Direct3D11: Sharing a texture between devices: black texture - c++

Question

I have two D3D11 devices, each with its own context but on the same adapter.
I am trying to share a texture beween the two, but the texture I recieve on the other side is always black.
HRESULT hr;
// Make a shared texture on device_A / context_A
D3D11_TEXTURE2D_DESC desc;
ZeroMemory(&desc, sizeof(desc));
desc.Width = 1024;
desc.Height = 1024;
desc.MipLevels = 1;
desc.ArraySize = 1;
desc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
desc.SampleDesc.Count = 1;
desc.SampleDesc.Quality = 0;
desc.Usage = D3D11_USAGE_DEFAULT;
desc.CPUAccessFlags = 0;
desc.MiscFlags = D3D11_RESOURCE_MISC_SHARED;
desc.BindFlags = D3D11_BIND_SHADER_RESOURCE | D3D11_BIND_RENDER_TARGET;
ID3D11Texture2D* copy_tex;
hr = device_A->CreateTexture2D(&desc, NULL, &copy_tex);
// Test the texture by filling it with some color
D3D11_RENDER_TARGET_VIEW_DESC rtvd = {};
rtvd.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
rtvd.ViewDimension = D3D11_RTV_DIMENSION_TEXTURE2D;
rtvd.Texture2D.MipSlice = 0;
ID3D11RenderTargetView* copy_tex_view = 0;
hr = device_A->CreateRenderTargetView(copy_tex, &rtvd, &copy_tex_view);
FLOAT clear_color[4] = {1, 0, 0, 1};
context_A->ClearRenderTargetView(copy_tex_view, clear_color);
// Now try to share it to device_B:
IDXGIResource* copy_tex_resource = 0;
hr = copy_tex->QueryInterface( __uuidof(IDXGIResource), (void**)&copy_tex_resource );
HANDLE copy_tex_shared_handle = 0;
hr = copy_tex_resource->GetSharedHandle(&copy_tex_shared_handle);
IDXGIResource* copy_tex_resource_mirror = 0;
hr = device_B->OpenSharedResource(copy_tex_shared_handle, __uuidof(ID3D11Texture2D), (void**)&copy_tex_resource_mirror);
ID3D11Texture2D* copy_tex_mirror = 0;
hr = copy_tex_resource_mirror->QueryInterface(__uuidof(ID3D11Texture2D), (void**)(&copy_tex_mirror));
However: the copy_tex_mirror texture is always black.
I don't get any HRESULT error codes, and can even use copy_tex_mirror on device_B / context_B normally, but I can't get the pixel data that I put into it on device_A.
Am I missing something?
Thanks in advance!

Answer 1

How do you know that the texture is always black? :-)
GPU operations are queued up by Direct3D, so when you open the shared resource on device_B, the ClearRenderTargetView() on device_A might not have been carried out yet. According to the MSDN library documentation on ID3D11Device::OpenSharedResource Method:
If a shared texture is updated on one device ID3D11DeviceContext::Flush must be called on that device.
We had a lot of issues such as this when we implemented shared textures between devices at work. If you add D3D9 or OpenGL to the mix, the pitfalls multiply..