[jira] [Commented] (FLINK-3974) enableObjectReuse fails when an operator chains to multiple downstream operators

["Aljoscha Krettek (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-3974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15329226#comment-15329226 ] 

Aljoscha Krettek commented on FLINK-3974:
-----------------------------------------

[~wanderingbort] do you want to open a PR with your fix or should I create a commit for you with the fix?


> enableObjectReuse fails when an operator chains to multiple downstream operators
> --------------------------------------------------------------------------------
>
>                 Key: FLINK-3974
>                 URL: https://issues.apache.org/jira/browse/FLINK-3974
>             Project: Flink
>          Issue Type: Bug
>          Components: DataStream API
>    Affects Versions: 1.0.3
>            Reporter: B Wyatt
>         Attachments: ReproFLINK3974.java, bwyatt-FLINK3974.1.patch
>
>
> Given a topology that looks like this:
> {code:java}
> DataStream<A> input = ...
> input
>     .map(MapFunction<A,B>...)
>     .addSink(...);
> input
>     .map(MapFunction<A,C>...)
>     ​.addSink(...);
> {code}
> enableObjectReuse() will cause an exception in the form of {{"java.lang.ClassCastException: B cannot be cast to A"}} to be thrown.
> It looks like the input operator calls {{Output<StreamRecord<A>>.collect}} which attempts to loop over the downstream operators and process them.
> However, the first map operation will call {{StreamRecord<>.replace}} which mutates the value stored in the StreamRecord<>.  
> As a result, when the {{Output<StreamRecord<A>>.collect}} call passes the {{StreamRecord<A>}} to the second map operation it is actually a {{StreamRecord<B>}} and behaves as if the two map operations were serial instead of parallel.



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