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https://issues.apache.org/jira/browse/FLINK-24455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17424642#comment-17424642
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Aitozi commented on FLINK-24455:
--------------------------------
More information about local debug the two case:
1. _run 'mvn package -pl
flink-rpc/flink-rpc-akka,flink-rpc/flink-rpc-akka-loader' on the command-line_ .
Debugging this case, I found that the new created submodule classloader only
contains the dependency of flink-rpc-akka.jar, which does not contain
{{RpcSystem.class}}. In the phase of loadClass of {{AkkaRpcSystem}}, it will
try to load it's parent class, then fails with ClassNotFoundException using
submodule classloader, because the {{RpcSystem.class}} is not in
flink-rpc-akka.jar. Then it will be loaded by ownerClassLoader (AppClassLoader)
successfully.
After that loaded {{AkkaRpcSystem#SubmoduleClassloader}} inherited from
{{RpcSystem#AppClassloader}} . It can pass when check
{{RpcSystem.class.isAssignableFrom(AkkaRpcSystem.class)}} . I am a little
confused here about how does two class loaded by different classloader can work
with {{isAssignableFrom}}, but it works. please give me some hints, if you have
idea [~chesnay] :) .
2. _add a test dependency on the flink-rpc-akka-loader test-jar_.
It adds the flink-rpc-core to Submodule classloader classpath, so when load
{{AkkaPrcSystem}}, it will reload the {{RpcSystem}} with
{{SubmoduleClassloader}}, which lead to the **not a subtype** exception above.
!screenshot-1.png!
> Flink runtime test can't work with FallbackAkkaRpcSystemLoader
> --------------------------------------------------------------
>
> Key: FLINK-24455
> URL: https://issues.apache.org/jira/browse/FLINK-24455
> Project: Flink
> Issue Type: Bug
> Components: Tests
> Reporter: Aitozi
> Priority: Major
> Attachments: image-2021-10-06-00-27-19-848.png, screenshot-1.png
>
>
> After [FLINK-24367|https://github.com/apache/flink/pull/17385/files], a
> {{FallbackAkkaRpcSystemLoader}} is provided, which should make it possible to
> run test directly without execute {{mvn package -pl
> flink-rpc/flink-rpc-akka,flink-rpc/flink-rpc-akka-loader}} in command line,
> but I still meet the exception
> !image-2021-10-06-00-27-19-848.png!
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