How WINAPI handle IAudioClient->SetEventHandle() works? - c++

Question

I'm writing an application that reading audio endpoint on windows, via WASAPI. For now I have similar code for capture thread (treat this code as minimal example):
DWORD CWASAPICapture::DoCaptureThread()
{
BYTE *pData;
UINT32 framesAvailable = 1;
DWORD flags, state;
HRESULT hr = CoInitializeEx(NULL, COINIT_MULTITHREADED);
if (FAILED(hr))
{
printf("Unable to initialize COM in render thread: %x\n", hr);
return hr;
}
while (framesAvailable != 0) {
// get the available data in the shared buffer.
state = WaitForSingleObject(_AudioSamplesReadyEvent, INFINITE);
hr = _CaptureClient->GetBuffer(&pData, &framesAvailable, &flags, NULL, NULL);
if ((state != 0) || (hr != S_OK)) {
// my breakpoint
assert(false);
}
UINT32 framesToCopy = min(framesAvailable, static_cast<UINT32>((_CaptureBufferSize - _CurrentCaptureIndex) / _FrameSize));
if (flags & AUDCLNT_BUFFERFLAGS_SILENT)
{
ZeroMemory(&_CaptureBuffer[_CurrentCaptureIndex], framesToCopy*_FrameSize);
} else {
CopyMemory(&_CaptureBuffer[_CurrentCaptureIndex], pData, framesToCopy*_FrameSize);
}
_CurrentCaptureIndex += framesToCopy*_FrameSize;
// release data
hr = _CaptureClient->ReleaseBuffer(framesAvailable);
assert(hr == S_OK);
}
CoUninitialize();
return 0;
}
In Init section I requested buffer for 1s duration, blockAlign equal to 8, so my captureBufferSize = 3528000 bytes. _AudioSamplesReadyEvent set as _AudioClient->SetEventHandle(_AudioSamplesReadyEvent). Packet size = 441. Other code based on official windows SDK CaptureSharedEventDriven example, this method I changed.
Problem:
Program always fails on my breakpoint (by design) and i'm watching into variables, expected values are hr = AUDCLNT_S_BUFFER_EMPTY (0x08890001) and _CurrentCaptureIndex = 3528000, and I even got this values like in 1 from 10 cases... Usually hr = AUDCLNT_S_BUFFER_EMPTY (0x08890001) and _CurrentCaptureIndex equals to random values, most often is 0, 3528 (8 packets) and 10584 (24 packets).
First of all, when I just started to use WaitForSingleObject with _AudioClient->SetEventHandle, I supposed it signals when buffer is filled for requested time in _AudioClient->Initialize() (MSDN description pretty fluent), but that wrong, next my suggestion was that it waits until a single packet with data got filled, but as my example shows, I don't have available frames in buffer. I tried ti use GetNextPacketSize nex to WaitSingleObject, but still the same result.
My questions is:
Why my example works that way?
What exactly IAudioClient->SetEventHandle() signaling about to WaitForSingleObject()?
How to read buffer of size I requested properly?
UPD1: Sleep() placed before while, instead of WaitForSingleObject() works fine, I get all frames for time my thread slept.
UPD2: minimal example