GitHub user StefanRRichter opened a pull request:

    https://github.com/apache/flink/pull/5880

    [FLINK-8836] Fix duplicate method in KryoSerializer to perform deep c…

    …opy of default/registered serializer instances.
    
    This method did create deep copies of registered or default serializer 
instances and
    as a result those serializer instances can accidentally be shared across 
different threads.
    
    ## Brief change log
    
    This PR fixes a problem with the `duplicate` method of `KryoSerializer`. We 
do now perform deep copies for default and registered serializer objects.
    
    Otherwise, if we share duplicated `KryoSerializer` instances across 
different threads, some of their internal serializers might be a shared 
instance of a stateful object. 
    
    ## Verifying this change
    
    This change added tests and can be verified by running 
`KryoSerializerConcurrencyTest`.
    
    ## Does this pull request potentially affect one of the following parts:
    
      - Dependencies (does it add or upgrade a dependency): (no)
      - The public API, i.e., is any changed class annotated with 
`@Public(Evolving)`: (no)
      - The serializers: (yes)
      - The runtime per-record code paths (performance sensitive): (no)
      - Anything that affects deployment or recovery: JobManager (and its 
components), Checkpointing, Yarn/Mesos, ZooKeeper: (indirectly)
      - 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/StefanRRichter/flink FLINK-8836

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

    https://github.com/apache/flink/pull/5880.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 #5880
    
----
commit 617ebd114b86d8f00d15e53dd649bb633fc717f9
Author: Stefan Richter <s.richter@...>
Date:   2018-04-19T13:10:07Z

    [FLINK-8836] Fix duplicate method in KryoSerializer to perform deep copy of 
default/registered serializer instances.
    
    This method did create deep copies of registered or default serializer 
instances and
    as a result those serializer instances can accidentally be shared across 
different threads.

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