scoped_refptr

用法：scoped_refptr只能引用显式实现了引用记数接口的类型：

0. 包含头文件：
   #include <ref_counted.h>
1. 基类先继承public base::RefCountedThreadSafe

例如：class MySlice : public base::RefCountedThreadSafe<Slice> {
......
}

2. 对象需前缀：

scoped_refptr<Slice> _slice;

3. 原理：

为啥对象需要scoped_refptr? 看下吗，它是把应用计数加一：

template <class T>
class scoped_refptr {
 public:
  scoped_refptr(T* p) : ptr_(p) {
    if (ptr_)
      ptr_->AddRef();
  }
  ~scoped_refptr() {
    if (ptr_)
      ptr_->Release();
  }
 protected:
  T* ptr_;
};

为啥需要继承public base::RefCountedThreadSafe？ 为了帮你实现引用计数的管理：

template <class T, typename Traits = DefaultRefCountedThreadSafeTraits<T> >
class RefCountedThreadSafe : public subtle::RefCountedThreadSafeBase {
 public:
  void AddRef() {
    subtle::RefCountedThreadSafeBase::AddRef();
  }
  void Release() {
    if (subtle::RefCountedThreadSafeBase::Release()) {
      Traits::Destruct(static_cast<T*>(this));
    }
  }
};
void RefCountedThreadSafeBase::AddRef() {
  AtomicRefCountInc(&ref_count_);
}