agile.h

//
// Copyright (C) Microsoft Corporation
// All rights reserved.
//
// Code in Details namespace is for internal usage within the library code
//

#ifndef _PLATFORM_AGILE_H_
#define _PLATFORM_AGILE_H_

#ifdef _MSC_VER
#pragma once
#endif  // _MSC_VER

#include <algorithm>
#include <wrl\client.h>

#if !defined(__cplusplus_winrt)
#error agile.h can only be used with /ZW
#endif

namespace Platform
{
	namespace Details
	{
		__declspec(dllimport) IUnknown* __stdcall GetObjectContext();
		__declspec(dllimport) HRESULT __stdcall GetProxyImpl(::IUnknown*, REFIID, ::IUnknown*, ::IUnknown**);
		__declspec(dllimport) HRESULT __stdcall ReleaseInContextImpl(::IUnknown*, ::IUnknown*);

		template <typename T>
		__declspec(no_refcount) inline HRESULT GetProxy(T ^ObjectIn, ::IUnknown *ContextCallBack, T ^*Proxy)
		{
			return GetProxyImpl(*reinterpret_cast<IUnknown**>(&ObjectIn), __uuidof(T^) , ContextCallBack, reinterpret_cast< ::IUnknown**>(Proxy));
		}

		template <typename T>
		inline HRESULT ReleaseInContext(T *ObjectIn, ::IUnknown *ContextCallBack)
		{
			return ReleaseInContextImpl(ObjectIn, ContextCallBack);
		}

		template <typename T>
		class AgileHelper
		{
			__abi_IUnknown* _p;
			bool _release;
		public:
			AgileHelper(__abi_IUnknown* p, bool release = true) : _p(p), _release(release)
			{
			}
			AgileHelper(AgileHelper && other) : _p(other._p), _release(other._release)
			{
				_other._p = nullptr;
				_other._release = true;
			}
			AgileHelper operator=(AgileHelper && other)
			{
				_p = other._p;
				_release = other._release;
				_other._p = nullptr;
				_other._release = true;
				return *this;
			}

			~AgileHelper()
			{
				if (_release && _p)
				{
					_p->__abi_Release();
				}
			}

			__declspec(no_refcount) __declspec(no_release_return)
				T^ operator->()
			{
				return reinterpret_cast<T^>(_p);
			}

			__declspec(no_refcount) __declspec(no_release_return)
				operator T^()
			{
				return reinterpret_cast<T^>(_p);
			}
		private:
			AgileHelper(const AgileHelper&);
			AgileHelper operator=(const AgileHelper&) ;
		};
		template <typename T>
		struct __remove_hat
		{
			typedef T type;
		};
		template <typename T>
		struct __remove_hat<T^>
		{
			typedef T type;
		};
		template <typename T>
		struct AgileTypeHelper
		{
			typename typedef __remove_hat<T>::type type;
			typename typedef __remove_hat<T>::type^ agileMemberType;
		};
	} // namespace Details

#pragma warning(push)
#pragma warning(disable: 4451) // Usage of ref class inside this context can lead to invalid marshaling of object across contexts

	template <
		typename T,
		bool TIsNotAgile = (__is_win_class(typename Details::AgileTypeHelper<T>::type) && !__is_winrt_agile(typename Details::AgileTypeHelper<T>::type)) ||
		__is_win_interface(typename Details::AgileTypeHelper<T>::type)
	>
	class Agile
	{
		static_assert(__is_win_class(typename Details::AgileTypeHelper<T>::type) || __is_win_interface(typename Details::AgileTypeHelper<T>::type), "Agile can only be used with ref class or interface class types");
		typename typedef Details::AgileTypeHelper<T>::agileMemberType TypeT;
		TypeT _object;
		::Microsoft::WRL::ComPtr< ::IUnknown> _contextCallback;
		ULONG_PTR _contextToken;

		enum class AgileState
		{
			NonAgilePointer = 0,
			AgilePointer = 1,
			Unknown = 2
		};
		AgileState _agileState;

		void CaptureContext()
		{
			_contextCallback = Details::GetObjectContext();
			__abi_ThrowIfFailed(CoGetContextToken(&_contextToken));
		}

		void SetObject(TypeT object)
		{
			// Capture context before setting the pointer
			// If context capture fails then nothing to cleanup
			Release();
			if (object != nullptr)
			{
				::Microsoft::WRL::ComPtr< ::IAgileObject> checkIfAgile;
				HRESULT hr = reinterpret_cast< ::IUnknown*>(object)->QueryInterface(__uuidof(::IAgileObject), &checkIfAgile);
				// Don't Capture context if object is agile
				if (hr != S_OK)
				{
					_agileState = AgileState::NonAgilePointer;
					CaptureContext();
				}
				else
				{
					_agileState = AgileState::AgilePointer;
				}
			}
			_object = object;
		}

	public:
		Agile() throw() : _object(nullptr), _contextToken(0), _agileState(AgileState::Unknown)
		{
		}

		Agile(nullptr_t) throw() : _object(nullptr), _contextToken(0), _agileState(AgileState::Unknown)
		{
		}

		explicit Agile(TypeT object) throw() : _object(nullptr), _contextToken(0), _agileState(AgileState::Unknown)
		{
			// Assumes that the source object is from the current context
			SetObject(object);
		}

		Agile(const Agile& object) throw() : _object(nullptr), _contextToken(0), _agileState(AgileState::Unknown)
		{
			// Get returns pointer valid for current context
			SetObject(object.Get());
		}

		Agile(Agile && object) throw() : _object(nullptr), _contextToken(0), _agileState(AgileState::Unknown)
		{
			// Assumes that the source object is from the current context
			Swap(object);
		}

		~Agile() throw()
		{
			Release();
		}

		TypeT Get() const
		{
			// Agile object, no proxy required
			if (_agileState == AgileState::AgilePointer || _object == nullptr)
			{
				return _object;
			}

			// Do the check for same context
			ULONG_PTR currentContextToken;
			__abi_ThrowIfFailed(CoGetContextToken(&currentContextToken));
			if (currentContextToken == _contextToken)
			{
				return _object;
			}

			// Different context and holding on to a non agile object
			// Do the costly work of getting a proxy
			TypeT localObject;
			__abi_ThrowIfFailed(Details::GetProxy(_object, _contextCallback.Get(), &localObject));

			if (_agileState == AgileState::Unknown)
			{
				// Object is agile if it implements IAgileObject
				// GetAddressOf captures the context with out knowing the type of object that it will hold
				::Microsoft::WRL::ComPtr< ::IAgileObject> checkIfAgile;
				HRESULT hr = reinterpret_cast<IUnknown*>(localObject)->QueryInterface(__uuidof(::IAgileObject), &checkIfAgile);
				if (hr == S_OK)
				{
					auto pThis = const_cast<Agile*>(this);
					pThis->_agileState = AgileState::AgilePointer;
					pThis->_contextToken = 0;
					pThis->_contextCallback = nullptr;
					return _object;
				}
				else
				{
					auto pThis = const_cast<Agile*>(this);
					pThis->_agileState = AgileState::NonAgilePointer;
				}
			}

			return localObject;
		}

		TypeT* GetAddressOf() throw()
		{
			Release();
			CaptureContext();
			return &_object;
		}

		TypeT* GetAddressOfForInOut() throw()
		{
			CaptureContext();
			return &_object;
		}

		TypeT operator->() const throw()
		{
			return Get();
		}

		Agile& operator=(nullptr_t) throw()
		{
			Release();
			return *this;
		}

		Agile& operator=(TypeT object) throw()
		{
			Agile(object).Swap(*this);
			return *this;
		}

		Agile& operator=(Agile object) throw()
		{
			// parameter is by copy which gets pointer valid for current context 
			object.Swap(*this);
			return *this;
		}

		void Swap(Agile& object)
		{
			std::swap(_object, object._object);
			std::swap(_contextCallback, object._contextCallback);
			std::swap(_contextToken, object._contextToken);
			std::swap(_agileState, object._agileState);
		}

		// Release the interface and set to NULL
		void Release() throw()
		{
			if (_object)
			{
				// Cast to IInspectable (no QI)
				IUnknown* pObject = *(::IUnknown**) (&_object);
				// Set ^ to null without release
				*(IUnknown**) (&_object) = nullptr;

				ULONG_PTR currentContextToken;
				__abi_ThrowIfFailed(CoGetContextToken(&currentContextToken));
				if (_contextToken == 0 || _contextCallback == nullptr || _contextToken == currentContextToken)
				{
					pObject->Release();
				}
				else
				{
					Details::ReleaseInContext(pObject, _contextCallback.Get());
				}
				_contextCallback = nullptr;
				_contextToken = 0;
				_agileState = AgileState::Unknown;
			}
		}

		bool operator==(nullptr_t) const throw()
		{
			return _object == nullptr;
		}

		bool operator==(const Agile& other) const throw()
		{
			return _object == other._object && _contextToken == other._contextToken;
		}

		bool operator < (const Agile& other) const throw()
		{
			if (reinterpret_cast<void*>(_object) < reinterpret_cast<void*>(other._object))
			{
				return true;
			}

			return _object == other._object && _contextToken < other._contextToken;
		}
	};

	template <typename T>
	class Agile<T, false>
	{
		static_assert(__is_win_class(typename Details::AgileTypeHelper<T>::type) || __is_win_interface(typename Details::AgileTypeHelper<T>::type), "Agile can only be used with ref class or interface class types");
		typename typedef Details::AgileTypeHelper<T>::agileMemberType TypeT;
		TypeT _object;

	public:
		Agile() throw() : _object(nullptr)
		{
		}

		Agile(nullptr_t) throw() : _object(nullptr)
		{
		}

		explicit Agile(TypeT object) throw() : _object(object)
		{
		}

		Agile(const Agile& object) throw() : _object(object._object)
		{
		}

		Agile(Agile && object) throw() : _object(nullptr)
		{
			Swap(object);
		}

		~Agile() throw()
		{
			Release();
		}

		TypeT Get() const
		{
			return _object;
		}

		TypeT* GetAddressOf() throw()
		{
			Release();
			return &_object;
		}

		TypeT* GetAddressOfForInOut() throw()
		{
			return &_object;
		}

		TypeT operator->() const throw()
		{
			return Get();
		}

		Agile& operator=(nullptr_t) throw()
		{
			Release();
			return *this;
		}

		Agile& operator=(TypeT object) throw()
		{
			if (_object != object)
			{
				_object = object;
			}
			return *this;
		}

		Agile& operator=(Agile object) throw()
		{
			object.Swap(*this);
			return *this;
		}

		// Release the interface and set to NULL
		void Release() throw()
		{
			_object = nullptr;
		}

		void Swap(Agile& object)
		{
			std::swap(_object, object._object);
		}

		bool operator==(nullptr_t) const throw()
		{
			return _object == nullptr;
		}

		bool operator==(const Agile& other) const throw()
		{
			return _object == other._object;
		}

		bool operator < (const Agile& other) const throw()
		{
			return reinterpret_cast<void*>(_object) < reinterpret_cast<void*>(other._object);
		}
	};

#pragma warning(pop)

	template<class U>
	bool operator==(nullptr_t, const Agile<U>& a) throw()
	{
		return a == nullptr;
	}

	template<class U>
	bool operator!=(const Agile<U>& a, nullptr_t) throw()
	{
		return !(a == nullptr);
	}

	template<class U>
	bool operator!=(nullptr_t, const Agile<U>& a) throw()
	{
		return !(a == nullptr);
	}

	template<class U>
	bool operator!=(const Agile<U>& a, const Agile<U>& b) throw()
	{
		return !(a == b);
	}

} // namespace Platform

#endif // _PLATFORM_AGILE_H_