[Fix] Fix stuck in `torch.einsum` when create dataset (#2065)

* Fix stuck in torch.einsum when create dataset

* Fix stuck in torch.einsum when create dataset

* Fix lint

* add comments

* Fix lint

tools/create_data.py

@@ -256,6 +256,11 @@ args = parser.parse_args()
 if __name__ == '__main__':
     from mmdet3d.utils import register_all_modules
     register_all_modules()
+
+    # Set to spawn mode to avoid stuck when process dataset creating
+    import multiprocessing
+    multiprocessing.set_start_method('spawn')
+
     if args.dataset == 'kitti':
         kitti_data_prep(
             root_path=args.root_path,