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https://issues.apache.org/jira/browse/FLINK-1325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14248287#comment-14248287
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ASF GitHub Bot commented on FLINK-1325:
---------------------------------------
Github user StephanEwen commented on the pull request:
https://github.com/apache/incubator-flink/pull/269#issuecomment-67166915
Looks good.
Here are some issues that we need to watch out for:
- I think we need to have the ASM dependency as a managed dependency in
the parent pom. There are different parts that use ASM in potentially different
versions (the JAR builder in a pending pull request uses ASM 5 to support
lambdas)
- Does the closure cleaner visit all methods? (I am not familiar enough
with ASM to figure that out from the code)
- Should we add a test where the outer field is accessed not from the
`map()` method itself, but from another method?
> 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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