Forbid other programs to use the virtual camera when already in use

[rnixik]

I set two formats: 720p and 480p for my virtual camera. I want to edit source code to forbid getting stream from the same camera when we are already streaming in other format like my real web come does. I'm not sure if this is possible with DShow. If you think is it possible, could you please suggest class or method to add mutex/if?