mlogagent_ClassPrepare.c

void JNICALL ClassPrepareCallback(jvmtiEnv *jvmti_env, JNIEnv *jni, jthread thread, jclass klass) {
  // Avoid re-entrancy, and return early if we already attached.
  if (in_prepare || attached) {
    return;
  }
  
  in_prepare = true;

  jclass clazz = (*jni)->FindClass(jni, classConfig->name);
  // In case we don't find the class, don't throw an exception
  (*jni)->ExceptionClear(jni);
  if (clazz != NULL) {
    attachMethodBreakpoint(jvmti_env, jni, clazz);
    (*jni)->DeleteLocalRef(jni, clazz);
    attached = true;
  }

  in_prepare = false;
}

void attachMethodBreakpoint(jvmtiEnv *jvmti_env, JNIEnv *jni, jclass clazz) {
  // Look for the method. Here,
  //    methodName is something like "someMethod"
  //    methodSignature is something like "(Lfrodo/Test$RealFile;)Ljava/lang/String;"
  jmethodID mid = (*jni)->GetMethodID(jni, clazz, methodName, methodSignature);
  if (mid != NULL) {
    // Actually set the method breakpoint
    assert(JVMTI_ERROR_NONE == (*jvmti_env)->SetBreakpoint(jvmti_env, mid, 0));
  } else {
    fprintf(stderr, "mlogagent: Can't find the method\n");
  }
}