fixbug: torch 2.0 dist train with error local rank (open-mmlab#1600)

Author: jihanyang

tools/train.py

@@ -33,7 +33,7 @@ def parse_config():
     parser.add_argument('--sync_bn', action='store_true', default=False, help='whether to use sync bn')
     parser.add_argument('--fix_random_seed', action='store_true', default=False, help='')
     parser.add_argument('--ckpt_save_interval', type=int, default=1, help='number of training epochs')
-    parser.add_argument('--local_rank', type=int, default=0, help='local rank for distributed training')
+    parser.add_argument('--local_rank', type=int, default=None, help='local rank for distributed training')
     parser.add_argument('--max_ckpt_save_num', type=int, default=30, help='max number of saved checkpoint')
     parser.add_argument('--merge_all_iters_to_one_epoch', action='store_true', default=False, help='')
     parser.add_argument('--set', dest='set_cfgs', default=None, nargs=argparse.REMAINDER,
@@ -71,6 +71,9 @@ def main():
         dist_train = False
         total_gpus = 1
     else:
+        if args.local_rank is None:
+            args.local_rank = int(os.environ.get('LOCAL_RANK', '0'))
+            
         total_gpus, cfg.LOCAL_RANK = getattr(common_utils, 'init_dist_%s' % args.launcher)(
             args.tcp_port, args.local_rank, backend='nccl'
         )