Source code for pytorch_lightning.loops.fit_loop
# 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 logging
import os
from typing import Any, Optional, Type
import pytorch_lightning as pl
from pytorch_lightning.accelerators import CUDAAccelerator
from pytorch_lightning.loops import Loop
from pytorch_lightning.loops.epoch import TrainingEpochLoop
from pytorch_lightning.loops.epoch.training_epoch_loop import _OUTPUTS_TYPE as _EPOCH_OUTPUTS_TYPE
from pytorch_lightning.loops.utilities import _is_max_limit_reached, _set_sampler_epoch
from pytorch_lightning.trainer.connectors.logger_connector.result import _ResultCollection
from pytorch_lightning.trainer.progress import Progress
from pytorch_lightning.trainer.supporters import CombinedLoader, TensorRunningAccum
from pytorch_lightning.utilities.exceptions import MisconfigurationException
from pytorch_lightning.utilities.fetching import (
AbstractDataFetcher,
DataFetcher,
DataLoaderIterDataFetcher,
InterBatchParallelDataFetcher,
)
from pytorch_lightning.utilities.model_helpers import is_overridden
from pytorch_lightning.utilities.rank_zero import rank_zero_debug, rank_zero_info, rank_zero_warn
from pytorch_lightning.utilities.signature_utils import is_param_in_hook_signature
log = logging.getLogger(__name__)
[docs]class FitLoop(Loop[None]):
"""This Loop iterates over the epochs to run the training.
Args:
min_epochs: The minimum number of epochs
max_epochs: The maximum number of epochs, can be set -1 to turn this limit off
"""
def __init__(
self,
min_epochs: Optional[int] = 0,
max_epochs: Optional[int] = None,
) -> None:
super().__init__()
if isinstance(max_epochs, int) and max_epochs < -1:
# Allow max_epochs to be zero, since this will be handled by fit_loop.done
raise MisconfigurationException(
f"`max_epochs` must be a non-negative integer or -1. You passed in {max_epochs}."
)
self.max_epochs = max_epochs
self.min_epochs = min_epochs
self.epoch_loop = TrainingEpochLoop()
self.epoch_progress = Progress()
self._is_fresh_start_epoch: bool = True
self._outputs: _EPOCH_OUTPUTS_TYPE = []
self._data_fetcher: Optional[AbstractDataFetcher] = None
@property
def total_batch_idx(self) -> int:
"""Returns the current batch index (across epochs)"""
return self.epoch_loop.total_batch_idx
@property
def batch_idx(self) -> int:
"""Returns the current batch index (within this epoch)"""
return self.epoch_loop.batch_idx
@property
def split_idx(self) -> int:
"""Returns the index of the current batch split (within the current batch) for bptt."""
return self.epoch_loop.batch_loop.split_idx
@property
def min_steps(self) -> Optional[int]:
# TODO(@justusschock): Why aren't we using the attribute in this class?
"""Returns the minimum number of steps to run."""
return self.epoch_loop.min_steps
@min_steps.setter
def min_steps(self, value: Optional[int]) -> None:
"""Sets the minimum number of steps (forwards to epoch_loop)"""
# TODO: 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."""
return self.epoch_loop.max_steps
@max_steps.setter
def max_steps(self, value: int) -> None:
"""Sets the maximum number of steps (forwards to epoch_loop)"""
# TODO: This setter is required by debugging connector (fast dev run), should be avoided
if value < -1:
raise MisconfigurationException(
f"`max_steps` must be a non-negative integer or -1 (infinite steps). You passed in {value}."
)
self.epoch_loop.max_steps = value
@property
def running_loss(self) -> TensorRunningAccum:
"""Returns the running loss."""
return self.epoch_loop.batch_loop.running_loss
@Loop.restarting.setter
def restarting(self, restarting: bool) -> None:
# if the last epoch completely finished, we are not actually restarting
values = self.epoch_progress.current.ready, self.epoch_progress.current.started
epoch_unfinished = any(v != self.epoch_progress.current.processed for v in values)
restarting = restarting and epoch_unfinished or self._iteration_based_training()
Loop.restarting.fset(self, restarting) # call the parent setter
@property
def prefetch_batches(self) -> int:
is_unsized = self.trainer.num_training_batches == float("inf")
inter_batch_parallelism = os.getenv("PL_INTER_BATCH_PARALLELISM", "0") == "1"
return 1 if is_unsized or inter_batch_parallelism else 0
@property
def _skip_backward(self) -> bool:
"""Determines whether the loop will skip backward during automatic optimization."""
return self.epoch_loop.batch_loop.optimizer_loop._skip_backward
@_skip_backward.setter
def _skip_backward(self, value: bool) -> None:
"""Determines whether the loop will skip backward during automatic optimization."""
self.epoch_loop.batch_loop.optimizer_loop._skip_backward = value
@property
def _results(self) -> _ResultCollection:
if self.trainer.training:
return self.epoch_loop._results
if self.trainer.validating:
return self.epoch_loop.val_loop._results
raise RuntimeError("`FitLoop._results` property isn't defined. Accessed outside of scope")
@property
def _should_stop_early(self) -> bool:
met_min_epochs = self.epoch_progress.current.processed >= self.min_epochs if self.min_epochs else True
met_min_steps = self.epoch_loop.global_step >= self.min_steps if self.min_steps else True
return met_min_epochs and met_min_steps
@property
def done(self) -> bool:
"""Evaluates when to leave the loop."""
if self.trainer.num_training_batches == 0:
rank_zero_info("`Trainer.fit` stopped: No training batches.")
return True
# TODO: Move track steps inside training loop and move part of these condition inside training loop
stop_steps = _is_max_limit_reached(self.epoch_loop.global_step, self.max_steps)
if stop_steps:
rank_zero_info(f"`Trainer.fit` stopped: `max_steps={self.max_steps!r}` reached.")
return True
# `processed` is increased before `on_train_epoch_end`, the hook where checkpoints are typically saved.
# we use it here because the checkpoint data won't have `completed` increased yet
assert isinstance(self.max_epochs, int)
stop_epochs = _is_max_limit_reached(self.epoch_progress.current.processed, self.max_epochs)
if stop_epochs:
# in case they are not equal, override so `trainer.current_epoch` has the expected value
self.epoch_progress.current.completed = self.epoch_progress.current.processed
rank_zero_info(f"`Trainer.fit` stopped: `max_epochs={self.max_epochs!r}` reached.")
return True
if self.trainer.should_stop and self._should_stop_early:
rank_zero_debug("`Trainer.fit` stopped: `trainer.should_stop` was set.")
return True
return False
@property
def skip(self) -> bool:
"""Whether we should skip the training and immediately return from the call to :meth:`run`."""
# since `trainer.num_training_batches` depends on the `train_dataloader` but that won't be called
# until `on_run_start`, we use `limit_train_batches` instead
return self.done or self.trainer.limit_train_batches == 0
[docs] def connect(self, epoch_loop: TrainingEpochLoop) -> None: # type: ignore[override]
"""Connects a training epoch loop to this fit loop."""
self.epoch_loop = epoch_loop
[docs] def reset(self) -> None:
"""Resets the internal state of this loop."""
if self.restarting:
self.epoch_progress.reset_on_restart()
[docs] def on_run_start(self) -> None:
"""Calls the ``on_train_start`` hook."""
# update the current_epoch in-case of checkpoint reload
if not self._iteration_based_training():
self.epoch_progress.current.completed = self.epoch_progress.current.processed
self.trainer.reset_train_dataloader(self.trainer.lightning_module)
# reload the evaluation dataloaders too for proper display in the progress bar
if self.epoch_loop._should_check_val_epoch():
self.epoch_loop.val_loop._reload_evaluation_dataloaders()
data_fetcher_cls = _select_data_fetcher(self.trainer)
self._data_fetcher = data_fetcher_cls(prefetch_batches=self.prefetch_batches)
self._is_fresh_start_epoch = True
self._results.to(device=self.trainer.lightning_module.device)
self.trainer._call_callback_hooks("on_train_start")
self.trainer._call_lightning_module_hook("on_train_start")
self.trainer._call_strategy_hook("on_train_start")
[docs] def on_advance_start(self) -> None:
"""Prepares the dataloader for training and calls the hook ``on_train_epoch_start``"""
model = self.trainer.lightning_module
# reset train dataloader
if not self._is_fresh_start_epoch and self.trainer._data_connector._should_reload_train_dl:
log.detail(f"{self.__class__.__name__}: resetting train dataloader")
self.trainer.reset_train_dataloader(model)
self._is_fresh_start_epoch = False
# reset outputs here instead of in `reset` as they are not accumulated between epochs
self._outputs = []
if self.trainer.train_dataloader is not None:
assert isinstance(self.trainer.train_dataloader, CombinedLoader)
_set_sampler_epoch(self.trainer.train_dataloader, self.epoch_progress.current.processed)
# changing gradient according accumulation_scheduler
self.trainer.accumulation_scheduler.on_train_epoch_start(self.trainer, self.trainer.lightning_module)
# stores accumulated grad fractions per batch
self.epoch_loop.batch_loop.accumulated_loss.reset(window_length=self.trainer.accumulate_grad_batches)
self.epoch_progress.increment_ready()
self.trainer._logger_connector.on_epoch_start()
self.trainer._call_callback_hooks("on_train_epoch_start")
self.trainer._call_lightning_module_hook("on_train_epoch_start")
self.epoch_progress.increment_started()
[docs] def advance(self) -> None:
"""Runs one whole epoch."""
log.detail(f"{self.__class__.__name__}: advancing loop")
assert self.trainer.train_dataloader is not None
dataloader = self.trainer.train_dataloader
def batch_to_device(batch: Any) -> Any:
batch = self.trainer.lightning_module._on_before_batch_transfer(batch, dataloader_idx=0)
batch = self.trainer._call_strategy_hook("batch_to_device", batch, dataloader_idx=0)
return batch
assert self._data_fetcher is not None
self._data_fetcher.setup(dataloader, batch_to_device=batch_to_device)
with self.trainer.profiler.profile("run_training_epoch"):
self._outputs = self.epoch_loop.run(self._data_fetcher)
[docs] def on_advance_end(self) -> None:
# inform logger the batch loop has finished
self.trainer._logger_connector.epoch_end_reached()
# get the model and call model.training_epoch_end
model = self.trainer.lightning_module
if is_overridden("training_epoch_end", model) and self._outputs:
epoch_end_outputs = self.epoch_loop._prepare_outputs_training_epoch_end(
self._outputs,
lightning_module=model,
num_optimizers=len(self.trainer.optimizers),
)
# run lightning module hook training_epoch_end
# refresh the result for custom logging at the epoch level
epoch_end_outputs = self.trainer._call_lightning_module_hook("training_epoch_end", epoch_end_outputs)
if epoch_end_outputs is not None:
raise MisconfigurationException(
"`training_epoch_end` expects a return of None. "
"HINT: remove the return statement in `training_epoch_end`."
)
# free memory
self._outputs = []
self.epoch_progress.increment_processed()
# call train epoch end hooks
self.trainer._call_callback_hooks("on_train_epoch_end")
self.trainer._call_lightning_module_hook("on_train_epoch_end")
self.trainer._logger_connector.on_epoch_end()
if self.epoch_loop._num_ready_batches_reached():
# if we are restarting and the above condition holds, it's because we are reloading an epoch-end checkpoint.
# since metric-based schedulers require access to metrics and those are not currently saved in the
# checkpoint, the plateau schedulers shouldn't be updated
self.epoch_loop.update_lr_schedulers("epoch", update_plateau_schedulers=not self.restarting)
# we manually decrease here because loggers expect that the same step is used when logging epoch-end metrics
# even when the batch loop has finished
self.epoch_loop._batches_that_stepped -= 1
# log epoch metrics
self.trainer._logger_connector.update_train_epoch_metrics()
self.epoch_loop._batches_that_stepped += 1
self.epoch_progress.increment_completed()
# if fault tolerant is enabled and process has been notified, exit.
self.trainer._exit_gracefully_on_signal()
[docs] def on_run_end(self) -> None:
"""Calls the ``on_train_end`` hook."""
log.detail(f"{self.__class__.__name__}: train run ended")
# hook
self.trainer._call_callback_hooks("on_train_end")
self.trainer._call_lightning_module_hook("on_train_end")
self.trainer._call_strategy_hook("on_train_end")
[docs] def teardown(self) -> None:
if self._data_fetcher is not None:
self._data_fetcher.teardown()
self._data_fetcher = None
self.epoch_loop.teardown()
def _should_accumulate(self) -> bool:
"""Whether the gradients should be accumulated."""
return self.epoch_loop._should_accumulate()
def _iteration_based_training(self) -> bool:
return self.trainer.max_steps != -1
def _select_data_fetcher(trainer: "pl.Trainer") -> Type[AbstractDataFetcher]:
training_step_fx = getattr(trainer.lightning_module, "training_step")
if is_param_in_hook_signature(training_step_fx, "dataloader_iter", explicit=True):
rank_zero_warn(
"Found `dataloader_iter` argument in the `training_step`. Note that the support for "
"this signature is experimental and the behavior is subject to change."
)
return DataLoaderIterDataFetcher
elif os.getenv("PL_INTER_BATCH_PARALLELISM", "0") == "1":
if not isinstance(trainer.accelerator, CUDAAccelerator):
raise MisconfigurationException("Inter batch parallelism is available only when using Nvidia GPUs.")
return InterBatchParallelDataFetcher
return DataFetcher