Pass torch.distributed launch process local rank as environment variable instead of argument (#16360)
Summary:
In `torch.distributed.launch.py`, it passes `local_rank` as argument and requires user's program to parse it. However, it would be more flexible for users and consistent with other variables, e.g. `RANK`, `MASTER_PORT`, `WORLD_SIZE`, if passing through environment variables.
https://github.com/pytorch/pytorch/blob/265ed8ff451c17eac82050b1767837ec924d9591/torch/distributed/launch.py#L200-L212
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16360
Differential Revision: D14070372
Pulled By: ezyang
fbshipit-source-id: c3f6a8e55ab513918cad09d1326eccdedb4d98c9
