[1 / 3] improvements to saving and loading callback state

CHANGELOG.md

@@ -9,10 +9,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Added
 
--
-
-
--
+- Added `state_id` property to the `Callback` base class ([#6886](https://github.com/PyTorchLightning/pytorch-lightning/pull/6886))
 
 
 -
@@ -32,7 +29,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 
 
--
+- Saved checkpoints will no longer use the type of a `Callback` as the key to avoid issues with unpickling ([#6886](https://github.com/PyTorchLightning/pytorch-lightning/pull/6886))
 
 
 -

pytorch_lightning/callbacks/base.py

@@ -17,7 +17,7 @@
 """
 
 import abc
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, List, Optional, Type
 
 import torch
 from torch.optim import Optimizer
@@ -33,6 +33,21 @@ class Callback(abc.ABC):
     Subclass this class and override any of the relevant hooks
     """
 
+    @property
+    def state_id(self) -> str:
+        """
+        Identifier for the state of the callback. Used to store and retrieve a callback's state from the
+        checkpoint dictionary by ``checkpoint["callbacks"][state_id]``. Implementations of a callback need to
+        provide a unique state id if 1) the callback has state and 2) it is desired to maintain the state of
+        multiple instances of that callback.
+        """
+        return self.__class__.__qualname__
+
+    @property
+    def _legacy_state_id(self) -> Type["Callback"]:
+        """State identifier for checkpoints saved prior to version 1.5.0."""
+        return type(self)
+
     def on_configure_sharded_model(self, trainer: "pl.Trainer", pl_module: "pl.LightningModule") -> None:
         """Called before configure sharded model"""
 

pytorch_lightning/trainer/callback_hook.py

@@ -15,7 +15,7 @@
 from abc import ABC
 from copy import deepcopy
 from inspect import signature
-from typing import Any, Callable, Dict, List, Optional, Type
+from typing import Any, Callable, Dict, List, Optional, Type, Union
 
 import torch
 
@@ -263,7 +263,7 @@ def __is_old_signature_on_load_checkpoint(fn: Callable) -> bool:
         parameters = list(signature(fn).parameters)
         return len(parameters) == 1 and parameters[0] != "args"
 
-    def on_save_checkpoint(self, checkpoint: Dict[str, Any]) -> Dict[Type, dict]:
+    def on_save_checkpoint(self, checkpoint: Dict[str, Any]) -> Dict[str, dict]:
         """Called when saving a model checkpoint."""
         callback_states = {}
         for callback in self.callbacks:
@@ -277,16 +277,15 @@ def on_save_checkpoint(self, checkpoint: Dict[str, Any]) -> Dict[Type, dict]:
             else:
                 state = callback.on_save_checkpoint(self, self.lightning_module, checkpoint)
             if state:
-                callback_states[type(callback)] = state
+                callback_states[callback.state_id] = state
         return callback_states
 
-    def on_load_checkpoint(self, checkpoint):
+    def on_load_checkpoint(self, checkpoint: Dict[str, Any]) -> None:
         """Called when loading a model checkpoint."""
-
         # Todo: the `callback_states` are dropped with TPUSpawn as they
         # can't be saved using `xm.save`
         # https://github.com/pytorch/xla/issues/2773
-        callback_states = checkpoint.get("callbacks")
+        callback_states: Dict[Union[Type, str], Dict] = checkpoint.get("callbacks")
 
         if callback_states is None:
             return
@@ -303,7 +302,7 @@ def on_load_checkpoint(self, checkpoint):
             )
 
         for callback in self.callbacks:
-            state = callback_states.get(type(callback))
+            state = callback_states.get(callback.state_id, callback_states.get(callback._legacy_state_id))
             if state:
                 state = deepcopy(state)
                 if self.__is_old_signature_on_load_checkpoint(callback.on_load_checkpoint):

pytorch_lightning/trainer/connectors/checkpoint_connector.py

@@ -308,7 +308,7 @@ def dump_checkpoint(self, weights_only: bool = False) -> dict:
             structured dictionary: {
                 'epoch':                     training epoch
                 'global_step':               training global step
-                'pytorch-lightning_version': PyTorch Lightning's version
+                'pytorch-lightning_version': The version of PyTorch Lightning that produced this checkpoint
                 'callbacks':                 "callback specific state"[] # if not weights_only
                 'optimizer_states':          "PT optim's state_dict"[]   # if not weights_only
                 'lr_schedulers':             "PT sched's state_dict"[]   # if not weights_only

tests/callbacks/test_callbacks.py

@@ -11,9 +11,10 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+from pathlib import Path
 from unittest.mock import call, Mock
 
-from pytorch_lightning import Trainer
+from pytorch_lightning import Callback, Trainer
 from tests.helpers import BoringModel
 
 
@@ -101,3 +102,33 @@ def configure_callbacks(self):
         trainer_fn(model)
         callbacks_after = trainer.callbacks.copy()
         assert callbacks_after == callbacks_after_fit
+
+
+class OldStatefulCallback(Callback):
+    def __init__(self, state):
+        self.state = state
+
+    @property
+    def state_id(self):
+        return type(self)
+
+    def on_save_checkpoint(self, *args):
+        return {"state": self.state}
+
+    def on_load_checkpoint(self, trainer, pl_module, callback_state):
+        self.state = callback_state["state"]
+
+
+def test_resume_callback_state_saved_by_type(tmpdir):
+    """Test that a legacy checkpoint that didn't use a state identifier before can still be loaded."""
+    model = BoringModel()
+    callback = OldStatefulCallback(state=111)
+    trainer = Trainer(default_root_dir=tmpdir, max_steps=1, callbacks=[callback])
+    trainer.fit(model)
+    ckpt_path = Path(trainer.checkpoint_callback.best_model_path)
+    assert ckpt_path.exists()
+
+    callback = OldStatefulCallback(state=222)
+    trainer = Trainer(default_root_dir=tmpdir, max_steps=2, callbacks=[callback], resume_from_checkpoint=ckpt_path)
+    trainer.fit(model)
+    assert callback.state == 111

tests/callbacks/test_early_stopping.py

@@ -76,7 +76,8 @@ def test_resume_early_stopping_from_checkpoint(tmpdir):
     checkpoint = torch.load(checkpoint_filepath)
     # the checkpoint saves "epoch + 1"
     early_stop_callback_state = early_stop_callback.saved_states[checkpoint["epoch"] - 1]
-    assert checkpoint["callbacks"][type(early_stop_callback)] == early_stop_callback_state
+    assert 4 == len(early_stop_callback.saved_states)
+    assert checkpoint["callbacks"]["EarlyStoppingTestRestore"] == early_stop_callback_state
 
     # ensure state is reloaded properly (assertion in the callback)
     early_stop_callback = EarlyStoppingTestRestore(early_stop_callback_state, monitor="train_loss")

tests/checkpointing/test_model_checkpoint.py

@@ -148,7 +148,7 @@ def on_validation_epoch_end(self):
         assert chk["epoch"] == epoch + 1
         assert chk["global_step"] == limit_train_batches * (epoch + 1)
 
-        mc_specific_data = chk["callbacks"][type(checkpoint)]
+        mc_specific_data = chk["callbacks"]["ModelCheckpoint"]
         assert mc_specific_data["dirpath"] == checkpoint.dirpath
         assert mc_specific_data["monitor"] == monitor
         assert mc_specific_data["current_score"] == score
@@ -259,7 +259,7 @@ def _make_assertions(epoch, ix, version=""):
         expected_global_step = per_val_train_batches * (global_ix + 1) + (leftover_train_batches * epoch_num)
         assert chk["global_step"] == expected_global_step
 
-        mc_specific_data = chk["callbacks"][type(checkpoint)]
+        mc_specific_data = chk["callbacks"]["ModelCheckpoint"]
         assert mc_specific_data["dirpath"] == checkpoint.dirpath
         assert mc_specific_data["monitor"] == monitor
         assert mc_specific_data["current_score"] == score
@@ -857,9 +857,7 @@ def test_model_checkpoint_save_last_checkpoint_contents(tmpdir):
 
     assert ckpt_last_epoch["epoch"] == ckpt_last["epoch"]
     assert ckpt_last_epoch["global_step"] == ckpt_last["global_step"]
-
-    ch_type = type(model_checkpoint)
-    assert ckpt_last["callbacks"][ch_type] == ckpt_last_epoch["callbacks"][ch_type]
+    assert ckpt_last["callbacks"]["ModelCheckpoint"] == ckpt_last_epoch["callbacks"]["ModelCheckpoint"]
 
     # it is easier to load the model objects than to iterate over the raw dict of tensors
     model_last_epoch = LogInTwoMethods.load_from_checkpoint(path_last_epoch)
@@ -1097,7 +1095,7 @@ def training_step(self, *args):
     trainer.fit(TestModel())
     assert model_checkpoint.current_score == 0.3
     ckpts = [torch.load(str(ckpt)) for ckpt in tmpdir.listdir()]
-    ckpts = [ckpt["callbacks"][type(model_checkpoint)] for ckpt in ckpts]
+    ckpts = [ckpt["callbacks"]["ModelCheckpoint"] for ckpt in ckpts]
     assert sorted(ckpt["current_score"] for ckpt in ckpts) == [0.1, 0.2, 0.3]
 
 

tests/trainer/connectors/test_callback_connector.py

@@ -76,11 +76,11 @@ def test_all_callback_states_saved_before_checkpoint_callback(tmpdir):
     trainer.fit(model)
 
     ckpt = torch.load(str(tmpdir / "all_states.ckpt"))
-    state0 = ckpt["callbacks"][type(callback0)]
-    state1 = ckpt["callbacks"][type(callback1)]
+    state0 = ckpt["callbacks"]["StatefulCallback0"]
+    state1 = ckpt["callbacks"]["StatefulCallback1"]
     assert "content0" in state0 and state0["content0"] == 0
     assert "content1" in state1 and state1["content1"] == 1
-    assert type(checkpoint_callback) in ckpt["callbacks"]
+    assert "ModelCheckpoint" in ckpt["callbacks"]
 
 
 def test_attach_model_callbacks():

tests/trainer/logging_/test_logger_connector.py

@@ -26,10 +26,11 @@
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from tests.helpers.boring_model import BoringModel, RandomDataset
 from tests.helpers.runif import RunIf
+from tests.models.test_hooks import get_members
 
 
 def test_fx_validator(tmpdir):
-    funcs_name = sorted(f for f in dir(Callback) if not f.startswith("_"))
+    funcs_name = sorted(get_members(Callback))
 
     callbacks_func = [
         "on_before_backward",