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https://issues.apache.org/jira/browse/FLINK-8836?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16383510#comment-16383510
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Stephan Ewen commented on FLINK-8836:
-------------------------------------

Is the concern that the default serializers themselves are stateful?

As far as I understood it so far, the Kryo object is stateful and not thread 
safe, hence needs to be exclusive to one thread at a time. Kryo does the 
tracking of object graphs and generic scopes, which makes it not thread safe 
during serialization / deserialization.
The serializers used by Kryo should be stateless and can thus sharable.

Please double check this assumption - if the serializers are actually stateful, 
then we need to see how we can handle that.
If they are not, we should be able to close this issue.

> Duplicating a KryoSerializer does not duplicate registered default serializers
> ------------------------------------------------------------------------------
>
>                 Key: FLINK-8836
>                 URL: https://issues.apache.org/jira/browse/FLINK-8836
>             Project: Flink
>          Issue Type: Bug
>          Components: Type Serialization System
>            Reporter: Tzu-Li (Gordon) Tai
>            Priority: Critical
>
> The {{duplicate()}} method of the {{KryoSerializer}} is as following:
> {code:java}
> public KryoSerializer<T> duplicate() {
>     return new KryoSerializer<>(this);
> }
> protected KryoSerializer(KryoSerializer<T> toCopy) {
>     defaultSerializers = toCopy.defaultSerializers;
>     defaultSerializerClasses = toCopy.defaultSerializerClasses;
>     kryoRegistrations = toCopy.kryoRegistrations;
>     ...
> }
> {code}
> Shortly put, when duplicating a {{KryoSerializer}}, the 
> {{defaultSerializers}} serializer instances are directly provided to the new 
> {{KryoSerializer}} instance.
>  This causes the fact that those default serializers are shared across two 
> different {{KryoSerializer}} instances, and therefore not a correct duplicate.



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