C++智能指针shared_ptr与weak_ptr的实现分析

template<typename _Ty>
class Mydeletor
{
public:
	Mydeletor() = default;
	void operator()(_Ty* p)const
	{
		if (p != NULL)
		{
			delete[]p;
		}
		p = NULL;
	}
};
template<typename _Ty>
class RefCnt
{
public:
	RefCnt(_Ty* p) :ptr(p), Uses(1), Weaks(0) 
    {
        cout <<"RefCnt construct"<<endl;
    }
	~RefCnt() {}
	void IncUses()
	{
		Uses += 1;
	}
	void IncWeaks()
	{
		Weaks += 1;
	}
protected:
	_Ty* ptr;
	std::atomic_int Uses;
	std::atomic_int Weaks;
	friend class M_shared_ptr<_Ty>;
	friend class M_weak_ptr<_Ty>;
};

template<typename _Ty,typename _De>
class M_shared_ptr
{
private:
	_Ty* Ptr;
	RefCnt<_Ty>* Ref;
	_De mdeletor;
public:
	M_shared_ptr(_Ty* p = nullptr) :Ptr(nullptr),Ref(nullptr)
	{
		if (p != nullptr)
		{
			Ptr = p;
			Ref = new RefCnt<_Ty>(p);
		}
	}
	M_shared_ptr(const M_shared_ptr& other):Ptr(other.Ptr),Ref(other.Ref)//拷贝构造
	{
		if (Ptr != NULL)
		{
			Ref->IncUses();
		}
	}
	M_shared_ptr(const M_weak_ptr<_Ty>& other):Ptr(other.GetRef()->ptr),Ref(other.GetRef())//用weak_ptr拷贝构造
	{
		if (Ptr != NULL)
		{
			Ref->IncUses();
		}
	}
	M_shared_ptr(M_shared_ptr&& other) :Ptr(other.Ptr), Ref(other.Ref)//移动构造
	{
		other.Ptr = NULL;
		other.Ref = NULL;
	}
	M_shared_ptr& operator=(const M_shared_ptr& other)//赋值
	{
		if (this == &other || Ptr == other.Ptr)  return *this;//自赋值，直接返回本身
		if (Ptr != NULL && --Ref->Uses == 0)//被赋值的智能指针对象拥有资源，
		{                                   //且该对象仅被该智能指针拥有
			mdeletor(Ptr);//释放该对象
			if (--Ref->Weaks == 0)//当弱引用计数为零时
			{
				delete Ref;//析构引用计数对象
				Ref = NULL;
			}
		}
		Ptr = other.Ptr;
		Ref = other.Ref;
		if (Ptr != NULL)
		{
			Ref->IncUses();
		}
		return *this;
	}
	M_shared_ptr& operator=(M_shared_ptr&& other)//移动赋值
	{
		if (this == &other)  return *this;
		if (Ptr == other.Ptr && Ptr != NULL)//当两个智能指针使用同一个对象时，且该对象不为空
		{
			other.Ptr = NULL;//去掉other的使用权
			other.Ref = NULL;
			Ref->Uses -= 1;//强引用计数-1
			return *this;
		}
		if (Ptr != NULL && --Ref->Uses == 0)
		{
			mdeletor(Ptr);
			if (--Ref->Weaks == 0)
			{
				delete Ref;
				Ref = NULL;
			}
		}
		Ptr = other.Ptr;
		Ref = other.Ref;
		other.Ptr = NULL;
		other.Ref = NULL;
		return *this;
	}
	~M_shared_ptr()
	{
		if (Ptr != NULL && --Ref->Uses == 0)
		{
			mdeletor(Ptr);
			if (--Ref->Weaks == 0)
			{
				delete Ref;
			}
		}
		Ref = NULL;
	}
	_Ty* get()const
	{
		return Ptr;
	}
	_Ty& operator*()
	{
		return *get();
	}
	_Ty* operator->()
	{
		return get();
	}
	size_t use_count()const
	{
		if (Ref == NULL)  return 0;
		return Ref->Uses;
	}
	void swap(M_shared_ptr& other)
	{
		std::swap(Ptr, other.Ptr);
		std::swap(Ref, other.Ref);
	}
	operator bool()const
	{
		return Ptr != NULL;
	}
	 friend class M_weak_ptr<_Ty>;
};

template<typename _Ty>
class M_weak_ptr
{
private:
	RefCnt<_Ty>* wRef;
public:
	size_t use_count()const
	{
		if (wRef == NULL)  return 0;
		return wRef->Uses;
	}
	size_t weak_count()const
	{
		if (wRef == NULL)  return 0;
		return wRef->Weaks;
	}
	RefCnt<_Ty>* GetRef() const
	{
		return wRef;
	}
	M_weak_ptr() :wRef(NULL) {}
	M_weak_ptr(const M_shared_ptr<_Ty>& other) :wRef(other.Ref)//共享指针构造
	{
		if (wRef!=NULL)
		{
			wRef->IncWeaks();
		}
	}
	M_weak_ptr(const M_weak_ptr& other) :wRef(other.wRef)//拷贝构造
	{
		if (wRef != NULL)
		{
			wRef->IncWeaks();
		}
	}
	M_weak_ptr(M_weak_ptr&& other) :wRef(other.wRef)//移动构造
	{
		other.wRef = NULL;
	}
	M_weak_ptr& operator=(const M_weak_ptr& other)
	{
		if (this == &other||wRef==other.wRef)  return *this;//自赋值或者是两个指针指向同一个对象
		if (this != NULL && --wRef->Weaks == 0)//是否自己独占对象
		{
			delete wRef;
		}
		wRef = other.wRef;
		if (wRef != NULL)
		{
			wRef->IncUses();
		}
		return *this;
	}
	M_weak_ptr& operator=(M_weak_ptr&& other)
	{
		//1 判断是否自赋值
		if (this == &other)  return *this;
		//2 判断是否是指向同一个对象的两个指针相互赋值
		if (wRef == other.wRef && wRef != NULL)//如果是
		{
			other.wRef = NULL;
			wRef->Weaks -= 1;
			return *this;
		}
		//3 两个指向不同对象的指针赋值
		if (this != NULL && --wRef->Weaks == 0)//是否自己独占对象
		{
			delete wRef;//如果独有
		}
		wRef = other.wRef;
		other.wRef = NULL;
		return *this;
	}
	M_weak_ptr& operator=(const M_shared_ptr<_Ty>& other)//共享智能指针给弱指针赋值
	{
		if (wRef == other.Ref)  return *this;

		if (wRef != NULL && --wRef->Uses == 0)
		{
			delete wRef;
		}
		wRef = other.Ref;
		if (wRef != NULL)
		{
			wRef->IncWeaks();
		}
		return *this;
	}
	M_weak_ptr& operator=( M_shared_ptr<_Ty>&& other) = delete;
	~M_weak_ptr()
	{
		if (wRef != NULL && --wRef->Weaks == 0)
		{
			delete wRef;
		}
		wRef = NULL;
	}
	bool expired()const//判断被引用的对象是否删除，若删除则返回真
	{
		return wRef->Uses == 0;
	}
	M_shared_ptr<_Ty> lock()const
	{
		M_shared_ptr<_Ty> tmp;
		tmp.Ptr = wRef->ptr;
		tmp.Ref = wRef;
		tmp.Ref->IncUses();
		return tmp;
	}
};

namespace boost
{
template<class T> class enable_shared_from_this
{
protected:
    enable_shared_from_this()
    {
    }
    enable_shared_from_this(enable_shared_from_this const &)
    {
    }
    enable_shared_from_this & operator=(enable_shared_from_this const &)
    {
        return *this;
    }
    ~enable_shared_from_this()
    {
    }
public:
    shared_ptr<T> shared_from_this()
    {
        shared_ptr<T> p( weak_this_ );
        BOOST_ASSERT( p.get() == this );
        return p;
    }
    shared_ptr<T const> shared_from_this() const
    {
        shared_ptr<T const> p( weak_this_ );
        BOOST_ASSERT( p.get() == this );
        return p;
    }
public: // actually private, but avoids compiler template friendship issues
    // Note: invoked automatically by shared_ptr; do not call
    template<class X, class Y> void _internal_accept_owner( shared_ptr<X> const * ppx, Y * py ) const
    {
        if( weak_this_.expired() )
        {
           //shared_ptr通过拷贝构造一个临时的shared_ptr，然后赋值给weak_ptr
           weak_this_ = shared_ptr<T>( *ppx, py );
        }
    }
private:
    mutable weak_ptr<T> weak_this_;
};
} // namespace boost

template<class Y>
explicit shared_ptr( Y * p ): px( p ), pn( p ) // Y must be complete
{
    boost::detail::sp_enable_shared_from_this( this, p, p );
}
template< class X, class Y, class T > inline void sp_enable_shared_from_this( boost::shared_ptr<X> const * ppx, Y const * py, boost::enable_shared_from_this< T > const * pe )
{
    if( pe != 0 )
    {
      //调用 enable_shared_from_this对象的函数 
      pe->_internal_accept_owner( ppx, const_cast< Y* >( py ) );
    }
}

#include <iOStream>
#include <memory>
class Demo
{
public:
    Demo()
    {
        std::cout << "constructor" << std::endl;
    }
    ~Demo()
    {
        std::cout << "destructor" << std::endl;
    }
    void StoreDemo(std::shared_ptr<Demo> ptr)
    {
        m_ptr = ptr;
    }
private:
    std::shared_ptr<Demo> m_ptr;
};
int main()
{
    std::shared_ptr<Demo> d_ptr(new Demo());
    d_ptr->StoreDemo(d_ptr); // this line is the bug
    return 0;
}

#include <iostream>
#include <memory>
class DemoB;
class DemoA
{
public:
	DemoA()
    {
		std::cout << "DemoA()" << std::endl;
    }
    ~DemoA()
    {
		std::cout << "~DemoA()" << std::endl;
    }
    void Set_Ptr(std::shared_ptr<DemoB>& ptr)
    {
		m_ptr_b = ptr;
    }
private:
    std::shared_ptr<DemoB> m_ptr_b;
};
class DemoB
{
public:
    DemoB()
    {
		std::cout << "DemoB()" << std::endl;
    }
    ~DemoB()
    {
		std::cout << "~DemoB()" << std::endl;
    }
    void Set_Ptr(std::shared_ptr<DemoA>& ptr)
    {
		m_ptr_a = ptr;
    }
private:
    std::shared_ptr<DemoA> m_ptr_a;
};
int main()
{
	std::shared_ptr<DemoA> ptr_a(new DemoA());
    std::shared_ptr<DemoB> ptr_b(new DemoB());
    ptr_a->Set_Ptr(ptr_b);
    ptr_b->Set_Ptr(ptr_a);
    std::cout << ptr_a.use_count() << " " << ptr_b.use_count() << std::endl;
	return 0;
}