[Enhance] Disable warning of subprocess launched by dataloader (#870)

* Disable warning of subprocess launched by dataloader

* Add type hint

mmengine/dataset/utils.py

 # Copyright (c) OpenMMLab. All rights reserved.
 import random
+import warnings
 from typing import Any, Mapping, Sequence
 
 import numpy as np
@@ -13,8 +14,11 @@ from mmengine.structures import BaseDataElement
 COLLATE_FUNCTIONS = Registry('Collate Functions')
 
 
-def worker_init_fn(worker_id: int, num_workers: int, rank: int,
-                   seed: int) -> None:
+def worker_init_fn(worker_id: int,
+                   num_workers: int,
+                   rank: int,
+                   seed: int,
+                   disable_subprocess_warning: bool = False) -> None:
     """This function will be called on each worker subprocess after seeding and
     before data loading.
 
@@ -31,6 +35,8 @@ def worker_init_fn(worker_id: int, num_workers: int, rank: int,
     np.random.seed(worker_seed)
     random.seed(worker_seed)
     torch.manual_seed(worker_seed)
+    if disable_subprocess_warning and worker_id != 0:
+        warnings.simplefilter('ignore')
 
 
 @COLLATE_FUNCTIONS.register_module()

mmengine/runner/runner.py

@@ -1367,12 +1367,20 @@ class Runner:
 
         # build dataloader
         init_fn: Optional[partial]
+
         if seed is not None:
+            disable_subprocess_warning = dataloader_cfg.pop(
+                'disable_subprocess_warning', False)
+            assert isinstance(
+                disable_subprocess_warning,
+                bool), ('disable_subprocess_warning should be a bool, but got '
+                        f'{type(disable_subprocess_warning)}')
             init_fn = partial(
                 worker_init_fn,
                 num_workers=dataloader_cfg.get('num_workers'),
                 rank=get_rank(),
-                seed=seed)
+                seed=seed,
+                disable_subprocess_warning=disable_subprocess_warning)
         else:
             init_fn = None