make train.py compatible with torchrun

Author: xwang233

train.py

@@ -355,6 +355,8 @@ def main():
     args.world_size = 1
     args.rank = 0  # global rank
     if args.distributed:
+        if 'LOCAL_RANK' in os.environ:
+            args.local_rank = int(os.getenv('LOCAL_RANK'))
         args.device = 'cuda:%d' % args.local_rank
         torch.cuda.set_device(args.local_rank)
         torch.distributed.init_process_group(backend='nccl', init_method='env://')