Why does the code shown below either finish normally or hang depending on which lines are commented/uncommented, as described in the table below?

Summary of table: if I initialise sufficiently large tensors in both processes without using "spawn", the program hangs. I can fix it by making either tensor smaller, or by using "spawn".

Note:

1. All memory is purely CPU, I don't even have CUDA installed on this computer
2. This issue does not occur if I replace torch with numpy, even if I make the array size 10x larger
3. Version information: Ubuntu 22.04.1 LTS, Python 3.10.12, torch 2.1.2+cpu