[refactor] Add state_dict to loops

CHANGELOG.md

@@ -84,13 +84,14 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 
 - Fault-tolerant training
-    * Add `{,load_}state_dict` to `ResultCollection` ([#7948](https://github.com/PyTorchLightning/pytorch-lightning/pull/7948))
+    * Added `{,load_}state_dict` to `ResultCollection` ([#7948](https://github.com/PyTorchLightning/pytorch-lightning/pull/7948))
+    * Added `{,load_}state_dict` to `Loops` ([#8197](https://github.com/PyTorchLightning/pytorch-lightning/pull/8197))
 
 
-- Add `rank_zero_only` to `LightningModule.log` function ([#7966](https://github.com/PyTorchLightning/pytorch-lightning/pull/7966))
+- Added `rank_zero_only` to `LightningModule.log` function ([#7966](https://github.com/PyTorchLightning/pytorch-lightning/pull/7966))
 
 
-- Add `metric_attribute` to `LightningModule.log` function ([#7966](https://github.com/PyTorchLightning/pytorch-lightning/pull/7966))
+- Added `metric_attribute` to `LightningModule.log` function ([#7966](https://github.com/PyTorchLightning/pytorch-lightning/pull/7966))
 
 
 - Added a warning if `Trainer(log_every_n_steps)` is a value too high for the training dataloader ([#7734](https://github.com/PyTorchLightning/pytorch-lightning/pull/7734))

pytorch_lightning/loops/base.py

@@ -13,11 +13,12 @@
 # limitations under the License.
 
 from abc import ABC, abstractmethod
-from typing import Any, Optional
+from typing import Any, Dict, Optional
 
 from deprecate import void
 
 import pytorch_lightning as pl
+from pytorch_lightning.utilities.exceptions import MisconfigurationException
 
 
 class Loop(ABC):
@@ -59,6 +60,10 @@ def skip(self) -> bool:
     def connect(self, trainer: 'pl.Trainer', *args: Any, **kwargs: Any) -> None:
         """Connects Loop with all the necessary things like connectors and accelerators."""
         # TODO(@justusschock): Make the trainer a weakref/proxy
+        if not isinstance(trainer, pl.Trainer):
+            raise MisconfigurationException(
+                f"Loop {self.__class__.__name__} should be connected to a `Trainer`, found: {trainer}."
+            )
         self.trainer = trainer
 
     def on_skip(self) -> Optional[Any]:
@@ -128,3 +133,10 @@ def on_run_end(self) -> Any:
 
     def teardown(self) -> None:
         """The very last method called inside :meth:`run`. Use to release memory etc."""
+
+    def load_state_dict(self, state_dict: Dict) -> None:
+        """Restore the loop state from the provided state_dict."""
+
+    def state_dict(self) -> Dict:
+        """Return the loop current states."""
+        return {}

pytorch_lightning/loops/epoch/training_epoch_loop.py

@@ -47,8 +47,8 @@ def __init__(self, min_steps: int, max_steps: int):
         self.batches_seen: int = 0
         self.is_last_batch: Optional[bool] = None
 
-        self.batch_loop: Optional[TrainingBatchLoop] = None
-        self.val_loop: Optional[loops.EvaluationLoop] = None
+        self.batch_loop = TrainingBatchLoop()
+        self.val_loop = loops.EvaluationLoop()
 
         self._dataloader_idx: Optional[int] = None
         self._warning_cache: WarningCache = WarningCache()
@@ -80,9 +80,7 @@ def done(self) -> bool:
     def connect(self, trainer: 'pl.Trainer', *args: Any, **kwargs: Any) -> None:
         """Connects the loop with all necessary parts like trainer and accelerators"""
         super().connect(trainer, *args, **kwargs)
-        self.batch_loop = TrainingBatchLoop()
         self.batch_loop.connect(trainer)
-        self.val_loop = loops.EvaluationLoop()
         self.val_loop.connect(trainer)
 
     def reset(self) -> None:
@@ -425,3 +423,10 @@ def _save_loggers_on_train_batch_end(self) -> None:
         should_flush_logs = self.trainer.logger_connector.should_flush_logs
         if should_flush_logs and self.trainer.is_global_zero and self.trainer.logger is not None:
             self.trainer.logger.save()
+
+    def state_dict(self) -> Dict:
+        return {"batch_loop": self.batch_loop.state_dict(), "val_loop": self.val_loop.state_dict()}
+
+    def load_state_dict(self, state_dict: Dict) -> None:
+        self.batch_loop.load_state_dict(state_dict["batch_loop"])
+        self.val_loop.load_state_dict(state_dict["val_loop"])

pytorch_lightning/loops/fit_loop.py

@@ -14,7 +14,7 @@
 
 import logging
 from contextlib import suppress
-from typing import Any, Optional
+from typing import Any, Dict, Optional
 
 import pytorch_lightning as pl
 from pytorch_lightning.loops import Loop
@@ -97,6 +97,12 @@ def min_steps(self) -> int:
         """Returns the minimum numnber of steps to run"""
         return self.epoch_loop.min_steps
 
+    @min_steps.setter
+    def min_steps(self, value: int) -> None:
+        """Sets the minimum number of steps (forwards to epoch_loop)"""
+        # TODO(@awaelchli): This setter is required by debugging connector (fast dev run), should be avoided
+        self.epoch_loop.min_steps = value
+
     @property
     def max_steps(self) -> int:
         """Returns the maximum number of steps to run"""
@@ -274,3 +280,9 @@ def _check_checkpoint_callback(self, should_update: bool, is_last: bool = False)
 
             for cb in callbacks:
                 cb.on_validation_end(self.trainer, model)
+
+    def state_dict(self) -> Dict:
+        return {"epoch_loop": self.epoch_loop.state_dict()}
+
+    def load_state_dict(self, state_dict: Dict) -> None:
+        self.epoch_loop.load_state_dict(state_dict["epoch_loop"])

pytorch_lightning/trainer/connectors/logger_connector/logger_connector.py

@@ -316,5 +316,5 @@ def progress_bar_metrics(self) -> Dict[str, float]:
     def teardown(self):
         self.trainer.fit_loop.epoch_loop._results.cpu()
         self.trainer.fit_loop.epoch_loop.val_loop._results.cpu()
-        self.trainer.validation_loop._results.cpu()
+        self.trainer.validate_loop._results.cpu()
         self.trainer.test_loop._results.cpu()

pytorch_lightning/trainer/progress.py

@@ -239,7 +239,7 @@ class TrainingEpochProgress(EpochProgress):
         current: Tracks the current epoch progress.
         batch: Tracks batch progress.
         optim: Tracks optimization progress.
-        val: Tracks validation_loop progress.
+        val: Tracks val_loop progress.
     """
 
     optim: OptimizationProgress = field(default_factory=OptimizationProgress)

pytorch_lightning/trainer/properties.py

@@ -16,7 +16,7 @@
 from abc import ABC
 from argparse import ArgumentParser, Namespace
 from pathlib import Path
-from typing import cast, List, Optional, Type, TypeVar, Union
+from typing import Any, cast, Dict, List, Optional, Type, TypeVar, Union
 
 import torch
 from torch.optim import Optimizer
@@ -63,7 +63,7 @@ class TrainerProperties(ABC):
     logger_connector: LoggerConnector
     state: TrainerState
     fit_loop: FitLoop
-    validation_loop: EvaluationLoop
+    validate_loop: EvaluationLoop
     test_loop: EvaluationLoop
     """
     Accelerator properties
@@ -493,7 +493,7 @@ def evaluation_loop(self) -> EvaluationLoop:
         if self.state.fn in (TrainerFn.FITTING, TrainerFn.TUNING):
             return self.fit_loop.epoch_loop.val_loop
         elif self.state.fn == TrainerFn.VALIDATING:
-            return self.validation_loop
+            return self.validate_loop
         if self.state.fn == TrainerFn.TESTING:
             return self.test_loop
         raise RuntimeError("The `Trainer.evaluation_loop` property isn't defined. Accessed outside of scope")

pytorch_lightning/trainer/trainer.py

@@ -344,11 +344,11 @@ def __init__(
         self.tuner = Tuner(self)
 
         self.fit_loop = FitLoop(min_epochs, max_epochs, min_steps, max_steps)
-        self.validation_loop = EvaluationLoop()
+        self.validate_loop = EvaluationLoop()
         self.test_loop = EvaluationLoop()
         self.predict_loop = PredictionLoop()
         self.fit_loop.connect(self)
-        self.validation_loop.connect(self)
+        self.validate_loop.connect(self)
         self.test_loop.connect(self)
         self.predict_loop.connect(self)
 

tests/loops/test_loop_state_dict.py

@@ -0,0 +1,47 @@
+# Copyright The PyTorch Lightning team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# 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.
+
+import pytest
+
+from pytorch_lightning.loops import FitLoop
+from pytorch_lightning.trainer.trainer import Trainer
+from pytorch_lightning.utilities.exceptions import MisconfigurationException
+
+
+def test_loops_state_dict_structure():
+    fit_loop = FitLoop()
+    with pytest.raises(MisconfigurationException, match="Loop FitLoop should be connected to a"):
+        fit_loop.connect(object())  # noqa
+
+    fit_loop.connect(Trainer())
+    state_dict = fit_loop.state_dict()
+    new_fit_loop = FitLoop()
+    new_fit_loop.load_state_dict(state_dict)
+    assert fit_loop.state_dict() == new_fit_loop.state_dict()
+
+
+def test_loops_state_dict_structure_with_trainer():
+    trainer = Trainer()
+    state_dict = trainer.loops_state_dict()
+    expected = {
+        "fit_loop": {
+            'epoch_loop': {
+                'batch_loop': {},
+                'val_loop': {},
+            }
+        },
+        "validate_loop": {},
+        "test_loop": {},
+    }
+    assert state_dict == expected