Change dict update order (#1108)

* Change dict update order

* Change dict() with {}

* Added comments with PR link

* Fixed comments according to Lint Job

mmcv/runner/epoch_based_runner.py

@@ -151,14 +151,17 @@ def save_checkpoint(self,
                 Defaults to True.
         """
         if meta is None:
-            meta = dict(epoch=self.epoch + 1, iter=self.iter)
-        elif isinstance(meta, dict):
-            meta.update(epoch=self.epoch + 1, iter=self.iter)
-        else:
+            meta = {}
+        elif not isinstance(meta, dict):
             raise TypeError(
                 f'meta should be a dict or None, but got {type(meta)}')
         if self.meta is not None:
             meta.update(self.meta)
+            # Note: meta.update(self.meta) should be done before
+            # meta.update(epoch=self.epoch + 1, iter=self.iter) otherwise
+            # there will be problems with resumed checkpoints.
+            # More details in https://github.com/open-mmlab/mmcv/pull/1108
+        meta.update(epoch=self.epoch + 1, iter=self.iter)
 
         filename = filename_tmpl.format(self.epoch + 1)
         filepath = osp.join(out_dir, filename)

mmcv/runner/iter_based_runner.py

@@ -195,14 +195,17 @@ def save_checkpoint(self,
                 latest checkpoint file. Defaults to True.
         """
         if meta is None:
-            meta = dict(iter=self.iter + 1, epoch=self.epoch + 1)
-        elif isinstance(meta, dict):
-            meta.update(iter=self.iter + 1, epoch=self.epoch + 1)
-        else:
+            meta = {}
+        elif not isinstance(meta, dict):
             raise TypeError(
                 f'meta should be a dict or None, but got {type(meta)}')
         if self.meta is not None:
             meta.update(self.meta)
+            # Note: meta.update(self.meta) should be done before
+            # meta.update(epoch=self.epoch + 1, iter=self.iter) otherwise
+            # there will be problems with resumed checkpoints.
+            # More details in https://github.com/open-mmlab/mmcv/pull/1108
+        meta.update(epoch=self.epoch + 1, iter=self.iter)
 
         filename = filename_tmpl.format(self.iter + 1)
         filepath = osp.join(out_dir, filename)