How to transform a method that has not been explicitly overridden

[huange7]

I have written a class that extends java.util.concurrent.ThreadPoolExecutor. In this class, I did not override the shutdown method of the parent class, but I would like to add instrumentation to the shutdown method. Is it possible to achieve this using the OpenTelemetry instrumentation?
Here's the code:

public class ThreadPoolExecutor extends java.util.concurrent.ThreadPoolExecutor {

    public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, @NotNull TimeUnit unit, @NotNull BlockingQueue<Runnable> workQueue) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
    }
}

[huange7]

Hi, @laurit. Do you have any practical suggestions? I would really appreciate it.

[laurit]

Use

opentelemetry-java-instrumentation/javaagent-extension-api/src/main/java/io/opentelemetry/javaagent/extension/instrumentation/TypeTransformer.java

Line 32 in 65ee951

void applyTransformer(AgentBuilder.Transformer transformer);

to add the overrider for the shutdown method. We don't have any samples in the agent on how to do this, you'll have to check byte-buddy or asm (whichever you prefer) documentation on how to add methods.

[huange7]

Thanks for your reply! I will try to do that.

[huange7]

Use

opentelemetry-java-instrumentation/javaagent-extension-api/src/main/java/io/opentelemetry/javaagent/extension/instrumentation/TypeTransformer.java

Line 32 in 65ee951

void applyTransformer(AgentBuilder.Transformer transformer);

to add the overrider for the shutdown method. We don't have any samples in the agent on how to do this, you'll have to check byte-buddy or asm (whichever you prefer) documentation on how to add methods.

Hi, @laurit . After using applyTransformer, I am unable to successfully add methods. Is there any docs that I can refer to for guidance?
Here is the code I added.

transformer.applyTransformer(new AgentBuilder.Transformer() {
      @Override
      public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder,
          TypeDescription typeDescription, ClassLoader classLoader, JavaModule module) {
        builder.defineMethod("shutdown", void.class, Visibility.PUBLIC).intercept(SuperMethodCall.INSTANCE);
        return builder;
      }
    });

or

transformer.applyTransformer(new AgentBuilder.Transformer() {
      @Override
      public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder,
          TypeDescription typeDescription, ClassLoader classLoader, JavaModule module) {
        return builder.defineMethod("shutdown", void.class, Visibility.PUBLIC).intercept(SuperMethodCall.INSTANCE);
      }
    });

Thanks.

[huange7]

I understand that the bytebuddy agent has the disableClassFormatChanges setting, which is likely the reason why my modifications are failing.

AgentBuilder agentBuilder =
        new AgentBuilder.Default()
            .disableClassFormatChanges()
            .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
            .with(new RedefinitionDiscoveryStrategy())
            .with(AgentBuilder.DescriptionStrategy.Default.POOL_ONLY)
            .with(AgentTooling.poolStrategy())
            .with(new ClassLoadListener())
            .with(AgentTooling.locationStrategy());

[laurit]

If byte buddy does not work try with asm

    transformer.applyTransformer(new AgentBuilder.Transformer() {
      @Override
      public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder,
          TypeDescription typeDescription, ClassLoader classLoader, JavaModule module,
          ProtectionDomain protectionDomain) {
        return builder.visit(new AsmVisitorWrapper() {
          @Override
          public int mergeWriter(int flags) {
            return flags | ClassWriter.COMPUTE_MAXS;
          }

          @Override
          @CanIgnoreReturnValue
          public int mergeReader(int flags) {
            return flags;
          }

          @Override
          public ClassVisitor wrap(TypeDescription instrumentedType, ClassVisitor classVisitor,
              Implementation.Context implementationContext, TypePool typePool,
              FieldList<FieldDescription.InDefinedShape> fields, MethodList<?> methods,
              int writerFlags, int readerFlags) {
            return new ClassVisitor(Opcodes.ASM9, classVisitor) {
              String superName;
              boolean hasShutdown;

              @Override
              public void visit(int version, int access, String name, String signature,
                  String superName, String[] interfaces) {
                this.superName = superName;
                super.visit(version, access, name, signature, superName, interfaces);
              }

              @Override
              public MethodVisitor visitMethod(int access, String name, String descriptor,
                  String signature, String[] exceptions) {
                if ("shutdown".equals(name)) {
                  hasShutdown = true;
                }
                return super.visitMethod(access, name, descriptor, signature, exceptions);
              }

              @Override
              public void visitEnd() {
                if (!hasShutdown) {
                  MethodVisitor mv = super.visitMethod(Opcodes.ACC_PUBLIC, "shutdown", "()V", null, null);
                  mv.visitCode();
                  mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "err", "Ljava/io/PrintStream;");
                  mv.visitLdcInsn("------- shutdown");
                  mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);
                  mv.visitVarInsn(Opcodes.ALOAD, 0);
                  mv.visitMethodInsn(Opcodes.INVOKESPECIAL, superName, "shutdown", "()V", false);
                  mv.visitInsn(Opcodes.RETURN);
                  mv.visitMaxs(0, 0);
                  mv.visitEnd();
                }
                super.visitEnd();
              }
            };
          }
        });
      }
    });

[huange7]

Your code is effective! Thank you very much for your assistance.👍🏻