[jira] [Closed] (FLINK-4257) Handle delegating algorithm change of class

["Greg Hogan (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-4257?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Greg Hogan closed FLINK-4257.
-----------------------------
    Resolution: Fixed

Fixed in 8210ff468d64fc50520011fc6fed9909d2a6b89a

> Handle delegating algorithm change of class
> -------------------------------------------
>
>                 Key: FLINK-4257
>                 URL: https://issues.apache.org/jira/browse/FLINK-4257
>             Project: Flink
>          Issue Type: Bug
>          Components: Gelly
>    Affects Versions: 1.1.0
>            Reporter: Greg Hogan
>            Assignee: Greg Hogan
>             Fix For: 1.2.0
>
>
> A class created by {{ProxyFactory}} can intercept and reinterpret method calls using its {{MethodHandler}}, but is restricted in that
> * the type of the proxy class cannot be changed
> * method return types must be honored
> We have algorithms such as {{VertexDegree}} and {{TriangleListing}} that change return type depending on configuration, even between single and dual input functions. This can be problematic, e.g. in {{OperatorTranslation}} where we test {{dataSet instanceof SingleInputOperator}} or {{dataSet instanceof TwoInputOperator}}.
> Even simply changing operator can be problematic, e.g. {{MapOperator.translateToDataFlow}} returns {{MapOperatorBase}} whereas {{ReduceOperator.translateToDataFlow}} returns {{SingleInputOperator}}.
> I see two ways to solve these issues. By adding a simple {{NoOpOperator}} that is skipped over during {{OperatorTranslation}} we could wrap all algorithm output and always be proxying the same class.
> Alternatively, making changes only within Gelly we can append a "no-op" pass-through {{MapFunction}} to any algorithm output which is not a {{SingleInputOperator}}. And {{Delegate}} can also walk the superclass hierarchy such we are always proxying {{SingleInputOperator}}.
> There is one additional issue. When we call {{DataSet.output}} the delegate's {{MethodHandler}} must reinterpret this call to add itself to the list of sinks.



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