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

["B Wyatt (JIRA)" <ji...@apache.org>]

B Wyatt created FLINK-3974:
------------------------------

             Summary: 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


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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