[Fix] Support compare numpy array dataset meta (#511)

* [Fix] Support compare numpy array dataset meta

* Add comment

mmengine/runner/runner.py

@@ -3,6 +3,7 @@
 import logging
 import os
 import os.path as osp
+import pickle
 import platform
 import time
 import warnings
@@ -1919,7 +1920,11 @@ def resume(self,
 
         resumed_dataset_meta = checkpoint['meta'].get('dataset_meta', None)
         dataset_meta = getattr(self.train_dataloader.dataset, 'metainfo', None)
-        if resumed_dataset_meta != dataset_meta:
+
+        # `resumed_dataset_meta` and `dataset_meta` could be object like
+        # np.ndarray, which cannot be directly judged as equal or not,
+        # therefore we just compared their dumped results.
+        if pickle.dumps(resumed_dataset_meta) != pickle.dumps(dataset_meta):
             warnings.warn(
                 'The dataset metainfo from the resumed checkpoint is '
                 'different from the current training dataset, please '