pplxtasks.h

/***
* ==++==
*
* Copyright (c) Microsoft Corporation. All rights reserved. 
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0
* 
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* ==--==
* =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
*
* Parallel Patterns Library - PPLx Tasks
*
* For the latest on this and related APIs, please see http://casablanca.codeplex.com.
*
* =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
****/

#pragma once

#ifndef _PPLXTASKS_H
#define _PPLXTASKS_H

#if (defined(_MSC_VER) && (_MSC_VER >= 1800)) && !CPPREST_FORCE_PPLX
#include <ppltasks.h>
namespace pplx = Concurrency;
#if (_MSC_VER >= 1900)
#include <concrt.h>
namespace Concurrency {
    namespace extensibility {
        typedef ::std::condition_variable condition_variable_t;
        typedef ::std::mutex critical_section_t;
        typedef ::std::unique_lock< ::std::mutex> scoped_critical_section_t;

        typedef ::Concurrency::event event_t;
        typedef ::Concurrency::reader_writer_lock reader_writer_lock_t;
        typedef ::Concurrency::reader_writer_lock::scoped_lock scoped_rw_lock_t;
        typedef ::Concurrency::reader_writer_lock::scoped_lock_read scoped_read_lock_t;

        typedef ::Concurrency::details::_ReentrantBlockingLock recursive_lock_t;
        typedef recursive_lock_t::_Scoped_lock scoped_recursive_lock_t;
    }
}
#endif // _MSC_VER >= 1900
#else

#include "pplx/pplx.h"

#if defined(__ANDROID__)
#include <jni.h>
void cpprest_init(JavaVM*);
#endif

// Cannot build using a compiler that is older than dev10 SP1
#if defined(_MSC_VER)
#if _MSC_FULL_VER < 160040219 /*IFSTRIP=IGN*/
#error ERROR: Visual Studio 2010 SP1 or later is required to build ppltasks
#endif /*IFSTRIP=IGN*/
#endif /* defined(_MSC_VER) */

#include <functional>
#include <vector>
#include <utility>
#include <exception>
#include <algorithm>

#if defined(_MSC_VER)
#if defined(__cplusplus_winrt)
#include <windows.h>
#include <ctxtcall.h>
#include <agile.h>
#include <winapifamily.h>
#ifndef _UITHREADCTXT_SUPPORT

#ifdef WINAPI_FAMILY /*IFSTRIP=IGN*/

// It is safe to include winapifamily as WINAPI_FAMILY was defined by the user
#include <winapifamily.h>

#if WINAPI_FAMILY == WINAPI_FAMILY_APP
    // UI thread context support is not required for desktop and Windows Store apps
    #define _UITHREADCTXT_SUPPORT 0
#elif WINAPI_FAMILY == WINAPI_FAMILY_DESKTOP_APP
    // UI thread context support is not required for desktop and Windows Store apps
    #define _UITHREADCTXT_SUPPORT 0
#else  /* WINAPI_FAMILY == WINAPI_FAMILY_DESKTOP_APP */
    #define _UITHREADCTXT_SUPPORT 1
#endif  /* WINAPI_FAMILY == WINAPI_FAMILY_DESKTOP_APP */

#else  /* WINAPI_FAMILY */
    // Not supported without a WINAPI_FAMILY setting.
    #define _UITHREADCTXT_SUPPORT 0
#endif  /* WINAPI_FAMILY */

#endif  /* _UITHREADCTXT_SUPPORT */

#if _UITHREADCTXT_SUPPORT
    #include <uithreadctxt.h>
#endif  /* _UITHREADCTXT_SUPPORT */

    #pragma detect_mismatch("_PPLTASKS_WITH_WINRT", "1")
#else /* defined(__cplusplus_winrt) */
    #pragma detect_mismatch("_PPLTASKS_WITH_WINRT", "0")
#endif /* defined(__cplusplus_winrt) */
#endif /* defined(_MSC_VER) */

#ifdef _DEBUG
    #define _DBG_ONLY(X) X
#else
    #define _DBG_ONLY(X)
#endif // #ifdef _DEBUG

// std::copy_exception changed to std::make_exception_ptr from VS 2010 to VS 11.
#ifdef _MSC_VER
#if _MSC_VER < 1700 /*IFSTRIP=IGN*/
namespace std
{
    template<class _E> exception_ptr make_exception_ptr(_E _Except)
    {
        return copy_exception(_Except);
    }
}
#endif /* _MSC_VER < 1700 */
#ifndef _PPLTASK_ASYNC_LOGGING
    #if _MSC_VER >= 1800 && defined(__cplusplus_winrt)
        #define _PPLTASK_ASYNC_LOGGING 1  // Only enable async logging under dev12 winrt
    #else
        #define _PPLTASK_ASYNC_LOGGING 0
    #endif
#endif /* !_PPLTASK_ASYNC_LOGGING */
#endif /* _MSC_VER */

#pragma pack(push,_CRT_PACKING)

#if defined(_MSC_VER)
#pragma warning(push)
#pragma warning(disable: 28197)
#pragma warning(disable: 4100) // Unreferenced formal parameter - needed for document generation
#pragma warning(disable: 4127) // constant express in if condition - we use it for meta programming
#endif /* defined(_MSC_VER) */

// All CRT public header files are required to be protected from the macro new
#pragma push_macro("new")
#undef new

// stuff ported from Dev11 CRT
// NOTE: this doesn't actually match std::declval. it behaves differently for void!
// so don't blindly change it to std::declval.
namespace stdx
{
    template<class _T>
    _T&& declval();
}


namespace pplx
{

typedef task_group_status task_status;

template <typename _Type> class task;
template <> class task<void>;

// In debug builds, default to 10 frames, unless this is overridden prior to #includ'ing ppltasks.h.  In retail builds, default to only one frame.
#ifndef PPL_TASK_SAVE_FRAME_COUNT
#ifdef _DEBUG
#define PPL_TASK_SAVE_FRAME_COUNT 10
#else
#define PPL_TASK_SAVE_FRAME_COUNT 1
#endif
#endif

#if PPL_TASK_SAVE_FRAME_COUNT > 1
#if defined(__cplusplus_winrt) && !defined(_DEBUG)
#pragma message ("WARNING: Redefinning PPL_TASK_SAVE_FRAME_COUNT under Release build for non-desktop applications is not supported; only one frame will be captured!")
#define _CAPTURE_CALLSTACK() ::pplx::details::_TaskCreationCallstack::_CaptureSingleFrameCallstack(_ReturnAddress())
#else
#define _CAPTURE_CALLSTACK() ::pplx::details::_TaskCreationCallstack::_CaptureMultiFramesCallstack(PPL_TASK_SAVE_FRAME_COUNT)
#endif
#else
#define _CAPTURE_CALLSTACK() ::pplx::details::_TaskCreationCallstack::_CaptureSingleFrameCallstack(_ReturnAddress())
#endif



inline bool _pplx_cdecl is_task_cancellation_requested()
{
    return ::pplx::details::_TaskCollection_t::_Is_cancellation_requested();
}


inline __declspec(noreturn) void _pplx_cdecl cancel_current_task()
{
    throw task_canceled();
}

namespace details
{
    class _TaskCreationCallstack
    {
    private:
        // If _M_SingleFrame != nullptr, there will be only one frame of callstacks, which is stored in _M_SingleFrame;
        // otherwise, _M_Frame will store all the callstack frames.
        void* _M_SingleFrame;
        std::vector<void *> _M_frames;
    public:
        _TaskCreationCallstack()
        {
            _M_SingleFrame = nullptr;
        }

        // Store one frame of callstack. This function works for both Debug / Release CRT.
        static _TaskCreationCallstack _CaptureSingleFrameCallstack(void *_SingleFrame)
        {
            _TaskCreationCallstack _csc;
            _csc._M_SingleFrame = _SingleFrame;
            return _csc;
        }

        // Capture _CaptureFrames number of callstack frames. This function only work properly for Desktop or Debug CRT.
        __declspec(noinline)
        static _TaskCreationCallstack _CaptureMultiFramesCallstack(size_t _CaptureFrames)
        {
            _TaskCreationCallstack _csc;
            _csc._M_frames.resize(_CaptureFrames);
            // skip 2 frames to make sure callstack starts from user code 
            _csc._M_frames.resize(::pplx::details::platform::CaptureCallstack(&_csc._M_frames[0], 2, _CaptureFrames));
            return _csc;
        }
    };
    typedef unsigned char _Unit_type;

    struct _TypeSelectorNoAsync {};
    struct _TypeSelectorAsyncOperationOrTask {};
    struct _TypeSelectorAsyncOperation : public _TypeSelectorAsyncOperationOrTask { };
    struct _TypeSelectorAsyncTask : public _TypeSelectorAsyncOperationOrTask { };
    struct _TypeSelectorAsyncAction {};
    struct _TypeSelectorAsyncActionWithProgress {};
    struct _TypeSelectorAsyncOperationWithProgress {};

    template<typename _Ty>
    struct _NormalizeVoidToUnitType
    {
        typedef _Ty _Type;
    };

    template<>
    struct _NormalizeVoidToUnitType<void>
    {
        typedef _Unit_type _Type;
    };

    template<typename _T>
    struct _IsUnwrappedAsyncSelector
    {
        static const bool _Value = true;
    };

    template<>
    struct _IsUnwrappedAsyncSelector<_TypeSelectorNoAsync>
    {
        static const bool _Value = false;
    };

    template <typename _Ty>
    struct _UnwrapTaskType
    {
        typedef _Ty _Type;
    };

    template <typename _Ty>
    struct _UnwrapTaskType<task<_Ty>>
    {
        typedef _Ty _Type;
    };

    template <typename _T>
    _TypeSelectorAsyncTask _AsyncOperationKindSelector(task<_T>);

    _TypeSelectorNoAsync _AsyncOperationKindSelector(...);

#if defined(__cplusplus_winrt)
    template <typename _Type>
    struct _Unhat
    {
        typedef _Type _Value;
    };

    template <typename _Type>
    struct _Unhat<_Type^>
    {
        typedef _Type _Value;
    };

    value struct _NonUserType { public: int _Dummy; };

    template <typename _Type, bool _IsValueTypeOrRefType = __is_valid_winrt_type(_Type)>
    struct _ValueTypeOrRefType
    {
        typedef _NonUserType _Value;
    };

    template <typename _Type>
    struct _ValueTypeOrRefType<_Type, true>
    {
        typedef _Type _Value;
    };

    template <typename _T1, typename _T2>
    _T2 _ProgressTypeSelector(Windows::Foundation::IAsyncOperationWithProgress<_T1,_T2>^);

    template <typename _T1>
    _T1 _ProgressTypeSelector(Windows::Foundation::IAsyncActionWithProgress<_T1>^);

    template <typename _Type>
    struct _GetProgressType
    {
        typedef decltype(_ProgressTypeSelector(stdx::declval<_Type>())) _Value;
    };

    template <typename _Type>
    struct _IsIAsyncInfo
    {
        static const bool _Value = __is_base_of(Windows::Foundation::IAsyncInfo, typename _Unhat<_Type>::_Value);
    };

    template <typename _T>
    _TypeSelectorAsyncOperation _AsyncOperationKindSelector(Windows::Foundation::IAsyncOperation<_T>^);

    _TypeSelectorAsyncAction _AsyncOperationKindSelector(Windows::Foundation::IAsyncAction^);

    template <typename _T1, typename _T2>
    _TypeSelectorAsyncOperationWithProgress _AsyncOperationKindSelector(Windows::Foundation::IAsyncOperationWithProgress<_T1, _T2>^);

    template <typename _T>
    _TypeSelectorAsyncActionWithProgress _AsyncOperationKindSelector(Windows::Foundation::IAsyncActionWithProgress<_T>^);

    template <typename _Type, bool _IsAsync = _IsIAsyncInfo<_Type>::_Value>
    struct _TaskTypeTraits
    {
        typedef typename _UnwrapTaskType<_Type>::_Type _TaskRetType;
        typedef decltype(_AsyncOperationKindSelector(stdx::declval<_Type>())) _AsyncKind;
        typedef typename _NormalizeVoidToUnitType<_TaskRetType>::_Type _NormalizedTaskRetType;

        static const bool _IsAsyncTask = _IsAsync;
        static const bool _IsUnwrappedTaskOrAsync = _IsUnwrappedAsyncSelector<_AsyncKind>::_Value;
    };

    template<typename _Type>
    struct _TaskTypeTraits<_Type, true >
    {
        typedef decltype(((_Type)nullptr)->GetResults()) _TaskRetType;
        typedef _TaskRetType _NormalizedTaskRetType;
        typedef decltype(_AsyncOperationKindSelector((_Type)nullptr)) _AsyncKind;

        static const bool _IsAsyncTask = true;
        static const bool _IsUnwrappedTaskOrAsync = _IsUnwrappedAsyncSelector<_AsyncKind>::_Value;
    };

#else  /* defined (__cplusplus_winrt) */
    template <typename _Type>
    struct _IsIAsyncInfo
    {
        static const bool _Value = false;
    };

    template <typename _Type, bool _IsAsync = false>
    struct _TaskTypeTraits
    {
        typedef typename _UnwrapTaskType<_Type>::_Type _TaskRetType;
        typedef decltype(_AsyncOperationKindSelector(stdx::declval<_Type>())) _AsyncKind;
        typedef typename _NormalizeVoidToUnitType<_TaskRetType>::_Type _NormalizedTaskRetType;

        static const bool _IsAsyncTask = false;
        static const bool _IsUnwrappedTaskOrAsync = _IsUnwrappedAsyncSelector<_AsyncKind>::_Value;
    };
#endif  /* defined (__cplusplus_winrt) */

    template <typename _Function> auto _IsCallable(_Function _Func, int) -> decltype(_Func(), std::true_type()) { (void)(_Func); return std::true_type(); }
    template <typename _Function> std::false_type _IsCallable(_Function, ...) { return std::false_type(); }

    template <>
    struct _TaskTypeTraits<void>
    {
        typedef void _TaskRetType;
        typedef _TypeSelectorNoAsync _AsyncKind;
        typedef _Unit_type _NormalizedTaskRetType;

        static const bool _IsAsyncTask = false;
        static const bool _IsUnwrappedTaskOrAsync = false;
    };

    template<typename _Type>
    task<_Type> _To_task(_Type t);
    
    template<typename _Func>
    task<void> _To_task_void(_Func f);
    
    struct _BadContinuationParamType{};

    template <typename _Function, typename _Type> auto _ReturnTypeHelper(_Type t, _Function _Func, int, int) -> decltype(_Func(_To_task(t)));
    template <typename _Function, typename _Type> auto _ReturnTypeHelper(_Type t, _Function _Func, int, ...) -> decltype(_Func(t));
    template <typename _Function, typename _Type> auto _ReturnTypeHelper(_Type t, _Function _Func, ...) -> _BadContinuationParamType;

    template <typename _Function, typename _Type> auto _IsTaskHelper(_Type t, _Function _Func, int, int) -> decltype(_Func(_To_task(t)), std::true_type());
    template <typename _Function, typename _Type> std::false_type _IsTaskHelper(_Type t, _Function _Func, int, ...);

    template <typename _Function> auto _VoidReturnTypeHelper(_Function _Func, int, int) -> decltype(_Func(_To_task_void(_Func)));
    template <typename _Function> auto _VoidReturnTypeHelper(_Function _Func, int, ...) -> decltype(_Func());

    template <typename _Function> auto _VoidIsTaskHelper(_Function _Func, int, int) -> decltype(_Func(_To_task_void(_Func)), std::true_type());
    template <typename _Function> std::false_type _VoidIsTaskHelper(_Function _Func, int, ...);

    template<typename _Function, typename _ExpectedParameterType>
    struct _FunctionTypeTraits
    {
        typedef decltype(_ReturnTypeHelper(stdx::declval<_ExpectedParameterType>(),stdx::declval<_Function>(), 0, 0)) _FuncRetType;
        static_assert(!std::is_same<_FuncRetType,_BadContinuationParamType>::value, "incorrect parameter type for the callable object in 'then'; consider _ExpectedParameterType or task<_ExpectedParameterType> (see below)");

        typedef decltype(_IsTaskHelper(stdx::declval<_ExpectedParameterType>(),stdx::declval<_Function>(), 0, 0)) _Takes_task;
    };

    template<typename _Function>
    struct _FunctionTypeTraits<_Function, void>
    {
        typedef decltype(_VoidReturnTypeHelper(stdx::declval<_Function>(), 0, 0)) _FuncRetType;
        typedef decltype(_VoidIsTaskHelper(stdx::declval<_Function>(), 0, 0)) _Takes_task;
    };

    template<typename _Function, typename _ReturnType>
    struct _ContinuationTypeTraits
    {
        typedef task<typename _TaskTypeTraits<typename _FunctionTypeTraits<_Function, _ReturnType>::_FuncRetType>::_TaskRetType> _TaskOfType;
    };

    // _InitFunctorTypeTraits is used to decide whether a task constructed with a lambda should be unwrapped. Depending on how the variable is
    // declared, the constructor may or may not perform unwrapping. For eg.
    //
    //  This declaration SHOULD NOT cause unwrapping
    //    task<task<void>> t1([]() -> task<void> {
    //        task<void> t2([]() {});
    //        return t2;
    //    });
    //
    // This declaration SHOULD cause unwrapping
    //    task<void>> t1([]() -> task<void> {
    //        task<void> t2([]() {});
    //        return t2;
    //    });
    // If the type of the task is the same as the return type of the function, no unwrapping should take place. Else normal rules apply.
    template <typename _TaskType, typename _FuncRetType>
    struct _InitFunctorTypeTraits
    {
        typedef typename _TaskTypeTraits<_FuncRetType>::_AsyncKind _AsyncKind;
        static const bool _IsAsyncTask = _TaskTypeTraits<_FuncRetType>::_IsAsyncTask;
        static const bool _IsUnwrappedTaskOrAsync = _TaskTypeTraits<_FuncRetType>::_IsUnwrappedTaskOrAsync;
    };

    template<typename T>
    struct _InitFunctorTypeTraits<T, T>
    {
        typedef _TypeSelectorNoAsync _AsyncKind;
        static const bool _IsAsyncTask = false;
        static const bool _IsUnwrappedTaskOrAsync = false;
    };

    struct _TaskProcThunk
    {
        _TaskProcThunk(const std::function<void ()> & _Callback) :
            _M_func(_Callback)
        {
        }

        static void _pplx_cdecl _Bridge(void *_PData)
        {
            _TaskProcThunk *_PThunk = reinterpret_cast<_TaskProcThunk *>(_PData);
            _Holder _ThunkHolder(_PThunk);
            _PThunk->_M_func();
        }
    private:

        // RAII holder
        struct _Holder
        {
            _Holder(_TaskProcThunk * _PThunk) : _M_pThunk(_PThunk)
            {
            }

            ~_Holder()
            {
                delete _M_pThunk;
            }

            _TaskProcThunk * _M_pThunk;

        private:
            _Holder& operator=(const _Holder&);
        };

        std::function<void()> _M_func;
        _TaskProcThunk& operator=(const _TaskProcThunk&);
    };

    static void _ScheduleFuncWithAutoInline(const std::function<void ()> & _Func, _TaskInliningMode_t _InliningMode)
    {
        _TaskCollection_t::_RunTask(&_TaskProcThunk::_Bridge, new _TaskProcThunk(_Func), _InliningMode);
    }

    class _ContextCallback
    {
        typedef std::function<void(void)> _CallbackFunction;

#if defined (__cplusplus_winrt)

    public:

        static _ContextCallback _CaptureCurrent()
        {
            _ContextCallback _Context;
            _Context._Capture();
            return _Context;
        }

        ~_ContextCallback()
        {
            _Reset();
        }

        _ContextCallback(bool _DeferCapture = false)
        {
            if (_DeferCapture)
            {
                _M_context._M_captureMethod = _S_captureDeferred;
            }
            else
            {
                _M_context._M_pContextCallback = nullptr;
            }
        }

        // Resolves a context that was created as _S_captureDeferred based on the environment (ancestor, current context).
        void _Resolve(bool _CaptureCurrent)
        {
            if(_M_context._M_captureMethod == _S_captureDeferred)
            {
                _M_context._M_pContextCallback = nullptr;

                if (_CaptureCurrent)
                {
                    if (_IsCurrentOriginSTA())
                    {
                        _Capture();
                    }
#if _UITHREADCTXT_SUPPORT
                    else
                    {
                        // This method will fail if not called from the UI thread.
                        HRESULT _Hr = CaptureUiThreadContext(&_M_context._M_pContextCallback);
                        if (FAILED(_Hr))
                        {
                            _M_context._M_pContextCallback = nullptr;
                        }
                    }
#endif  /* _UITHREADCTXT_SUPPORT */
                }
            }
        }

        void _Capture()
        {
            HRESULT _Hr = CoGetObjectContext(IID_IContextCallback, reinterpret_cast<void **>(&_M_context._M_pContextCallback));
            if (FAILED(_Hr))
            {
                _M_context._M_pContextCallback = nullptr;
            }
        }

        _ContextCallback(const _ContextCallback& _Src)
        {
            _Assign(_Src._M_context._M_pContextCallback);
        }

        _ContextCallback(_ContextCallback&& _Src)
        {
            _M_context._M_pContextCallback = _Src._M_context._M_pContextCallback;
            _Src._M_context._M_pContextCallback = nullptr;
        }

        _ContextCallback& operator=(const _ContextCallback& _Src)
        {
            if (this != &_Src)
            {
                _Reset();
                _Assign(_Src._M_context._M_pContextCallback);
            }
            return *this;
        }

        _ContextCallback& operator=(_ContextCallback&& _Src)
        {
            if (this != &_Src)
            {
                _M_context._M_pContextCallback = _Src._M_context._M_pContextCallback;
                _Src._M_context._M_pContextCallback = nullptr;
            }
            return *this;
        }

        bool _HasCapturedContext() const
        {
            _ASSERTE(_M_context._M_captureMethod != _S_captureDeferred);
            return (_M_context._M_pContextCallback != nullptr);
        }

        void _CallInContext(_CallbackFunction _Func) const
        {
            if (!_HasCapturedContext())
            {
                _Func();
            }
            else
            {
                ComCallData callData;
                ZeroMemory(&callData, sizeof(callData));
                callData.pUserDefined = reinterpret_cast<void *>(&_Func);

                HRESULT _Hr = _M_context._M_pContextCallback->ContextCallback(&_Bridge, &callData, IID_ICallbackWithNoReentrancyToApplicationSTA, 5, nullptr);
                if (FAILED(_Hr))
                {
                    throw ::Platform::Exception::CreateException(_Hr);
                }
            }
        }

        bool operator==(const _ContextCallback& _Rhs) const
        {
            return (_M_context._M_pContextCallback == _Rhs._M_context._M_pContextCallback);
        }

        bool operator!=(const _ContextCallback& _Rhs) const
        {
            return !(operator==(_Rhs));
        }

    private:
       void _Reset()
        {
            if (_M_context._M_captureMethod != _S_captureDeferred && _M_context._M_pContextCallback != nullptr)
            {
                _M_context._M_pContextCallback->Release();
            }
        }

        void _Assign(IContextCallback *_PContextCallback)
        {
            _M_context._M_pContextCallback = _PContextCallback;
            if (_M_context._M_captureMethod != _S_captureDeferred && _M_context._M_pContextCallback != nullptr)
            {
                _M_context._M_pContextCallback->AddRef();
            }
        }

        static HRESULT __stdcall _Bridge(ComCallData *_PParam)
        {
            _CallbackFunction *pFunc = reinterpret_cast<_CallbackFunction *>(_PParam->pUserDefined);
            (*pFunc)();
            return S_OK;
        }

        // Returns the origin information for the caller (runtime / Windows Runtime apartment as far as task continuations need know)
        static bool _IsCurrentOriginSTA()
        {
            APTTYPE _AptType;
            APTTYPEQUALIFIER _AptTypeQualifier;

            HRESULT hr = CoGetApartmentType(&_AptType, &_AptTypeQualifier);
            if (SUCCEEDED(hr))
            {
                // We determine the origin of a task continuation by looking at where .then is called, so we can tell whether
                // to need to marshal the continuation back to the originating apartment. If an STA thread is in executing in
                // a neutral aparment when it schedules a continuation, we will not marshal continuations back to the STA,
                // since variables used within a neutral apartment are expected to be apartment neutral.
                switch(_AptType)
                {
                    case APTTYPE_MAINSTA:
                    case APTTYPE_STA:
                        return true;
                    default:
                        break;
                }
            }
            return false;
        }

        union
        {
            IContextCallback *_M_pContextCallback;
            size_t _M_captureMethod;
        } _M_context;

        static const size_t _S_captureDeferred = 1;
#else  /* defined (__cplusplus_winrt) */
    public:

        static _ContextCallback _CaptureCurrent()
        {
            return _ContextCallback();
        }

        _ContextCallback(bool = false)
        {
        }

        _ContextCallback(const _ContextCallback&)
        {
        }

        _ContextCallback(_ContextCallback&&)
        {
        }

        _ContextCallback& operator=(const _ContextCallback&)
        {
            return *this;
        }

        _ContextCallback& operator=(_ContextCallback&&)
        {
            return *this;
        }

        bool _HasCapturedContext() const
        {
            return false;
        }

        void _Resolve(bool) const
        {
        }

        void _CallInContext(_CallbackFunction _Func) const
        {
            _Func();
        }

        bool operator==(const _ContextCallback&) const
        {
            return true;
        }

        bool operator!=(const _ContextCallback&) const
        {
            return false;
        }

#endif  /* defined (__cplusplus_winrt) */
    };

    template<typename _Type>
    struct _ResultHolder
    {
        void Set(const _Type& _type)
        {
            _Result = _type;
        }

        _Type Get()
        {
            return _Result;
        }

        _Type _Result;
    };

#if defined (__cplusplus_winrt)

    template<typename _Type>
    struct _ResultHolder<_Type^>
    {
        void Set(_Type^ const & _type)
        {
           _M_Result = _type;
        }

        _Type^ Get()
        {
            return _M_Result.Get();
        }
    private:
        // ::Platform::Agile handle specialization of all hats
        // including ::Platform::String and ::Platform::Array
        ::Platform::Agile<_Type^> _M_Result;
    };

    //
    // The below are for composability with tasks auto-created from when_any / when_all / && / || constructs.
    //
    template<typename _Type>
    struct _ResultHolder<std::vector<_Type^>>
    {
        void Set(const std::vector<_Type^>& _type)
        {
            _Result.reserve(_type.size());

            for (auto _PTask = _type.begin(); _PTask != _type.end(); ++_PTask)
            {
                _Result.emplace_back(*_PTask);
            }
        }

        std::vector<_Type^> Get()
        {
            // Return vectory<T^> with the objects that are marshaled in the proper appartment
            std::vector<_Type^> _Return;
            _Return.reserve(_Result.size());

            for (auto _PTask = _Result.begin(); _PTask != _Result.end(); ++_PTask)
            {
                _Return.push_back(_PTask->Get()); // Platform::Agile will marshal the object to appropriate appartment if neccessary
            }

            return _Return;
        }

        std::vector< ::Platform::Agile<_Type^> > _Result;
    };

    template<typename _Type>
    struct _ResultHolder<std::pair<_Type^, void*> >
    {
        void Set(const std::pair<_Type^, size_t>& _type)
        {
            _M_Result = _type;
        }

        std::pair<_Type^, size_t> Get()
        {
            return std::make_pair(_M_Result.first.Get(), _M_Result.second);
        }
    private:
        std::pair< ::Platform::Agile<_Type^>, size_t> _M_Result;
    };

#endif  /* defined (__cplusplus_winrt) */

    // An exception thrown by the task body is captured in an exception holder and it is shared with all value based continuations rooted at the task.
    // The exception is 'observed' if the user invokes get()/wait() on any of the tasks that are sharing this exception holder. If the exception
    // is not observed by the time the internal object owned by the shared pointer destructs, the process will fail fast.
    struct _ExceptionHolder
    {
    private:
        void ReportUnhandledError()
        {
#if _MSC_VER >= 1800 && defined(__cplusplus_winrt)
            if (_M_winRTException != nullptr)
            {
                ::Platform::Details::ReportUnhandledError(_M_winRTException);
            }
#endif  /* defined (__cplusplus_winrt) */
        }
    public:
        explicit _ExceptionHolder(const std::exception_ptr& _E, const _TaskCreationCallstack &_stackTrace) :
        _M_exceptionObserved(0), _M_stdException(_E), _M_stackTrace(_stackTrace)
#if defined (__cplusplus_winrt)
            , _M_winRTException(nullptr)
#endif  /* defined (__cplusplus_winrt) */
        {
        }

#if defined (__cplusplus_winrt)
        explicit _ExceptionHolder(::Platform::Exception^ _E, const _TaskCreationCallstack &_stackTrace) :
        _M_exceptionObserved(0),  _M_winRTException(_E), _M_stackTrace(_stackTrace)
        {
        }
#endif  /* defined (__cplusplus_winrt) */

        __declspec(noinline)
        ~_ExceptionHolder()
        {
            if (_M_exceptionObserved == 0)
            {
                // If you are trapped here, it means an exception thrown in task chain didn't get handled.
                // Please add task-based continuation to handle all exceptions coming from tasks.
                // this->_M_stackTrace keeps the creation callstack of the task generates this exception.
                _REPORT_PPLTASK_UNOBSERVED_EXCEPTION();
            }
        }

        void _RethrowUserException()
        {
            if (_M_exceptionObserved == 0)
            {
                atomic_exchange(_M_exceptionObserved, 1l);
            }

#if defined (__cplusplus_winrt)
            if (_M_winRTException != nullptr)
            {
                throw _M_winRTException;
            }
#endif  /* defined (__cplusplus_winrt) */
            std::rethrow_exception(_M_stdException);
        }

        // A variable that remembers if this exception was every rethrown into user code (and hence handled by the user). Exceptions that
        // are unobserved when the exception holder is destructed will terminate the process.
        atomic_long _M_exceptionObserved;

        // Either _M_stdException or _M_winRTException is populated based on the type of exception encountered.
        std::exception_ptr _M_stdException;
#if defined (__cplusplus_winrt)
        ::Platform::Exception^ _M_winRTException;
#endif  /* defined (__cplusplus_winrt) */

        // Disassembling this value will point to a source instruction right after a call instruction. If the call is to create_task,
        // a task constructor or the then method, the task created by that method is the one that encountered this exception. If the call
        // is to task_completion_event::set_exception, the set_exception method was the source of the exception.
        // DO NOT REMOVE THIS VARIABLE. It is extremely helpful for debugging.
        _TaskCreationCallstack _M_stackTrace;

    };

#if defined (__cplusplus_winrt)
    template<typename _AsyncOperationType, typename _CompletionHandlerType, typename _Result>
    ref struct _AsyncInfoImpl abstract : Windows::Foundation::IAsyncOperation<_Result>
    {
    internal:
        // The async action, action with progress or operation with progress that this stub forwards to.
        ::Platform::Agile<_AsyncOperationType> _M_asyncInfo;

        Windows::Foundation::AsyncOperationCompletedHandler<_Result>^ _M_CompletedHandler;

        _AsyncInfoImpl( _AsyncOperationType _AsyncInfo ) : _M_asyncInfo(_AsyncInfo) {}

    public:
        virtual void Cancel() { _M_asyncInfo.Get()->Cancel(); }
        virtual void Close() { _M_asyncInfo.Get()->Close(); }

        virtual property Windows::Foundation::HResult ErrorCode
        {
            Windows::Foundation::HResult get()
            {
                return _M_asyncInfo.Get()->ErrorCode;
            }
        }

        virtual property UINT Id
        {
            UINT get()
            {
                return _M_asyncInfo.Get()->Id;
            }
        }

        virtual property Windows::Foundation::AsyncStatus Status
        {
            Windows::Foundation::AsyncStatus get()
            {
                return _M_asyncInfo.Get()->Status;
            }
        }

        virtual _Result GetResults() { throw std::runtime_error("derived class must implement"); }

        virtual property Windows::Foundation::AsyncOperationCompletedHandler<_Result>^ Completed
        {
            Windows::Foundation::AsyncOperationCompletedHandler<_Result>^ get()
            {
                return _M_CompletedHandler;
            }

            void set(Windows::Foundation::AsyncOperationCompletedHandler<_Result>^ value)
            {
                _M_CompletedHandler = value;
                _M_asyncInfo.Get()->Completed = ref new _CompletionHandlerType([&](_AsyncOperationType, Windows::Foundation::AsyncStatus status) {
                    _M_CompletedHandler->Invoke(this, status);
                });
            }
        }
    };

    template<typename _Result, typename _Progress>
    ref struct _IAsyncOperationWithProgressToAsyncOperationConverter sealed :
        _AsyncInfoImpl<Windows::Foundation::IAsyncOperationWithProgress<_Result,_Progress>^,
                      Windows::Foundation::AsyncOperationWithProgressCompletedHandler<_Result,_Progress>,
                      _Result>
    {
    internal:
        _IAsyncOperationWithProgressToAsyncOperationConverter(Windows::Foundation::IAsyncOperationWithProgress<_Result,_Progress>^ _Operation) :
            _AsyncInfoImpl<Windows::Foundation::IAsyncOperationWithProgress<_Result,_Progress>^,
                          Windows::Foundation::AsyncOperationWithProgressCompletedHandler<_Result,_Progress>,
                          _Result>(_Operation) {}

    public:
        virtual _Result GetResults() override { return _M_asyncInfo.Get()->GetResults(); }
    };

    ref struct _IAsyncActionToAsyncOperationConverter sealed :
        _AsyncInfoImpl<Windows::Foundation::IAsyncAction^,
                      Windows::Foundation::AsyncActionCompletedHandler,
                      details::_Unit_type>
    {
    internal:
        _IAsyncActionToAsyncOperationConverter(Windows::Foundation::IAsyncAction^ _Operation) :
            _AsyncInfoImpl<Windows::Foundation::IAsyncAction^,
                          Windows::Foundation::AsyncActionCompletedHandler,
                          details::_Unit_type>(_Operation) {}

    public:
        virtual details::_Unit_type GetResults() override
        {
            // Invoke GetResults on the IAsyncAction to allow exceptions to be thrown to higher layers before returning a dummy value.
            _M_asyncInfo.Get()->GetResults();
            return details::_Unit_type();
        }
    };

    template<typename _Progress>
    ref struct _IAsyncActionWithProgressToAsyncOperationConverter sealed :
        _AsyncInfoImpl<Windows::Foundation::IAsyncActionWithProgress<_Progress>^,
                      Windows::Foundation::AsyncActionWithProgressCompletedHandler<_Progress>,
                      details::_Unit_type>
    {
    internal:
        _IAsyncActionWithProgressToAsyncOperationConverter(Windows::Foundation::IAsyncActionWithProgress<_Progress>^ _Action) :
            _AsyncInfoImpl<Windows::Foundation::IAsyncActionWithProgress<_Progress>^,
                          Windows::Foundation::AsyncActionWithProgressCompletedHandler<_Progress>,
                          details::_Unit_type>(_Action) {}
    public:
        virtual details::_Unit_type GetResults() override
        {
            // Invoke GetResults on the IAsyncActionWithProgress to allow exceptions to be thrown before returning a dummy value.
            _M_asyncInfo.Get()->GetResults();
            return details::_Unit_type();
        }
    };
#endif  /* defined (__cplusplus_winrt) */
} // namespace details


class task_continuation_context : public details::_ContextCallback
{
public:

    
    static task_continuation_context use_default()
    {
#if defined (__cplusplus_winrt)
        // The callback context is created with the context set to CaptureDeferred and resolved when it is used in .then()
        return task_continuation_context(true); // sets it to deferred, is resolved in the constructor of _ContinuationTaskHandle
#else  /* defined (__cplusplus_winrt) */
        return task_continuation_context();
#endif  /* defined (__cplusplus_winrt) */
    }

#if defined (__cplusplus_winrt)
    
    static task_continuation_context use_arbitrary()
    {
        task_continuation_context _Arbitrary(true);
        _Arbitrary._Resolve(false);
        return _Arbitrary;
    }

    
    static task_continuation_context use_current()
    {
        task_continuation_context _Current(true);
        _Current._Resolve(true);
        return _Current;
    }
#endif  /* defined (__cplusplus_winrt) */

private:

    task_continuation_context(bool _DeferCapture = false) : details::_ContextCallback(_DeferCapture)
    {
    }
};

class task_options;
namespace details
{
    struct _Internal_task_options
    {
        bool _M_hasPresetCreationCallstack;
        _TaskCreationCallstack _M_presetCreationCallstack;

        void _set_creation_callstack(const _TaskCreationCallstack &_callstack)
        {
            _M_hasPresetCreationCallstack = true;
            _M_presetCreationCallstack = _callstack;
        }
        _Internal_task_options()
        {
            _M_hasPresetCreationCallstack = false;
        }
    };

    inline _Internal_task_options &_get_internal_task_options(task_options &options);
    inline const _Internal_task_options &_get_internal_task_options(const task_options &options);
}
class task_options
{
public:


    task_options()
        : _M_Scheduler(get_ambient_scheduler()),
          _M_CancellationToken(cancellation_token::none()),
          _M_ContinuationContext(task_continuation_context::use_default()),
          _M_HasCancellationToken(false),
          _M_HasScheduler(false)
    {
    }

    task_options(cancellation_token _Token)
        : _M_Scheduler(get_ambient_scheduler()),
          _M_CancellationToken(_Token),
          _M_ContinuationContext(task_continuation_context::use_default()),
          _M_HasCancellationToken(true),
          _M_HasScheduler(false)
    {
    }

    task_options(task_continuation_context _ContinuationContext)
        : _M_Scheduler(get_ambient_scheduler()),
          _M_CancellationToken(cancellation_token::none()),
          _M_ContinuationContext(_ContinuationContext),
          _M_HasCancellationToken(false),
          _M_HasScheduler(false)
    {
    }

    task_options(cancellation_token _Token, task_continuation_context _ContinuationContext)
        : _M_Scheduler(get_ambient_scheduler()),
          _M_CancellationToken(_Token),
          _M_ContinuationContext(_ContinuationContext),
          _M_HasCancellationToken(false),
          _M_HasScheduler(false)
    {
    }

    template<typename _SchedType>
    task_options(std::shared_ptr<_SchedType> _Scheduler)
        : _M_Scheduler(std::move(_Scheduler)),
          _M_CancellationToken(cancellation_token::none()),
          _M_ContinuationContext(task_continuation_context::use_default()),
          _M_HasCancellationToken(false),
          _M_HasScheduler(true)
    {
    }

    task_options(scheduler_interface& _Scheduler)
        : _M_Scheduler(&_Scheduler),
          _M_CancellationToken(cancellation_token::none()),
          _M_ContinuationContext(task_continuation_context::use_default()),
          _M_HasCancellationToken(false),
          _M_HasScheduler(true)
    {
    }

    task_options(scheduler_ptr _Scheduler)
        : _M_Scheduler(std::move(_Scheduler)),
          _M_CancellationToken(cancellation_token::none()),
          _M_ContinuationContext(task_continuation_context::use_default()),
          _M_HasCancellationToken(false),
          _M_HasScheduler(true)
    {
    }

    task_options(const task_options& _TaskOptions)
        : _M_Scheduler(_TaskOptions.get_scheduler()),
          _M_CancellationToken(_TaskOptions.get_cancellation_token()),
          _M_ContinuationContext(_TaskOptions.get_continuation_context()),
          _M_HasCancellationToken(_TaskOptions.has_cancellation_token()),
          _M_HasScheduler(_TaskOptions.has_scheduler())        
    {
    }

    void set_cancellation_token(cancellation_token _Token)
    {
        _M_CancellationToken = _Token;
       _M_HasCancellationToken = true;
    }

    void set_continuation_context(task_continuation_context _ContinuationContext)
    {
        _M_ContinuationContext = _ContinuationContext;
    }

    bool has_cancellation_token() const
    {
        return _M_HasCancellationToken;
    }

    cancellation_token get_cancellation_token() const
    {
        return _M_CancellationToken;
    }

    task_continuation_context get_continuation_context() const
    {
        return _M_ContinuationContext;
    }

    bool has_scheduler() const
    {
        return _M_HasScheduler;
    }

    scheduler_ptr get_scheduler() const
    {
        return _M_Scheduler;
    }

private:

    task_options const& operator=(task_options const& _Right);
    friend details::_Internal_task_options &details::_get_internal_task_options(task_options &);
    friend const details::_Internal_task_options &details::_get_internal_task_options(const task_options &);

    scheduler_ptr _M_Scheduler;
    cancellation_token _M_CancellationToken;
    task_continuation_context _M_ContinuationContext;
    details::_Internal_task_options _M_InternalTaskOptions;
    bool _M_HasCancellationToken;
    bool _M_HasScheduler;
};

namespace details
{
    inline _Internal_task_options & _get_internal_task_options(task_options &options)
    {
        return options._M_InternalTaskOptions;
    }
    inline const _Internal_task_options & _get_internal_task_options(const task_options &options)
    {
        return options._M_InternalTaskOptions;
    }

    struct _Task_impl_base;
    template<typename _ReturnType> struct _Task_impl;

    template<typename _ReturnType>
    struct _Task_ptr
    {
        typedef std::shared_ptr<_Task_impl<_ReturnType>> _Type;
        static _Type _Make(_CancellationTokenState * _Ct, scheduler_ptr _Scheduler_arg) { return std::make_shared<_Task_impl<_ReturnType>>(_Ct, _Scheduler_arg); }
    };

    typedef _TaskCollection_t::_TaskProcHandle_t _UnrealizedChore_t;
    typedef std::shared_ptr<_Task_impl_base> _Task_ptr_base;

    // The weak-typed base task handler for continuation tasks.
    struct _ContinuationTaskHandleBase : _UnrealizedChore_t
    {
        _ContinuationTaskHandleBase * _M_next;
        task_continuation_context _M_continuationContext;
        bool _M_isTaskBasedContinuation;

        // This field gives inlining scheduling policy for current chore.
        _TaskInliningMode_t _M_inliningMode;
        
        virtual _Task_ptr_base _GetTaskImplBase() const = 0;

        _ContinuationTaskHandleBase() : 
            _M_next(nullptr), _M_continuationContext(task_continuation_context::use_default()), _M_isTaskBasedContinuation(false), _M_inliningMode(details::_NoInline)
        {
        }

        virtual ~_ContinuationTaskHandleBase() {}
    };

#if _PPLTASK_ASYNC_LOGGING
    // GUID used for identifying causality logs from PPLTask
    const ::Platform::Guid _PPLTaskCausalityPlatformID(0x7A76B220, 0xA758, 0x4E6E, 0xB0, 0xE0, 0xD7, 0xC6, 0xD7, 0x4A, 0x88, 0xFE);

    __declspec(selectany) volatile long _isCausalitySupported = 0;

    inline bool _IsCausalitySupported()
    {
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
        if (_isCausalitySupported == 0)
        {
            long _causality = 1;
            OSVERSIONINFOEX _osvi = {};
            _osvi.dwOSVersionInfoSize = sizeof(OSVERSIONINFOEX);

            // The Causality is supported on Windows version higher than Windows 8
            _osvi.dwMajorVersion = 6;
            _osvi.dwMinorVersion = 3;

            DWORDLONG _conditionMask = 0;
            VER_SET_CONDITION( _conditionMask, VER_MAJORVERSION, VER_GREATER_EQUAL );
            VER_SET_CONDITION( _conditionMask, VER_MINORVERSION, VER_GREATER_EQUAL );

            if ( ::VerifyVersionInfo(&_osvi, VER_MAJORVERSION | VER_MINORVERSION, _conditionMask)) 
            {
                _causality = 2;
            }

            _isCausalitySupported = _causality;
            return _causality == 2;
        }

        return _isCausalitySupported == 2 ? true : false;
#else
        return true;
#endif
    }

    // Stateful logger rests inside task_impl_base. 
    struct _TaskEventLogger
    {
        _Task_impl_base *_M_task;
        bool _M_scheduled;
        bool _M_taskPostEventStarted;

        // Log before scheduling task
        void _LogScheduleTask(bool _isContinuation)
        {
            if (details::_IsCausalitySupported())
            {
                ::Windows::Foundation::Diagnostics::AsyncCausalityTracer::TraceOperationCreation(::Windows::Foundation::Diagnostics::CausalityTraceLevel::Required, ::Windows::Foundation::Diagnostics::CausalitySource::Library, 
                    _PPLTaskCausalityPlatformID, reinterpret_cast<unsigned long long>(_M_task), 
                    _isContinuation ? "pplx::PPLTask::ScheduleContinuationTask" : "pplx::PPLTask::ScheduleTask", 0);
                _M_scheduled = true;
            } 
        }

        // It will log the cancel event but not canceled state. _LogTaskCompleted will log the terminal state, which includes cancel state.
        void _LogCancelTask()
        {
            if (details::_IsCausalitySupported())
            {
                ::Windows::Foundation::Diagnostics::AsyncCausalityTracer::TraceOperationRelation(::Windows::Foundation::Diagnostics::CausalityTraceLevel::Important, ::Windows::Foundation::Diagnostics::CausalitySource::Library,
                    _PPLTaskCausalityPlatformID, reinterpret_cast<unsigned long long>(_M_task), ::Windows::Foundation::Diagnostics::CausalityRelation::Cancel);

            } 
        }

        // Log when task reaches terminal state. Note: the task can reach a terminal state (by cancellation or exception) without having run
        void _LogTaskCompleted();

        // Log when task body (which includes user lambda and other scheduling code) begin to run
        void _LogTaskExecutionStarted() { }

        // Log when task body finish executing
        void _LogTaskExecutionCompleted()
        {
            if (_M_taskPostEventStarted && details::_IsCausalitySupported())
            {
                ::Windows::Foundation::Diagnostics::AsyncCausalityTracer::TraceSynchronousWorkCompletion(::Windows::Foundation::Diagnostics::CausalityTraceLevel::Required, ::Windows::Foundation::Diagnostics::CausalitySource::Library,
                    ::Windows::Foundation::Diagnostics::CausalitySynchronousWork::CompletionNotification);
            }
        }

        // Log right before user lambda being invoked
        void _LogWorkItemStarted()
        {
            if (details::_IsCausalitySupported())
            {
                ::Windows::Foundation::Diagnostics::AsyncCausalityTracer::TraceSynchronousWorkStart(::Windows::Foundation::Diagnostics::CausalityTraceLevel::Required, ::Windows::Foundation::Diagnostics::CausalitySource::Library,
                    _PPLTaskCausalityPlatformID, reinterpret_cast<unsigned long long>(_M_task), ::Windows::Foundation::Diagnostics::CausalitySynchronousWork::Execution);
            }
        }

        // Log right after user lambda being invoked
        void _LogWorkItemCompleted()
        {
            if (details::_IsCausalitySupported())
            {
                ::Windows::Foundation::Diagnostics::AsyncCausalityTracer::TraceSynchronousWorkCompletion(::Windows::Foundation::Diagnostics::CausalityTraceLevel::Required, ::Windows::Foundation::Diagnostics::CausalitySource::Library,
                    ::Windows::Foundation::Diagnostics::CausalitySynchronousWork::Execution);

                ::Windows::Foundation::Diagnostics::AsyncCausalityTracer::TraceSynchronousWorkStart(::Windows::Foundation::Diagnostics::CausalityTraceLevel::Required, ::Windows::Foundation::Diagnostics::CausalitySource::Library,
                    _PPLTaskCausalityPlatformID, reinterpret_cast<unsigned long long>(_M_task), ::Windows::Foundation::Diagnostics::CausalitySynchronousWork::CompletionNotification);
                _M_taskPostEventStarted = true;
            }
        }
        
        _TaskEventLogger(_Task_impl_base *_task): _M_task(_task)
        {
            _M_scheduled = false;
            _M_taskPostEventStarted = false;
        }
    };

    // Exception safe logger for user lambda
    struct _TaskWorkItemRAIILogger
    {
        _TaskEventLogger &_M_logger;
        _TaskWorkItemRAIILogger(_TaskEventLogger &_taskHandleLogger): _M_logger(_taskHandleLogger)
        {
            _M_logger._LogWorkItemStarted();
        }

        ~_TaskWorkItemRAIILogger()
        {
            _M_logger._LogWorkItemCompleted();
        }
        _TaskWorkItemRAIILogger &operator =(const _TaskWorkItemRAIILogger &); // cannot be assigned
    };

#else
    inline void _LogCancelTask(_Task_impl_base *) {}
    struct _TaskEventLogger
    {
        void _LogScheduleTask(bool) {}
        void _LogCancelTask() {}
        void _LogWorkItemStarted() {}
        void _LogWorkItemCompleted() {}
        void _LogTaskExecutionStarted() {}
        void _LogTaskExecutionCompleted() {}
        void _LogTaskCompleted() {}
        _TaskEventLogger(_Task_impl_base *) {}
    };
    struct _TaskWorkItemRAIILogger
    {
        _TaskWorkItemRAIILogger(_TaskEventLogger &) {}
    };
#endif

    template<typename _ReturnType, typename _DerivedTaskHandle, typename _BaseTaskHandle>
    struct _PPLTaskHandle : _BaseTaskHandle
    {
        _PPLTaskHandle(const typename _Task_ptr<_ReturnType>::_Type & _PTask) : _M_pTask(_PTask)
        {
        }

        virtual ~_PPLTaskHandle() 
        {
            // Here is the sink of all task completion code paths
            _M_pTask->_M_taskEventLogger._LogTaskCompleted();
        }

        virtual void invoke() const
        {
            // All exceptions should be rethrown to finish cleanup of the task collection. They will be caught and handled
            // by the runtime.
            _ASSERTE((bool)_M_pTask);
            if (!_M_pTask->_TransitionedToStarted())
            {
                static_cast<const _DerivedTaskHandle *>(this)->_SyncCancelAndPropagateException();
                return;
            }

            _M_pTask->_M_taskEventLogger._LogTaskExecutionStarted();
            try
            {
                // All derived task handle must implement this contract function.
                static_cast<const _DerivedTaskHandle *>(this)->_Perform();
            }
            catch(const task_canceled &)
            {
                _M_pTask->_Cancel(true);
            }
            catch(const _Interruption_exception &)
            {
                _M_pTask->_Cancel(true);
            }
#if defined (__cplusplus_winrt)
            catch(::Platform::Exception^ _E)
            {
                _M_pTask->_CancelWithException(_E);
            }
#endif  /* defined (__cplusplus_winrt) */
            catch(...)
            {
                _M_pTask->_CancelWithException(std::current_exception());
            }
            _M_pTask->_M_taskEventLogger._LogTaskExecutionCompleted();
        }

        // Cast _M_pTask pointer to "type-less" _Task_impl_base pointer, which can be used in _ContinuationTaskHandleBase.
        // The return value should be automatically optimized by R-value ref.
        _Task_ptr_base _GetTaskImplBase() const
        {
            return _M_pTask;
        }

        typename _Task_ptr<_ReturnType>::_Type _M_pTask;
    private:
        _PPLTaskHandle const & operator=(_PPLTaskHandle const&);    // no assignment operator
    };

    
    struct _Task_impl_base
    {
        enum _TaskInternalState
        {
            // Tracks the state of the task, rather than the task collection on which the task is scheduled
            _Created,
            _Started,
            _PendingCancel,
            _Completed,
            _Canceled
        };
// _M_taskEventLogger - 'this' : used in base member initializer list
#if defined(_MSC_VER)
#pragma warning(push)
#pragma warning(disable: 4355)
#endif
        _Task_impl_base(_CancellationTokenState * _PTokenState, scheduler_ptr _Scheduler_arg) 
                          : _M_TaskState(_Created),
                            _M_fFromAsync(false), _M_fUnwrappedTask(false),
                            _M_pRegistration(nullptr), _M_Continuations(nullptr), _M_TaskCollection(_Scheduler_arg),
                            _M_taskEventLogger(this)                           
        {
            // Set cancelation token
            _M_pTokenState = _PTokenState;
            _ASSERTE(_M_pTokenState != nullptr);
            if (_M_pTokenState != _CancellationTokenState::_None())
                _M_pTokenState->_Reference();
        }
#if defined(_MSC_VER)
#pragma warning(pop)
#endif

        virtual ~_Task_impl_base()
        {
            _ASSERTE(_M_pTokenState != nullptr);
            if (_M_pTokenState != _CancellationTokenState::_None())
            {
                _M_pTokenState->_Release();
            }
        }

        task_status _Wait()
        {
            bool _DoWait = true;

#if defined (__cplusplus_winrt)
            if (_IsNonBlockingThread())
            {
                // In order to prevent Windows Runtime STA threads from blocking the UI, calling task.wait() task.get() is illegal
                // if task has not been completed.
                if (!_IsCompleted() && !_IsCanceled())
                {
                    throw invalid_operation("Illegal to wait on a task in a Windows Runtime STA");
                }
                else
                {
                    // Task Continuations are 'scheduled' *inside* the chore that is executing on the ancestors's task group. If a continuation
                    // needs to be marshalled to a different apartment, instead of scheduling, we make a synchronous cross apartment COM
                    // call to execute the continuation. If it then happens to do something which waits on the ancestor (say it calls .get(), which
                    // task based continuations are wont to do), waiting on the task group results in on the chore that is making this
                    // synchronous callback, which causes a deadlock. To avoid this, we test the state ancestor's event , and we will NOT wait on
                    // if it has finished execution (which means now we are on the inline synchronous callback).
                    _DoWait = false;
                }
            }
#endif  /* defined (__cplusplus_winrt) */
            if (_DoWait)
            {
                // If this task was created from a Windows Runtime async operation, do not attempt to inline it. The
                // async operation will take place on a thread in the appropriate apartment Simply wait for the completed
                // event to be set.
                if (_M_fFromAsync)
                {
                    _M_TaskCollection._Wait();
                }
                else
                {
                    // Wait on the task collection to complete. The task collection is guaranteed to still be
                    // valid since the task must be still within scope so that the _Task_impl_base destructor
                    // has not yet been called. This call to _Wait potentially inlines execution of work.
                    try
                    {
                        // Invoking wait on a task collection resets the state of the task collection. This means that
                        // if the task collection itself were canceled, or had encountered an exception, only the first
                        // call to wait will receive this status. However, both cancellation and exceptions flowing through
                        // tasks set state in the task impl itself.

                        // When it returns cancelled, either work chore or the cancel thread should already have set task's state
                        // properly -- cancelled state or completed state (because there was no interruption point).
                        // For tasks with unwrapped tasks, we should not change the state of current task, since the unwrapped task are still running.
                        _M_TaskCollection._RunAndWait();
                    }
                    catch(details::_Interruption_exception&)
                    {
                        // The _TaskCollection will never be an interruption point since it has a none token.
                        _ASSERTE(false);
                    }
                    catch(task_canceled&)
                    {
                        // task_canceled is a special exception thrown by cancel_current_task. The spec states that cancel_current_task
                        // must be called from code that is executed within the task (throwing it from parallel work created by and waited
                        // upon by the task is acceptable). We can safely assume that the task wrapper _PPLTaskHandle::operator() has seen
                        // the exception and canceled the task. Swallow the exception here.
                        _ASSERTE(_IsCanceled());
                    }
#if defined (__cplusplus_winrt)
                    catch(::Platform::Exception^ _E)
                    {
                        // Its possible the task body hasn't seen the exception, if so we need to cancel with exception here.
                        if(!_HasUserException())
                        {
                            _CancelWithException(_E);
                        }
                        // Rethrow will mark the exception as observed.
                        _M_exceptionHolder->_RethrowUserException();
                    }
#endif  /* defined (__cplusplus_winrt) */
                    catch(...)
                    {
                        // Its possible the task body hasn't seen the exception, if so we need to cancel with exception here.
                        if(!_HasUserException())
                        {
                            _CancelWithException(std::current_exception());
                        }
                        // Rethrow will mark the exception as observed.
                        _M_exceptionHolder->_RethrowUserException();
                    }

                    // If the lambda body for this task (executed or waited upon in _RunAndWait above) happened to return a task
                    // which is to be unwrapped and plumbed to the output of this task, we must not only wait on the lambda body, we must
                    // wait on the **INNER** body. It is in theory possible that we could inline such if we plumb a series of things through;
                    // however, this takes the tact of simply waiting upon the completion signal.
                    if (_M_fUnwrappedTask)
                    {
                        _M_TaskCollection._Wait();
                    }
                }
            }

            if (_HasUserException())
            {
                _M_exceptionHolder->_RethrowUserException();
            }
            else if (_IsCanceled())
            {
                return canceled;
            }
            _ASSERTE(_IsCompleted());
            return completed;
        }

        virtual bool _CancelAndRunContinuations(bool _SynchronousCancel, bool _UserException, bool _PropagatedFromAncestor, const std::shared_ptr<_ExceptionHolder>& _ExHolder) = 0;

        bool _Cancel(bool _SynchronousCancel)
        {
            // Send in a dummy value for exception. It is not used when the first parameter is false.
            return _CancelAndRunContinuations(_SynchronousCancel, false, false, _M_exceptionHolder);
        }

        bool _CancelWithExceptionHolder(const std::shared_ptr<_ExceptionHolder>& _ExHolder, bool _PropagatedFromAncestor)
        {
            // This task was canceled because an ancestor task encountered an exception.
            return _CancelAndRunContinuations(true, true, _PropagatedFromAncestor, _ExHolder);
        }

#if defined (__cplusplus_winrt)
        bool _CancelWithException(::Platform::Exception^ _Exception)
        {
            // This task was canceled because the task body encountered an exception.
            _ASSERTE(!_HasUserException());
            return _CancelAndRunContinuations(true, true, false, std::make_shared<_ExceptionHolder>(_Exception, _GetTaskCreationCallstack()));
        }
#endif  /* defined (__cplusplus_winrt) */

        bool _CancelWithException(const std::exception_ptr& _Exception)
        {
            // This task was canceled because the task body encountered an exception.
            _ASSERTE(!_HasUserException());
            return _CancelAndRunContinuations(true, true, false, std::make_shared<_ExceptionHolder>(_Exception, _GetTaskCreationCallstack()));
        }

        void _RegisterCancellation(std::weak_ptr<_Task_impl_base> _WeakPtr)
        {
            _ASSERTE(details::_CancellationTokenState::_IsValid(_M_pTokenState));

            auto _CancellationCallback = [_WeakPtr](){
                // Taking ownership of the task prevents dead lock during destruction
                // if the destructor waits for the cancellations to be finished
                auto _task = _WeakPtr.lock();
                if (_task != nullptr)
                    _task->_Cancel(false);
            };

            _M_pRegistration = new details::_CancellationTokenCallback<decltype(_CancellationCallback)>(_CancellationCallback);
            _M_pTokenState->_RegisterCallback(_M_pRegistration);
        }

        void _DeregisterCancellation()
        {
            if (_M_pRegistration != nullptr)
            {
                _M_pTokenState->_DeregisterCallback(_M_pRegistration);
                _M_pRegistration->_Release();
                _M_pRegistration = nullptr;
            }
        }

        bool _IsCreated()
        {
            return (_M_TaskState == _Created);
        }

        bool _IsStarted()
        {
            return (_M_TaskState == _Started);
        }

        bool _IsPendingCancel()
        {
            return (_M_TaskState == _PendingCancel);
        }

        bool _IsCompleted()
        {
            return (_M_TaskState == _Completed);
        }

        bool _IsCanceled()
        {
            return (_M_TaskState == _Canceled);
        }

        bool _HasUserException()
        {
            return static_cast<bool>(_M_exceptionHolder);
        }

        const std::shared_ptr<_ExceptionHolder>& _GetExceptionHolder()
        {
            _ASSERTE(_HasUserException());
            return _M_exceptionHolder;
        }

        bool _IsApartmentAware()
        {
            return _M_fFromAsync;
        }

        void _SetAsync(bool _Async = true)
        {
            _M_fFromAsync = _Async;
        }

        _TaskCreationCallstack _GetTaskCreationCallstack()
        {
            return _M_pTaskCreationCallstack;
        }

        void _SetTaskCreationCallstack(const _TaskCreationCallstack &_Callstack)
        {
            _M_pTaskCreationCallstack = _Callstack;
        }

        void _ScheduleTask(_UnrealizedChore_t * _PTaskHandle, _TaskInliningMode_t _InliningMode)
        {
            try
            {
                _M_TaskCollection._ScheduleTask(_PTaskHandle, _InliningMode);
            }
            catch(const task_canceled &)
            {
                // task_canceled is a special exception thrown by cancel_current_task. The spec states that cancel_current_task
                // must be called from code that is executed within the task (throwing it from parallel work created by and waited
                // upon by the task is acceptable). We can safely assume that the task wrapper _PPLTaskHandle::operator() has seen
                // the exception and canceled the task. Swallow the exception here.
                _ASSERTE(_IsCanceled());
            }
            catch(const _Interruption_exception &)
            {
                // The _TaskCollection will never be an interruption point since it has a none token.
                _ASSERTE(false);
            }
            catch(...)
            {
                // The exception could have come from two places:
                //   1. From the chore body, so it already should have been caught and canceled.
                //      In this case swallow the exception.
                //   2. From trying to actually schedule the task on the scheduler.
                //      In this case cancel the task with the current exception, otherwise the
                //      task will never be signaled leading to deadlock when waiting on the task.
                if (!_HasUserException())
                {
                    _CancelWithException(std::current_exception());
                }
            }
        }

        
        void _RunContinuation(_ContinuationTaskHandleBase * _PTaskHandle)
        {
            _Task_ptr_base _ImplBase = _PTaskHandle->_GetTaskImplBase();
            if (_IsCanceled() && !_PTaskHandle->_M_isTaskBasedContinuation)
            {
                if (_HasUserException())
                {
                    // If the ancestor encountered an exception, transfer the exception to the continuation
                    // This traverses down the tree to propagate the exception.
                    _ImplBase->_CancelWithExceptionHolder(_GetExceptionHolder(), true);
                }
                else
                {
                    // If the ancestor was canceled, then your own execution should be canceled.
                    // This traverses down the tree to cancel it.
                    _ImplBase->_Cancel(true);
                }
            }
            else
            {
                // This can only run when the ancestor has completed or it's a task based continuation that fires when a task is canceled
                // (with or without a user exception).
                _ASSERTE(_IsCompleted() || _PTaskHandle->_M_isTaskBasedContinuation);
                _ASSERTE(!_ImplBase->_IsCanceled());
                return _ImplBase->_ScheduleContinuationTask(_PTaskHandle);
            }

            // If the handle is not scheduled, we need to manually delete it.
            delete _PTaskHandle;
        }

        // Schedule a continuation to run
        void _ScheduleContinuationTask(_ContinuationTaskHandleBase * _PTaskHandle)
        {
            
            _M_taskEventLogger._LogScheduleTask(true);
            // Ensure that the continuation runs in proper context (this might be on a Concurrency Runtime thread or in a different Windows Runtime apartment)
            if (_PTaskHandle->_M_continuationContext._HasCapturedContext())
            {
                // For those continuations need to be scheduled inside captured context, we will try to apply automatic inlining to their inline modes,
                // if they haven't been specified as _ForceInline yet. This change will encourage those continuations to be executed inline so that reduce
                // the cost of marshaling.
                // For normal continuations we won't do any change here, and their inline policies are completely decided by ._ThenImpl method.
                if (_PTaskHandle->_M_inliningMode != details::_ForceInline)
                {
                    _PTaskHandle->_M_inliningMode = details::_DefaultAutoInline;
                }
                _ScheduleFuncWithAutoInline([_PTaskHandle]() {
                    // Note that we cannot directly capture "this" pointer, instead, we should use _TaskImplPtr, a shared_ptr to the _Task_impl_base.
                    // Because "this" pointer will be invalid as soon as _PTaskHandle get deleted. _PTaskHandle will be deleted after being scheduled.
                    auto _TaskImplPtr = _PTaskHandle->_GetTaskImplBase();
                    if (details::_ContextCallback::_CaptureCurrent() == _PTaskHandle->_M_continuationContext)
                    {
                        _TaskImplPtr->_ScheduleTask(_PTaskHandle, details::_ForceInline);
                    }
                    else
                    {
                        //
                        // It's entirely possible that the attempt to marshal the call into a differing context will fail. In this case, we need to handle
                        // the exception and mark the continuation as canceled with the appropriate exception. There is one slight hitch to this:
                        //
                        // NOTE: COM's legacy behavior is to swallow SEH exceptions and marshal them back as HRESULTS. This will in effect turn an SEH into
                        // a C++ exception that gets tagged on the task. One unfortunate result of this is that various pieces of the task infrastructure will
                        // not be in a valid state after this in /EHsc (due to the lack of destructors running, etc...).
                        //
                        try
                        {
                            // Dev10 compiler needs this!
                            auto _PTaskHandle1 = _PTaskHandle;
                            _PTaskHandle->_M_continuationContext._CallInContext( [_PTaskHandle1, _TaskImplPtr](){
                                _TaskImplPtr->_ScheduleTask(_PTaskHandle1, details::_ForceInline);
                            });
                        }
#if defined (__cplusplus_winrt)
                        catch(::Platform::Exception^ _E)
                        {
                            _TaskImplPtr->_CancelWithException(_E);
                        }
#endif  /* defined (__cplusplus_winrt) */
                        catch(...)
                        {
                            _TaskImplPtr->_CancelWithException(std::current_exception());
                        }
                    }
                }, _PTaskHandle->_M_inliningMode);
            }
            else
            {
                _ScheduleTask(_PTaskHandle, _PTaskHandle->_M_inliningMode);
            }
        }

        
        void _ScheduleContinuation(_ContinuationTaskHandleBase * _PTaskHandle)
        {
            enum { _Nothing, _Schedule, _Cancel, _CancelWithException } _Do = _Nothing;

            // If the task has canceled, cancel the continuation. If the task has completed, execute the continuation right away.
            // Otherwise, add it to the list of pending continuations
            {
                ::pplx::extensibility::scoped_critical_section_t _LockHolder(_M_ContinuationsCritSec);
                if (_IsCompleted() || (_IsCanceled() && _PTaskHandle->_M_isTaskBasedContinuation))
                {
                    _Do = _Schedule;
                }
                else if (_IsCanceled())
                {
                    if (_HasUserException())
                    {
                        _Do = _CancelWithException;
                    }
                    else
                    {
                        _Do = _Cancel;
                    }
                }
                else
                {
                    // chain itself on the continuation chain.
                    _PTaskHandle->_M_next = _M_Continuations;
                    _M_Continuations = _PTaskHandle;
                }
            }

            // Cancellation and execution of continuations should be performed after releasing the lock. Continuations off of
            // async tasks may execute inline.
            switch (_Do)
            {
                case _Schedule:
                {
                    _PTaskHandle->_GetTaskImplBase()->_ScheduleContinuationTask(_PTaskHandle);
                    break;
                }
                case _Cancel:
                {
                    // If the ancestor was canceled, then your own execution should be canceled.
                    // This traverses down the tree to cancel it.
                    _PTaskHandle->_GetTaskImplBase()->_Cancel(true);

                    delete _PTaskHandle;
                    break;
                }
                case _CancelWithException:
                {
                    // If the ancestor encountered an exception, transfer the exception to the continuation
                    // This traverses down the tree to propagate the exception.
                    _PTaskHandle->_GetTaskImplBase()->_CancelWithExceptionHolder(_GetExceptionHolder(), true);

                    delete _PTaskHandle;
                    break;
                }
                case _Nothing:
                default:
                    // In this case, we have inserted continuation to continuation chain,
                    // nothing more need to be done, just leave.
                    break;
            }
        }

        void _RunTaskContinuations()
        {
            // The link list can no longer be modified at this point,
            // since all following up continuations will be scheduled by themselves.
            _ContinuationList _Cur = _M_Continuations, _Next;
            _M_Continuations = nullptr;
            while (_Cur)
            {
                // Current node might be deleted after running,
                // so we must fetch the next first.
                _Next = _Cur->_M_next;
                _RunContinuation(_Cur);
                _Cur = _Next;
            }
        }

#if defined (__cplusplus_winrt)
        static bool  _IsNonBlockingThread()
        {
            APTTYPE _AptType;
            APTTYPEQUALIFIER _AptTypeQualifier;

            HRESULT hr = CoGetApartmentType(&_AptType, &_AptTypeQualifier);
            //
            // If it failed, it's not a Windows Runtime/COM initialized thread. This is not a failure.
            //
            if (SUCCEEDED(hr))
            {
                switch(_AptType)
                {
                case APTTYPE_STA:
                case APTTYPE_MAINSTA:
                    return true;
                    break;
                case APTTYPE_NA:
                    switch(_AptTypeQualifier)
                    {
                    // A thread executing in a neutral apartment is either STA or MTA. To find out if this thread is allowed
                    // to wait, we check the app qualifier. If it is an STA thread executing in a neutral apartment, waiting
                    // is illegal, because the thread is responsible for pumping messages and waiting on a task could take the
                    // thread out of circulation for a while.
                    case APTTYPEQUALIFIER_NA_ON_STA:
                    case APTTYPEQUALIFIER_NA_ON_MAINSTA:
                        return true;
                        break;
                    }
                    break;
                }
            }

#if _UITHREADCTXT_SUPPORT
            // This method is used to throw an exepection in _Wait() if called within STA.  We
            // want the same behavior if _Wait is called on the UI thread.
            if (SUCCEEDED(CaptureUiThreadContext(nullptr)))
            {
                return true;
            }
#endif  /* _UITHREADCTXT_SUPPORT */

            return false;
        }

        template<typename _ReturnType, typename>
        static void _AsyncInit(const typename _Task_ptr<_ReturnType>::_Type & _OuterTask,
                               Windows::Foundation::IAsyncOperation<typename details::_ValueTypeOrRefType<_ReturnType>::_Value>^ _AsyncOp)
        {
            // This method is invoked either when a task is created from an existing async operation or
            // when a lambda that creates an async operation executes.

            // If the outer task is pending cancel, cancel the async operation before setting the completed handler. The COM reference on
            // the IAsyncInfo object will be released when all ^references to the operation go out of scope.

            // This assertion uses the existence of taskcollection to determine if the task was created from an event.
            // That is no longer valid as even tasks created from a user lambda could have no underlying taskcollection
            // when a custom scheduler is used.
            // _ASSERTE((!_OuterTask->_M_TaskCollection._IsCreated() || _OuterTask->_M_fUnwrappedTask) && !_OuterTask->_IsCanceled());

            // Pass the shared_ptr by value into the lambda instead of using 'this'.
            _AsyncOp->Completed = ref new Windows::Foundation::AsyncOperationCompletedHandler<_ReturnType>(
              [_OuterTask](Windows::Foundation::IAsyncOperation<typename details::_ValueTypeOrRefType<_ReturnType>::_Value>^ _Operation, Windows::Foundation::AsyncStatus _Status) mutable
            {
                if (_Status == Windows::Foundation::AsyncStatus::Canceled)
                {
                    _OuterTask->_Cancel(true);
                }
                else if (_Status == Windows::Foundation::AsyncStatus::Error)
                {
                    _OuterTask->_CancelWithException(::Platform::Exception::ReCreateException(static_cast<int>(_Operation->ErrorCode.Value)));
                }
                else
                {
                    _ASSERTE(_Status == Windows::Foundation::AsyncStatus::Completed);
                    _OuterTask->_FinalizeAndRunContinuations(_Operation->GetResults());
                }

                // Take away this shared pointers reference on the task instead of waiting for the delegate to be released. It could
                // be released on a different thread after a delay, and not releasing the reference here could cause the tasks to hold
                // on to resources longer than they should. As an example, without this reset, writing to a file followed by reading from
                // it using the Windows Runtime Async APIs causes a sharing violation.
                // Using const_cast is the workaround for failed mutable keywords
                const_cast<_Task_ptr<_ReturnType>::_Type &>(_OuterTask).reset();
             });
            _OuterTask->_SetUnwrappedAsyncOp(_AsyncOp);
        }
#endif  /* defined (__cplusplus_winrt) */

        template<typename _ReturnType, typename _InternalReturnType>
        static void _AsyncInit(const typename _Task_ptr<_ReturnType>::_Type& _OuterTask, const task<_InternalReturnType> & _UnwrappedTask)
        {
            _ASSERTE(_OuterTask->_M_fUnwrappedTask && !_OuterTask->_IsCanceled());
                       
            //
            // We must ensure that continuations off _OuterTask (especially exception handling ones) continue to function in the
            // presence of an exception flowing out of the inner task _UnwrappedTask. This requires an exception handling continuation
            // off the inner task which does the appropriate funnelling to the outer one. We use _Then instead of then to prevent
            // the exception from being marked as observed by our internal continuation. This continuation must be scheduled regardless
            // of whether or not the _OuterTask task is canceled.
            //
            _UnwrappedTask._Then([_OuterTask] (task<_InternalReturnType> _AncestorTask) {

                if (_AncestorTask._GetImpl()->_IsCompleted())
                {
                    _OuterTask->_FinalizeAndRunContinuations(_AncestorTask._GetImpl()->_GetResult());
                }
                else
                {
                    _ASSERTE(_AncestorTask._GetImpl()->_IsCanceled());
                    if (_AncestorTask._GetImpl()->_HasUserException())
                    {
                        // Set _PropagatedFromAncestor to false, since _AncestorTask is not an ancestor of _UnwrappedTask.
                        // Instead, it is the enclosing task.
                        _OuterTask->_CancelWithExceptionHolder(_AncestorTask._GetImpl()->_GetExceptionHolder(), false);
                    }
                    else
                    {
                        _OuterTask->_Cancel(true);
                    }
                }
            }, nullptr, details::_DefaultAutoInline);

        }

        scheduler_ptr _GetScheduler() const
        {
            return _M_TaskCollection._GetScheduler();
        }

        // Tracks the internal state of the task
        volatile _TaskInternalState _M_TaskState;
        // Set to true either if the ancestor task had the flag set to true, or if the lambda that does the work of this task returns an
        // async operation or async action that is unwrapped by the runtime.
        bool _M_fFromAsync;
        // Set to true when a continuation unwraps a task or async operation.
        bool _M_fUnwrappedTask;

        // An exception thrown by the task body is captured in an exception holder and it is shared with all value based continuations rooted at the task.
        // The exception is 'observed' if the user invokes get()/wait() on any of the tasks that are sharing this exception holder. If the exception
        // is not observed by the time the internal object owned by the shared pointer destructs, the process will fail fast.
        std::shared_ptr<_ExceptionHolder> _M_exceptionHolder;

        ::pplx::extensibility::critical_section_t _M_ContinuationsCritSec;

        // The cancellation token state.
        _CancellationTokenState * _M_pTokenState;

        // The registration on the token.
        _CancellationTokenRegistration * _M_pRegistration;

        typedef _ContinuationTaskHandleBase * _ContinuationList;
        _ContinuationList _M_Continuations;

        // The async task collection wrapper
        ::pplx::details::_TaskCollection_t _M_TaskCollection;

        // Callstack for function call (constructor or .then) that created this task impl.
        _TaskCreationCallstack _M_pTaskCreationCallstack;

        _TaskEventLogger _M_taskEventLogger;
   private:
        // Must not be copied by value:
        _Task_impl_base(const _Task_impl_base&);
        _Task_impl_base const & operator=(_Task_impl_base const&);
    };

#if _PPLTASK_ASYNC_LOGGING
    inline void _TaskEventLogger::_LogTaskCompleted()
    {
        if (_M_scheduled)
        {
            ::Windows::Foundation::AsyncStatus _State;
            if (_M_task->_IsCompleted())
                _State = ::Windows::Foundation::AsyncStatus::Completed;
            else if (_M_task->_HasUserException())
                _State = ::Windows::Foundation::AsyncStatus::Error;
            else
                _State = ::Windows::Foundation::AsyncStatus::Canceled;

            if (details::_IsCausalitySupported())
            {
                ::Windows::Foundation::Diagnostics::AsyncCausalityTracer::TraceOperationCompletion(::Windows::Foundation::Diagnostics::CausalityTraceLevel::Required, ::Windows::Foundation::Diagnostics::CausalitySource::Library,
                    _PPLTaskCausalityPlatformID, reinterpret_cast<unsigned long long>(_M_task), _State);
            }
        }
    }
#endif
    
    
    template<typename _ReturnType>
    struct _Task_impl : public _Task_impl_base
    {
#if defined (__cplusplus_winrt)
        typedef Windows::Foundation::IAsyncOperation<typename details::_ValueTypeOrRefType<_ReturnType>::_Value> _AsyncOperationType;
#endif // defined(__cplusplus_winrt)
        _Task_impl(_CancellationTokenState * _Ct, scheduler_ptr _Scheduler_arg)
            : _Task_impl_base(_Ct, _Scheduler_arg)
        {
#if defined (__cplusplus_winrt)
            _M_unwrapped_async_op = nullptr;
#endif  /* defined (__cplusplus_winrt) */
        }

        virtual ~_Task_impl()
        {
            // We must invoke _DeregisterCancellation in the derived class destructor. Calling it in the base class destructor could cause
            // a partially initialized _Task_impl to be in the list of registrations for a cancellation token.
            _DeregisterCancellation();
        }

        virtual bool _CancelAndRunContinuations(bool _SynchronousCancel, bool _UserException, bool _PropagatedFromAncestor, const std::shared_ptr<_ExceptionHolder> & _ExceptionHolder_arg)
        {
            bool _RunContinuations = false;
            {
                ::pplx::extensibility::scoped_critical_section_t _LockHolder(_M_ContinuationsCritSec);
                if (_UserException)
                {
                    _ASSERTE(_SynchronousCancel && !_IsCompleted());
                    // If the state is _Canceled, the exception has to be coming from an ancestor.
                    _ASSERTE(!_IsCanceled() || _PropagatedFromAncestor);

                    // We should not be canceled with an exception more than once.
                    _ASSERTE(!_HasUserException());

                    // Mark _PropagatedFromAncestor as used.
                    (void)_PropagatedFromAncestor;

                    if (_M_TaskState == _Canceled)
                    {
                        // If the task has finished cancelling there should not be any continuation records in the array.
                        return false;
                    }
                    else
                    {
                        _ASSERTE(_M_TaskState != _Completed);
                        _M_exceptionHolder = _ExceptionHolder_arg;
                    }
                }
                else
                {
                    // Completed is a non-cancellable state, and if this is an asynchronous cancel, we're unable to do better than the last async cancel
                    // which is to say, cancellation is already initiated, so return early.
                    if (_IsCompleted() || _IsCanceled() || (_IsPendingCancel() && !_SynchronousCancel))
                    {
                        _ASSERTE(!_IsCompleted() || !_HasUserException());
                        return false;
                    }
                    _ASSERTE(!_SynchronousCancel || !_HasUserException());
                }

                if (_SynchronousCancel)
                {
                    // Be aware that this set must be done BEFORE _M_Scheduled being set, or race will happen between this and wait()
                    _M_TaskState = _Canceled;                    
                    // Cancellation completes the task, so all dependent tasks must be run to cancel them
                    // They are canceled when they begin running (see _RunContinuation) and see that their
                    // ancestor has been canceled.
                    _RunContinuations = true;
                }
                else
                {
                    _ASSERTE(!_UserException);

                    if (_IsStarted())
                    {
#if defined (__cplusplus_winrt)
                        if (_M_unwrapped_async_op != nullptr)
                        {
                            // We will only try to cancel async operation but not unwrapped tasks, since unwrapped tasks cannot be canceled without its token.
                            _M_unwrapped_async_op->Cancel();
                        }
#endif  /* defined (__cplusplus_winrt) */
                        _M_TaskCollection._Cancel();
                    }

                    // The _M_TaskState variable transitions to _Canceled when cancellation is completed (the task is not executing user code anymore).
                    // In the case of a synchronous cancel, this can happen immediately, whereas with an asynchronous cancel, the task has to move from
                    // _Started to _PendingCancel before it can move to _Canceled when it is finished executing.
                    _M_TaskState = _PendingCancel;

                    _M_taskEventLogger._LogCancelTask();
                }

                
            }

            // Only execute continuations and mark the task as completed if we were able to move the task to the _Canceled state.
            if (_RunContinuations)
            {
                _M_TaskCollection._Complete();

                if (_M_Continuations)
                {
                    // Scheduling cancellation with automatic inlining.
                    _ScheduleFuncWithAutoInline([=](){ _RunTaskContinuations(); }, details::_DefaultAutoInline);
                }
            }
            return true;
        }

        void _FinalizeAndRunContinuations(_ReturnType _Result)
        {
            _M_Result.Set(_Result);

            {
                //
                // Hold this lock to ensure continuations being concurrently either get added
                // to the _M_Continuations vector or wait for the result
                //
                ::pplx::extensibility::scoped_critical_section_t _LockHolder(_M_ContinuationsCritSec);

                // A task could still be in the _Created state if it was created with a task_completion_event.
                // It could also be in the _Canceled state for the same reason.
                _ASSERTE(!_HasUserException() && !_IsCompleted());
                if (_IsCanceled())
                {
                    return;
                }

                // Always transition to "completed" state, even in the face of unacknowledged pending cancellation
                _M_TaskState = _Completed;
            }
            _M_TaskCollection._Complete();
            _RunTaskContinuations();
        }

        //
        // This method is invoked when the starts executing. The task returns early if this method returns true.
        //
        bool _TransitionedToStarted()
        {
            ::pplx::extensibility::scoped_critical_section_t _LockHolder(_M_ContinuationsCritSec);
            // Canceled state could only result from antecedent task's canceled state, but that code path will not reach here.
            _ASSERTE(!_IsCanceled());
            if (_IsPendingCancel())
                return false;

            _ASSERTE(_IsCreated());
            _M_TaskState = _Started;
            return true;
        }

#if defined (__cplusplus_winrt)
        void _SetUnwrappedAsyncOp(_AsyncOperationType^ _AsyncOp)
        {
            ::pplx::extensibility::scoped_critical_section_t _LockHolder(_M_ContinuationsCritSec);
            // Cancel the async operation if the task itself is canceled, since the thread that canceled the task missed it.
            if (_IsPendingCancel())
            {
                _ASSERTE(!_IsCanceled());
                _AsyncOp->Cancel();
            }
            else
            {
                _M_unwrapped_async_op = _AsyncOp;
            }
        }
#endif  /* defined (__cplusplus_winrt) */

        // Return true if the task has reached a terminal state
        bool _IsDone()
        {     
            return _IsCompleted() || _IsCanceled();
        }

        _ReturnType _GetResult()
        {
            return _M_Result.Get();
        }

        _ResultHolder<_ReturnType>                 _M_Result;        // this means that the result type must have a public default ctor.
#if defined (__cplusplus_winrt)
        _AsyncOperationType^                        _M_unwrapped_async_op;
#endif  /* defined (__cplusplus_winrt) */
    };

    template<typename _ResultType>
    struct _Task_completion_event_impl
    {
    private:
        _Task_completion_event_impl(const _Task_completion_event_impl&);
        _Task_completion_event_impl& operator=(const _Task_completion_event_impl&);

    public:

        typedef std::vector<typename _Task_ptr<_ResultType>::_Type> _TaskList;

        _Task_completion_event_impl() :
            _M_fHasValue(false), _M_fIsCanceled(false)
        {
        }

        bool _HasUserException()
        {
            return _M_exceptionHolder != nullptr;
        }

        ~_Task_completion_event_impl()
        {
            for( auto _TaskIt = _M_tasks.begin(); _TaskIt != _M_tasks.end(); ++_TaskIt )
            {
                _ASSERTE(!_M_fHasValue && !_M_fIsCanceled);
                // Cancel the tasks since the event was never signaled or canceled.
                (*_TaskIt)->_Cancel(true);
            }
        }

        // We need to protect the loop over the array, so concurrent_vector would not have helped
        _TaskList                           _M_tasks;
        ::pplx::extensibility::critical_section_t             _M_taskListCritSec;
        _ResultHolder<_ResultType>         _M_value;
        std::shared_ptr<_ExceptionHolder>   _M_exceptionHolder;
        bool                                _M_fHasValue;
        bool                                _M_fIsCanceled;
    };

    // Utility method for dealing with void functions
    inline std::function<_Unit_type(void)> _MakeVoidToUnitFunc(const std::function<void(void)>& _Func)
    {
        return [=]() -> _Unit_type { _Func(); return _Unit_type(); };
    }

    template <typename _Type>
    std::function<_Type(_Unit_type)> _MakeUnitToTFunc(const std::function<_Type(void)>& _Func)
    {
        return [=](_Unit_type) -> _Type { return _Func(); };
    }

    template <typename _Type>
    std::function<_Unit_type(_Type)> _MakeTToUnitFunc(const std::function<void(_Type)>& _Func)
    {
        return [=](_Type t) -> _Unit_type { _Func(t); return _Unit_type(); };
    }

    inline std::function<_Unit_type(_Unit_type)> _MakeUnitToUnitFunc(const std::function<void(void)>& _Func)
    {
        return [=](_Unit_type) -> _Unit_type { _Func(); return _Unit_type(); };
    }
} // namespace details


template<typename _ResultType>
class task_completion_event
{
public:
    
    task_completion_event() 
        : _M_Impl(std::make_shared<details::_Task_completion_event_impl<_ResultType>>()) 
    {
    }

    
    bool set(_ResultType _Result) const // 'const' (even though it's not deep) allows to safely pass events by value into lambdas
    {
        // Subsequent sets are ignored. This makes races to set benign: the first setter wins and all others are ignored.
        if (_IsTriggered())
        {
            return false;
        }

        _TaskList _Tasks;
        bool _RunContinuations = false;
        {
            ::pplx::extensibility::scoped_critical_section_t _LockHolder(_M_Impl->_M_taskListCritSec);

            if (!_IsTriggered())
            {
                _M_Impl->_M_value.Set(_Result);
                _M_Impl->_M_fHasValue = true;

                _Tasks.swap(_M_Impl->_M_tasks);
                _RunContinuations = true;
            }
        }

        if (_RunContinuations)
        {
            for( auto _TaskIt = _Tasks.begin(); _TaskIt != _Tasks.end(); ++_TaskIt )
            {
                // If current task was cancelled by a cancellation_token, it would be in cancel pending state.
                if ((*_TaskIt)->_IsPendingCancel())
                    (*_TaskIt)->_Cancel(true);
                else
                {
                    // Tasks created with task_completion_events can be marked as async, (we do this in when_any and when_all
                    // if one of the tasks involved is an async task). Since continuations of async tasks can execute inline, we
                    // need to run continuations after the lock is released.
                    (*_TaskIt)->_FinalizeAndRunContinuations(_M_Impl->_M_value.Get());
                }
            }
            if (_M_Impl->_HasUserException())
            {
                _M_Impl->_M_exceptionHolder.reset();
            }
            return true;
        }

        return false;
    }

    template<typename _E>
    __declspec(noinline) // Ask for no inlining so that the _ReturnAddress intrinsic gives us the expected result
    bool set_exception(_E _Except) const // 'const' (even though it's not deep) allows to safely pass events by value into lambdas
    {
        // It is important that _CAPTURE_CALLSTACK() evaluate to the instruction after the call instruction for set_exception.
        return _Cancel(std::make_exception_ptr(_Except), _CAPTURE_CALLSTACK());
    }

    
    __declspec(noinline) // Ask for no inlining so that the _CAPTURE_CALLSTACK gives us the expected result
    bool set_exception(std::exception_ptr _ExceptionPtr) const // 'const' (even though it's not deep) allows to safely pass events by value into lambdas
    {
        // It is important that _CAPTURE_CALLSTACK() evaluate to the instruction after the call instruction for set_exception.
        return _Cancel(_ExceptionPtr, _CAPTURE_CALLSTACK());
    }

    bool _Cancel() const
    {
        // Cancel with the stored exception if one exists.
        return _CancelInternal();
    }

    template<typename _ExHolderType>
    bool _Cancel(_ExHolderType _ExHolder, const details::_TaskCreationCallstack &_SetExceptionAddressHint = details::_TaskCreationCallstack ()) const
    {
        bool _Canceled;
        if(_StoreException(_ExHolder, _SetExceptionAddressHint))
        {
            _Canceled = _CancelInternal();
            _ASSERTE(_Canceled);
        }
        else
        {
            _Canceled = false;
        }
        return _Canceled;
    }

    template<typename _ExHolderType>
    bool _StoreException(_ExHolderType _ExHolder, const details::_TaskCreationCallstack &_SetExceptionAddressHint = details::_TaskCreationCallstack ()) const
    {
        ::pplx::extensibility::scoped_critical_section_t _LockHolder(_M_Impl->_M_taskListCritSec);
        if (!_IsTriggered() && !_M_Impl->_HasUserException())
        {
            // Create the exception holder only if we have ensured there we will be successful in setting it onto the
            // task completion event. Failing to do so will result in an unobserved task exception.
            _M_Impl->_M_exceptionHolder = _ToExceptionHolder(_ExHolder, _SetExceptionAddressHint);
            return true;
        }
        return false;
    }

    bool _IsTriggered() const
    {
        return _M_Impl->_M_fHasValue || _M_Impl->_M_fIsCanceled;
    }

private:

    static std::shared_ptr<details::_ExceptionHolder> _ToExceptionHolder(const std::shared_ptr<details::_ExceptionHolder>& _ExHolder, const details::_TaskCreationCallstack&)
    {
        return _ExHolder;
    }

    static std::shared_ptr<details::_ExceptionHolder> _ToExceptionHolder(std::exception_ptr _ExceptionPtr, const details::_TaskCreationCallstack &_SetExceptionAddressHint)
    {
        return std::make_shared<details::_ExceptionHolder>(_ExceptionPtr, _SetExceptionAddressHint);
    }


    template <typename T> friend class task; // task can register itself with the event by calling the private _RegisterTask
    template <typename T> friend class task_completion_event;

    typedef typename details::_Task_completion_event_impl<_ResultType>::_TaskList _TaskList;

    bool _CancelInternal() const
    {
        // Cancellation of task completion events is an internal only utility. Our usage is such that _CancelInternal
        // will never be invoked if the task completion event has been set.
        _ASSERTE(!_M_Impl->_M_fHasValue);
        if (_M_Impl->_M_fIsCanceled)
        {
            return false;
        }

        _TaskList _Tasks;
        bool _Cancel = false;
        {
            ::pplx::extensibility::scoped_critical_section_t _LockHolder(_M_Impl->_M_taskListCritSec);
            _ASSERTE(!_M_Impl->_M_fHasValue);
            if (!_M_Impl->_M_fIsCanceled)
            {
                _M_Impl->_M_fIsCanceled = true;
                _Tasks.swap(_M_Impl->_M_tasks);
                _Cancel = true;
            }
        }

        bool _UserException = _M_Impl->_HasUserException();

        if (_Cancel)
        {
            for( auto _TaskIt = _Tasks.begin(); _TaskIt != _Tasks.end(); ++_TaskIt )
            {
                // Need to call this after the lock is released. See comments in set().
                if (_UserException)
                {
                    (*_TaskIt)->_CancelWithExceptionHolder(_M_Impl->_M_exceptionHolder, true);
                }
                else
                {
                    (*_TaskIt)->_Cancel(true);
                }
            }
        }
        return _Cancel;
    }

    void _RegisterTask(const typename details::_Task_ptr<_ResultType>::_Type & _TaskParam)
    {
        ::pplx::extensibility::scoped_critical_section_t _LockHolder(_M_Impl->_M_taskListCritSec);

        //If an exception was already set on this event, then cancel the task with the stored exception.
        if(_M_Impl->_HasUserException())
        {
            _TaskParam->_CancelWithExceptionHolder(_M_Impl->_M_exceptionHolder, true);
        }
        else if (_M_Impl->_M_fHasValue)
        {
            _TaskParam->_FinalizeAndRunContinuations(_M_Impl->_M_value.Get());
        }
        else
        {
            _M_Impl->_M_tasks.push_back(_TaskParam);
        }
    }

    std::shared_ptr<details::_Task_completion_event_impl<_ResultType>> _M_Impl;
};


template<>
class task_completion_event<void>
{
public:
    
    bool set() const // 'const' (even though it's not deep) allows to safely pass events by value into lambdas
    {
        return _M_unitEvent.set(details::_Unit_type());
    }

    template<typename _E>
    __declspec(noinline) // Ask for no inlining so that the _ReturnAddress intrinsic gives us the expected result
    bool set_exception(_E _Except) const // 'const' (even though it's not deep) allows to safely pass events by value into lambdas
    {
        return _M_unitEvent._Cancel(std::make_exception_ptr(_Except), _CAPTURE_CALLSTACK());
    }

    
    __declspec(noinline) // Ask for no inlining so that the _CAPTURE_CALLSTACK intrinsic gives us the expected result
    bool set_exception(std::exception_ptr _ExceptionPtr) const // 'const' (even though it's not deep) allows to safely pass events by value into lambdas
    {
        // It is important that _CAPTURE_CALLSTACK() evaluate to the instruction after the call instruction for set_exception.
        return _M_unitEvent._Cancel(_ExceptionPtr, _CAPTURE_CALLSTACK());
    }

    void _Cancel() const // 'const' (even though it's not deep) allows to safely pass events by value into lambdas
    {
        _M_unitEvent._Cancel();
    }

    void _Cancel(const std::shared_ptr<details::_ExceptionHolder>& _ExHolder) const
    {
        _M_unitEvent._Cancel(_ExHolder);
    }

    bool _StoreException(const std::shared_ptr<details::_ExceptionHolder>& _ExHolder) const
    {
        return _M_unitEvent._StoreException(_ExHolder);
    }

    bool _IsTriggered() const
    {
        return _M_unitEvent._IsTriggered();
    }

private:
    template <typename T> friend class task; // task can register itself with the event by calling the private _RegisterTask

    void _RegisterTask(details::_Task_ptr<details::_Unit_type>::_Type _TaskParam)
    {
        _M_unitEvent._RegisterTask(_TaskParam);
    }

    // The void event contains an event a dummy type so common code can be used for events with void and non-void results.
    task_completion_event<details::_Unit_type> _M_unitEvent;
};

namespace details
{
    //
    // Compile-time validation helpers
    //

    // Task constructor validation: issue helpful diagnostics for common user errors. Do not attempt full validation here.
    //
    // Anything callable is fine
    template<typename _ReturnType, typename _Ty>
    auto _IsValidTaskCtor(_Ty _Param, int,int,int,int) -> decltype(_Param(), std::true_type());

#if defined (__cplusplus_winrt)
    // Anything that has GetResults is fine: this covers all async operations
    template<typename _ReturnType, typename _Ty>
    auto _IsValidTaskCtor(_Ty _Param, int, int, int,...) -> decltype(_Param->GetResults(), std::true_type());
#endif

    // Allow parameters with set: this covers task_completion_event
    template<typename _ReturnType, typename _Ty>
    auto _IsValidTaskCtor(_Ty _Param, int, int, ...) -> decltype(_Param.set(stdx::declval<_ReturnType>()), std::true_type());

    template<typename _ReturnType, typename _Ty>
    auto _IsValidTaskCtor(_Ty _Param, int, ...) -> decltype(_Param.set(), std::true_type());

    // All else is invalid
    template<typename _ReturnType, typename _Ty>
    std::false_type _IsValidTaskCtor(_Ty _Param, ...);

    template<typename _ReturnType, typename _Ty>
    void _ValidateTaskConstructorArgs(_Ty _Param)
    {
        static_assert(std::is_same<decltype(_IsValidTaskCtor<_ReturnType>(_Param,0,0,0,0)),std::true_type>::value,
#if defined (__cplusplus_winrt)
            "incorrect argument for task constructor; can be a callable object, an asynchronous operation, or a task_completion_event"
#else  /* defined (__cplusplus_winrt) */
            "incorrect argument for task constructor; can be a callable object or a task_completion_event"
#endif  /* defined (__cplusplus_winrt) */
            );
#if defined (__cplusplus_winrt)
        static_assert(!(std::is_same<_Ty,_ReturnType>::value && details::_IsIAsyncInfo<_Ty>::_Value),
            "incorrect template argument for task; consider using the return type of the async operation");
#endif  /* defined (__cplusplus_winrt) */
    }

#if defined (__cplusplus_winrt)
    // Helpers for create_async validation
    //
    // A parameter lambda taking no arguments is valid
    template<typename _Ty>
    static auto _IsValidCreateAsync(_Ty _Param, int, int, int, int) -> decltype(_Param(), std::true_type());

    // A parameter lambda taking an cancellation_token argument is valid
    template<typename _Ty>
    static auto _IsValidCreateAsync(_Ty _Param, int, int, int, ...) -> decltype(_Param(cancellation_token::none()), std::true_type());

    // A parameter lambda taking a progress report argument is valid
    template<typename _Ty>
    static auto _IsValidCreateAsync(_Ty _Param, int, int, ...) -> decltype(_Param(details::_ProgressReporterCtorArgType()), std::true_type());

    // A parameter lambda taking a progress report and a cancellation_token argument is valid
    template<typename _Ty>
    static auto _IsValidCreateAsync(_Ty _Param, int, ...) -> decltype(_Param(details::_ProgressReporterCtorArgType(), cancellation_token::none()), std::true_type());

    // All else is invalid
    template<typename _Ty>
    static std::false_type _IsValidCreateAsync(_Ty _Param, ...);
#endif  /* defined (__cplusplus_winrt) */
}
template<typename _InpType, typename _OutType>
class _Continuation_func_transformer
{
public:
    static auto _Perform(std::function<_OutType(_InpType)> _Func) -> decltype(_Func)
    {
        return _Func;
    }
};

template<typename _OutType>
class _Continuation_func_transformer<void, _OutType>
{
public:
    static auto _Perform(std::function<_OutType(void)> _Func) -> decltype(details::_MakeUnitToTFunc<_OutType>(_Func))
    {
        return details::_MakeUnitToTFunc<_OutType>(_Func);
    }
};

template<typename _InType>
class _Continuation_func_transformer<_InType, void>
{
public:
    static auto _Perform(std::function<void(_InType)> _Func) -> decltype(details::_MakeTToUnitFunc<_InType>(_Func))
    {
        return details::_MakeTToUnitFunc<_InType>(_Func);
    }
};

template<>
class _Continuation_func_transformer<void, void>
{
public:
    static auto _Perform(std::function<void(void)> _Func) -> decltype(details::_MakeUnitToUnitFunc(_Func))
    {
        return details::_MakeUnitToUnitFunc(_Func);
    }
};

// A helper class template that transforms an intial task lambda returns void into a lambda that returns a non-void type (details::_Unit_type is used
// to substitute for void). This is to minimize the special handling required for 'void'.
template<typename _RetType>
class _Init_func_transformer
{
public:
    static auto _Perform(std::function<_RetType(void)> _Func) -> decltype(_Func)
    {
        return _Func;
    }
};

template<>
class _Init_func_transformer<void>
{
public:
    static auto _Perform(std::function<void(void)> _Func) -> decltype(details::_MakeVoidToUnitFunc(_Func))
    {
        return details::_MakeVoidToUnitFunc(_Func);
    }
};


template<typename _ReturnType>
class task
{
public:
    
    typedef _ReturnType result_type;

    
    task() : _M_Impl(nullptr)
    {
        // The default constructor should create a task with a nullptr impl. This is a signal that the
        // task is not usable and should throw if any wait(), get() or then() APIs are used.
    }

    
    template<typename _Ty>
    __declspec(noinline) // Ask for no inlining so that the _CAPTURE_CALLSTACK gives us the expected result
    explicit task(_Ty _Param)
    {
        task_options _TaskOptions;
        details::_ValidateTaskConstructorArgs<_ReturnType,_Ty>(_Param);

        _CreateImpl(_TaskOptions.get_cancellation_token()._GetImplValue(), _TaskOptions.get_scheduler());
        // Do not move the next line out of this function. It is important that _CAPTURE_CALLSTACK() evaluate to the the call site of the task constructor.
        _SetTaskCreationCallstack(_CAPTURE_CALLSTACK());

        _TaskInitMaybeFunctor(_Param, details::_IsCallable(_Param,0));
    }

    
    template<typename _Ty>
    __declspec(noinline) // Ask for no inlining so that the _CAPTURE_CALLSTACK gives us the expected result
    explicit task(_Ty _Param, const task_options &_TaskOptions)
    {
        details::_ValidateTaskConstructorArgs<_ReturnType,_Ty>(_Param);

        _CreateImpl(_TaskOptions.get_cancellation_token()._GetImplValue(), _TaskOptions.get_scheduler());
        // Do not move the next line out of this function. It is important that _CAPTURE_CALLSTACK() evaluate to the the call site of the task constructor.
        _SetTaskCreationCallstack(details::_get_internal_task_options(_TaskOptions)._M_hasPresetCreationCallstack ? details::_get_internal_task_options(_TaskOptions)._M_presetCreationCallstack : _CAPTURE_CALLSTACK());
        
        _TaskInitMaybeFunctor(_Param, details::_IsCallable(_Param,0));
    }

    
    task(const task& _Other): _M_Impl(_Other._M_Impl) {}

    
    task(task&& _Other): _M_Impl(std::move(_Other._M_Impl)) {}

    
    task& operator=(const task& _Other)
    {
        if (this != &_Other)
        {
            _M_Impl = _Other._M_Impl;
        }
        return *this;
    }

    
    task& operator=(task&& _Other)
    {
        if (this != &_Other)
        {
            _M_Impl = std::move(_Other._M_Impl);
        }
        return *this;
    }

    
    template<typename _Function>
    __declspec(noinline) // Ask for no inlining so that the _CAPTURE_CALLSTACK gives us the expected result
    auto then(const _Function& _Func) const -> typename details::_ContinuationTypeTraits<_Function, _ReturnType>::_TaskOfType
    {
        task_options _TaskOptions;
        details::_get_internal_task_options(_TaskOptions)._set_creation_callstack(_CAPTURE_CALLSTACK());
        return _ThenImpl<_ReturnType, _Function>(_Func, _TaskOptions);
    }

    
    template<typename _Function>
    __declspec(noinline) // Ask for no inlining so that the _CAPTURE_CALLSTACK gives us the expected result
    auto then(const _Function& _Func, task_options _TaskOptions) const -> typename details::_ContinuationTypeTraits<_Function, _ReturnType>::_TaskOfType
    {
        details::_get_internal_task_options(_TaskOptions)._set_creation_callstack(_CAPTURE_CALLSTACK());
        return _ThenImpl<_ReturnType, _Function>(_Func, _TaskOptions);
    }

    
    template<typename _Function>
    __declspec(noinline) // Ask for no inlining so that the _CAPTURE_CALLSTACK gives us the expected result
    auto then(const _Function& _Func, cancellation_token _CancellationToken, task_continuation_context _ContinuationContext) const -> typename details::_ContinuationTypeTraits<_Function, _ReturnType>::_TaskOfType
    {
        task_options _TaskOptions(_CancellationToken, _ContinuationContext);
        details::_get_internal_task_options(_TaskOptions)._set_creation_callstack(_CAPTURE_CALLSTACK());
        return _ThenImpl<_ReturnType, _Function>(_Func, _TaskOptions);
    }

    
    task_status wait() const
    {
        if (!_M_Impl)
        {
            throw invalid_operation("wait() cannot be called on a default constructed task.");
        }

        return _M_Impl->_Wait();
    }

    
    _ReturnType get() const
    {
        if (!_M_Impl)
        {
            throw invalid_operation("get() cannot be called on a default constructed task.");
        }

        if (_M_Impl->_Wait() == canceled)
        {
            throw task_canceled();  
        }

        return _M_Impl->_GetResult();
    }

    bool is_done() const
    {
        if (!_M_Impl)
        {
            throw invalid_operation("is_done() cannot be called on a default constructed task.");
        }

        return _M_Impl->_IsDone();
    }

    scheduler_ptr scheduler() const
    {
        if (!_M_Impl)
        {
            throw invalid_operation("scheduler() cannot be called on a default constructed task.");
        }

        return _M_Impl->_GetScheduler();
    }

    
    bool is_apartment_aware() const
    {
        if (!_M_Impl)
        {
            throw invalid_operation("is_apartment_aware() cannot be called on a default constructed task.");
        }
        return _M_Impl->_IsApartmentAware();
    }

    
    bool operator==(const task<_ReturnType>& _Rhs) const
    {
        return (_M_Impl == _Rhs._M_Impl);
    }

    
    bool operator!=(const task<_ReturnType>& _Rhs) const
    {
        return !operator==(_Rhs);
    }

    void _CreateImpl(details::_CancellationTokenState * _Ct, scheduler_ptr _Scheduler)
    {
        _ASSERTE(_Ct != nullptr);
        _M_Impl = details::_Task_ptr<_ReturnType>::_Make(_Ct, _Scheduler);
        if (_Ct != details::_CancellationTokenState::_None())
        {
            _M_Impl->_RegisterCancellation(_M_Impl);
        }
    }

    const typename details::_Task_ptr<_ReturnType>::_Type & _GetImpl() const
    {
        return _M_Impl;
    }

    void _SetImpl(const typename details::_Task_ptr<_ReturnType>::_Type & _Impl)
    {
        _ASSERTE(!_M_Impl);
        _M_Impl = _Impl;
    }

    void _SetImpl(typename details::_Task_ptr<_ReturnType>::_Type && _Impl)
    {
        _ASSERTE(!_M_Impl);
        _M_Impl = std::move(_Impl);
    }

    void _SetAsync(bool _Async = true)
    {
        _GetImpl()->_SetAsync(_Async);
    }

    void _SetTaskCreationCallstack(const details::_TaskCreationCallstack &_callstack)
    {
        _GetImpl()->_SetTaskCreationCallstack(_callstack);
    }

    template<typename _Function>
    auto _Then(const _Function& _Func, details::_CancellationTokenState *_PTokenState, 
        details::_TaskInliningMode_t _InliningMode = details::_ForceInline) const -> typename details::_ContinuationTypeTraits<_Function, _ReturnType>::_TaskOfType
    {
        // inherit from antecedent
        auto _Scheduler = _GetImpl()->_GetScheduler();

        return _ThenImpl<_ReturnType, _Function>(_Func, _PTokenState, task_continuation_context::use_default(), _Scheduler, _CAPTURE_CALLSTACK(), _InliningMode);
    }

private:
    template <typename T> friend class task;

     
    // The task handle type used to construct an 'initial task' - a task with no dependents.
    template <typename _InternalReturnType, typename _Function, typename _TypeSelection>
    struct _InitialTaskHandle : 
        details::_PPLTaskHandle<_ReturnType, _InitialTaskHandle<_InternalReturnType, _Function, _TypeSelection>, details::_UnrealizedChore_t>
    {
        _Function _M_function;
        _InitialTaskHandle(const typename details::_Task_ptr<_ReturnType>::_Type & _TaskImpl, const _Function & _func)
            : details::_PPLTaskHandle<_ReturnType, _InitialTaskHandle<_InternalReturnType, _Function, _TypeSelection>, details::_UnrealizedChore_t>::_PPLTaskHandle(_TaskImpl)
            , _M_function(_func)
        {
        }

        virtual ~_InitialTaskHandle() {}

        template <typename _Func>
        auto _LogWorkItemAndInvokeUserLambda(_Func && _func) const -> decltype(_func())
        {
            details::_TaskWorkItemRAIILogger _LogWorkItem(this->_M_pTask->_M_taskEventLogger);
            CASABLANCA_UNREFERENCED_PARAMETER(_LogWorkItem);
            return _func();
        }

        void _Perform() const
        {
            _Init(_TypeSelection());
        }

        void _SyncCancelAndPropagateException() const
        {
            this->_M_pTask->_Cancel(true);
        }

        //
        // Overload 0: returns _InternalReturnType
        //
        // This is the most basic task with no unwrapping
        //
        void _Init(details::_TypeSelectorNoAsync) const
        {
            this->_M_pTask->_FinalizeAndRunContinuations(_LogWorkItemAndInvokeUserLambda(_Init_func_transformer<_InternalReturnType>::_Perform(_M_function)));
        }

        //
        // Overload 1: returns IAsyncOperation<_InternalReturnType>^ (only uder /ZW)
        //                   or
        //             returns task<_InternalReturnType>
        //
        // This is task whose functor returns an async operation or a task which will be unwrapped for continuation
        // Depending on the output type, the right _AsyncInit gets invoked
        //
        void _Init(details::_TypeSelectorAsyncOperationOrTask) const
        {
            details::_Task_impl_base::_AsyncInit<_ReturnType, _InternalReturnType>(this->_M_pTask, _LogWorkItemAndInvokeUserLambda(_M_function));
        }

#if defined (__cplusplus_winrt)
        //
        // Overload 2: returns IAsyncAction^
        //
        // This is task whose functor returns an async action which will be unwrapped for continuation
        //
        void _Init(details::_TypeSelectorAsyncAction) const
        {
            details::_Task_impl_base::_AsyncInit<_ReturnType, _InternalReturnType>(this->_M_pTask, ref new details::_IAsyncActionToAsyncOperationConverter(_LogWorkItemAndInvokeUserLambda(_M_function)));
        }

        //
        // Overload 3: returns IAsyncOperationWithProgress<_InternalReturnType, _ProgressType>^
        //
        // This is task whose functor returns an async operation with progress which will be unwrapped for continuation
        //
        void _Init(details::_TypeSelectorAsyncOperationWithProgress) const
        {
            typedef details::_GetProgressType<decltype(_M_function())>::_Value _ProgressType;

            details::_Task_impl_base::_AsyncInit<_ReturnType, _InternalReturnType>(this->_M_pTask,
                    ref new details::_IAsyncOperationWithProgressToAsyncOperationConverter<_InternalReturnType,_ProgressType>(_LogWorkItemAndInvokeUserLambda(_M_function)));
        }

        //
        // Overload 4: returns IAsyncActionWithProgress<_ProgressType>^
        //
        // This is task whose functor returns an async action with progress which will be unwrapped for continuation
        //
        void _Init(details::_TypeSelectorAsyncActionWithProgress) const
        {
            typedef details::_GetProgressType<decltype(_M_function())>::_Value _ProgressType;

            details::_Task_impl_base::_AsyncInit<_ReturnType, _InternalReturnType>(this->_M_pTask, 
                ref new details::_IAsyncActionWithProgressToAsyncOperationConverter<_ProgressType>(_LogWorkItemAndInvokeUserLambda(_M_function)));
        }
#endif  /* defined (__cplusplus_winrt) */
    };


    template <typename _InternalReturnType, typename _ContinuationReturnType, typename _Function, typename _IsTaskBased, typename _TypeSelection>
    struct _ContinuationTaskHandle :
        details::_PPLTaskHandle<typename details::_NormalizeVoidToUnitType<_ContinuationReturnType>::_Type,
        _ContinuationTaskHandle<_InternalReturnType, _ContinuationReturnType, _Function, _IsTaskBased, _TypeSelection>, details::_ContinuationTaskHandleBase>
    {
        typedef typename details::_NormalizeVoidToUnitType<_ContinuationReturnType>::_Type _NormalizedContinuationReturnType;

        typename details::_Task_ptr<_ReturnType>::_Type _M_ancestorTaskImpl;
        _Function _M_function;

        _ContinuationTaskHandle(const typename details::_Task_ptr<_ReturnType>::_Type & _AncestorImpl,
            const typename details::_Task_ptr<_NormalizedContinuationReturnType>::_Type & _ContinuationImpl,
            const _Function & _Func, const task_continuation_context & _Context, details::_TaskInliningMode_t _InliningMode)
                : details::_PPLTaskHandle<typename details::_NormalizeVoidToUnitType<_ContinuationReturnType>::_Type,
                    _ContinuationTaskHandle<_InternalReturnType, _ContinuationReturnType, _Function, _IsTaskBased, _TypeSelection>, details::_ContinuationTaskHandleBase>
                    ::_PPLTaskHandle(_ContinuationImpl)
                , _M_ancestorTaskImpl(_AncestorImpl)
                , _M_function(_Func)
        {
            this->_M_isTaskBasedContinuation = _IsTaskBased::value;
            this->_M_continuationContext = _Context;
            this->_M_continuationContext._Resolve(_AncestorImpl->_IsApartmentAware());
            this->_M_inliningMode = _InliningMode;
        }

        virtual ~_ContinuationTaskHandle() {}

        template <typename _Func, typename _Arg>
        auto _LogWorkItemAndInvokeUserLambda(_Func && _func, _Arg && _value) const -> decltype(_func(std::forward<_Arg>(_value)))
        {
            details::_TaskWorkItemRAIILogger _LogWorkItem(this->_M_pTask->_M_taskEventLogger);
            CASABLANCA_UNREFERENCED_PARAMETER(_LogWorkItem);
            return _func(std::forward<_Arg>(_value));
        }

        void _Perform() const
        {
            _Continue(_IsTaskBased(), _TypeSelection());
        }

        void _SyncCancelAndPropagateException() const
        {
            if (_M_ancestorTaskImpl->_HasUserException())
            {
                // If the ancestor encountered an exception, transfer the exception to the continuation
                // This traverses down the tree to propagate the exception.
                this->_M_pTask->_CancelWithExceptionHolder(_M_ancestorTaskImpl->_GetExceptionHolder(), true);
            }
            else
            {
                // If the ancestor was canceled, then your own execution should be canceled.
                // This traverses down the tree to cancel it.
                this->_M_pTask->_Cancel(true);
            }
        }

        //
        // Overload 0-0: _InternalReturnType -> _TaskType
        //
        // This is a straight task continuation which simply invokes its target with the ancestor's completion argument
        //
        void _Continue(std::false_type, details::_TypeSelectorNoAsync) const
        {
            this->_M_pTask->_FinalizeAndRunContinuations(
                _LogWorkItemAndInvokeUserLambda(_Continuation_func_transformer<_InternalReturnType, _ContinuationReturnType>::_Perform(_M_function), _M_ancestorTaskImpl->_GetResult()));
        }

        //
        // Overload 0-1: _InternalReturnType -> IAsyncOperation<_TaskType>^ (only uder /ZW)
        //               or
        //               _InternalReturnType -> task<_TaskType>
        //
        // This is a straight task continuation which returns an async operation or a task which will be unwrapped for continuation
        // Depending on the output type, the right _AsyncInit gets invoked
        //
        void _Continue(std::false_type, details::_TypeSelectorAsyncOperationOrTask) const
        {
            typedef typename details::_FunctionTypeTraits<_Function, _InternalReturnType>::_FuncRetType _FuncOutputType;

            details::_Task_impl_base::_AsyncInit<_NormalizedContinuationReturnType, _ContinuationReturnType>(
                this->_M_pTask, 
                _LogWorkItemAndInvokeUserLambda(_Continuation_func_transformer<_InternalReturnType, _FuncOutputType>::_Perform(_M_function), _M_ancestorTaskImpl->_GetResult())
            );
        }

#if defined (__cplusplus_winrt)
        //
        // Overload 0-2: _InternalReturnType -> IAsyncAction^
        //
        // This is a straight task continuation which returns an async action which will be unwrapped for continuation
        //
        void _Continue(std::false_type, details::_TypeSelectorAsyncAction) const
        {
            typedef details::_FunctionTypeTraits<_Function, _InternalReturnType>::_FuncRetType _FuncOutputType;

            details::_Task_impl_base::_AsyncInit<_NormalizedContinuationReturnType, _ContinuationReturnType>(
                this->_M_pTask,
                ref new details::_IAsyncActionToAsyncOperationConverter(
                    _LogWorkItemAndInvokeUserLambda(_Continuation_func_transformer<_InternalReturnType, _FuncOutputType>::_Perform(_M_function), _M_ancestorTaskImpl->_GetResult())));
        }

        //
        // Overload 0-3: _InternalReturnType -> IAsyncOperationWithProgress<_TaskType, _ProgressType>^
        //
        // This is a straight task continuation which returns an async operation with progress which will be unwrapped for continuation
        //
        void _Continue(std::false_type, details::_TypeSelectorAsyncOperationWithProgress) const
        {
            typedef details::_FunctionTypeTraits<_Function, _InternalReturnType>::_FuncRetType _FuncOutputType;

            auto _OpWithProgress = _LogWorkItemAndInvokeUserLambda(_Continuation_func_transformer<_InternalReturnType, _FuncOutputType>::_Perform(_M_function), _M_ancestorTaskImpl->_GetResult());
            typedef details::_GetProgressType<decltype(_OpWithProgress)>::_Value _ProgressType;

            details::_Task_impl_base::_AsyncInit<_NormalizedContinuationReturnType, _ContinuationReturnType>(
                this->_M_pTask,
                ref new details::_IAsyncOperationWithProgressToAsyncOperationConverter<_ContinuationReturnType, _ProgressType>(_OpWithProgress));
        }

        //
        // Overload 0-4: _InternalReturnType -> IAsyncActionWithProgress<_ProgressType>^
        //
        // This is a straight task continuation which returns an async action with progress which will be unwrapped for continuation
        //
        void _Continue(std::false_type, details::_TypeSelectorAsyncActionWithProgress) const
        {
            typedef details::_FunctionTypeTraits<_Function, _InternalReturnType>::_FuncRetType _FuncOutputType;

            auto _OpWithProgress = _LogWorkItemAndInvokeUserLambda(_Continuation_func_transformer<_InternalReturnType, _FuncOutputType>::_Perform(_M_function), _M_ancestorTaskImpl->_GetResult());
            typedef details::_GetProgressType<decltype(_OpWithProgress)>::_Value _ProgressType;

            details::_Task_impl_base::_AsyncInit<_NormalizedContinuationReturnType, _ContinuationReturnType>(
                this->_M_pTask,
                ref new details::_IAsyncActionWithProgressToAsyncOperationConverter<_ProgressType>(_OpWithProgress));
        }

#endif  /* defined (__cplusplus_winrt) */

        //
        // Overload 1-0: task<_InternalReturnType> -> _TaskType
        //
        // This is an exception handling type of continuation which takes the task rather than the task's result.
        //
        void _Continue(std::true_type, details::_TypeSelectorNoAsync) const
        {
            typedef task<_InternalReturnType> _FuncInputType;
            task<_InternalReturnType> _ResultTask;
            _ResultTask._SetImpl(std::move(_M_ancestorTaskImpl));
            this->_M_pTask->_FinalizeAndRunContinuations(
                _LogWorkItemAndInvokeUserLambda(_Continuation_func_transformer<_FuncInputType, _ContinuationReturnType>::_Perform(_M_function), std::move(_ResultTask)));
        }

        //
        // Overload 1-1: task<_InternalReturnType> -> IAsyncOperation<_TaskType>^
        //                                            or
        //                                            task<_TaskType>
        //
        // This is an exception handling type of continuation which takes the task rather than
        // the task's result. It also returns an async operation or a task which will be unwrapped
        // for continuation
        //
        void _Continue(std::true_type, details::_TypeSelectorAsyncOperationOrTask) const
        {
            // The continuation takes a parameter of type task<_Input>, which is the same as the ancestor task.
            task<_InternalReturnType> _ResultTask;
            _ResultTask._SetImpl(std::move(_M_ancestorTaskImpl));
            details::_Task_impl_base::_AsyncInit<_NormalizedContinuationReturnType, _ContinuationReturnType>(this->_M_pTask, 
                _LogWorkItemAndInvokeUserLambda(_M_function, std::move(_ResultTask)));
        }

#if defined (__cplusplus_winrt)

        //
        // Overload 1-2: task<_InternalReturnType> -> IAsyncAction^
        //
        // This is an exception handling type of continuation which takes the task rather than
        // the task's result. It also returns an async action which will be unwrapped for continuation
        //
        void _Continue(std::true_type, details::_TypeSelectorAsyncAction) const
        {
            // The continuation takes a parameter of type task<_Input>, which is the same as the ancestor task.
            task<_InternalReturnType> _ResultTask;
            _ResultTask._SetImpl(std::move(_M_ancestorTaskImpl));
            details::_Task_impl_base::_AsyncInit<_NormalizedContinuationReturnType, _ContinuationReturnType>(this->_M_pTask,
                ref new details::_IAsyncActionToAsyncOperationConverter(_LogWorkItemAndInvokeUserLambda(_M_function, std::move(_ResultTask))));
        }

        //
        // Overload 1-3: task<_InternalReturnType> -> IAsyncOperationWithProgress<_TaskType, _ProgressType>^
        //
        // This is an exception handling type of continuation which takes the task rather than
        // the task's result. It also returns an async operation with progress which will be unwrapped
        // for continuation
        //
        void _Continue(std::true_type, details::_TypeSelectorAsyncOperationWithProgress) const
        {
            // The continuation takes a parameter of type task<_Input>, which is the same as the ancestor task.
            task<_InternalReturnType> _ResultTask;
            _ResultTask._SetImpl(std::move(_M_ancestorTaskImpl));

            typedef details::_GetProgressType<decltype(_M_function(_ResultTask))>::_Value _ProgressType;

            details::_Task_impl_base::_AsyncInit<_NormalizedContinuationReturnType, _ContinuationReturnType>(this->_M_pTask,
                    ref new details::_IAsyncOperationWithProgressToAsyncOperationConverter<_ContinuationReturnType, _ProgressType>(
                    _LogWorkItemAndInvokeUserLambda(_M_function, std::move(_ResultTask))));
        }

        //
        // Overload 1-4: task<_InternalReturnType> -> IAsyncActionWithProgress<_ProgressType>^
        //
        // This is an exception handling type of continuation which takes the task rather than
        // the task's result. It also returns an async operation with progress which will be unwrapped
        // for continuation
        //
        void _Continue(std::true_type, details::_TypeSelectorAsyncActionWithProgress) const
        {
            // The continuation takes a parameter of type task<_Input>, which is the same as the ancestor task.
            task<_InternalReturnType> _ResultTask;
            _ResultTask._SetImpl(std::move(_M_ancestorTaskImpl));

            typedef details::_GetProgressType<decltype(_M_function(_ResultTask))>::_Value _ProgressType;

            details::_Task_impl_base::_AsyncInit<_NormalizedContinuationReturnType, _ContinuationReturnType>(this->_M_pTask,
                    ref new details::_IAsyncActionWithProgressToAsyncOperationConverter<_ProgressType>(
                    _LogWorkItemAndInvokeUserLambda(_M_function, std::move(_ResultTask))));
        }
#endif  /* defined (__cplusplus_winrt) */
    };

    template<typename _InternalReturnType, typename _Function>
    void _TaskInitWithFunctor(const _Function& _Func)
    {
        typedef typename details::_InitFunctorTypeTraits<_InternalReturnType, decltype(_Func())> _Async_type_traits;

        _M_Impl->_M_fFromAsync = _Async_type_traits::_IsAsyncTask;
        _M_Impl->_M_fUnwrappedTask = _Async_type_traits::_IsUnwrappedTaskOrAsync;
        _M_Impl->_M_taskEventLogger._LogScheduleTask(false);
        _M_Impl->_ScheduleTask(new _InitialTaskHandle<_InternalReturnType, _Function, typename _Async_type_traits::_AsyncKind>(_GetImpl(), _Func), details::_NoInline);
    }

    void _TaskInitNoFunctor(task_completion_event<_ReturnType>& _Event)
    {
        _Event._RegisterTask(_M_Impl);
    }

#if defined (__cplusplus_winrt)
    void _TaskInitAsyncOp(Windows::Foundation::IAsyncOperation<typename details::_ValueTypeOrRefType<_ReturnType>::_Value>^ _AsyncOp)
    {
        _M_Impl->_M_fFromAsync = true;

        // Mark this task as started here since we can set the state in the constructor without acquiring a lock. Once _AsyncInit
        // returns a completion could execute concurrently and the task must be fully initialized before that happens.
        _M_Impl->_M_TaskState = details::_Task_impl_base::_Started;
        // Pass the shared pointer into _AsyncInit for storage in the Async Callback.
        details::_Task_impl_base::_AsyncInit<_ReturnType, _ReturnType>(_M_Impl, _AsyncOp);
    }

    void _TaskInitNoFunctor(Windows::Foundation::IAsyncOperation<typename details::_ValueTypeOrRefType<_ReturnType>::_Value>^ _AsyncOp)
    {
        _TaskInitAsyncOp(_AsyncOp);
    }

    template<typename _Progress>
    void _TaskInitNoFunctor(Windows::Foundation::IAsyncOperationWithProgress<typename details::_ValueTypeOrRefType<_ReturnType>::_Value, _Progress>^ _AsyncOp)
    {
        _TaskInitAsyncOp(ref new details::_IAsyncOperationWithProgressToAsyncOperationConverter<typename details::_ValueTypeOrRefType<_ReturnType>::_Value, _Progress>(_AsyncOp));
    }
#endif  /* defined (__cplusplus_winrt) */

    template<typename _Function>
    void _TaskInitMaybeFunctor(_Function & _Func, std::true_type)
    {
        _TaskInitWithFunctor<_ReturnType, _Function>(_Func);
    }

    template<typename _Ty>
    void _TaskInitMaybeFunctor(_Ty & _Param, std::false_type)
    {
        _TaskInitNoFunctor(_Param);
    }

    template<typename _InternalReturnType, typename _Function>
    auto _ThenImpl(const _Function& _Func, const task_options& _TaskOptions) const -> typename details::_ContinuationTypeTraits<_Function, _InternalReturnType>::_TaskOfType
    {
        if (!_M_Impl)
        {
            throw invalid_operation("then() cannot be called on a default constructed task.");
        }

        details::_CancellationTokenState *_PTokenState = _TaskOptions.has_cancellation_token() ? _TaskOptions.get_cancellation_token()._GetImplValue() : nullptr;
        auto _Scheduler = _TaskOptions.has_scheduler() ? _TaskOptions.get_scheduler() : _GetImpl()->_GetScheduler();
        auto _CreationStack = details::_get_internal_task_options(_TaskOptions)._M_hasPresetCreationCallstack ? details::_get_internal_task_options(_TaskOptions)._M_presetCreationCallstack : details::_TaskCreationCallstack();
        return _ThenImpl<_InternalReturnType, _Function>(_Func, _PTokenState, _TaskOptions.get_continuation_context(), _Scheduler, _CreationStack);
    }

    template<typename _InternalReturnType, typename _Function>
    auto _ThenImpl(const _Function& _Func, details::_CancellationTokenState *_PTokenState, const task_continuation_context& _ContinuationContext, scheduler_ptr _Scheduler, details::_TaskCreationCallstack _CreationStack,
        details::_TaskInliningMode_t _InliningMode = details::_NoInline) const -> typename details::_ContinuationTypeTraits<_Function, _InternalReturnType>::_TaskOfType
    {
        if (!_M_Impl)
        {
            throw invalid_operation("then() cannot be called on a default constructed task.");
        }

        typedef details::_FunctionTypeTraits<_Function, _InternalReturnType> _Function_type_traits;
        typedef details::_TaskTypeTraits<typename _Function_type_traits::_FuncRetType> _Async_type_traits;
        typedef typename _Async_type_traits::_TaskRetType _TaskType;

        //
        // A **nullptr** token state indicates that it was not provided by the user. In this case, we inherit the antecedent's token UNLESS this is a
        // an exception handling continuation. In that case, we break the chain with a _None. That continuation is never canceled unless the user
        // explicitly passes the same token.
        //
        if (_PTokenState == nullptr)
        {
            if (_Function_type_traits::_Takes_task::value)
            {
                _PTokenState = details::_CancellationTokenState::_None();
            }
            else
            {
                _PTokenState = _GetImpl()->_M_pTokenState;
            }
        }

        task<_TaskType> _ContinuationTask;
        _ContinuationTask._CreateImpl(_PTokenState, _Scheduler);

        _ContinuationTask._GetImpl()->_M_fFromAsync = (_GetImpl()->_M_fFromAsync || _Async_type_traits::_IsAsyncTask);
        _ContinuationTask._GetImpl()->_M_fUnwrappedTask = _Async_type_traits::_IsUnwrappedTaskOrAsync;
        _ContinuationTask._SetTaskCreationCallstack(_CreationStack);

        _GetImpl()->_ScheduleContinuation(new _ContinuationTaskHandle<_InternalReturnType, _TaskType, _Function, typename _Function_type_traits::_Takes_task, typename _Async_type_traits::_AsyncKind>(
            _GetImpl(), _ContinuationTask._GetImpl(), _Func, _ContinuationContext, _InliningMode));

        return _ContinuationTask;
    }

    // The underlying implementation for this task
    typename details::_Task_ptr<_ReturnType>::_Type _M_Impl;
};


template<>
class task<void>
{
public:
    
    typedef void result_type;

    
    task() : _M_unitTask()
    {
        // The default constructor should create a task with a nullptr impl. This is a signal that the
        // task is not usable and should throw if any wait(), get() or then() APIs are used.
    }

    
    template<typename _Ty>
    __declspec(noinline) // Ask for no inlining so that the _CAPTURE_CALLSTACK gives us the expected result
    explicit task(_Ty _Param, const task_options& _TaskOptions = task_options())
    {
        details::_ValidateTaskConstructorArgs<void,_Ty>(_Param);

        _M_unitTask._CreateImpl(_TaskOptions.get_cancellation_token()._GetImplValue(), _TaskOptions.get_scheduler());
        // Do not move the next line out of this function. It is important that _CAPTURE_CALLSTACK() evaluate to the the call site of the task constructor.
        _M_unitTask._SetTaskCreationCallstack(details::_get_internal_task_options(_TaskOptions)._M_hasPresetCreationCallstack ? details::_get_internal_task_options(_TaskOptions)._M_presetCreationCallstack : _CAPTURE_CALLSTACK());

        _TaskInitMaybeFunctor(_Param, details::_IsCallable(_Param,0));
    }

    
    task(const task& _Other): _M_unitTask(_Other._M_unitTask){}

    
    task(task&& _Other) : _M_unitTask(std::move(_Other._M_unitTask)) {}

    
    task& operator=(const task& _Other)
    {
        if (this != &_Other)
        {
            _M_unitTask = _Other._M_unitTask;
        }
        return *this;
    }

    
    task& operator=(task&& _Other)
    {
        if (this != &_Other)
        {
            _M_unitTask = std::move(_Other._M_unitTask);
        }
        return *this;
    }

    
    template<typename _Function>
    __declspec(noinline) // Ask for no inlining so that the _CAPTURE_CALLSTACK gives us the expected result
    auto then(const _Function& _Func, task_options _TaskOptions = task_options()) const -> typename details::_ContinuationTypeTraits<_Function, void>::_TaskOfType
    {
        details::_get_internal_task_options(_TaskOptions)._set_creation_callstack(_CAPTURE_CALLSTACK());
        return _M_unitTask._ThenImpl<void, _Function>(_Func, _TaskOptions);
    }

    
    template<typename _Function>
    __declspec(noinline) // Ask for no inlining so that the _CAPTURE_CALLSTACK gives us the expected result
    auto then(const _Function& _Func, cancellation_token _CancellationToken, task_continuation_context _ContinuationContext) const -> typename details::_ContinuationTypeTraits<_Function, void>::_TaskOfType
    {
        task_options _TaskOptions(_CancellationToken, _ContinuationContext);
        details::_get_internal_task_options(_TaskOptions)._set_creation_callstack(_CAPTURE_CALLSTACK());
        return _M_unitTask._ThenImpl<void, _Function>(_Func, _TaskOptions);
    }

    
    task_status wait() const
    {
        return _M_unitTask.wait();
    }

    
    void get() const
    {
        _M_unitTask.get();
    }

    bool is_done() const
    {
        return _M_unitTask.is_done();
    }

    scheduler_ptr scheduler() const
    {
        return _M_unitTask.scheduler();
    }

    
    bool is_apartment_aware() const
    {
        return _M_unitTask.is_apartment_aware();
    }

    
    bool operator==(const task<void>& _Rhs) const
    {
        return (_M_unitTask == _Rhs._M_unitTask);
    }

    
    bool operator!=(const task<void>& _Rhs) const
    {
        return !operator==(_Rhs);
    }

    void _CreateImpl(details::_CancellationTokenState * _Ct, scheduler_ptr _Scheduler)
    {
        _M_unitTask._CreateImpl(_Ct, _Scheduler);
    }

    const details::_Task_ptr<details::_Unit_type>::_Type & _GetImpl() const
    {
        return _M_unitTask._M_Impl;
    }

    void _SetImpl(const details::_Task_ptr<details::_Unit_type>::_Type & _Impl)
    {
        _M_unitTask._SetImpl(_Impl);
    }

    void _SetImpl(details::_Task_ptr<details::_Unit_type>::_Type && _Impl)
    {
        _M_unitTask._SetImpl(std::move(_Impl));
    }

    void _SetAsync(bool _Async = true)
    {
        _M_unitTask._SetAsync(_Async);
    }

    void _SetTaskCreationCallstack(const details::_TaskCreationCallstack &_callstack)
    {
        _M_unitTask._SetTaskCreationCallstack(_callstack);
    }

    template<typename _Function>
    auto _Then(const _Function& _Func, details::_CancellationTokenState *_PTokenState, 
        details::_TaskInliningMode_t _InliningMode = details::_ForceInline) const -> typename details::_ContinuationTypeTraits<_Function, void>::_TaskOfType
    {
        // inherit from antecedent
        auto _Scheduler = _GetImpl()->_GetScheduler();

        return _M_unitTask._ThenImpl<void, _Function>(_Func, _PTokenState, task_continuation_context::use_default(), _Scheduler, _CAPTURE_CALLSTACK(), _InliningMode);
    }

private:
    template <typename T> friend class task;
    template <typename T> friend class task_completion_event;

    void _TaskInitNoFunctor(task_completion_event<void>& _Event)
    {
        _M_unitTask._TaskInitNoFunctor(_Event._M_unitEvent);
    }

#if defined (__cplusplus_winrt)
    void _TaskInitNoFunctor(Windows::Foundation::IAsyncAction^ _AsyncAction)
    {
         _M_unitTask._TaskInitAsyncOp(ref new details::_IAsyncActionToAsyncOperationConverter(_AsyncAction));
    }

    template<typename _P>
    void _TaskInitNoFunctor(Windows::Foundation::IAsyncActionWithProgress<_P>^ _AsyncActionWithProgress)
    {
        _M_unitTask._TaskInitAsyncOp(ref new details::_IAsyncActionWithProgressToAsyncOperationConverter<_P>(_AsyncActionWithProgress));
    }
#endif  /* defined (__cplusplus_winrt) */

    template<typename _Function>
    void _TaskInitMaybeFunctor(_Function & _Func, std::true_type)
    {
        _M_unitTask._TaskInitWithFunctor<void, _Function>(_Func);
    }

    template<typename _T>
    void _TaskInitMaybeFunctor(_T & _Param, std::false_type)
    {
        _TaskInitNoFunctor(_Param);
    }

    // The void task contains a task of a dummy type so common code can be used for tasks with void and non-void results.
    task<details::_Unit_type> _M_unitTask;
};

namespace details
{

#if defined (__cplusplus_winrt)
    // Unwrap functions for asyncOperations
    template<typename _Ty>
    _Ty _GetUnwrappedType(Windows::Foundation::IAsyncOperation<_Ty>^);

    void _GetUnwrappedType(Windows::Foundation::IAsyncAction^);

    template<typename _Ty, typename _Progress>
    _Ty _GetUnwrappedType(Windows::Foundation::IAsyncOperationWithProgress<_Ty, _Progress>^);

    template<typename _Progress>
    void _GetUnwrappedType(Windows::Foundation::IAsyncActionWithProgress<_Progress>^);
#endif  /* defined (__cplusplus_winrt) */

    // Unwrap task<T>
    template<typename _Ty>
    _Ty _GetUnwrappedType(task<_Ty>);

    // Unwrap all supportted types
    template<typename _Ty>
    auto _GetUnwrappedReturnType(_Ty _Arg, int) -> decltype(_GetUnwrappedType(_Arg));
    // fallback
    template<typename _Ty>
    _Ty _GetUnwrappedReturnType(_Ty, ...);


    // Non-Callable
    template<typename _Ty>
    _Ty _GetTaskType(task_completion_event<_Ty>, std::false_type);

    // Non-Callable
    template<typename _Ty>
    auto _GetTaskType(_Ty _NonFunc, std::false_type) -> decltype(_GetUnwrappedType(_NonFunc));

    // Callable
    template<typename _Ty>
    auto _GetTaskType(_Ty _Func, std::true_type) -> decltype(_GetUnwrappedReturnType(_Func(), 0));

    // Special callable returns void
    void _GetTaskType(std::function<void()>, std::true_type);
    struct _BadArgType{};

    template<typename _Ty>
    auto _FilterValidTaskType(_Ty _Param, int) -> decltype(_GetTaskType(_Param, _IsCallable(_Param, 0)));

    template<typename _Ty>
    _BadArgType _FilterValidTaskType(_Ty _Param, ...);

    template<typename _Ty>
    struct _TaskTypeFromParam
    {
        typedef decltype(_FilterValidTaskType(stdx::declval<_Ty>(), 0)) _Type;
    };
} // namespace details


template<typename _Ty>
__declspec(noinline)
auto create_task(_Ty _Param, task_options _TaskOptions = task_options()) -> task<typename details::_TaskTypeFromParam<_Ty>::_Type>
{
    static_assert(!std::is_same<typename details::_TaskTypeFromParam<_Ty>::_Type,details::_BadArgType>::value,
#if defined (__cplusplus_winrt)
            "incorrect argument for create_task; can be a callable object, an asynchronous operation, or a task_completion_event"
#else  /* defined (__cplusplus_winrt) */
            "incorrect argument for create_task; can be a callable object or a task_completion_event"
#endif  /* defined (__cplusplus_winrt) */
    );
    details::_get_internal_task_options(_TaskOptions)._set_creation_callstack(_CAPTURE_CALLSTACK());
    task<typename details::_TaskTypeFromParam<_Ty>::_Type> _CreatedTask(_Param, _TaskOptions);
    return _CreatedTask;
}


template<typename _ReturnType>
__declspec(noinline)
task<_ReturnType> create_task(const task<_ReturnType>& _Task)
{
    task<_ReturnType> _CreatedTask(_Task);
    return _CreatedTask;
}

#if defined (__cplusplus_winrt)
namespace details
{
    template<typename _T>
    task<_T> _To_task_helper(Windows::Foundation::IAsyncOperation<_T>^ op)
    {
        return task<_T>(op);
    }

    template<typename _T, typename _Progress>
    task<_T> _To_task_helper(Windows::Foundation::IAsyncOperationWithProgress<_T, _Progress>^ op)
    {
        return task<_T>(op);
    }

    inline task<void> _To_task_helper(Windows::Foundation::IAsyncAction^ op)
    {
        return task<void>(op);
    }

    template<typename _Progress>
    task<void> _To_task_helper(Windows::Foundation::IAsyncActionWithProgress<_Progress>^ op)
    {
        return task<void>(op);
    }

    template<typename _ProgressType>
    class _ProgressDispatcherBase
    {
    public:

        virtual ~_ProgressDispatcherBase()
        {
        }

        virtual void _Report(const _ProgressType& _Val) = 0;
    };

    template<typename _ProgressType, typename _ClassPtrType>
    class _ProgressDispatcher : public _ProgressDispatcherBase<_ProgressType>
    {
    public:

        virtual ~_ProgressDispatcher()
        {
        }

        _ProgressDispatcher(_ClassPtrType _Ptr) : _M_ptr(_Ptr)
        {
        }

        virtual void _Report(const _ProgressType& _Val)
        {
            _M_ptr->_FireProgress(_Val);
        }

    private:

        _ClassPtrType _M_ptr;
    };
    class _ProgressReporterCtorArgType{};
} // namespace details


template<typename _ProgressType>
class progress_reporter
{
    typedef std::shared_ptr<details::_ProgressDispatcherBase<_ProgressType>> _PtrType;

public:

    
    void report(const _ProgressType& _Val) const
    {
        _M_dispatcher->_Report(_Val);
    }

    template<typename _ClassPtrType>
    static progress_reporter _CreateReporter(_ClassPtrType _Ptr)
    {
        progress_reporter _Reporter;
        details::_ProgressDispatcherBase<_ProgressType> *_PDispatcher = new details::_ProgressDispatcher<_ProgressType, _ClassPtrType>(_Ptr);
        _Reporter._M_dispatcher = _PtrType(_PDispatcher);
        return _Reporter;
    }
    progress_reporter() {}

private:
    progress_reporter(details::_ProgressReporterCtorArgType);

    _PtrType _M_dispatcher;
};

namespace details
{
    //
    // maps internal definitions for AsyncStatus and defines states that are not client visible
    //
    enum _AsyncStatusInternal
    {
        _AsyncCreated = -1,  // externally invisible
        // client visible states (must match AsyncStatus exactly)
        _AsyncStarted = 0,   // Windows::Foundation::AsyncStatus::Started,
        _AsyncCompleted = 1, // Windows::Foundation::AsyncStatus::Completed,
        _AsyncCanceled = 2, // Windows::Foundation::AsyncStatus::Canceled,
        _AsyncError = 3,     // Windows::Foundation::AsyncStatus::Error,
        // non-client visible internal states
        _AsyncCancelPending,
        _AsyncClosed,
        _AsyncUndefined
    };

    //
    // designates whether the "GetResults" method returns a single result (after complete fires) or multiple results
    // (which are progressively consumable between Start state and before Close is called)
    //
    enum _AsyncResultType
    {
        SingleResult    = 0x0001,
        MultipleResults = 0x0002
    };

    // ***************************************************************************
    // Template type traits and helpers for async production APIs:
    //

    struct _ZeroArgumentFunctor { };
    struct _OneArgumentFunctor { };
    struct _TwoArgumentFunctor { };

    // ****************************************
    // CLASS TYPES:

    // ********************
    // TWO ARGUMENTS:

    // non-void arg:
    template<typename _Class, typename _ReturnType, typename _Arg1, typename _Arg2>
    _Arg1 _Arg1ClassHelperThunk(_ReturnType (_Class::*)(_Arg1, _Arg2) const);

    // non-void arg:
    template<typename _Class, typename _ReturnType, typename _Arg1, typename _Arg2>
    _Arg2 _Arg2ClassHelperThunk(_ReturnType (_Class::*)(_Arg1, _Arg2) const);

    template<typename _Class, typename _ReturnType, typename _Arg1, typename _Arg2>
    _ReturnType _ReturnTypeClassHelperThunk(_ReturnType (_Class::*)(_Arg1, _Arg2) const);

    template<typename _Class, typename _ReturnType, typename _Arg1, typename _Arg2>
    _TwoArgumentFunctor _ArgumentCountHelper(_ReturnType (_Class::*)(_Arg1, _Arg2) const);

    // ********************
    // ONE ARGUMENT:

    // non-void arg:
    template<typename _Class, typename _ReturnType, typename _Arg1>
    _Arg1 _Arg1ClassHelperThunk(_ReturnType (_Class::*)(_Arg1) const);

    // non-void arg:
    template<typename _Class, typename _ReturnType, typename _Arg1>
    void _Arg2ClassHelperThunk(_ReturnType (_Class::*)(_Arg1) const);

    template<typename _Class, typename _ReturnType, typename _Arg1>
    _ReturnType _ReturnTypeClassHelperThunk(_ReturnType (_Class::*)(_Arg1) const);

    template<typename _Class, typename _ReturnType, typename _Arg1>
    _OneArgumentFunctor _ArgumentCountHelper(_ReturnType (_Class::*)(_Arg1) const);

    // ********************
    // ZERO ARGUMENT:

    // void arg:
    template<typename _Class, typename _ReturnType>
    void _Arg1ClassHelperThunk(_ReturnType (_Class::*)() const);

    // void arg:
    template<typename _Class, typename _ReturnType>
    void _Arg2ClassHelperThunk(_ReturnType (_Class::*)() const);

    // void arg:
    template<typename _Class, typename _ReturnType>
    _ReturnType _ReturnTypeClassHelperThunk(_ReturnType (_Class::*)() const);

    template<typename _Class, typename _ReturnType>
    _ZeroArgumentFunctor _ArgumentCountHelper(_ReturnType (_Class::*)() const);

    // ****************************************
    // POINTER TYPES:

    // ********************
    // TWO ARGUMENTS:

    template<typename _ReturnType, typename _Arg1, typename _Arg2>
    _Arg1 _Arg1PFNHelperThunk(_ReturnType(__cdecl *)(_Arg1, _Arg2));

    template<typename _ReturnType, typename _Arg1, typename _Arg2>
    _Arg2 _Arg2PFNHelperThunk(_ReturnType(__cdecl *)(_Arg1, _Arg2));

    template<typename _ReturnType, typename _Arg1, typename _Arg2>
    _ReturnType _ReturnTypePFNHelperThunk(_ReturnType(__cdecl *)(_Arg1, _Arg2));

    template<typename _ReturnType, typename _Arg1, typename _Arg2>
    _TwoArgumentFunctor _ArgumentCountHelper(_ReturnType(__cdecl *)(_Arg1, _Arg2));

    template<typename _ReturnType, typename _Arg1, typename _Arg2>
    _Arg1 _Arg1PFNHelperThunk(_ReturnType(__stdcall *)(_Arg1, _Arg2));

    template<typename _ReturnType, typename _Arg1, typename _Arg2>
    _Arg2 _Arg2PFNHelperThunk(_ReturnType(__stdcall *)(_Arg1, _Arg2));

    template<typename _ReturnType, typename _Arg1, typename _Arg2>
    _ReturnType _ReturnTypePFNHelperThunk(_ReturnType(__stdcall *)(_Arg1, _Arg2));

    template<typename _ReturnType, typename _Arg1, typename _Arg2>
    _TwoArgumentFunctor _ArgumentCountHelper(_ReturnType(__stdcall *)(_Arg1, _Arg2));

    template<typename _ReturnType, typename _Arg1, typename _Arg2>
    _Arg1 _Arg1PFNHelperThunk(_ReturnType(__fastcall *)(_Arg1, _Arg2));

    template<typename _ReturnType, typename _Arg1, typename _Arg2>
    _Arg2 _Arg2PFNHelperThunk(_ReturnType(__fastcall *)(_Arg1, _Arg2));

    template<typename _ReturnType, typename _Arg1, typename _Arg2>
    _ReturnType _ReturnTypePFNHelperThunk(_ReturnType(__fastcall *)(_Arg1, _Arg2));

    template<typename _ReturnType, typename _Arg1, typename _Arg2>
    _TwoArgumentFunctor _ArgumentCountHelper(_ReturnType(__fastcall *)(_Arg1, _Arg2));

    // ********************
    // ONE ARGUMENT:

    template<typename _ReturnType, typename _Arg1>
    _Arg1 _Arg1PFNHelperThunk(_ReturnType(__cdecl *)(_Arg1));

    template<typename _ReturnType, typename _Arg1>
    void _Arg2PFNHelperThunk(_ReturnType(__cdecl *)(_Arg1));

    template<typename _ReturnType, typename _Arg1>
    _ReturnType _ReturnTypePFNHelperThunk(_ReturnType(__cdecl *)(_Arg1));

    template<typename _ReturnType, typename _Arg1>
    _OneArgumentFunctor _ArgumentCountHelper(_ReturnType(__cdecl *)(_Arg1));

    template<typename _ReturnType, typename _Arg1>
    _Arg1 _Arg1PFNHelperThunk(_ReturnType(__stdcall *)(_Arg1));

    template<typename _ReturnType, typename _Arg1>
    void _Arg2PFNHelperThunk(_ReturnType(__stdcall *)(_Arg1));

    template<typename _ReturnType, typename _Arg1>
    _ReturnType _ReturnTypePFNHelperThunk(_ReturnType(__stdcall *)(_Arg1));

    template<typename _ReturnType, typename _Arg1>
    _OneArgumentFunctor _ArgumentCountHelper(_ReturnType(__stdcall *)(_Arg1));

    template<typename _ReturnType, typename _Arg1>
    _Arg1 _Arg1PFNHelperThunk(_ReturnType(__fastcall *)(_Arg1));

    template<typename _ReturnType, typename _Arg1>
    void _Arg2PFNHelperThunk(_ReturnType(__fastcall *)(_Arg1));

    template<typename _ReturnType, typename _Arg1>
    _ReturnType _ReturnTypePFNHelperThunk(_ReturnType(__fastcall *)(_Arg1));

    template<typename _ReturnType, typename _Arg1>
    _OneArgumentFunctor _ArgumentCountHelper(_ReturnType(__fastcall *)(_Arg1));

    // ********************
    // ZERO ARGUMENT:

    template<typename _ReturnType>
    void _Arg1PFNHelperThunk(_ReturnType(__cdecl *)());

    template<typename _ReturnType>
    void _Arg2PFNHelperThunk(_ReturnType(__cdecl *)());

    template<typename _ReturnType>
    _ReturnType _ReturnTypePFNHelperThunk(_ReturnType(__cdecl *)());

    template<typename _ReturnType>
    _ZeroArgumentFunctor _ArgumentCountHelper(_ReturnType(__cdecl *)());

    template<typename _ReturnType>
    void _Arg1PFNHelperThunk(_ReturnType(__stdcall *)());

    template<typename _ReturnType>
    void _Arg2PFNHelperThunk(_ReturnType(__stdcall *)());

    template<typename _ReturnType>
    _ReturnType _ReturnTypePFNHelperThunk(_ReturnType(__stdcall *)());

    template<typename _ReturnType>
    _ZeroArgumentFunctor _ArgumentCountHelper(_ReturnType(__stdcall *)());

    template<typename _ReturnType>
    void _Arg1PFNHelperThunk(_ReturnType(__fastcall *)());

    template<typename _ReturnType>
    void _Arg2PFNHelperThunk(_ReturnType(__fastcall *)());

    template<typename _ReturnType>
    _ReturnType _ReturnTypePFNHelperThunk(_ReturnType(__fastcall *)());

    template<typename _ReturnType>
    _ZeroArgumentFunctor _ArgumentCountHelper(_ReturnType(__fastcall *)());

    template<typename _T>
    struct _FunctorArguments
    {
        static const size_t _Count = 0;
    };

    template<>
    struct _FunctorArguments<_OneArgumentFunctor>
    {
        static const size_t _Count = 1;
    };

    template<>
    struct _FunctorArguments<_TwoArgumentFunctor>
    {
        static const size_t _Count = 2;
    };

    template<typename _T>
    struct _FunctorTypeTraits
    {
        typedef decltype(_ArgumentCountHelper(&(_T::operator()))) _ArgumentCountType;
        static const size_t _ArgumentCount = _FunctorArguments<_ArgumentCountType>::_Count;

        typedef decltype(_ReturnTypeClassHelperThunk(&(_T::operator()))) _ReturnType;
        typedef decltype(_Arg1ClassHelperThunk(&(_T::operator()))) _Argument1Type;
        typedef decltype(_Arg2ClassHelperThunk(&(_T::operator()))) _Argument2Type;
    };

    template<typename _T>
    struct _FunctorTypeTraits<_T *>
    {
        typedef decltype(_ArgumentCountHelper(stdx::declval<_T*>())) _ArgumentCountType;
        static const size_t _ArgumentCount = _FunctorArguments<_ArgumentCountType>::_Count;

        typedef decltype(_ReturnTypePFNHelperThunk(stdx::declval<_T*>())) _ReturnType;
        typedef decltype(_Arg1PFNHelperThunk(stdx::declval<_T*>())) _Argument1Type;
        typedef decltype(_Arg2PFNHelperThunk(stdx::declval<_T*>())) _Argument2Type;
    };

    template<typename _T>
    struct _ProgressTypeTraits
    {
        static const bool _TakesProgress = false;
        typedef void _ProgressType;
    };

    template<typename _T>
    struct _ProgressTypeTraits<progress_reporter<_T>>
    {
        static const bool _TakesProgress = true;
        typedef typename _T _ProgressType;
    };


    template<typename _T, size_t count = _FunctorTypeTraits<_T>::_ArgumentCount>
    struct _CAFunctorOptions
    {
        static const bool _TakesProgress = false;
        static const bool _TakesToken = false;
        typedef void _ProgressType;
    };

    template<typename _T>
    struct _CAFunctorOptions<_T, 1>
    {
    private:

        typedef typename _FunctorTypeTraits<_T>::_Argument1Type _Argument1Type;

    public:

        static const bool _TakesProgress = _ProgressTypeTraits<_Argument1Type>::_TakesProgress;
        static const bool _TakesToken = !_TakesProgress;
        typedef typename _ProgressTypeTraits<_Argument1Type>::_ProgressType _ProgressType;
    };

    template<typename _T>
    struct _CAFunctorOptions<_T, 2>
    {
    private:

        typedef typename _FunctorTypeTraits<_T>::_Argument1Type _Argument1Type;

    public:

        static const bool _TakesProgress = true;
        static const bool _TakesToken = true;
        typedef typename _ProgressTypeTraits<_Argument1Type>::_ProgressType _ProgressType;
    };

    ref class _Zip
    {
    };

    // ***************************************************************************
    // Async Operation Task Generators
    //

    //
    // Functor returns an IAsyncInfo - result needs to be wrapped in a task:
    //
    template<typename _AsyncSelector, typename _ReturnType>
    struct _SelectorTaskGenerator
    {
        template<typename _Function>
        static task<_ReturnType> _GenerateTask_0(const _Function& _Func, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<_ReturnType>(_Func(), _taskOptinos);
        }

        template<typename _Function>
        static task<_ReturnType> _GenerateTask_1C(const _Function& _Func, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<_ReturnType>(_Func(_Cts.get_token()), _taskOptinos);
        }

        template<typename _Function, typename _ProgressObject>
        static task<_ReturnType> _GenerateTask_1P(const _Function& _Func, const _ProgressObject& _Progress, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<_ReturnType>(_Func(_Progress), _taskOptinos);
        }

        template<typename _Function, typename _ProgressObject>
        static task<_ReturnType> _GenerateTask_2PC(const _Function& _Func, const _ProgressObject& _Progress, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<_ReturnType>(_Func(_Progress, _Cts.get_token()), _taskOptinos);
        }
    };

    template<typename _AsyncSelector>
    struct _SelectorTaskGenerator<_AsyncSelector, void>
    {
        template<typename _Function>
        static task<void> _GenerateTask_0(const _Function& _Func, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<void>(_Func(), _taskOptinos);
        }

        template<typename _Function>
        static task<void> _GenerateTask_1C(const _Function& _Func, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<void>(_Func(_Cts.get_token()), _taskOptinos);
        }

        template<typename _Function, typename _ProgressObject>
        static task<void> _GenerateTask_1P(const _Function& _Func, const _ProgressObject& _Progress, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<void>(_Func(_Progress), _taskOptinos);
        }

        template<typename _Function, typename _ProgressObject>
        static task<void> _GenerateTask_2PC(const _Function& _Func, const _ProgressObject& _Progress, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<void>(_Func(_Progress, _Cts.get_token()), _taskOptinos);
        }
    };

    //
    // Functor returns a result - it needs to be wrapped in a task:
    //
    template<typename _ReturnType>
    struct _SelectorTaskGenerator<_TypeSelectorNoAsync, _ReturnType>
    {

#pragma warning(push)
#pragma warning(disable: 4702)
        template<typename _Function>
        static task<_ReturnType> _GenerateTask_0(const _Function& _Func, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<_ReturnType>( [=]() -> _ReturnType {
                _Task_generator_oversubscriber_t _Oversubscriber;
                (_Oversubscriber);
                return _Func();
            }, _taskOptinos);
        }
#pragma warning(pop)

        template<typename _Function>
        static task<_ReturnType> _GenerateTask_1C(const _Function& _Func, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<_ReturnType>( [=]() -> _ReturnType {
                _Task_generator_oversubscriber_t _Oversubscriber;
                (_Oversubscriber);
                return _Func(_Cts.get_token());
            }, _taskOptinos);
        }

        template<typename _Function, typename _ProgressObject>
        static task<_ReturnType> _GenerateTask_1P(const _Function& _Func, const _ProgressObject& _Progress, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<_ReturnType>( [=]() -> _ReturnType {
                _Task_generator_oversubscriber_t _Oversubscriber;
                (_Oversubscriber);
                return _Func(_Progress);
            }, _taskOptinos);
        }

        template<typename _Function, typename _ProgressObject>
        static task<_ReturnType> _GenerateTask_2PC(const _Function& _Func, const _ProgressObject& _Progress, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<_ReturnType>( [=]() -> _ReturnType {
                _Task_generator_oversubscriber_t _Oversubscriber;
                (_Oversubscriber);
                return _Func(_Progress, _Cts.get_token());
            }, _taskOptinos);
        }
    };

    template<>
    struct _SelectorTaskGenerator<_TypeSelectorNoAsync, void>
    {
        template<typename _Function>
        static task<void> _GenerateTask_0(const _Function& _Func, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<void>( [=]() {
                _Task_generator_oversubscriber_t _Oversubscriber;
                (_Oversubscriber);
                _Func();
            }, _taskOptinos);
        }

        template<typename _Function>
        static task<void> _GenerateTask_1C(const _Function& _Func, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<void>( [=]() {
                _Task_generator_oversubscriber_t _Oversubscriber;
                (_Oversubscriber);
                _Func(_Cts.get_token());
            }, _taskOptinos);
        }

        template<typename _Function, typename _ProgressObject>
        static task<void> _GenerateTask_1P(const _Function& _Func, const _ProgressObject& _Progress, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<void>( [=]() {
                _Task_generator_oversubscriber_t _Oversubscriber;
                (_Oversubscriber);
                _Func(_Progress);
            }, _taskOptinos);
        }

        template<typename _Function, typename _ProgressObject>
        static task<void> _GenerateTask_2PC(const _Function& _Func, const _ProgressObject& _Progress, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            task_options _taskOptinos(_Cts.get_token());
            details::_get_internal_task_options(_taskOptinos)._set_creation_callstack(_callstack);
            return task<void>( [=]() {
                _Task_generator_oversubscriber_t _Oversubscriber;
                (_Oversubscriber);
                _Func(_Progress, _Cts.get_token());
            }, _taskOptinos);
        }
    };

    //
    // Functor returns a task - the task can directly be returned:
    //
    template<typename _ReturnType>
    struct _SelectorTaskGenerator<_TypeSelectorAsyncTask, _ReturnType>
    {
        template<typename _Function>
        static task<_ReturnType> _GenerateTask_0(const _Function& _Func, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            return _Func();
        }

        template<typename _Function>
        static task<_ReturnType> _GenerateTask_1C(const _Function& _Func, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            return _Func(_Cts.get_token());
        }

        template<typename _Function, typename _ProgressObject>
        static task<_ReturnType> _GenerateTask_1P(const _Function& _Func, const _ProgressObject& _Progress, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            return _Func(_Progress);
        }

        template<typename _Function, typename _ProgressObject>
        static task<_ReturnType> _GenerateTask_2PC(const _Function& _Func, const _ProgressObject& _Progress, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            return _Func(_Progress, _Cts.get_token());
        }
    };

    template<>
    struct _SelectorTaskGenerator<_TypeSelectorAsyncTask, void>
    {
        template<typename _Function>
        static task<void> _GenerateTask_0(const _Function& _Func, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            return _Func();
        }

        template<typename _Function>
        static task<void> _GenerateTask_1C(const _Function& _Func, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            return _Func(_Cts.get_token());
        }

        template<typename _Function, typename _ProgressObject>
        static task<void> _GenerateTask_1P(const _Function& _Func, const _ProgressObject& _Progress, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            return _Func(_Progress);
        }

        template<typename _Function, typename _ProgressObject>
        static task<void> _GenerateTask_2PC(const _Function& _Func, const _ProgressObject& _Progress, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            return _Func(_Progress, _Cts.get_token());
        }
    };

    template<typename _Generator, bool _TakesToken, bool TakesProgress>
    struct _TaskGenerator
    {
    };

    template<typename _Generator>
    struct _TaskGenerator<_Generator, false, false>
    {
        template<typename _Function, typename _ClassPtr, typename _ProgressType>
        static auto _GenerateTask(const _Function& _Func, _ClassPtr _Ptr, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
            -> decltype(_Generator::_GenerateTask_0(_Func, _Cts, _callstack))
        {
            return _Generator::_GenerateTask_0(_Func, _Cts, _callstack);
        }
    };

    template<typename _Generator>
    struct _TaskGenerator<_Generator, true, false>
    {
        template<typename _Function, typename _ClassPtr, typename _ProgressType>
        static auto _GenerateTask(const _Function& _Func, _ClassPtr _Ptr, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
            -> decltype(_Generator::_GenerateTask_0(_Func, _Cts, _callstack))
        {
            return _Generator::_GenerateTask_1C(_Func, _Cts, _callstack);
        }
    };

    template<typename _Generator>
    struct _TaskGenerator<_Generator, false, true>
    {
        template<typename _Function, typename _ClassPtr, typename _ProgressType>
        static auto _GenerateTask(const _Function& _Func, _ClassPtr _Ptr, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
            -> decltype(_Generator::_GenerateTask_0(_Func, _Cts, _callstack))
        {
            return _Generator::_GenerateTask_1P(_Func, progress_reporter<_ProgressType>::_CreateReporter(_Ptr), _Cts, _callstack);
        }
    };

    template<typename _Generator>
    struct _TaskGenerator<_Generator, true, true>
    {
        template<typename _Function, typename _ClassPtr, typename _ProgressType>
        static auto _GenerateTask(const _Function& _Func, _ClassPtr _Ptr, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
            -> decltype(_Generator::_GenerateTask_0(_Func, _Cts, _callstack))
        {
            return _Generator::_GenerateTask_2PC(_Func, progress_reporter<_ProgressType>::_CreateReporter(_Ptr), _Cts, _callstack);
        }
    };

    // ***************************************************************************
    // Async Operation Attributes Classes
    //
    // These classes are passed through the hierarchy of async base classes in order to hold multiple attributes of a given async construct in
    // a single container. An attribute class must define:
    //
    // Mandatory:
    // -------------------------
    //
    // _AsyncBaseType           : The Windows Runtime interface which is being implemented.
    // _CompletionDelegateType  : The Windows Runtime completion delegate type for the interface.
    // _ProgressDelegateType    : If _TakesProgress is true, the Windows Runtime progress delegate type for the interface. If it is false, an empty Windows Runtime type.
    // _ReturnType              : The return type of the async construct (void for actions / non-void for operations)
    //
    // _TakesProgress           : An indication as to whether or not
    //
    // _Generate_Task           : A function adapting the user's function into what's necessary to produce the appropriate task
    //
    // Optional:
    // -------------------------
    //

    template<typename _Function, typename _ProgressType, typename _ReturnType, typename _TaskTraits, bool _TakesToken, bool _TakesProgress>
    struct _AsyncAttributes
    {
    };

    template<typename _Function, typename _ProgressType, typename _ReturnType, typename _TaskTraits, bool _TakesToken>
    struct _AsyncAttributes<_Function, _ProgressType, _ReturnType, _TaskTraits, _TakesToken, true>
    {
        typedef typename Windows::Foundation::IAsyncOperationWithProgress<_ReturnType, _ProgressType> _AsyncBaseType;
        typedef typename Windows::Foundation::AsyncOperationProgressHandler<_ReturnType, _ProgressType> _ProgressDelegateType;
        typedef typename Windows::Foundation::AsyncOperationWithProgressCompletedHandler<_ReturnType, _ProgressType> _CompletionDelegateType;
        typedef typename _ReturnType _ReturnType;
        typedef typename _ProgressType _ProgressType;
        typedef typename _TaskTraits::_AsyncKind _AsyncKind;
        typedef typename _SelectorTaskGenerator<_AsyncKind, _ReturnType> _SelectorTaskGenerator;
        typedef typename _TaskGenerator<_SelectorTaskGenerator, _TakesToken, true> _TaskGenerator;

        static const bool _TakesProgress = true;
        static const bool _TakesToken = _TakesToken;

        template<typename _Function, typename _ClassPtr>
        static task<_ReturnType> _Generate_Task(const _Function& _Func, _ClassPtr _Ptr, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            return _TaskGenerator::_GenerateTask<_Function, _ClassPtr, _ProgressType>(_Func, _Ptr, _Cts, _callstack);
        }
    };

    template<typename _Function, typename _ProgressType, typename _ReturnType, typename _TaskTraits, bool _TakesToken>
    struct _AsyncAttributes<_Function, _ProgressType, _ReturnType, _TaskTraits, _TakesToken, false>
    {
        typedef typename Windows::Foundation::IAsyncOperation<_ReturnType> _AsyncBaseType;
        typedef _Zip _ProgressDelegateType;
        typedef typename Windows::Foundation::AsyncOperationCompletedHandler<_ReturnType> _CompletionDelegateType;
        typedef typename _ReturnType _ReturnType;
        typedef typename _TaskTraits::_AsyncKind _AsyncKind;
        typedef typename _SelectorTaskGenerator<_AsyncKind, _ReturnType> _SelectorTaskGenerator;
        typedef typename _TaskGenerator<_SelectorTaskGenerator, _TakesToken, false> _TaskGenerator;

        static const bool _TakesProgress = false;
        static const bool _TakesToken = _TakesToken;

        template<typename _Function, typename _ClassPtr>
        static task<_ReturnType> _Generate_Task(const _Function& _Func, _ClassPtr _Ptr, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            return _TaskGenerator::_GenerateTask<_Function, _ClassPtr, _ProgressType>(_Func, _Ptr, _Cts, _callstack);
        }
    };

    template<typename _Function, typename _ProgressType, typename _TaskTraits, bool _TakesToken>
    struct _AsyncAttributes<_Function, _ProgressType, void, _TaskTraits, _TakesToken, true>
    {
        typedef typename Windows::Foundation::IAsyncActionWithProgress<_ProgressType> _AsyncBaseType;
        typedef typename Windows::Foundation::AsyncActionProgressHandler<_ProgressType> _ProgressDelegateType;
        typedef typename Windows::Foundation::AsyncActionWithProgressCompletedHandler<_ProgressType> _CompletionDelegateType;
        typedef void _ReturnType;
        typedef typename _ProgressType _ProgressType;
        typedef typename _TaskTraits::_AsyncKind _AsyncKind;
        typedef typename _SelectorTaskGenerator<_AsyncKind, _ReturnType> _SelectorTaskGenerator;
        typedef typename _TaskGenerator<_SelectorTaskGenerator, _TakesToken, true> _TaskGenerator;

        static const bool _TakesProgress = true;
        static const bool _TakesToken = _TakesToken;

        template<typename _Function, typename _ClassPtr>
        static task<_ReturnType> _Generate_Task(const _Function& _Func, _ClassPtr _Ptr, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            return _TaskGenerator::_GenerateTask<_Function, _ClassPtr, _ProgressType>(_Func, _Ptr, _Cts, _callstack);
        }
    };

    template<typename _Function, typename _ProgressType, typename _TaskTraits, bool _TakesToken>
    struct _AsyncAttributes<_Function, _ProgressType, void, _TaskTraits, _TakesToken, false>
    {
        typedef typename Windows::Foundation::IAsyncAction _AsyncBaseType;
        typedef _Zip _ProgressDelegateType;
        typedef typename Windows::Foundation::AsyncActionCompletedHandler _CompletionDelegateType;
        typedef void _ReturnType;
        typedef typename _TaskTraits::_AsyncKind _AsyncKind;
        typedef typename _SelectorTaskGenerator<_AsyncKind, _ReturnType> _SelectorTaskGenerator;
        typedef typename _TaskGenerator<_SelectorTaskGenerator, _TakesToken, false> _TaskGenerator;

        static const bool _TakesProgress = false;
        static const bool _TakesToken = _TakesToken;

        template<typename _Function, typename _ClassPtr>
        static task<_ReturnType> _Generate_Task(const _Function& _Func, _ClassPtr _Ptr, cancellation_token_source _Cts, const _TaskCreationCallstack & _callstack)
        {
            return _TaskGenerator::_GenerateTask<_Function, _ClassPtr, _ProgressType>(_Func, _Ptr, _Cts, _callstack);
        }
    };

    template<typename _Function>
    struct _AsyncLambdaTypeTraits
    {
        typedef typename _FunctorTypeTraits<_Function>::_ReturnType _ReturnType;
        typedef typename _FunctorTypeTraits<_Function>::_Argument1Type _Argument1Type;
        typedef typename _CAFunctorOptions<_Function>::_ProgressType _ProgressType;

        static const bool _TakesProgress = _CAFunctorOptions<_Function>::_TakesProgress;
        static const bool _TakesToken = _CAFunctorOptions<_Function>::_TakesToken;

        typedef typename _TaskTypeTraits<_ReturnType> _TaskTraits;
        typedef typename _AsyncAttributes<_Function, _ProgressType, typename _TaskTraits::_TaskRetType, _TaskTraits, _TakesToken, _TakesProgress> _AsyncAttributes;
    };

    // ***************************************************************************
    // AsyncInfo (and completion) Layer:
    //

    //
    // Internal base class implementation for async operations (based on internal Windows representation for ABI level async operations)
    //
    template < typename _Attributes, _AsyncResultType resultType = SingleResult >
    ref class _AsyncInfoBase abstract : _Attributes::_AsyncBaseType
    {
    internal:

        _AsyncInfoBase() : 
            _M_currentStatus(_AsyncStatusInternal::_AsyncCreated), 
            _M_errorCode(S_OK),
            _M_completeDelegate(nullptr),
            _M_CompleteDelegateAssigned(0),
            _M_CallbackMade(0)
        {
            _M_id = ::pplx::details::platform::GetNextAsyncId();
        }

    public:
        virtual typename _Attributes::_ReturnType GetResults()
        {
            throw ::Platform::Exception::CreateException(E_UNEXPECTED);
        }

        virtual property unsigned int Id
        {
            unsigned int get()
            {
                _CheckValidStateForAsyncInfoCall();

                return _M_id;
            }

            void set(unsigned int id)
            {
                _CheckValidStateForAsyncInfoCall();

                if (id == 0)
                {
                    throw ::Platform::Exception::CreateException(E_INVALIDARG);
                }
                else if (_M_currentStatus != _AsyncStatusInternal::_AsyncCreated)
                {
                    throw ::Platform::Exception::CreateException(E_ILLEGAL_METHOD_CALL);
                }

                _M_id = id;
            }
        }

        virtual property Windows::Foundation::AsyncStatus Status
        {
            Windows::Foundation::AsyncStatus get()
            {
                _CheckValidStateForAsyncInfoCall();

                _AsyncStatusInternal _Current = _M_currentStatus;

                //
                // Map our internal cancel pending to cancelled. This way "pending cancelled" looks to the outside as "cancelled" but
                // can still transition to "completed" if the operation completes without acknowledging the cancellation request
                //
                switch(_Current)
                {
                    case _AsyncCancelPending:
                        _Current = _AsyncCanceled;
                        break;
                    case _AsyncCreated:
                        _Current = _AsyncStarted;
                        break;
                    default:
                        break;
                }

                return static_cast<Windows::Foundation::AsyncStatus>(_Current);
            }
        }

        virtual property Windows::Foundation::HResult ErrorCode
        {
            Windows::Foundation::HResult get()
            {
                _CheckValidStateForAsyncInfoCall();

                Windows::Foundation::HResult _Hr;
                _Hr.Value = _M_errorCode;
                return _Hr;
            }
        }

        virtual property typename _Attributes::_ProgressDelegateType^ Progress
        {
            typename typename _Attributes::_ProgressDelegateType^ get()
            {
                return _GetOnProgress();
            }

            void set(typename _Attributes::_ProgressDelegateType^ _ProgressHandler)
            {
                _PutOnProgress(_ProgressHandler);
            }
        }

        virtual void Cancel()
        {
            if (_TransitionToState(_AsyncCancelPending))
            {
                _OnCancel();
            }
        }

        virtual void Close()
        {
            if (_TransitionToState(_AsyncClosed))
            {
                _OnClose();
            }
            else
            {
                if (_M_currentStatus != _AsyncClosed) // Closed => Closed transition is just ignored
                {
                    throw ::Platform::Exception::CreateException(E_ILLEGAL_STATE_CHANGE);
                }
            }
        }

        virtual property typename _Attributes::_CompletionDelegateType^ Completed
        {
            typename _Attributes::_CompletionDelegateType^ get()
            {
                _CheckValidStateForDelegateCall();
                return _M_completeDelegate;
            }

            void set(typename _Attributes::_CompletionDelegateType^ _CompleteHandler)
            {
                _CheckValidStateForDelegateCall();
                // this delegate property is "write once"
                if (InterlockedIncrement(&_M_CompleteDelegateAssigned) == 1)
                {
                    _M_completeDelegateContext = _ContextCallback::_CaptureCurrent();
                    _M_completeDelegate = _CompleteHandler;
                    // Guarantee that the write of _M_completeDelegate is ordered with respect to the read of state below
                    // as perceived from _FireCompletion on another thread.
                    MemoryBarrier();
                    if (_IsTerminalState())
                    {
                        _FireCompletion();
                    }
                }
                else
                {
                    throw ::Platform::Exception::CreateException(E_ILLEGAL_DELEGATE_ASSIGNMENT);
                }
            }
        }


    protected private:

        // _Start - this is not externally visible since async operations "hot start" before returning to the caller
        void _Start()
        {
            if (_TransitionToState(_AsyncStarted))
            {
                _OnStart();
            }
            else
            {
                throw ::Platform::Exception::CreateException(E_ILLEGAL_STATE_CHANGE);
            }
        }


        void _FireCompletion()
        {
            _TryTransitionToCompleted();

            // we guarantee that completion can only ever be fired once
            if (_M_completeDelegate != nullptr && InterlockedIncrement(&_M_CallbackMade) == 1)
            {
                _M_completeDelegateContext._CallInContext([=] {
                    _M_completeDelegate((_Attributes::_AsyncBaseType^)this, this->Status);
                    _M_completeDelegate = nullptr;
                });
            }
        }

        virtual typename _Attributes::_ProgressDelegateType^ _GetOnProgress()
        {
            throw ::Platform::Exception::CreateException(E_UNEXPECTED);
        }

        virtual void _PutOnProgress(typename _Attributes::_ProgressDelegateType^ _ProgressHandler)
        {
            throw ::Platform::Exception::CreateException(E_UNEXPECTED);
        }

        bool _TryTransitionToCompleted()
        {
            return _TransitionToState(_AsyncStatusInternal::_AsyncCompleted);
        }

        bool _TryTransitionToCancelled()
        {
            return _TransitionToState(_AsyncStatusInternal::_AsyncCanceled);
        }

        bool _TryTransitionToError(const HRESULT error)
        {
            _InterlockedCompareExchange(reinterpret_cast<volatile LONG*>(&_M_errorCode), error, S_OK);
            return _TransitionToState(_AsyncStatusInternal::_AsyncError);
        }

        // This method checks to see if the delegate properties can be
        // modified in the current state and generates the appropriate
        // error hr in the case of violation.
        inline void _CheckValidStateForDelegateCall()
        {
            if (_M_currentStatus == _AsyncClosed)
            {
                throw ::Platform::Exception::CreateException(E_ILLEGAL_METHOD_CALL);
            }
        }

        // This method checks to see if results can be collected in the
        // current state and generates the appropriate error hr in
        // the case of a violation.
        inline void _CheckValidStateForResultsCall()
        {
            _AsyncStatusInternal _Current = _M_currentStatus;

            if (_Current == _AsyncError)
            {
                throw ::Platform::Exception::CreateException(_M_errorCode);
            }
#pragma warning(push)
#pragma warning(disable: 4127) // Conditional expression is constant
            // single result illegal before transition to Completed or Cancelled state
            if (resultType == SingleResult)
#pragma warning(pop)
            {
                if (_Current != _AsyncCompleted)
                {
                    throw ::Platform::Exception::CreateException(E_ILLEGAL_METHOD_CALL);
                }
            }
            // multiple results can be called after Start has been called and before/after Completed
            else if (_Current != _AsyncStarted &&
                     _Current != _AsyncCancelPending &&
                     _Current != _AsyncCanceled &&
                     _Current != _AsyncCompleted)
            {
                throw ::Platform::Exception::CreateException(E_ILLEGAL_METHOD_CALL);
            }
        }

        // This method can be called by derived classes periodically to determine
        // whether the asynchronous operation should continue processing or should
        // be halted.
        inline bool _ContinueAsyncOperation()
        {
            return (_M_currentStatus == _AsyncStarted);
        }

        // These two methods are used to allow the async worker implementation do work on
        // state transitions. No real "work" should be done in these methods. In other words
        // they should not block for a long time on UI timescales.
        virtual void _OnStart() = 0;
        virtual void _OnClose() = 0;
        virtual void _OnCancel() = 0;

    private:

        // This method is used to check if calls to the AsyncInfo properties
        // (id, status, errorcode) are legal in the current state. It also
        // generates the appropriate error hr to return in the case of an
        // illegal call.
        inline void _CheckValidStateForAsyncInfoCall()
        {
            _AsyncStatusInternal _Current = _M_currentStatus;
            if (_Current == _AsyncClosed)
            {
                throw ::Platform::Exception::CreateException(E_ILLEGAL_METHOD_CALL);
            }
            else if (_Current == _AsyncCreated)
            {
                throw ::Platform::Exception::CreateException(E_ASYNC_OPERATION_NOT_STARTED);
            }

        }

        inline bool _TransitionToState(const _AsyncStatusInternal _NewState)
        {
            _AsyncStatusInternal _Current = _M_currentStatus;

            // This enforces the valid state transitions of the asynchronous worker object
            // state machine.
            switch(_NewState)
            {
            case _AsyncStatusInternal::_AsyncStarted:
                if (_Current != _AsyncCreated)
                {
                    return false;
                }
                break;
            case _AsyncStatusInternal::_AsyncCompleted:
                if (_Current != _AsyncStarted && _Current != _AsyncCancelPending)
                {
                    return false;
                }
                break;
            case _AsyncStatusInternal::_AsyncCancelPending:
                if (_Current != _AsyncStarted)
                {
                    return false;
                }
                break;
            case _AsyncStatusInternal::_AsyncCanceled:
                if (_Current != _AsyncStarted && _Current != _AsyncCancelPending)
                {
                    return false;
                }
                break;
            case _AsyncStatusInternal::_AsyncError:
                if (_Current != _AsyncStarted && _Current != _AsyncCancelPending)
                {
                    return false;
                }
                break;
            case _AsyncStatusInternal::_AsyncClosed:
                if (!_IsTerminalState(_Current))
                {
                    return false;
                }
                break;
            default:
                return false;
                break;
            }

            // attempt the transition to the new state
            // Note: if currentStatus_ == _Current, then there was no intervening write
            // by the async work object and the swap succeeded.
            _AsyncStatusInternal _RetState = static_cast<_AsyncStatusInternal>(
                    _InterlockedCompareExchange(reinterpret_cast<volatile LONG*>(&_M_currentStatus),
                                                _NewState,
                                                static_cast<LONG>(_Current)));

            // ICE returns the former state, if the returned state and the
            // state we captured at the beginning of this method are the same,
            // the swap succeeded.
            return (_RetState == _Current);
        }

        inline bool _IsTerminalState()
        {
            return _IsTerminalState(_M_currentStatus);
        }

        inline bool _IsTerminalState(_AsyncStatusInternal status)
        {
            return (status == _AsyncError ||
                    status == _AsyncCanceled ||
                    status == _AsyncCompleted ||
                    status == _AsyncClosed);
        }

    private:

        _ContextCallback        _M_completeDelegateContext;
        typename _Attributes::_CompletionDelegateType^  volatile _M_completeDelegate;
        _AsyncStatusInternal volatile                   _M_currentStatus;
        HRESULT volatile                                _M_errorCode;
        unsigned int                                    _M_id;
        long volatile                                   _M_CompleteDelegateAssigned;
        long volatile                                   _M_CallbackMade;
    };

    // ***************************************************************************
    // Progress Layer (optional):
    //

    template< typename _Attributes, bool _HasProgress, _AsyncResultType _ResultType = SingleResult >
    ref class _AsyncProgressBase abstract : _AsyncInfoBase<_Attributes, _ResultType>
    {
    };

    template< typename _Attributes, _AsyncResultType _ResultType>
    ref class _AsyncProgressBase<_Attributes, true, _ResultType> abstract : _AsyncInfoBase<_Attributes, _ResultType>
    {
    internal:

        _AsyncProgressBase() : _AsyncInfoBase<_Attributes, _ResultType>(),
            _M_progressDelegate(nullptr)
        {
        }

        virtual typename _Attributes::_ProgressDelegateType^ _GetOnProgress() override
        {
            _CheckValidStateForDelegateCall();
            return _M_progressDelegate;
        }

        virtual void _PutOnProgress(typename _Attributes::_ProgressDelegateType^ _ProgressHandler) override
        {
            _CheckValidStateForDelegateCall();
            _M_progressDelegate = _ProgressHandler;
            _M_progressDelegateContext = _ContextCallback::_CaptureCurrent();
        }

        void _FireProgress(const typename _Attributes::_ProgressType& _ProgressValue)
        {
            if (_M_progressDelegate != nullptr)
            {
                _M_progressDelegateContext._CallInContext([=] {
                    _M_progressDelegate((_Attributes::_AsyncBaseType^)this, _ProgressValue);
                });
            }
        }

    private:

        _ContextCallback _M_progressDelegateContext;
        typename _Attributes::_ProgressDelegateType^ _M_progressDelegate;
    };

    template<typename _Attributes, _AsyncResultType _ResultType = SingleResult>
    ref class _AsyncBaseProgressLayer abstract : _AsyncProgressBase<_Attributes, _Attributes::_TakesProgress, _ResultType>
    {
    };

    // ***************************************************************************
    // Task Adaptation Layer:
    //

    //
    // _AsyncTaskThunkBase provides a bridge between IAsync<Action/Operation> and task.
    //
    template<typename _Attributes, typename _ReturnType>
    ref class _AsyncTaskThunkBase abstract : _AsyncBaseProgressLayer<_Attributes>
    {
    public:

        virtual _ReturnType GetResults() override
        {
            _CheckValidStateForResultsCall();
            return _M_task.get();
        }

    internal:

        typedef task<_ReturnType> _TaskType;

        _AsyncTaskThunkBase(const _TaskType& _Task)
            : _M_task(_Task)
        {
        }

        _AsyncTaskThunkBase()
        {
        }

    protected:

        virtual void _OnStart() override
        {
            _M_task.then( [=](_TaskType _Antecedent) {
                try
                {
                    _Antecedent.get();
                }
                catch(task_canceled&)
                {
                    _TryTransitionToCancelled();
                }
                catch(::Platform::Exception^ _Ex)
                {
                    _TryTransitionToError(_Ex->HResult);
                }
                catch(...)
                {
                    _TryTransitionToError(E_FAIL);
                }
                _FireCompletion();
            });
        }

    internal:

        _TaskType _M_task;
        cancellation_token_source _M_cts;
    };

    template<typename _Attributes>
    ref class _AsyncTaskThunk : _AsyncTaskThunkBase<_Attributes, typename _Attributes::_ReturnType>
    {
    internal:

        _AsyncTaskThunk(const _TaskType& _Task) :
            _AsyncTaskThunkBase(_Task)
        {
        }

        _AsyncTaskThunk()
        {
        }

    protected:

        virtual void _OnClose() override
        {
        }

        virtual void _OnCancel() override
        {
            _M_cts.cancel();
        }
    };

    // ***************************************************************************
    // Async Creation Layer:
    //
    template<typename _Function>
    ref class _AsyncTaskGeneratorThunk sealed : _AsyncTaskThunk<typename _AsyncLambdaTypeTraits<_Function>::_AsyncAttributes>
    {
    internal:

        typedef typename _AsyncLambdaTypeTraits<_Function>::_AsyncAttributes _Attributes;
        typedef typename _AsyncTaskThunk<_Attributes> _Base;
        typedef typename _Attributes::_AsyncBaseType _AsyncBaseType;

        _AsyncTaskGeneratorThunk(const _Function& _Func, const _TaskCreationCallstack &_callstack) : _M_func(_Func), _M_creationCallstack(_callstack)
        {
            // Virtual call here is safe as the class is declared 'sealed'
            _Start();
        }

    protected:

        //
        // The only thing we must do different from the base class is we must spin the hot task on transition from Created->Started. Otherwise,
        // let the base thunk handle everything.
        //

        virtual void _OnStart() override
        {
            //
            // Call the appropriate task generator to actually produce a task of the expected type. This might adapt the user lambda for progress reports,
            // wrap the return result in a task, or allow for direct return of a task depending on the form of the lambda.
            //
            _M_task = _Attributes::_Generate_Task(_M_func, this, _M_cts, _M_creationCallstack);
            _Base::_OnStart();
        }

        virtual void _OnCancel() override
        {
            _Base::_OnCancel();
        }

    private:
        _TaskCreationCallstack _M_creationCallstack;
        _Function _M_func;
    };
} // namespace details


template<typename _Function>
__declspec(noinline)
details::_AsyncTaskGeneratorThunk<_Function> ^create_async(const _Function& _Func)
{
    static_assert(std::is_same<decltype(details::_IsValidCreateAsync(_Func,0,0,0,0)),std::true_type>::value,
        "argument to create_async must be a callable object taking zero, one or two arguments");
    return ref new details::_AsyncTaskGeneratorThunk<_Function>(_Func, _CAPTURE_CALLSTACK());
}

#endif  /* defined (__cplusplus_winrt) */

namespace details
{
    // Helper struct for when_all operators to know when tasks have completed
    template<typename _Type>
    struct _RunAllParam
    {
        _RunAllParam() : _M_completeCount(0), _M_numTasks(0)
        {
        }

        void _Resize(size_t _Len, bool _SkipVector = false)
        {
            _M_numTasks = _Len;
            if (!_SkipVector)
            {
                _M_vector._Result.resize(_Len);
            }
        }

        task_completion_event<_Unit_type>       _M_completed;
        _ResultHolder<std::vector<_Type> >      _M_vector;
        _ResultHolder<_Type>                    _M_mergeVal;
        atomic_size_t                           _M_completeCount;
        size_t                                  _M_numTasks;
    };

    template<typename _Type>
    struct _RunAllParam<std::vector<_Type> >
    {
        _RunAllParam() : _M_completeCount(0), _M_numTasks(0)
        {
        }

        void _Resize(size_t _Len, bool _SkipVector = false)
        {
            _M_numTasks = _Len;
            
            if (!_SkipVector)
            {
                _M_vector.resize(_Len);
            }
        }

        task_completion_event<_Unit_type>       _M_completed;
        std::vector<_ResultHolder<std::vector<_Type> > >  _M_vector;
        atomic_size_t                           _M_completeCount;
        size_t                                  _M_numTasks;
    };

    // Helper struct specialization for void
    template<>
    struct _RunAllParam<_Unit_type>
    {
        _RunAllParam() : _M_completeCount(0), _M_numTasks(0)
        {
        }

        void _Resize(size_t _Len)
        {
            _M_numTasks = _Len;
        }

        task_completion_event<_Unit_type> _M_completed;
        atomic_size_t _M_completeCount;
        size_t _M_numTasks;
    };

    inline void _JoinAllTokens_Add(const cancellation_token_source& _MergedSrc, _CancellationTokenState *_PJoinedTokenState)
    {
        if (_PJoinedTokenState != nullptr && _PJoinedTokenState != _CancellationTokenState::_None())
        {
            cancellation_token _T = cancellation_token::_FromImpl(_PJoinedTokenState);
            _T.register_callback( [=](){
                _MergedSrc.cancel();
                });
        }
    }

    template<typename _ElementType, typename _Function, typename _TaskType>
    void _WhenAllContinuationWrapper(_RunAllParam<_ElementType>* _PParam, _Function _Func, task<_TaskType>& _Task)
    {
        if (_Task._GetImpl()->_IsCompleted())
        {
            _Func();
            if (atomic_increment(_PParam->_M_completeCount) == _PParam->_M_numTasks)
            {
                // Inline execute its direct continuation, the _ReturnTask
                _PParam->_M_completed.set(_Unit_type());
                // It's safe to delete it since all usage of _PParam in _ReturnTask has been finished.
                delete _PParam;
            }
        }
        else
        {
            _ASSERTE(_Task._GetImpl()->_IsCanceled());
            if (_Task._GetImpl()->_HasUserException())
            {
                // _Cancel will return false if the TCE is already canceled with or without exception
                _PParam->_M_completed._Cancel(_Task._GetImpl()->_GetExceptionHolder());
            }
            else
            {
                _PParam->_M_completed._Cancel();
            }

            if (atomic_increment(_PParam->_M_completeCount) == _PParam->_M_numTasks)
            {
                delete _PParam;
            }
        }
    }

    template<typename _ElementType, typename _Iterator>
    struct _WhenAllImpl
    {
        static task<std::vector<_ElementType>> _Perform(const task_options& _TaskOptions, _Iterator _Begin, _Iterator _End)
        {
            _CancellationTokenState *_PTokenState = _TaskOptions.has_cancellation_token() ? _TaskOptions.get_cancellation_token()._GetImplValue() : nullptr;

            auto _PParam = new _RunAllParam<_ElementType>();
            cancellation_token_source _MergedSource;

            // Step1: Create task completion event.
            task_options _Options(_TaskOptions);
            _Options.set_cancellation_token(_MergedSource.get_token());
            task<_Unit_type> _All_tasks_completed(_PParam->_M_completed, _Options);
            // The return task must be created before step 3 to enforce inline execution.
            auto _ReturnTask = _All_tasks_completed._Then([=](_Unit_type) -> std::vector<_ElementType> {
                return _PParam->_M_vector.Get();
            }, nullptr);

            // Step2: Combine and check tokens, and count elements in range.
            if (_PTokenState)
            {
                _JoinAllTokens_Add(_MergedSource, _PTokenState);
                _PParam->_Resize(static_cast<size_t>(std::distance(_Begin, _End)));
            }
            else
            {
                size_t _TaskNum = 0;
                for (auto _PTask = _Begin; _PTask != _End; ++_PTask)
                {
                    _TaskNum++;
                    _JoinAllTokens_Add(_MergedSource, _PTask->_GetImpl()->_M_pTokenState);
                }
                _PParam->_Resize(_TaskNum);
            }

            // Step3: Check states of previous tasks.
            if( _Begin == _End )
            {
                _PParam->_M_completed.set(_Unit_type());
                delete _PParam;
            }
            else
            {
                size_t _Index = 0;
                for (auto _PTask = _Begin; _PTask != _End; ++_PTask)
                {
                    if (_PTask->is_apartment_aware())
                    {
                        _ReturnTask._SetAsync();
                    }

                    _PTask->_Then([_PParam, _Index](task<_ElementType> _ResultTask) {

                        auto _PParamCopy = _PParam;
                        auto _IndexCopy = _Index;
                        auto _Func = [_PParamCopy, _IndexCopy, &_ResultTask](){
                            _PParamCopy->_M_vector._Result[_IndexCopy] = _ResultTask._GetImpl()->_GetResult();
                        };

                        _WhenAllContinuationWrapper(_PParam, _Func, _ResultTask);
                    }, _CancellationTokenState::_None()); 

                    _Index++;
                }
            }

            return _ReturnTask;
        }
    };

    template<typename _ElementType, typename _Iterator>
    struct _WhenAllImpl<std::vector<_ElementType>, _Iterator>
    {
        static task<std::vector<_ElementType>> _Perform(const task_options& _TaskOptions, _Iterator _Begin, _Iterator _End)
        {
            _CancellationTokenState *_PTokenState = _TaskOptions.has_cancellation_token() ? _TaskOptions.get_cancellation_token()._GetImplValue() : nullptr;

            auto _PParam = new _RunAllParam<std::vector<_ElementType>>();
            cancellation_token_source _MergedSource;

            // Step1: Create task completion event.
            task_options _Options(_TaskOptions);
            _Options.set_cancellation_token(_MergedSource.get_token());
            task<_Unit_type> _All_tasks_completed(_PParam->_M_completed, _Options);
            // The return task must be created before step 3 to enforce inline execution.
            auto _ReturnTask = _All_tasks_completed._Then([=](_Unit_type) -> std::vector<_ElementType> {
                _ASSERTE(_PParam->_M_completeCount ==  _PParam->_M_numTasks);
                std::vector<_ElementType> _Result;
                for(size_t _I = 0; _I < _PParam->_M_numTasks; _I++)
                {
                    const std::vector<_ElementType>& _Vec = _PParam->_M_vector[_I].Get();
                    _Result.insert(_Result.end(), _Vec.begin(), _Vec.end());
                }
                return _Result;
            }, nullptr);

            // Step2: Combine and check tokens, and count elements in range.
            if (_PTokenState)
            {
                _JoinAllTokens_Add(_MergedSource, _PTokenState);
                _PParam->_Resize(static_cast<size_t>(std::distance(_Begin, _End)));
            }
            else
            {
                size_t _TaskNum = 0;
                for (auto _PTask = _Begin; _PTask != _End; ++_PTask)
                {
                    _TaskNum++;
                    _JoinAllTokens_Add(_MergedSource, _PTask->_GetImpl()->_M_pTokenState);
                }
                _PParam->_Resize(_TaskNum);
            }

            // Step3: Check states of previous tasks.
            if( _Begin == _End )
            {
                _PParam->_M_completed.set(_Unit_type());
                delete _PParam;
            }
            else
            {
                size_t _Index = 0;
                for (auto _PTask = _Begin; _PTask != _End; ++_PTask)
                {
                    if (_PTask->is_apartment_aware())
                    {
                        _ReturnTask._SetAsync();
                    }

                    _PTask->_Then([_PParam, _Index](task<std::vector<_ElementType>> _ResultTask) {

                        auto _PParamCopy = _PParam;
                        auto _IndexCopy = _Index;
                        auto _Func = [_PParamCopy, _IndexCopy, &_ResultTask]() {
                            _PParamCopy->_M_vector[_IndexCopy].Set(_ResultTask._GetImpl()->_GetResult());
                        };

                        _WhenAllContinuationWrapper(_PParam, _Func, _ResultTask);
                    }, _CancellationTokenState::_None());

                    _Index++;
                }
            }

            return  _ReturnTask;
        }
    };

    template<typename _Iterator>
    struct _WhenAllImpl<void, _Iterator>
    {
        static task<void> _Perform(const task_options& _TaskOptions, _Iterator _Begin, _Iterator _End)
        {
            _CancellationTokenState *_PTokenState = _TaskOptions.has_cancellation_token() ? _TaskOptions.get_cancellation_token()._GetImplValue() : nullptr;

            auto _PParam = new _RunAllParam<_Unit_type>();
            cancellation_token_source _MergedSource;

            // Step1: Create task completion event.
            task_options _Options(_TaskOptions);
            _Options.set_cancellation_token(_MergedSource.get_token());
            task<_Unit_type> _All_tasks_completed(_PParam->_M_completed, _Options);
            // The return task must be created before step 3 to enforce inline execution.
            auto _ReturnTask = _All_tasks_completed._Then([=](_Unit_type) {
            }, nullptr);

            // Step2: Combine and check tokens, and count elements in range.
            if (_PTokenState)
            {
                _JoinAllTokens_Add(_MergedSource, _PTokenState);
                _PParam->_Resize(static_cast<size_t>(std::distance(_Begin, _End)));
            }
            else
            {
                size_t _TaskNum = 0;
                for (auto _PTask = _Begin; _PTask != _End; ++_PTask)
                {
                    _TaskNum++;
                    _JoinAllTokens_Add(_MergedSource, _PTask->_GetImpl()->_M_pTokenState);
                }
                _PParam->_Resize(_TaskNum);
            }

            // Step3: Check states of previous tasks.
            if( _Begin == _End )
            {
                _PParam->_M_completed.set(_Unit_type());
                delete _PParam;
            }
            else
            {
                for (auto _PTask = _Begin; _PTask != _End; ++_PTask)
                {
                    if (_PTask->is_apartment_aware())
                    {
                        _ReturnTask._SetAsync();
                    }

                    _PTask->_Then([_PParam](task<void> _ResultTask) {
                        auto _Func = [](){};
                        _WhenAllContinuationWrapper(_PParam, _Func, _ResultTask);
                    }, _CancellationTokenState::_None());
                }
            }

            return _ReturnTask;
        }
    };

    template<typename _ReturnType>
    task<std::vector<_ReturnType>> _WhenAllVectorAndValue(const task<std::vector<_ReturnType>>& _VectorTask, const task<_ReturnType>& _ValueTask,
                                                          bool _OutputVectorFirst)
    {
        auto _PParam = new _RunAllParam<_ReturnType>();
        cancellation_token_source _MergedSource;

        // Step1: Create task completion event.
        task<_Unit_type> _All_tasks_completed(_PParam->_M_completed, _MergedSource.get_token());
        // The return task must be created before step 3 to enforce inline execution.
        auto _ReturnTask = _All_tasks_completed._Then([=](_Unit_type) -> std::vector<_ReturnType> {
            _ASSERTE(_PParam->_M_completeCount == 2);
            auto _Result = _PParam->_M_vector.Get(); // copy by value
            auto _mergeVal = _PParam->_M_mergeVal.Get();

            if (_OutputVectorFirst == true)
            {                
                _Result.push_back(_mergeVal);
            }
            else
            {
                _Result.insert(_Result.begin(), _mergeVal);
            }
            return _Result;
        }, nullptr);

        // Step2: Combine and check tokens.
        _JoinAllTokens_Add(_MergedSource, _VectorTask._GetImpl()->_M_pTokenState);
        _JoinAllTokens_Add(_MergedSource, _ValueTask._GetImpl()->_M_pTokenState);

        // Step3: Check states of previous tasks.
        _PParam->_Resize(2, true);

        if (_VectorTask.is_apartment_aware() || _ValueTask.is_apartment_aware())
        {
            _ReturnTask._SetAsync();
        }
        _VectorTask._Then([_PParam](task<std::vector<_ReturnType>> _ResultTask) {
            auto _PParamCopy = _PParam;
            auto _Func = [_PParamCopy, &_ResultTask]() {
                auto _ResultLocal = _ResultTask._GetImpl()->_GetResult();
                _PParamCopy->_M_vector.Set(_ResultLocal);
            };

            _WhenAllContinuationWrapper(_PParam, _Func, _ResultTask);
        }, _CancellationTokenState::_None());
        _ValueTask._Then([_PParam](task<_ReturnType> _ResultTask) {
            auto _PParamCopy = _PParam;
            auto _Func = [_PParamCopy, &_ResultTask]() {
                auto _ResultLocal = _ResultTask._GetImpl()->_GetResult();
                _PParamCopy->_M_mergeVal.Set(_ResultLocal);
            };

            _WhenAllContinuationWrapper(_PParam, _Func, _ResultTask);
        }, _CancellationTokenState::_None());

        return _ReturnTask;
    }
} // namespace details


template <typename _Iterator>
auto when_all(_Iterator _Begin, _Iterator _End, const task_options& _TaskOptions = task_options()) 
    -> decltype (details::_WhenAllImpl<typename std::iterator_traits<_Iterator>::value_type::result_type, _Iterator>::_Perform(_TaskOptions, _Begin, _End))
{
    typedef typename std::iterator_traits<_Iterator>::value_type::result_type _ElementType;
    return details::_WhenAllImpl<_ElementType, _Iterator>::_Perform(_TaskOptions, _Begin, _End);
}


template<typename _ReturnType>
task<std::vector<_ReturnType>> operator&&(const task<_ReturnType> & _Lhs, const task<_ReturnType> & _Rhs)
{
    task<_ReturnType> _PTasks[2] = {_Lhs, _Rhs};
    return when_all(_PTasks, _PTasks+2);
}


template<typename _ReturnType>
task<std::vector<_ReturnType>> operator&&(const task<std::vector<_ReturnType>> & _Lhs, const task<_ReturnType> & _Rhs)
{
    return details::_WhenAllVectorAndValue(_Lhs, _Rhs, true);
}


template<typename _ReturnType>
task<std::vector<_ReturnType>> operator&&(const task<_ReturnType> & _Lhs, const task<std::vector<_ReturnType>> & _Rhs)
{
    return details::_WhenAllVectorAndValue(_Rhs, _Lhs, false);
}


template<typename _ReturnType>
task<std::vector<_ReturnType>> operator&&(const task<std::vector<_ReturnType>> & _Lhs, const task<std::vector<_ReturnType>> & _Rhs)
{
    task<std::vector<_ReturnType>> _PTasks[2] = {_Lhs, _Rhs};
    return when_all(_PTasks, _PTasks+2);
}


inline task<void> operator&&(const task<void> & _Lhs, const task<void> & _Rhs)
{
    task<void> _PTasks[2] = {_Lhs, _Rhs};
    return when_all(_PTasks, _PTasks+2);
}

namespace details
{
    // Helper struct for when_any operators to know when tasks have completed
    template <typename _CompletionType>
    struct _RunAnyParam
    {
        _RunAnyParam() : _M_exceptionRelatedToken(nullptr), _M_completeCount(0), _M_numTasks(0), _M_fHasExplicitToken(false)
        {
        }
        ~_RunAnyParam()
        {
            if (_CancellationTokenState::_IsValid(_M_exceptionRelatedToken))
                _M_exceptionRelatedToken->_Release();
        }
        task_completion_event<_CompletionType>      _M_Completed;
        cancellation_token_source                   _M_cancellationSource;
        _CancellationTokenState *                   _M_exceptionRelatedToken;
        atomic_size_t                               _M_completeCount;
        size_t                                      _M_numTasks;
        bool                                        _M_fHasExplicitToken;
    };

    template<typename _CompletionType, typename _Function, typename _TaskType>
    void _WhenAnyContinuationWrapper(_RunAnyParam<_CompletionType> * _PParam, const _Function & _Func, task<_TaskType>& _Task)
    {
        bool _IsTokenCancled = !_PParam->_M_fHasExplicitToken && _Task._GetImpl()->_M_pTokenState != _CancellationTokenState::_None() && _Task._GetImpl()->_M_pTokenState->_IsCanceled();
        if (_Task._GetImpl()->_IsCompleted() && !_IsTokenCancled)
        {
            _Func();
            if (atomic_increment(_PParam->_M_completeCount) == _PParam->_M_numTasks)
            {
                delete _PParam;
            }
        }
        else
        {
            _ASSERTE(_Task._GetImpl()->_IsCanceled() || _IsTokenCancled);
            if (_Task._GetImpl()->_HasUserException() && !_IsTokenCancled)
            {
                if (_PParam->_M_Completed._StoreException(_Task._GetImpl()->_GetExceptionHolder()))
                {
                    // This can only enter once.
                    _PParam->_M_exceptionRelatedToken = _Task._GetImpl()->_M_pTokenState;
                    _ASSERTE(_PParam->_M_exceptionRelatedToken);
                    // Deref token will be done in the _PParam destructor.
                    if (_PParam->_M_exceptionRelatedToken != _CancellationTokenState::_None())
                    {
                        _PParam->_M_exceptionRelatedToken->_Reference();
                    }
                }
            }
            
            if (atomic_increment(_PParam->_M_completeCount) == _PParam->_M_numTasks)
            {
                // If no one has be completed so far, we need to make some final cancellation decision.
                if (!_PParam->_M_Completed._IsTriggered())
                {
                    // If we already explicit token, we can skip the token join part.
                    if (!_PParam->_M_fHasExplicitToken)
                    {
                        if (_PParam->_M_exceptionRelatedToken)
                        {
                            _JoinAllTokens_Add(_PParam->_M_cancellationSource, _PParam->_M_exceptionRelatedToken);
                        }
                        else
                        {
                            // If haven't captured any exception token yet, there was no exception for all those tasks,
                            // so just pick a random token (current one) for normal cancellation.
                            _JoinAllTokens_Add(_PParam->_M_cancellationSource, _Task._GetImpl()->_M_pTokenState);
                        }
                    }
                    // Do exception cancellation or normal cancellation based on whether it has stored exception.
                    _PParam->_M_Completed._Cancel();
                }
                delete _PParam;
            }
        }
    }

    template<typename _ElementType, typename _Iterator>
    struct _WhenAnyImpl
    {
        static task<std::pair<_ElementType, size_t>> _Perform(const task_options& _TaskOptions, _Iterator _Begin, _Iterator _End)
        {
            if( _Begin == _End )
            {
                throw invalid_operation("when_any(begin, end) cannot be called on an empty container.");
            }
            _CancellationTokenState *_PTokenState = _TaskOptions.has_cancellation_token() ? _TaskOptions.get_cancellation_token()._GetImplValue() : nullptr;
            auto _PParam = new _RunAnyParam<std::pair<std::pair<_ElementType, size_t>, _CancellationTokenState *>>();
            
            if (_PTokenState)
            {
                _JoinAllTokens_Add(_PParam->_M_cancellationSource, _PTokenState);
                _PParam->_M_fHasExplicitToken = true;
            }
            
            task_options _Options(_TaskOptions);
            _Options.set_cancellation_token(_PParam->_M_cancellationSource.get_token());
            task<std::pair<std::pair<_ElementType, size_t>, _CancellationTokenState *>> _Any_tasks_completed(_PParam->_M_Completed, _Options); 

            // Keep a copy ref to the token source
            auto _CancellationSource = _PParam->_M_cancellationSource;

            _PParam->_M_numTasks = static_cast<size_t>(std::distance(_Begin, _End));
            size_t _Index = 0;
            for (auto _PTask = _Begin; _PTask != _End; ++_PTask)
            {
                if (_PTask->is_apartment_aware())
                {
                    _Any_tasks_completed._SetAsync();
                }

                _PTask->_Then([_PParam, _Index](task<_ElementType> _ResultTask) {
                    auto _PParamCopy = _PParam; // Dev10
                    auto _IndexCopy = _Index; // Dev10
                    auto _Func = [&_ResultTask, _PParamCopy, _IndexCopy]() {
                        _PParamCopy->_M_Completed.set(std::make_pair(std::make_pair(_ResultTask._GetImpl()->_GetResult(), _IndexCopy),  _ResultTask._GetImpl()->_M_pTokenState));
                    };

                    _WhenAnyContinuationWrapper(_PParam, _Func, _ResultTask);
                }, _CancellationTokenState::_None());

                _Index++;
            }

            // All _Any_tasks_completed._SetAsync() must be finished before this return continuation task being created.
            return _Any_tasks_completed._Then([=](std::pair<std::pair<_ElementType, size_t>, _CancellationTokenState *> _Result) -> std::pair<_ElementType, size_t> {
                _ASSERTE(_Result.second);
                if (!_PTokenState)
                {
                    _JoinAllTokens_Add(_CancellationSource, _Result.second);
                }
                return _Result.first;
            }, nullptr);
        }
    };

    template<typename _Iterator>
    struct _WhenAnyImpl<void, _Iterator>
    {
        static task<size_t> _Perform(const task_options& _TaskOptions, _Iterator _Begin, _Iterator _End)
        {
            if( _Begin == _End )
            {
                throw invalid_operation("when_any(begin, end) cannot be called on an empty container.");
            }

            _CancellationTokenState *_PTokenState = _TaskOptions.has_cancellation_token() ? _TaskOptions.get_cancellation_token()._GetImplValue() : nullptr;
            auto _PParam = new _RunAnyParam<std::pair<size_t, _CancellationTokenState *>>();
            
            if (_PTokenState)
            {
                _JoinAllTokens_Add(_PParam->_M_cancellationSource, _PTokenState);
                _PParam->_M_fHasExplicitToken = true;
            }

            task_options _Options(_TaskOptions);
            _Options.set_cancellation_token(_PParam->_M_cancellationSource.get_token());
            task<std::pair<size_t, _CancellationTokenState *>> _Any_tasks_completed(_PParam->_M_Completed, _Options);

            // Keep a copy ref to the token source
            auto _CancellationSource = _PParam->_M_cancellationSource;

            _PParam->_M_numTasks = static_cast<size_t>(std::distance(_Begin, _End));
            size_t _Index = 0;
            for (auto _PTask = _Begin; _PTask != _End; ++_PTask)
            {
                if (_PTask->is_apartment_aware())
                {
                    _Any_tasks_completed._SetAsync();
                }

                _PTask->_Then([_PParam, _Index](task<void> _ResultTask) {
                    auto _PParamCopy = _PParam; // Dev10
                    auto _IndexCopy = _Index; // Dev10
                    auto _Func = [&_ResultTask, _PParamCopy, _IndexCopy]() {
                        _PParamCopy->_M_Completed.set(std::make_pair(_IndexCopy, _ResultTask._GetImpl()->_M_pTokenState));
                    };
                    _WhenAnyContinuationWrapper(_PParam, _Func, _ResultTask);
                }, _CancellationTokenState::_None());

                _Index++;
            }

            // All _Any_tasks_completed._SetAsync() must be finished before this return continuation task being created.
            return _Any_tasks_completed._Then([=](std::pair<size_t, _CancellationTokenState *> _Result) -> size_t {
                _ASSERTE(_Result.second);
                if (!_PTokenState)
                {
                    _JoinAllTokens_Add(_CancellationSource, _Result.second);
                }
                return _Result.first;
            }, nullptr);
        }
    };
} // namespace details


template<typename _Iterator>
auto when_any(_Iterator _Begin, _Iterator _End, const task_options& _TaskOptions = task_options())
    -> decltype (details::_WhenAnyImpl<typename std::iterator_traits<_Iterator>::value_type::result_type, _Iterator>::_Perform(_TaskOptions, _Begin, _End))
{
    typedef typename std::iterator_traits<_Iterator>::value_type::result_type _ElementType;
    return details::_WhenAnyImpl<_ElementType, _Iterator>::_Perform(_TaskOptions, _Begin, _End);
}


template<typename _Iterator>
auto when_any(_Iterator _Begin, _Iterator _End, cancellation_token _CancellationToken)
    -> decltype (details::_WhenAnyImpl<typename std::iterator_traits<_Iterator>::value_type::result_type, _Iterator>::_Perform(_CancellationToken._GetImplValue(), _Begin, _End))
{
    typedef typename std::iterator_traits<_Iterator>::value_type::result_type _ElementType;
    return details::_WhenAnyImpl<_ElementType, _Iterator>::_Perform(_CancellationToken._GetImplValue(), _Begin, _End);
}


template<typename _ReturnType>
task<_ReturnType> operator||(const task<_ReturnType> & _Lhs, const task<_ReturnType> & _Rhs)
{
    auto _PParam = new details::_RunAnyParam<std::pair<_ReturnType, size_t>>();

    task<std::pair<_ReturnType, size_t>> _Any_tasks_completed(_PParam->_M_Completed, _PParam->_M_cancellationSource.get_token());
    // Chain the return continuation task here to ensure it will get inline execution when _M_Completed.set is called,
    // So that _PParam can be used before it getting deleted.
    auto _ReturnTask = _Any_tasks_completed._Then([=](std::pair<_ReturnType, size_t> _Ret) -> _ReturnType {
        _ASSERTE(_Ret.second);
        _JoinAllTokens_Add(_PParam->_M_cancellationSource, reinterpret_cast<details::_CancellationTokenState *>(_Ret.second));
        return _Ret.first;
    }, nullptr);

    if (_Lhs.is_apartment_aware() || _Rhs.is_apartment_aware())
    {
        _ReturnTask._SetAsync();
    }

    _PParam->_M_numTasks = 2;
    auto _Continuation = [_PParam](task<_ReturnType> _ResultTask) {
        //  Dev10 compiler bug
        auto _PParamCopy = _PParam;
        auto _Func = [&_ResultTask, _PParamCopy]() {
            _PParamCopy->_M_Completed.set(std::make_pair(_ResultTask._GetImpl()->_GetResult(), reinterpret_cast<size_t>(_ResultTask._GetImpl()->_M_pTokenState)));
        };
        _WhenAnyContinuationWrapper(_PParam, _Func, _ResultTask);
    };

    _Lhs._Then(_Continuation, details::_CancellationTokenState::_None());
    _Rhs._Then(_Continuation, details::_CancellationTokenState::_None());

    return _ReturnTask;
}


template<typename _ReturnType>
task<std::vector<_ReturnType>> operator||(const task<std::vector<_ReturnType>> & _Lhs, const task<_ReturnType> & _Rhs)
{
    auto _PParam = new details::_RunAnyParam<std::pair<std::vector<_ReturnType>, details::_CancellationTokenState *>>();

    task<std::pair<std::vector<_ReturnType>, details::_CancellationTokenState *>> _Any_tasks_completed(_PParam->_M_Completed, _PParam->_M_cancellationSource.get_token());

    // Chain the return continuation task here to ensure it will get inline execution when _M_Completed.set is called,
    // So that _PParam can be used before it getting deleted.
    auto _ReturnTask = _Any_tasks_completed._Then([=](std::pair<std::vector<_ReturnType>, details::_CancellationTokenState *> _Ret) -> std::vector<_ReturnType> {
        _ASSERTE(_Ret.second);
        _JoinAllTokens_Add(_PParam->_M_cancellationSource, _Ret.second);
        return _Ret.first;
    }, nullptr);

    if (_Lhs.is_apartment_aware() || _Rhs.is_apartment_aware())
    {
        _ReturnTask._SetAsync();
    }

    _PParam->_M_numTasks = 2;
    _Lhs._Then([_PParam](task<std::vector<_ReturnType>> _ResultTask) {
        //  Dev10 compiler bug
        auto _PParamCopy = _PParam;
        auto _Func = [&_ResultTask, _PParamCopy]() {
            auto _Result = _ResultTask._GetImpl()->_GetResult();
            _PParamCopy->_M_Completed.set(std::make_pair(_Result, _ResultTask._GetImpl()->_M_pTokenState));
        };
        _WhenAnyContinuationWrapper(_PParam, _Func, _ResultTask);
    }, details::_CancellationTokenState::_None());

    
    _Rhs._Then([_PParam](task<_ReturnType> _ResultTask) 
    {
        auto _PParamCopy = _PParam;
        auto _Func = [&_ResultTask, _PParamCopy]() {
            auto _Result = _ResultTask._GetImpl()->_GetResult();

            std::vector<_ReturnType> _Vec;
            _Vec.push_back(_Result);
            _PParamCopy->_M_Completed.set(std::make_pair(_Vec, _ResultTask._GetImpl()->_M_pTokenState));
        };
        _WhenAnyContinuationWrapper(_PParam, _Func, _ResultTask);
    }, details::_CancellationTokenState::_None());

    return _ReturnTask;
}


template<typename _ReturnType>
task<std::vector<_ReturnType>> operator||(const task<_ReturnType> & _Lhs, const task<std::vector<_ReturnType>> & _Rhs)
{
    return _Rhs || _Lhs;
}


inline task<void> operator||(const task<void> & _Lhs, const task<void> & _Rhs)
{
    auto _PParam = new details::_RunAnyParam<std::pair<details::_Unit_type, details::_CancellationTokenState *>>();

    task<std::pair<details::_Unit_type, details::_CancellationTokenState *>> _Any_task_completed(_PParam->_M_Completed, _PParam->_M_cancellationSource.get_token());
    // Chain the return continuation task here to ensure it will get inline execution when _M_Completed.set is called,
    // So that _PParam can be used before it getting deleted.
    auto _ReturnTask = _Any_task_completed._Then([=](std::pair<details::_Unit_type, details::_CancellationTokenState *> _Ret) { 
        _ASSERTE(_Ret.second);
        details::_JoinAllTokens_Add(_PParam->_M_cancellationSource, _Ret.second);
    }, nullptr);

    if (_Lhs.is_apartment_aware() || _Rhs.is_apartment_aware())
    {
        _ReturnTask._SetAsync();
    }

    _PParam->_M_numTasks = 2;
    auto _Continuation = [_PParam](task<void> _ResultTask) mutable {
        //  Dev10 compiler needs this.
        auto _PParam1 = _PParam;
        auto _Func = [&_ResultTask, _PParam1]() {
            _PParam1->_M_Completed.set(std::make_pair(details::_Unit_type(), _ResultTask._GetImpl()->_M_pTokenState));
        };
        _WhenAnyContinuationWrapper(_PParam, _Func, _ResultTask);
    };

    _Lhs._Then(_Continuation, details::_CancellationTokenState::_None());
    _Rhs._Then(_Continuation, details::_CancellationTokenState::_None());

    return _ReturnTask;
}

template<typename _Ty>
task<_Ty> task_from_result(_Ty _Param, const task_options& _TaskOptions = task_options())
{
    task_completion_event<_Ty> _Tce;
    _Tce.set(_Param);
    return create_task(_Tce, _TaskOptions);
}

// Work around VS 2010 compiler bug
#if _MSC_VER == 1600
inline task<bool> task_from_result(bool _Param)
{
    task_completion_event<bool> _Tce;
    _Tce.set(_Param);
    return create_task(_Tce, task_options());
}
#endif
inline task<void> task_from_result(const task_options& _TaskOptions = task_options())
{
    task_completion_event<void> _Tce;
    _Tce.set();
    return create_task(_Tce, _TaskOptions);
}

template<typename _TaskType, typename _ExType>
task<_TaskType> task_from_exception(_ExType _Exception, const task_options& _TaskOptions = task_options())
{
    task_completion_event<_TaskType> _Tce;
    _Tce.set_exception(_Exception);
    return create_task(_Tce, _TaskOptions);
}

namespace details
{
    inline
    task<bool> do_while(std::function<task<bool>(void)> func)
    {
        task<bool> first = func();
        return first.then([=](bool guard) -> task<bool> {
            if (guard)
                return do_while(func);
            else
                return first;
            });
    }

} // namespace details

} // namespace Concurrency

#pragma pop_macro("new")

#if defined(_MSC_VER)
#pragma warning(pop)
#endif
#pragma pack(pop)

#endif // (defined(_MSC_VER) && (_MSC_VER >= 1800))

#ifndef _CONCRT_H
#ifndef _LWRCASE_CNCRRNCY
#define _LWRCASE_CNCRRNCY
// Note to reader: we're using lower-case namespace names everywhere, but the 'Concurrency' namespace
// is capitalized for historical reasons. The alias let's us pretend that style issue doesn't exist.
namespace Concurrency {}
namespace concurrency = Concurrency;
#endif
#endif

#endif // _PPLXTASKS_H