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Posted to notifications@skywalking.apache.org by GitBox <gi...@apache.org> on 2021/08/15 12:16:43 UTC
[GitHub] [skywalking] daimingzhi commented on issue #3661: "java -ext.dirs" is not supported
daimingzhi commented on issue #3661:
URL: https://github.com/apache/skywalking/issues/3661#issuecomment-899041830
I built a demo for testing this case and found `-Xbootclasspath/a` is not able to resolve it
you can found the demo in https://github.com/daimingzhi/skywalkingTestDemo.git
I tested two scenarios：
- enhance instance（intercept constructor of instance or intercept method of instance）
- enhance class
## Scenario one
In the first scenario, the application starts normally, but the enhancement did not take effect, and the following log can be found in file `skywalking-api.log`
```
ERROR 2021-08-15 14:18:47:133 main SkyWalkingAgent : Enhance class com.easy4coding.jar.Person error.
org.apache.skywalking.apm.agent.core.plugin.PluginException: Can't create InstanceMethodsAroundInterceptor.
at org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.InstMethodsInter.<init>(InstMethodsInter.java:98)
at org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.ClassEnhancePluginDefine.enhanceInstance(ClassEnhancePluginDefine.java:177)
at org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.ClassEnhancePluginDefine.enhance(ClassEnhancePluginDefine.java:74)
at org.apache.skywalking.apm.agent.core.plugin.AbstractClassEnhancePluginDefine.define(AbstractClassEnhancePluginDefine.java:77)
at org.apache.skywalking.apm.agent.SkyWalkingAgent$Transformer.transform(SkyWalkingAgent.java:144)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.doTransform(AgentBuilder.java:10325)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:10263)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.access$1600(AgentBuilder.java:10029)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$LegacyVmDispatcher.run(AgentBuilder.java:10648)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$LegacyVmDispatcher.run(AgentBuilder.java:10595)
at java.security.AccessController.doPrivileged(Native Method)
at org.apache.skywalking.apm.dependencies.net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:10186)
at sun.instrument.TransformerManager.transform(TransformerManager.java:188)
at sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:428)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:411)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:264)
at com.easy4coding.agent.MainClass.main(MainClass.java:13)
Caused by: java.lang.ClassNotFoundException: Can't find org.apache.skywalking.apm.plugin.tomcat78x.ExtNonStaticInterceptor
at org.apache.skywalking.apm.agent.core.plugin.loader.AgentClassLoader.findClass(AgentClassLoader.java:118)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at org.apache.skywalking.apm.agent.core.plugin.loader.InterceptorInstanceLoader.load(InterceptorInstanceLoader.java:71)
at org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.InstMethodsInter.<init>(InstMethodsInter.java:96)
... 29 more
```
I debugged the code to find more detailed messages.
We used `AgentClassLoader` which parent classLoader is `ExtClassLoader`（because the class we wanted to enhance is loaded by `ExtClassLoader`）, to load a Interceptor defined in `skywalking.jar`，but `skywalking.jar` is loader by `AppClassLoader`。Therefore,the load will fail with an `classNotFoundException` thrown
## Scenario two
In the second scenario, the application starts failed.
This is because, when a static method is enhanced, `ByteBuddy` generates a static field for the class. The field is of type `StaticMethodsInter`, which will be set approach by reflection and this behavior will trigger loading of `StaticMethodsInter`
however,the enhanced class is loaded by `ExtClassLoader`，and it can not load `StaticMethodsInter` from `skywalking.jar` .
It can be seen from the above，use `BootstrapClassLoader` to load the class need to enhanced may not take effect。because, the same as `ExtClassLoader`,`BootstrapClassLoader` can not load any class from `skywalking.jar` .
In my demo,I did like this to resolve this problem.
```java
@Override
public boolean isBootstrapInstrumentation() {
return true;
}
```
Maybe skywalking can support some configuration to config default return value of this method instead of using "false". For example, We can use `Plugin.BootstrapInstrumentation.dirs=apm-sniffer\apm-sdk-plugin\httpClient-4.x-plugin` to make all methods named `isBootstrapInstrumentation` in `apm-sniffer\apm-sdk-plugin\httpClient-4.x-plugin` directory return true。
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