Reply To: Modifying field values for neighboring cells inside a postprocessor
Ok, you obviously invested a lot of thought into how to implement this already (thanks for sharing and sorry for my repeated doubts, I am not used to people in this forum working at this level in the code)!
In this case I suggest you go ahead with the atomic-based approach you outlined and we go from there.
The PerBlock-scope simply allows you to access the entire concrete block instance (i.e. without most of the virtual interface layers so you will be able to access the raw memory from there). Currently, the only public user of this approach is the StatisticsPostProcessor, you can check out the GPU implementation in src/core/platform/gpu/cuda/statistics.hh.