【jvm学习笔记九】java的clone方法实现

这篇我们学习下jvm的clone实现，具体实现在jvm.cpp中：

  if (!klass->is_cloneable()) {
    // 若不支持clone方法（即未实现cloneable接口），则抛出异常
    ResourceMark rm(THREAD);
    THROW_MSG_0(vmSymbols::java_lang_CloneNotSupportedException(), klass->external_name());
  }

  // 获取对象大小，并分配对象空间
  const int size = obj->size();
  oop new_obj_oop = NULL;
  if (obj->is_array()) {
    const int length = ((arrayOop)obj())->length();
    new_obj_oop = CollectedHeap::array_allocate(klass, size, length, CHECK_NULL);
  } else {
    new_obj_oop = CollectedHeap::obj_allocate(klass, size, CHECK_NULL);
  }

  // 复制对象属性
  Copy::conjoint_jlongs_atomic((jlong*)obj(), (jlong*)new_obj_oop,
                               (size_t)align_object_size(size) / HeapWordsPerLong);
  // 初始化对象头
  new_obj_oop->init_mark();

  // Store check (mark entire object and let gc sort it out)
  BarrierSet* bs = Universe::heap()->barrier_set();
  bs->write_region(MemRegion((HeapWord*)new_obj_oop, size));

  Handle new_obj(THREAD, new_obj_oop);
  // Special handling for MemberNames.  Since they contain Method* metadata, they
  // must be registered so that RedefineClasses can fix metadata contained in them.
  if (java_lang_invoke_MemberName::is_instance(new_obj()) &&
      java_lang_invoke_MemberName::is_method(new_obj())) {
    Method* method = (Method*)java_lang_invoke_MemberName::vmtarget(new_obj());
    // MemberName may be unresolved, so doesn't need registration until resolved.
    if (method != NULL) {
      methodHandle m(THREAD, method);
      // This can safepoint and redefine method, so need both new_obj and method
      // in a handle, for two different reasons.  new_obj can move, method can be
      // deleted if nothing is using it on the stack.
      m->method_holder()->add_member_name(new_obj());
    }
  }

  // 实现了finalizer接口，需要注册到相关队列中
  if (klass->has_finalizer()) {
    assert(obj->is_instance(), "should be instanceOop");
    new_obj_oop = InstanceKlass::register_finalizer(instanceOop(new_obj()), CHECK_NULL);
    new_obj = Handle(THREAD, new_obj_oop);
  }

  return JNIHandles::make_local(env, new_obj());

clone方法主要是复制对象，当然只是浅拷贝。里面一些方法等处理不清楚原因，先略过。