仪器removeTransformer在不同线程中不工作

Question

我正在尝试学习仪器以添加变形器，removeTransformer和reTransformer。

我试图添加变压器，它运作良好。

当我添加变压器后，如下图所示，除去变压器，它也很好。

public static void premain(String agentArgs, Instrumentation instrumentation) { 
    ClassFileTransformer transformer = new ClassFileTransformer() { 
     public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { 
      if (!className.contains("Test")) { 
       return classfileBuffer; 
      } 
      ClassReader cr = new ClassReader(classfileBuffer); 

      ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES); 
      cr.accept(new FieldAdapter(cw, new FieldNode(ASM5, Opcodes.ACC_PRIVATE, "hello", Type.getDescriptor(String.class), "test", "first")), 0); 
      return cw.toByteArray(); 
     } 
    }; 

    instrumentation.addTransformer(transformer, true); 
    instrumentation.removeTransformer(transformer); 
    } 

但是，当我试图在不同线程中移除变压器时，它不起作用。

public static void premain(String agentArgs, Instrumentation instrumentation) { 
    ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor(); 

    ClassFileTransformer transformer = new ClassFileTransformer() { 
     public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { 
      if (!className.contains("Test")) { 
       return classfileBuffer; 
      } 
      ClassReader cr = new ClassReader(classfileBuffer); 

      ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES); 
      cr.accept(new FieldAdapter(cw, new FieldNode(ASM5, Opcodes.ACC_PRIVATE, "hello", Type.getDescriptor(String.class), "test", "first")), 0); 
      return cw.toByteArray(); 
     } 
    }; 
    instrumentation.addTransformer(transformer, true); 

    executor.scheduleAtFixedRate(new RemoveTransform(instrumentation, transformer), 3, 10, TimeUnit.SECONDS); 
} 
static class RemoveTransform implements Runnable { 
    private Instrumentation instrumentation; 
    private ClassFileTransformer classFileTransformer; 
    public RemoveTransform(Instrumentation instrumentation, ClassFileTransformer classFileTransformer) { 
     this.instrumentation = instrumentation; 
     this.classFileTransformer = classFileTransformer; 
    } 

    public void run() { 
     System.out.println("removed transform....."); 
     instrumentation.removeTransformer(classFileTransformer); 
    } 
} 

我检查了输出，我肯定是移除变压器执行的线程。

Answer 1

当你移除一个变压器时，这并不意味着那些已经在复位时转换到旧状态的类。要发生这种情况，您必须显式重新转换已经加载的类。我假设在你的第一个例子中，所讨论的类在变换器被移除后被加载，而在第二个例子中这不再是真的。

类文件转换器可以从任何线程中删除。