040.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #6040
    
----
commit 8de5f37549607460659e171f9c3b48d0090383c0
Author: snuyanzin <snuyanzin@...>
Date:   2018-05-17T16:12:04Z

    added test and fix for FLINK-9349 by usage of CopyOnWriteArrayList

commit eee524e2d2a86af5252ed939000c12a2604917e9
Author: snuyanzin <snuyanzin@...>
Date:   2018-05-17T16:35:10Z

    fix checkstyle

----


> KafkaConnector Exception  while fetching from multiple kafka topics
> -------------------------------------------------------------------
>
>                 Key: FLINK-9349
>                 URL: https://issues.apache.org/jira/browse/FLINK-9349
>             Project: Flink
>          Issue Type: Bug
>          Components: Kafka Connector
>    Affects Versions: 1.4.0, 1.5.0
>            Reporter: Vishal Santoshi
>            Priority: Critical
>         Attachments: Flink9349Test.java
>
>
> ./flink-connectors/flink-connector-kafka-0.9/src/main/java/org/apache/flink/streaming/connectors/kafka/internal/Kafka09Fetcher.java
>  
> It seems the List subscribedPartitionStates was being modified when 
> runFetchLoop iterated the List.
> This can happen if, e.g., FlinkKafkaConsumer runs the following code 
> concurrently:
>                 kafkaFetcher.addDiscoveredPartitions(discoveredPartitions);
>  
> {code:java}
>  java.util.ConcurrentModificationException
>       at 
> java.util.LinkedList$ListItr.checkForComodification(LinkedList.java:966)
>       at java.util.LinkedList$ListItr.next(LinkedList.java:888)
>       at 
> org.apache.flink.streaming.connectors.kafka.internal.Kafka09Fetcher.runFetchLoop(Kafka09Fetcher.java:134)
> {code}



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