Потоки или коллбэки?

while (Flag == false) { }

while (Flag == false) { sleep(SomeTime); }

void Play_Proc(HWND hWnd)
{
    MMRESULT result;
    static HWAVEOUT hWaveOut;
    static WAVEHDR  WaveOutHdr;
 
    WAVEFORMATEX wfx;
    wfx.wFormatTag = WAVE_FORMAT_PCM;     //  simple, uncompressed format
    wfx.nChannels = 1;                    //  1=mono, 2=stereo
    wfx.nSamplesPerSec = sampleRate;      //  44100
    wfx.wBitsPerSample = 16;              //  16 for high quality, 8 for telephone-grade
    wfx.nBlockAlign = (wfx.wBitsPerSample >> 3) * wfx.nChannels;
    wfx.nAvgBytesPerSec = wfx.nBlockAlign * wfx.nSamplesPerSec;
    wfx.cbSize = 0;                       //  size of _extra_ info
 
    result = waveOutOpen(&hWaveOut, WAVE_MAPPER, &wfx, (DWORD_PTR) hwndGraphOut, 0L, CALLBACK_WINDOW);
    if (result) {
        //wchar_t fault[256];
        //waveOutGetErrorText(result, fault, 256);
        MessageBoxW(NULL, L"Ошибка открытия выходного потока", L"Error", MB_OK | MB_ICONEXCLAMATION | MB_TASKMODAL);
        return;
    }
    WaveOutHdr.lpData = (LPSTR)waveOut.buf;
    WaveOutHdr.dwBufferLength = NUMPTS*2;
    WaveOutHdr.dwBytesRecorded = 0;
    WaveOutHdr.dwUser = 0L;
    WaveOutHdr.dwFlags = 0L;
    WaveOutHdr.dwLoops = 0L;
    waveOutPrepareHeader(hWaveOut, &WaveOutHdr, sizeof(WAVEHDR));
    result = waveOutWrite(hWaveOut, &WaveOutHdr, sizeof(WAVEHDR));
    if (result) {
        MessageBoxW(NULL, L"Ошибка выдачи в выходной поток", L"Error", MB_OK | MB_ICONEXCLAMATION | MB_TASKMODAL);
        return;
    }
}

LRESULT CALLBACK GraphWndProc( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam )
{
    switch(msg)
    {
    case MM_WIM_DATA:
        waveInUnprepareHeader((HWAVEIN) wParam, (LPWAVEHDR) lParam, sizeof(WAVEHDR));
        waveInClose((HWAVEIN) wParam);
        SetWindowTextW(hwndSta1, L"MM_WIM_DATA");
        InvalidateRgn(hwndGraphIn, NULL, TRUE);
        SendMessage(hwndGraphIn, WM_PAINT, 0, 0);
        break;
    case MM_WOM_DONE:
        waveOutUnprepareHeader((HWAVEOUT) wParam, (LPWAVEHDR) lParam, sizeof(WAVEHDR)); 
        waveOutClose((HWAVEOUT) wParam);
        SetWindowTextW(hwndSta1, L"MM_WOM_DONE");
        break;
..................

    static HWAVEOUT hWaveOut;
    static WAVEHDR  WaveOutHdr;