[GitHub] [skywalking] luanwenfei-venus opened a new issue, #9700: [Bug]

[GitBox <gi...@apache.org>]

luanwenfei-venus opened a new issue, #9700:
URL: https://github.com/apache/skywalking/issues/9700

   ### Search before asking
   
   - [X] I had searched in the [issues](https://github.com/apache/skywalking/issues?q=is%3Aissue) and found no similar issues.
   
   
   ### Apache SkyWalking Component
   
   Java Agent (apache/skywalking-java)
   
   ### What happened
   
   I have found the reason for this problem. The problem described in #9698 will occur when the classes that skywalking is intended to enhance and they are used in agents added before skywalking.
   The reason ad follow :
   Skywalking uses byte-buddy, when it structures byte-buddy's AgentBuilder, it select 'SinglePass (Default)' as  it's 'DiscoveryStrategy'.
   ```
   /**
    * A discovery strategy that considers all loaded types supplied by {@link Instrumentation#getAllLoadedClasses()}.
    */
   enum SinglePass implements AgentBuilder.RedefinitionStrategy.DiscoveryStrategy {
   
       /**
        * The singleton instance.
        */
       INSTANCE;
   
       /**
        * {@inheritDoc}
        */
       public Iterable<Iterable<Class<?>>> resolve(Instrumentation instrumentation) {
           return Collections.<Iterable<Class<?>>>singleton(Arrays.<Class<?>>asList(instrumentation.getAllLoadedClasses()));
       }
   }
   ```
   DiscovertStrategy.SinglePass will discovery all loaded classes and then if skywaling need to enhance them in AgentBuilder.installOn, they will be retransformed.
   
   ![image](https://user-images.githubusercontent.com/51258211/192675277-2b83e445-2bc1-4646-9308-b91440338cf3.png)
   
   In AgentBuilder.installOn process: 
   1. As first step in the picture, the classes that have been not loaded will be transform,.
   2. As second step in the picture,the classes tha have been loaded will be discovered by 'DiscovertStrategy.SinglePass' and will be 
   retransformed.
   
   We quoted the 'instrumentation. RetransformClasses()' restrictions:
   
   > The retransformation must not add, remove or rename fields or methods, change the signatures of methods, **or change inheritance.**
   
   It means that，when agent try to retransform classes, the above restrictions need to be observed.But i find that, when skywalking enhance a classes, it will change the class's inheritance.
   ![image](https://user-images.githubusercontent.com/51258211/192676732-4a0e6c94-e6a7-4ae5-99b3-a249d8a7a2b0.png)
   If this class(can be system class) has been loaded by other agent before skywalking's premain，when skywalking enhance this class the Instrumentation.retransformClasses() will throw:
   ```
   java.lang.UnsupportedOperationException: class redefinition failed: attempted to change superclass or interfaces
   ```
   Because skywalking attemp to change a class's inheritace in retransform process.
   
   ### What you expected to happen
   
   I hope it can help skywalking. And i expect skywalking-java can coexist with other agents.
   
   ### How to reproduce
   
   Agent version:8.11.0
   Plugin：apm-guava-eventbus-plugin
   The command is like '-javaagent:xxxx-agent.jar -javaagent:skywalking-agent.jar'.
   
   ### Anything else
   
   _No response_
   
   ### Are you willing to submit PR?
   
   - [X] Yes I am willing to submit a PR!
   
   ### Code of Conduct
   
   - [X] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)
   


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[GitHub] [skywalking] luanwenfei-venus closed issue #9700: [Bug] The reason for 'java.lang.UnsupportedOperationException: class redefinition failed: attempted to change superclass or interfaces'.

[GitBox <gi...@apache.org>]

luanwenfei-venus closed issue #9700: [Bug] The reason for 'java.lang.UnsupportedOperationException: class redefinition failed: attempted to change superclass or interfaces'.
URL: https://github.com/apache/skywalking/issues/9700


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