bool VM_RedefineClasses::doit_prologue() {

  {- -------------------------------------------
  (1) コンストラクタ引数が不正な値であれば, ここで false をリターン.
      ---------------------------------------- -}

      if (_class_count == 0) {
        _res = JVMTI_ERROR_NONE;
        return false;
      }
      if (_class_defs == NULL) {
        _res = JVMTI_ERROR_NULL_POINTER;
        return false;
      }
      for (int i = 0; i < _class_count; i++) {
        if (_class_defs[i].klass == NULL) {
          _res = JVMTI_ERROR_INVALID_CLASS;
          return false;
        }
        if (_class_defs[i].class_byte_count == 0) {
          _res = JVMTI_ERROR_INVALID_CLASS_FORMAT;
          return false;
        }
        if (_class_defs[i].class_bytes == NULL) {
          _res = JVMTI_ERROR_NULL_POINTER;
          return false;
        }
      }

  {- -------------------------------------------
  (1) (トレース出力)
      ---------------------------------------- -}

      // Start timer after all the sanity checks; not quite accurate, but
      // better than adding a bunch of stop() calls.
      RC_TIMER_START(_timer_vm_op_prologue);

  {- -------------------------------------------
  (1) VM_RedefineClasses::load_new_class_versions() を呼んで, 新しいクラス定義情報を読み込む.
      (なお, もし失敗した場合はここで false をリターン)
      ---------------------------------------- -}

      // We first load new class versions in the prologue, because somewhere down the
      // call chain it is required that the current thread is a Java thread.
      _res = load_new_class_versions(Thread::current());
      if (_res != JVMTI_ERROR_NONE) {
        // Free os::malloc allocated memory in load_new_class_version.
        os::free(_scratch_classes);
        RC_TIMER_STOP(_timer_vm_op_prologue);
        return false;
      }

  {- -------------------------------------------
  (1) (トレース出力)
      ---------------------------------------- -}

      RC_TIMER_STOP(_timer_vm_op_prologue);

  {- -------------------------------------------
  (1) true をリターン
      ---------------------------------------- -}

      return true;
    }