(D3D11) Reading texel on separate thread

Question

In D3D10, I load a staging texture onto my GPU memory, then map it in order to access its texel data on the CPU. This is done on a separate thread, not the thread I render with. I just call the device methods, and it works.

In D3D11 I load the staging texture onto my GPU, but to access it (i.e. Map it) I need to use the Context, not the device. Can't use the immediate context, since the immediate context can only be used by a single thread at a time. But I also can't use a deferred context to Read from the texture to the CPU:

"If you call Map on a deferred context, you can only pass D3D11_MAP_WRITE_DISCARD, D3D11_MAP_WRITE_NO_OVERWRITE, or both to the MapType parameter. Other D3D11_MAP-typed values are not supported for a deferred context."

http://msdn.microsoft.com/en-us/library/ff476457.aspx

Ok, so what am I supposed to do now? It is common to use textures to store certain data (heightmaps for instance) and you obviously have to be able to access that data for it to be useful. Is there no way for me to do this in a separate thread with D3D11?

Answer 1

You should map the staging texture using the immediate context on the render thread, then use the contents as you wish on your second thread. Even in D3D10, the call to map the texture for read ends up putting a synchronization point in the command buffer (refer to this article), effectively serializing your threads. The D3D11 API makes an effort to discourage hidden performance costs like this.