struct TASK_DATA
{
    LONG _dwTaskCount, _dwRefCount, _dwReadyCount;
    HANDLE _hEvent[2];
    ULONG _iLoop;
    bool _bExit;

    TASK_DATA() : _dwRefCount(1), _dwTaskCount(0), _hEvent{}, _bExit(false), _dwReadyCount(0), _iLoop(0) {}

    ~TASK_DATA() {
        if (_hEvent[1]) CloseHandle(_hEvent[1]);
        if (_hEvent[0]) CloseHandle(_hEvent[0]);
    }

    void AddRef()
    {
        InterlockedIncrementNoFence(&_dwRefCount);
    }

    void Release()
    {
        if (!InterlockedDecrement(&_dwRefCount))
        {
            delete this;
        }
    }

    ULONG Start(ULONG i)
    {
        ULONG n = 0;
        if ((_hEvent[0] = CreateEvent(0, TRUE, FALSE, 0)) &&
            (_hEvent[1] = CreateEvent(0, TRUE, FALSE, 0)))
        {
            do
            {
                n += AddThread();
            } while (--i);
        }

        if (n)
        {
            SetEvent(_hEvent[0]);
        }
        return n;
    }

    ULONG AddThread()
    {
        AddRef();
        if (HANDLE hThread = CreateThread(0, 0, s_CalcThread, this, 0, 0))
        {
            _dwTaskCount++;
            CloseHandle(hThread);
            return 1;
        }
        Release();
        return 0;
    }

    void EndTask(bool bReadyForNewTask)
    {
        if (bReadyForNewTask)
        {
            InterlockedIncrementNoFence(&_dwReadyCount);
        }

        if (!InterlockedDecrement(&_dwTaskCount))
        {
            MessageBoxW(0, L"do some calc synthesis stuff.", L"", MB_ICONWARNING);

            if (_dwTaskCount = _dwReadyCount)
            {
                _dwReadyCount = 0;
                ResetEvent(_hEvent[_iLoop]);
                SetEvent(_hEvent[_iLoop = 1 - _iLoop]);
            }
        }
    }

    void CalcThread()
    {
        bool bReadyForNewTask = true;

        WCHAR sz[64], wz[64];
        swprintf_s(wz, L"[%x]", GetCurrentThreadId());

        int i = 1, j = 0;
        do
        {
            if (WaitForSingleObject(_hEvent[i = 1 - i], INFINITE) == WAIT_OBJECT_0 &&  !_bExit)
            {
                swprintf_s(sz, L"do some calc stuff #%u", j++);
                MessageBoxW(0, sz, wz, MB_ICONINFORMATION);
            }
            else
            {
                bReadyForNewTask = false;
            }

            EndTask(bReadyForNewTask);

        } while (bReadyForNewTask);

        Release();
    }

    static ULONG WINAPI s_CalcThread(void* This)
    {
        reinterpret_cast<TASK_DATA*>(This)->CalcThread();
        return 0;
    }
};

void demo()
{
    if (TASK_DATA* p = new TASK_DATA)
    {
        if (p->Start(3))
        {
            MessageBoxW(0, L"Task Start", 0, MB_ICONWARNING);
            p->_bExit = true;
        }
        p->Release();

        MessageBoxW(0, L"Task End", 0, MB_ICONWARNING);
    }
}