Add is_last_batch to progress tracking

CHANGELOG.md

@@ -24,6 +24,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 - Progress tracking
     * Integrate `TrainingEpochLoop.total_batch_idx` ([#8598](https://github.com/PyTorchLightning/pytorch-lightning/pull/8598))
+    * Add `BatchProgress` and integrate `TrainingEpochLoop.is_last_batch` ([#9657](https://github.com/PyTorchLightning/pytorch-lightning/pull/9657))
     * Avoid optional `Tracker` attributes ([#9320](https://github.com/PyTorchLightning/pytorch-lightning/pull/9320))
     * Reset `current` progress counters when restarting an epoch loop that had already finished ([#9371](https://github.com/PyTorchLightning/pytorch-lightning/pull/9371))
     * Call `reset_on_restart` in the loop's `reset` hook instead of when loading a checkpoint ([#9561](https://github.com/PyTorchLightning/pytorch-lightning/pull/9561))

pytorch_lightning/loops/epoch/training_epoch_loop.py

@@ -20,7 +20,7 @@
 from pytorch_lightning.loops.optimization.closure import OutputResult
 from pytorch_lightning.loops.utilities import _prepare_dataloader_iter
 from pytorch_lightning.trainer.connectors.logger_connector.result import ResultCollection
-from pytorch_lightning.trainer.progress import Progress, SchedulerProgress
+from pytorch_lightning.trainer.progress import BatchProgress, SchedulerProgress
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from pytorch_lightning.utilities.model_helpers import is_overridden
 from pytorch_lightning.utilities.types import STEP_OUTPUT
@@ -43,9 +43,7 @@ def __init__(self, min_steps: int, max_steps: int):
         self.max_steps: int = max_steps
 
         self.global_step: int = 0
-        # manually tracking which is the last batch is necessary for iterable dataset support
-        self.is_last_batch: Optional[bool] = None
-        self.batch_progress = Progress()
+        self.batch_progress = BatchProgress()
         self.scheduler_progress = SchedulerProgress()
 
         self.batch_loop: Optional[TrainingBatchLoop] = None
@@ -94,18 +92,16 @@ def reset(self) -> None:
         assert self.batch_loop is not None
         assert self.batch_loop.optimizer_loop is not None
         if self.restarting:
-            self.batch_progress.current.reset_on_restart()
+            self.batch_progress.reset_on_restart()
             self.scheduler_progress.current.reset_on_restart()
             self.batch_loop.optimizer_loop.optim_progress.reset_on_restart()
 
-        self.is_last_batch = False
-
         # track epoch output
         self._epoch_output = [[] for _ in range(self.batch_loop.num_active_optimizers(self.total_batch_idx))]
 
         if not self.restarting or self._num_training_batches_reached():
-            self.batch_progress.current.reset()
-            self.scheduler_progress.current.reset()
+            self.batch_progress.reset_on_epoch()
+            self.scheduler_progress.reset_on_epoch()
             self.batch_loop.optimizer_loop.optim_progress.reset_on_epoch()
 
     def on_run_start(self, dataloader_iter: Iterator, **kwargs: Any) -> None:
@@ -127,6 +123,7 @@ def advance(self, *args: Any, **kwargs: Any) -> None:
             StopIteration: When the epoch is canceled by the user returning -1
         """
         batch_idx, (batch, is_last) = next(self.dataloader_iter)
+        self.batch_progress.is_last_batch = is_last
 
         if not self.trainer.data_connector.train_data_fetcher.store_on_device:
             with self.trainer.profiler.profile("training_batch_to_device"):
@@ -139,8 +136,6 @@ def advance(self, *args: Any, **kwargs: Any) -> None:
 
         self.batch_progress.increment_processed()
 
-        self.is_last_batch = is_last
-
         # when returning -1 from train_step, we end epoch early
         if batch_output.signal == -1:
             raise StopIteration
@@ -178,7 +173,7 @@ def on_advance_end(self):
         # -----------------------------------------
         # VALIDATE IF NEEDED + CHECKPOINT CALLBACK
         # -----------------------------------------
-        should_check_val = self._should_check_val_fx(self.batch_idx, self.is_last_batch)
+        should_check_val = self._should_check_val_fx(self.batch_idx, self.batch_progress.is_last_batch)
         if should_check_val:
             self.trainer.validating = True
             self._run_validation()
@@ -259,7 +254,9 @@ def _accumulated_batches_reached(self) -> bool:
 
     def _num_training_batches_reached(self) -> bool:
         """Checks if we are in the last batch or if there are more batches to follow."""
-        return self.batch_progress.current.ready == self.trainer.num_training_batches or self.is_last_batch
+        return (
+            self.batch_progress.current.ready == self.trainer.num_training_batches or self.batch_progress.is_last_batch
+        )
 
     def _should_accumulate(self) -> bool:
         """Checks if the optimizer step should be performed or gradients should be accumulated for the current

pytorch_lightning/trainer/progress.py

@@ -148,6 +148,9 @@ def from_defaults(cls, tracker_cls: Type[ReadyCompletedTracker], **kwargs: int)
         """Utility function to easily create an instance from keyword arguments to both ``Tracker``s."""
         return cls(total=tracker_cls(**kwargs), current=tracker_cls(**kwargs))
 
+    def reset_on_epoch(self) -> None:
+        self.current.reset()
+
     def reset_on_restart(self) -> None:
         self.current.reset_on_restart()
 
@@ -158,8 +161,9 @@ def load_state_dict(self, state_dict: dict) -> None:
 
 @dataclass
 class DataLoaderProgress(Progress):
-    """Tracks the dataloader progress These counters are local to a trainer rank. By default, they are not globally
-    synced across all ranks.
+    """Tracks dataloader progress.
+
+    These counters are local to a trainer rank. By default, they are not globally synced across all ranks.
 
     Args:
         total: Tracks the total dataloader progress.
@@ -170,10 +174,30 @@ class DataLoaderProgress(Progress):
     current: ReadyCompletedTracker = field(default_factory=ReadyCompletedTracker)
 
 
+@dataclass
+class BatchProgress(Progress):
+    """Tracks batch progress.
+
+    These counters are local to a trainer rank. By default, they are not globally synced across all ranks.
+
+    Args:
+        total: Tracks the total dataloader progress.
+        current: Tracks the current dataloader progress.
+        is_last_batch: Whether the batch is the last one. This is useful for iterable datasets.
+    """
+
+    is_last_batch: bool = False
+
+    def reset_on_epoch(self) -> None:
+        super().reset_on_epoch()
+        self.is_last_batch = False
+
+
 @dataclass
 class SchedulerProgress(Progress):
-    """Tracks the scheduler progress. These counters are local to a trainer rank. By default, they are not globally
-    synced across all ranks.
+    """Tracks scheduler progress.
+
+    These counters are local to a trainer rank. By default, they are not globally synced across all ranks.
 
     Args:
         total: Tracks the total scheduler progress.
@@ -197,8 +221,8 @@ class OptimizerProgress(BaseProgress):
     zero_grad: Progress = field(default_factory=lambda: Progress.from_defaults(StartedTracker))
 
     def reset_on_epoch(self) -> None:
-        self.step.current.reset()
-        self.zero_grad.current.reset()
+        self.step.reset_on_epoch()
+        self.zero_grad.reset_on_epoch()
 
     def reset_on_restart(self) -> None:
         self.step.reset_on_restart()

pytorch_lightning/trainer/trainer.py

@@ -1892,7 +1892,7 @@ def min_steps(self) -> Optional[int]:
 
     @property
     def is_last_batch(self) -> bool:
-        return self.fit_loop.epoch_loop.is_last_batch
+        return self.fit_loop.epoch_loop.batch_progress.is_last_batch
 
     @property
     def fit_loop(self) -> FitLoop:

tests/loops/test_loop_state_dict.py

@@ -51,6 +51,7 @@ def test_loops_state_dict_structure():
             "epoch_loop.batch_progress": {
                 "total": {"ready": 0, "started": 0, "processed": 0, "completed": 0},
                 "current": {"ready": 0, "started": 0, "processed": 0, "completed": 0},
+                "is_last_batch": False,
             },
             "epoch_loop.scheduler_progress": {
                 "total": {"ready": 0, "completed": 0},

tests/loops/test_loops.py

@@ -20,7 +20,9 @@
 
 import pytest
 import torch
+from torch.utils.data import DataLoader
 
+from pl_examples.bug_report_model import RandomDataset
 from pytorch_lightning import Trainer
 from pytorch_lightning.callbacks import ModelCheckpoint
 from pytorch_lightning.loops import Loop, TrainingBatchLoop
@@ -443,6 +445,7 @@ def configure_optimizers_multiple(self):
                 "processed": stop_batch,
                 "completed": stop_batch,
             },
+            "is_last_batch": False,
         },
         "epoch_loop.scheduler_progress": {
             "total": {"ready": nbe_sch_steps + be_sch_steps, "completed": nbe_sch_steps + be_sch_steps},
@@ -548,13 +551,16 @@ def configure_optimizers_multiple(self):
 
             return optimizers, lr_schedulers
 
+        def train_dataloader(self):
+            # override to test the `is_last_batch` value
+            return DataLoader(RandomDataset(32, n_batches))
+
     model = TestModel()
     model.training_epoch_end = None
 
     trainer = Trainer(
         default_root_dir=tmpdir,
         max_epochs=n_epochs,
-        limit_train_batches=n_batches,
         limit_val_batches=0,
         accumulate_grad_batches=accumulate_grad_batches,
         progress_bar_refresh_rate=0,
@@ -563,6 +569,8 @@ def configure_optimizers_multiple(self):
     )
     trainer.fit(model)
 
+    assert trainer.num_training_batches == n_batches
+
     ckpt_path = trainer.checkpoint_callback.best_model_path
     assert os.path.exists(ckpt_path)
     checkpoint = torch.load(ckpt_path)
@@ -607,6 +615,7 @@ def configure_optimizers_multiple(self):
                 "processed": n_batches,
                 "completed": n_batches,
             },
+            "is_last_batch": True,
         },
         "epoch_loop.scheduler_progress": {
             "total": {"ready": n_sch_steps_total, "completed": n_sch_steps_total},