[Enhance] prevent deadlock in

mmcv/runner/iter_based_runner.py

@@ -34,6 +34,7 @@ class IterLoader:
             self._epoch += 1
             if hasattr(self._dataloader.sampler, 'set_epoch'):
                 self._dataloader.sampler.set_epoch(self._epoch)
+            time.sleep(2)  # Prevent possible deadlock during epoch transition
             self.iter_loader = iter(self._dataloader)
             data = next(self.iter_loader)