[jira] [Assigned] (FLINK-1325) Add a closure cleaner for Java

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

     [ https://issues.apache.org/jira/browse/FLINK-1325?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Aljoscha Krettek reassigned FLINK-1325:
---------------------------------------

    Assignee: Aljoscha Krettek

> Add a closure cleaner for Java
> ------------------------------
>
>                 Key: FLINK-1325
>                 URL: https://issues.apache.org/jira/browse/FLINK-1325
>             Project: Flink
>          Issue Type: Improvement
>          Components: Java API
>            Reporter: Stephan Ewen
>            Assignee: Aljoscha Krettek
>
> The Java API could really need a simple closure cleaner.
> All functions that are implemented as anonymous subclasses hold a reference to the enclosing class, unless they are implemented as part of a static method.
> That reference (called {{this$0}}) causes serialization to fail, as it draws non serializable classes into the function, even in cases where the function makes no access to the enclosing data.
> It is possible to manually set this reference to {{null}}, using reflection, or using a debugger. Then the serialization succeeds.
> I suggest to add a closure cleaner that uses an ASM visitor over the function's code to see if there is any access to the {{this$0}} field. In case there is non, the field should be set to {{null}}.
> The problem can be reproduced with the simple program below:
> {code}
> public class Test {
>   public void runProgram() throws Exception {
>     ExecutionEnvironment env = ExecutionEnvironment .getExecutionEnvironment();
>     env.generateSequence(1, 10)
>         .map(new MapFunction<Long, Long>() {
>           public Long map(Long value) {
>             return value * 2;
>           }
>         })
>         .print();
>     env.execute();
>   }
>   public static void main(String[] args) throws Exception {
>     new Test().runProgram();
>   }
> }
> {code}



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