lujiajing1126 opened a new issue #6966:
URL: https://github.com/apache/skywalking/issues/6966
- Why do you submit this issue?
- [x] Question or discussion
- [x] Bug
- [ ] Requirement
- [ ] Feature or performance improvement
___
### Question
Discussion the `java.lang.ClassCastException` problem reported in issues
#6554, #5817, #6648 and #6760.
And try to resolve this problem.
___
### Bug
- Which version of SkyWalking, OS, and JRE?
I suppose all the versions up to the latest Skywalking 8.5.0 are affected
- What happened?
In the `skywalking-api.log`, we may find,
```
ERROR 2021-05-18 17:40:02:384 http-nio-8080-exec-1 InstMethodsInter :
class[class com.example.classloaderdemo.controller.HealthController] before
method[health] intercept failure
java.lang.ClassCastException:
org.apache.skywalking.apm.plugin.spring.mvc.commons.JavaxServletRequestHolder
cannot be cast to
org.apache.skywalking.apm.plugin.spring.mvc.commons.RequestHolder
at
org.apache.skywalking.apm.plugin.spring.mvc.commons.interceptor.AbstractMethodInterceptor.beforeMethod(AbstractMethodInterceptor.java:100)
at
org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.InstMethodsInter.intercept(InstMethodsInter.java:76)
at
com.example.classloaderdemo.controller.HealthController.health(HealthController.java)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at
org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:197)
at
org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:141)
at
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106)
at
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:894)
at
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)
at
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
at
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1060)
at
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:962)
at
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
at
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:626)
at
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at
org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
at
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at
org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
at
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at
org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
at
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
at
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
at
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
at
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
at
org.apache.catalina.core.StandardHostValve.invoke$original$G32s1bTQ(StandardHostValve.java:143)
at
org.apache.catalina.core.StandardHostValve.invoke$original$G32s1bTQ$accessor$ku9vVTW5(StandardHostValve.java)
at
org.apache.catalina.core.StandardHostValve$auxiliary$7vA1kjbB.call(Unknown
Source)
at
org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.InstMethodsInter.intercept(InstMethodsInter.java:86)
at
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java)
at
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
at
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
at
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357)
at
org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
at
org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
at
org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:893)
at
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1707)
at
org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
```
As @zifeihan has concluded in
https://github.com/apache/skywalking/issues/5817#issuecomment-751446913, the
problem is easy to be understood. Just to take a glance of this story, the
simplest way to reproduce the problem is to run a spring boot application with
[`spring-boot-devtools`](https://docs.spring.io/spring-boot/docs/1.5.16.RELEASE/reference/html/using-boot-devtools.html)
in IDEA.
```xml
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
```
with a controller,
```java
package com.example.classloaderdemo.controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class HealthController {
@GetMapping(path = "/healthz")
public String health() {
return "OK";
}
}
```
If we use [`Arthas`](https://arthas.aliyun.com/doc/index.html) to examine
this particular class
`org.apache.skywalking.apm.plugin.spring.mvc.commons.RequestHolder`, we can
find the following results,
```
[arthas@22299]$ sc -d
org.apache.skywalking.apm.plugin.spring.mvc.commons.RequestHolder
class-info
org.apache.skywalking.apm.plugin.spring.mvc.commons.JavaxServletRequestHolder
code-source
name
org.apache.skywalking.apm.plugin.spring.mvc.commons.JavaxServletRequestHolder
isInterface false
isAnnotation false
isEnum false
isAnonymousClass false
isArray false
isLocalClass false
isMemberClass false
isPrimitive false
isSynthetic false
simple-name JavaxServletRequestHolder
modifier public
annotation
interfaces
org.apache.skywalking.apm.plugin.spring.mvc.commons.RequestHolder
super-class +-java.lang.Object
class-loader
+-org.apache.skywalking.apm.agent.core.plugin.loader.AgentClassLoader@6ba76699
+-sun.misc.Launcher$AppClassLoader@18b4aac2
+-sun.misc.Launcher$ExtClassLoader@3feba861
classLoaderHash 6ba76699
class-info
org.apache.skywalking.apm.plugin.spring.mvc.commons.RequestHolder
code-source
name
org.apache.skywalking.apm.plugin.spring.mvc.commons.RequestHolder
isInterface true
isAnnotation false
isEnum false
isAnonymousClass false
isArray false
isLocalClass false
isMemberClass false
isPrimitive false
isSynthetic false
simple-name RequestHolder
modifier abstract,interface,public
annotation
interfaces
super-class
class-loader
+-org.apache.skywalking.apm.agent.core.plugin.loader.AgentClassLoader@77f6031b
+-org.springframework.boot.devtools.restart.classloader.RestartClassLoader@6bce6c13
+-sun.misc.Launcher$AppClassLoader@18b4aac2
+-sun.misc.Launcher$ExtClassLoader@3feba861
classLoaderHash 77f6031b
class-info
org.apache.skywalking.apm.plugin.spring.mvc.commons.RequestHolder
code-source
name
org.apache.skywalking.apm.plugin.spring.mvc.commons.RequestHolder
isInterface true
isAnnotation false
isEnum false
isAnonymousClass false
isArray false
isLocalClass false
isMemberClass false
isPrimitive false
isSynthetic false
simple-name RequestHolder
modifier abstract,interface,public
annotation
interfaces
super-class
class-loader
+-org.apache.skywalking.apm.agent.core.plugin.loader.AgentClassLoader@6ba76699
+-sun.misc.Launcher$AppClassLoader@18b4aac2
+-sun.misc.Launcher$ExtClassLoader@3feba861
classLoaderHash 6ba76699
Affect(row-cnt:3) cost in 30 ms.
```
1.
`org.apache.skywalking.apm.plugin.spring.mvc.commons.JavaxServletRequestHolder`
together with its parent
`org.apache.skywalking.apm.plugin.spring.mvc.commons.RequestHolder` appear to
be loaded by the `AgentClassLoader@6ba76699`. This happened when the spring
internal class `org.springframework.web.method.HandlerMethod#getBean` was
enhanced since the `HandlerMethod` class was loaded by `AppClassLoader`.
2. Afterwards, the `RestController` annotation is captured. However, the
controller class `HealthController` is loaded by another classloader
`org.springframework.boot.devtools.restart.classloader.RestartClassLoader@6bce6c13`
which further causes the Skywalking agent to create a new instance of
AgentClassLoader, i.e. `AgentClassLoader@77f6031b`.
Finally, since `RequestHolder` sits in both two classloaders, they are not
the same one, thus not inter-changeable.
___
### Requirement or improvement
As a conclusion, the root-cause of the problem is the abstraction of
`RequestHolder` which **exists in the plugin** and will be potentially loaded
by different instances of `AgentClassLoader`.
But I suppose the abstraction can be fully removed since we only take
advantage of it in `AbstractMethodInterceptor`.
If so, I believe this issue can be resolved, since either
`javax.servlet.http.HttpServletRequest` or
`org.springframework.http.server.reactive.ServerHttpResponse` can be only
loaded by the same classloader due to the
parent delegation model, e.g. `AppClassLoader` or
[`org.springframework.boot.loader.LaunchedURLClassLoader`](https://docs.spring.io/spring-boot/docs/current/api/org/springframework/boot/loader/LaunchedURLClassLoader.html)
in spring boot execution environment.
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