NVVL-PyTorch1.1 hangs when program exits

[jsjason]

We've successfully updated NVVL to work with PyTorch 1.1 so that we can use the latest version of PyTorch when running RnB... except for that fact that there are times where the program does not terminate cleanly. Apparently, processes running NVVL fail to exit and live on as zombie processes:

I'm suspecting that this has something to do with cpp-side objects not being deleted correctly, but I'm not sure where to start from.