[Fix] Fix compatibility of persistent_workers. (#379)

mmengine/runner/runner.py

@@ -1382,6 +1382,13 @@ class Runner:
         else:
             init_fn = None
 
+        # `persistent_workers` requires pytorch version >= 1.7
+        if ('persistent_workers' in dataloader_cfg
+                and digit_version(TORCH_VERSION) < digit_version('1.7.0')):
+            warnings.warn('`persistent_workers` is only available when '
+                          'pytorch version >= 1.7')
+            dataloader_cfg.pop('persistent_workers')
+
         # The default behavior of `collat_fn` in dataloader is to
         # merge a list of samples to form a mini-batch of Tensor(s).
         # However, to make this more flexible, collate_fn in MMengine does