Deliver/include/Log4CPP/Common.Include/ExclusiveHolder.tlh

//-----------------------------------------------------------------------------
//		用排他锁实现的并发共享数据的模板类. 
//	不是 dll, 没有版本号, 因此要手工编写版本号
//	V1, 2013-09-03, 5.1.1 中发布, 使用 Synchronize.hpp
//	V2, 2018-03-02, 7.0 中发布, 改用 std::recursive_mutex 及 std::lock_guard
//	V3, 2020-09-30, 7.3 中发布, 删除 XDWHolder, 改用 std::unique_ptr. 同时修改了文件名
//	V4, 2022-09-30, LockHolder 中, 删除 std::unique_ptr, 直接用 std::lock_guard < std::recursive_mutex > m_Lock;
//      这样可以避免一次 new / delete
//-----------------------------------------------------------------------------


#pragma once

#include <memory>
#include <mutex>


//-----------------------------------------------------------------------------
//		ExclusiveHolder.tlh
//	允许互斥访问一个指针对象
//-----------------------------------------------------------------------------

template <typename T>
class ExclusiveHolder
{
protected:
	T * m_pObject;

public:
	ExclusiveHolder ();
	explicit ExclusiveHolder (T * object);

	virtual ~ExclusiveHolder ();

private:
//	禁止拷贝构造函数
	ExclusiveHolder (const ExclusiveHolder & h) = delete;
//	禁止复制
	ExclusiveHolder & operator = (const ExclusiveHolder & h) = delete;

public:
	void Attach (T * object);
	T * Detach ();

	ExclusiveHolder & operator = (T * object);

	bool IsEmpty () const;

	void Release ();

	std::recursive_mutex & GetMutex ()  { return m_Mutex; }

protected:
	mutable std::recursive_mutex m_Mutex;

public:
	class LockHolder
	{
	public:
		LockHolder (const ExclusiveHolder * holder)
			: m_Lock { std::lock_guard < std::recursive_mutex > (holder->m_Mutex) }
			, m_Holder (holder)
		{
			assert (m_Holder);
		}

		~LockHolder () = default;

		LockHolder (LockHolder && from)
		{
			m_Lock.swap (from.m_Lock);
			m_Holder = from.m_Holder;
		}

	private:
//	可以对同一个 ExclusiveHolder 对象反复调用 Lock, 但是 LockHolder 还是不要拷贝构造了吧
		//	禁止拷贝构造函数
		LockHolder (const LockHolder & h) = delete;
		//	禁止复制
		LockHolder & operator = (const LockHolder & h) = delete;

	public:
		T * As ()
		{
			return m_Holder->m_pObject;
		}
		const T * As () const
		{
			return m_Holder->m_pObject;
		}

		template <typename C> C * AS ()
		{
			return m_Holder->m_pObject;
		}
		template <typename C> const C * AS () const
		{
			return m_Holder->m_pObject;
		}

		T * operator -> ()
		{
			return As ();
		}
		const T * operator -> ()  const
		{
			return As ();
		}

		T & operator * ()
		{
			return *As ();
		}
		const T & operator * ()  const
		{
			return *As ();
		}

		operator bool () const
		{
			return As ();
		}

	protected:
		std::lock_guard < std::recursive_mutex > m_Lock;
		const ExclusiveHolder * m_Holder;
	};

public:
	inline LockHolder Lock ()
	{
		return LockHolder (this);
	}

	inline LockHolder Lock () const
	{
		return LockHolder (this);
	}

	template <typename FuncType, typename ... Args>
	auto Action (FuncType && action, Args && ... args) -> typename std::invoke_result <FuncType, T *, Args && ...>::type
	{
		LockHolder holder (this);
		return action (holder.As (), args...);
	}

#if 0
	template <typename FuncType, typename ... Args>
	auto Action (FuncType && action, Args && ... args) const -> typename std::invoke_result <FuncType, const T *, Args && ...>::type
	{
		LockHolder holder (this);
		return action (holder.As (), args...);
	}
#endif

};