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https://issues.apache.org/jira/browse/FLINK-33949?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17800913#comment-17800913
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Wencong Liu commented on FLINK-33949:
-------------------------------------
Suppose we have two completely independent interfaces, I and J, both declaring
a default method M with the same signature. Now, if there is a class T that
implements both interfaces I and J but *does not override* the conflicting
method M, the compiler would not know which interface's default method
implementation to use, as they both have equal priority. If the code containing
class T tries to invoke this method at runtime, the JVM would throw an
{{IncompatibleClassChangeError}} because it is faced with an impossible
decision: it does not know which interface’s default implementation to call.
However, if M is abstract in I or J, the implementation class T *must* provides
an explicit implementation of the method. So no matter how interfaces I or J
change (as long as the signature of their method M does not change), it will
not affect the behavior of the implementation class T or cause an
{{{}IncompatibleClassChangeError{}}}. Class T will continue to use its own
method M implementation, disregarding any default implementations from the two
interfaces.
I have create a test case, where the StreamingRuntimeContext will be added a
method return TestObject:
{code:java}
public class TestObject implements TestInterface1, TestInterface2 {
@Override
public String getResult() {
return "777";
}
}
public interface TestInterface1 {
String getResult();
}
public interface TestInterface2 {
default String getResult() {
return "666";
}
}{code}
The job code is in the follows. The job is compiled with the modifiled
StreamingRuntimeContext in Flink.
{code:java}
public static void main(String[] args) throws Exception {
StreamExecutionEnvironment executionEnvironment =
StreamExecutionEnvironment.getExecutionEnvironment();
DataStreamSource<Integer> source =
executionEnvironment.fromData(3, 2, 1, 4, 5, 6, 7, 8);
SingleOutputStreamOperator<String> result = source.map(new
RichMapFunction<Integer, String>() {
@Override
public String map(Integer integer) {
StreamingRuntimeContext runtimeContext =
(StreamingRuntimeContext)getRuntimeContext();
return runtimeContext.getTestObject().getResult();
}
});
CloseableIterator<String> jobResult = result.executeAndCollect();
while (jobResult.hasNext())
System.out.println(jobResult.next());
} {code}
When I change the abstract method getResult into default in TestInterface1 and
recompiled Flink. The job is still able to finish without any code changes and
exceptions.
Therefore, I think the METHOD_ABSTRACT_NOW_DEFAULT doesn't break source
compatibility. WDYT?
> METHOD_ABSTRACT_NOW_DEFAULT should be both source compatible and binary
> compatible
> ----------------------------------------------------------------------------------
>
> Key: FLINK-33949
> URL: https://issues.apache.org/jira/browse/FLINK-33949
> Project: Flink
> Issue Type: Bug
> Components: Test Infrastructure
> Affects Versions: 1.19.0
> Reporter: Wencong Liu
> Priority: Major
> Fix For: 1.19.0
>
>
> Currently I'm trying to refactor some APIs annotated by @Public in
> [FLIP-382: Unify the Provision of Diverse Metadata for Context-like APIs -
> Apache Flink - Apache Software
> Foundation|https://cwiki.apache.org/confluence/display/FLINK/FLIP-382%3A+Unify+the+Provision+of+Diverse+Metadata+for+Context-like+APIs].
> When an abstract method is changed into a default method, the japicmp maven
> plugin names this change METHOD_ABSTRACT_NOW_DEFAULT and considers it as
> source incompatible and binary incompatible.
> The reason maybe that if the abstract method becomes default, the logic in
> the default method will be ignored by the previous implementations.
> I create a test case in which a job is compiled with newly changed default
> method and submitted to the previous version. There is no exception thrown.
> Therefore, the METHOD_ABSTRACT_NOW_DEFAULT shouldn't be incompatible both for
> source and binary. We could add the following settings to override the
> default values for binary and source compatibility, such as:
> {code:java}
> <overrideCompatibilityChangeParameters>
> <overrideCompatibilityChangeParameter>
> <compatibilityChange>METHOD_ABSTRACT_NOW_DEFAULT</compatibilityChange>
> <binaryCompatible>true</binaryCompatible>
> <sourceCompatible>true</sourceCompatible>
> </overrideCompatibilityChangeParameter>
> </overrideCompatibilityChangeParameters> {code}
> By the way, currently the master branch checks both source compatibility and
> binary compatibility between minor versions. According to Flink's API
> compatibility constraints, the master branch shouldn't check binary
> compatibility. There is already jira FLINK-33009 to track it and we should
> fix it as soon as possible.
>
>
>
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