[Bug] NPE in RegistryProtocol.ExporterChangeableWrapper#unregister when shutting down application

[binfeiruci]

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Apache Dubbo Component

Java SDK (apache/dubbo)

Dubbo Version

Dubbo Java 3.2.5, OpenJDK 1.8

Steps to reproduce this issue

Got the warn log below sometimes when shutting down our Dubbo-Spring integrated application.

 [DUBBO] null, dubbo version: 3.2.6-HA.1.0.5-RELEASE, current host: 10.232.232.201, error code: 99-0. This may be caused by unknown error in registry module, go to https://dubbo.apache.org/faq/99/0 to find instructions. 
java.lang.NullPointerException
  org.apache.dubbo.registry.integration.RegistryProtocol$ExporterChangeableWrapper.unregister(RegistryProtocol.java:1052)
  org.apache.dubbo.registry.integration.RegistryProtocol$DestroyableExporter.unregister(RegistryProtocol.java:760)
  org.apache.dubbo.config.ServiceConfig.unexport(ServiceConfig.java:208)
  ...

The corresponding thread name is SpringApplicationShutdownHook.

What you expected to happen

DubboShutdownHook waited DubboDeployApplicationListener(within SpringApplicationShutdownHook thread) to destroy the applicationMode for 10 seconds(default), then it will continue executing. If things happened in the order below, we will get this warn log.

1. RegistryProtocol.ExporterChangeableWrapper#unregister loop applicationModel.getPubModuleModels() in thread SpringApplicationShutdownHook
2. DubboShutdownHook destroy a moduleModel, set the moduleModel's serviceRepository to null.
3. RegistryProtocol.ExporterChangeableWrapper#unregister will get NPE when calling moduleModel.getServiceRepository().getExportedServices()

Anything else

No response

Are you willing to submit a pull request to fix on your own?

• [X] Yes I am willing to submit a pull request on my own!

Code of Conduct

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[wcy666103]

I think it is similar to this issue https://github.com/apache/dubbo/issues/10150#issuecomment-2201586582 , can you help us solve this problem through pr?

[oxsean]

Please add a readable title.