Source code for pytorch_lightning.core.optimizer
# Copyright The Lightning AI 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.
from contextlib import contextmanager
from dataclasses import fields
from typing import Any, Callable, Dict, Generator, List, Optional, Tuple, Union
from weakref import proxy
import torch
from torch import optim
from torch.optim import Optimizer
import pytorch_lightning as pl
from lightning_fabric.utilities.types import _Stateful, Optimizable, ReduceLROnPlateau
from pytorch_lightning.utilities.exceptions import MisconfigurationException
from pytorch_lightning.utilities.model_helpers import is_overridden
from pytorch_lightning.utilities.rank_zero import rank_zero_warn
from pytorch_lightning.utilities.types import LRSchedulerConfig, LRSchedulerTypeTuple
def do_nothing_closure() -> None:
return
[docs]class LightningOptimizer:
"""This class is used to wrap the user optimizers and handle properly the backward and optimizer_step logic
across accelerators, AMP, accumulate_grad_batches."""
def __init__(self, optimizer: Optimizer):
# copy most of the `Optimizer` methods into this instance. `__del__` is skipped in case the optimizer has
# implemented custom logic which we would not want to call on destruction of the `LightningOptimizer`
self.__dict__ = {k: v for k, v in optimizer.__dict__.items() if k not in ("step", "__del__")}
# For Horovod
if hasattr(optimizer, "skip_synchronize"):
self.__class__ = type(
"Lightning" + optimizer.__class__.__name__, (self.__class__, optimizer.__class__.__bases__[0]), {}
)
self.skip_synchronize = optimizer.skip_synchronize
self.synchronize = optimizer.synchronize
else:
self.__class__ = type("Lightning" + optimizer.__class__.__name__, (self.__class__, optimizer.__class__), {})
self._optimizer = optimizer
self._strategy: Optional[pl.strategies.Strategy] = None
self._optimizer_idx = 0
# to inject logic around the optimizer step, particularly useful with manual optimization
self._on_before_step = do_nothing_closure
self._on_after_step = do_nothing_closure
@property
def optimizer(self) -> Optimizer:
return self._optimizer
@classmethod
def _to_lightning_optimizer(
cls, optimizer: Union[Optimizer, "LightningOptimizer"], strategy: "pl.strategies.Strategy", opt_idx: int
) -> "LightningOptimizer":
if isinstance(optimizer, LightningOptimizer):
# the user could return a `LightningOptimizer` from `configure_optimizers`, see test:
# tests/core/test_lightning_optimizer.py::test_lightning_optimizer[False]
lightning_optimizer = optimizer
else:
lightning_optimizer = cls(optimizer)
lightning_optimizer._strategy = proxy(strategy)
lightning_optimizer._optimizer_idx = opt_idx
return lightning_optimizer
[docs] @contextmanager
def toggle_model(self, sync_grad: bool = True) -> Generator[None, None, None]:
"""This function is just a helper for advanced users.
Considering the current optimizer as A and all other optimizers as B.
Toggling means all parameters from B exclusive to A will have ``requires_grad`` set to False.
When performing gradient accumulation, there is no need to perform grad synchronization
during the accumulation phase.
Setting `sync_grad` to False will block this synchronization and improve performance.
"""
# local import here to avoid circular import
from pytorch_lightning.loops.utilities import _block_parallel_sync_behavior
assert self._strategy is not None
lightning_module = self._strategy.lightning_module
assert lightning_module is not None
with _block_parallel_sync_behavior(self._strategy, block=(not sync_grad)):
lightning_module.toggle_optimizer(self, self._optimizer_idx)
yield
lightning_module.untoggle_optimizer(self._optimizer_idx)
[docs] def step(self, closure: Optional[Callable[[], Any]] = None, **kwargs: Any) -> Any:
"""Performs a single optimization step (parameter update).
Args:
closure: An optional optimizer closure.
kwargs: Any additional arguments to the ``optimizer.step()`` call.
Returns:
The output from the step call, which is generally the output of the closure execution.
Example::
# Scenario for a GAN using manual optimization
def training_step(...):
opt_gen, opt_dis = self.optimizers()
...
# compute generator loss
loss_gen = self.compute_generator_loss(...)
# zero_grad needs to be called before backward
opt_gen.zero_grad()
self.manual_backward(loss_gen)
opt_gen.step()
# compute discriminator loss
loss_dis = self.compute_discriminator_loss(...)
# zero_grad needs to be called before backward
opt_dis.zero_grad()
self.manual_backward(loss_dis)
opt_dis.step()
# A more advanced example
def training_step(self, batch, batch_idx, ...):
opt_gen, opt_dis = self.optimizers()
...
accumulated_grad_batches = batch_idx % 2 == 0
# compute generator loss
def closure_gen():
loss_gen = self.compute_generator_loss(...)
self.manual_backward(loss_gen)
if accumulated_grad_batches:
opt_gen.zero_grad()
with opt_gen.toggle_model(sync_grad=accumulated_grad_batches):
opt_gen.step(closure=closure_gen)
def closure_dis():
loss_dis = self.compute_discriminator_loss(...)
self.manual_backward(loss_dis)
if accumulated_grad_batches:
opt_dis.zero_grad()
with opt_dis.toggle_model(sync_grad=accumulated_grad_batches):
opt_dis.step(closure=closure_dis)
"""
self._on_before_step()
if closure is None:
closure = do_nothing_closure
elif not callable(closure):
raise MisconfigurationException("When `optimizer.step(closure)` is called, the closure should be callable")
assert self._strategy is not None
step_output = self._strategy.optimizer_step(self._optimizer, self._optimizer_idx, closure, **kwargs)
self._on_after_step()
return step_output
def _init_optimizers_and_lr_schedulers(
model: "pl.LightningModule",
) -> Tuple[List[Optimizer], List[LRSchedulerConfig], List[int]]:
"""Calls `LightningModule.configure_optimizers` and parses and validates the output."""
optim_conf = model.trainer._call_lightning_module_hook("configure_optimizers", pl_module=model)
if optim_conf is None:
rank_zero_warn(
"`LightningModule.configure_optimizers` returned `None`, this fit will run with no optimizer",
)
optim_conf = _MockOptimizer()
optimizers, lr_schedulers, optimizer_frequencies, monitor = _configure_optimizers(optim_conf)
lr_scheduler_configs = (
_configure_schedulers_automatic_opt(lr_schedulers, monitor)
if model.automatic_optimization
else _configure_schedulers_manual_opt(lr_schedulers)
)
_set_scheduler_opt_idx(optimizers, lr_scheduler_configs)
_validate_scheduler_api(lr_scheduler_configs, model)
return optimizers, lr_scheduler_configs, optimizer_frequencies
def _configure_optimizers(
optim_conf: Union[Dict[str, Any], List, Optimizer, Tuple]
) -> Tuple[List, List, List, Optional[str]]:
optimizers, lr_schedulers, optimizer_frequencies = [], [], []
monitor = None
# single output, single optimizer
if isinstance(optim_conf, Optimizable):
optimizers = [optim_conf]
# two lists, optimizer + lr schedulers
elif (
isinstance(optim_conf, (list, tuple))
and len(optim_conf) == 2
and isinstance(optim_conf[0], list)
and all(isinstance(opt, Optimizable) for opt in optim_conf[0])
):
opt, sch = optim_conf
optimizers = opt
lr_schedulers = sch if isinstance(sch, list) else [sch]
# single dictionary
elif isinstance(optim_conf, dict):
_validate_optim_conf(optim_conf)
optimizers = [optim_conf["optimizer"]]
monitor = optim_conf.get("monitor", None)
lr_schedulers = [optim_conf["lr_scheduler"]] if "lr_scheduler" in optim_conf else []
# multiple dictionaries
elif isinstance(optim_conf, (list, tuple)) and all(isinstance(d, dict) for d in optim_conf):
for opt_dict in optim_conf:
_validate_optim_conf(opt_dict)
optimizers = [opt_dict["optimizer"] for opt_dict in optim_conf]
scheduler_dict = (
lambda scheduler, opt_idx: dict(scheduler, opt_idx=opt_idx)
if isinstance(scheduler, dict)
else {"scheduler": scheduler, "opt_idx": opt_idx}
)
lr_schedulers = [
scheduler_dict(opt_dict["lr_scheduler"], opt_idx)
for opt_idx, opt_dict in enumerate(optim_conf)
if "lr_scheduler" in opt_dict
]
optimizer_frequencies = [
opt_dict["frequency"] for opt_dict in optim_conf if opt_dict.get("frequency", None) is not None
]
# assert that if frequencies are present, they are given for all optimizers
if optimizer_frequencies and len(optimizer_frequencies) != len(optimizers):
raise ValueError("A frequency must be given to each optimizer.")
# single list or tuple, multiple optimizer
elif isinstance(optim_conf, (list, tuple)) and all(isinstance(opt, Optimizable) for opt in optim_conf):
optimizers = list(optim_conf)
# unknown configuration
else:
raise MisconfigurationException(
"Unknown configuration for model optimizers."
" Output from `model.configure_optimizers()` should be one of:\n"
" * `Optimizer`\n"
" * [`Optimizer`]\n"
" * ([`Optimizer`], [`LRScheduler`])\n"
' * {"optimizer": `Optimizer`, (optional) "lr_scheduler": `LRScheduler`}\n'
' * A list of the previously described dict format, with an optional "frequency" key (int)'
)
return optimizers, lr_schedulers, optimizer_frequencies, monitor
def _configure_schedulers_automatic_opt(schedulers: list, monitor: Optional[str]) -> List[LRSchedulerConfig]:
"""Convert each scheduler into `LRSchedulerConfig` with relevant information, when using automatic
optimization."""
lr_scheduler_configs = []
for scheduler in schedulers:
if isinstance(scheduler, dict):
# check provided keys
supported_keys = {field.name for field in fields(LRSchedulerConfig)}
extra_keys = scheduler.keys() - supported_keys
if extra_keys:
rank_zero_warn(
f"Found unsupported keys in the lr scheduler dict: {extra_keys}."
" HINT: remove them from the output of `configure_optimizers`.",
category=RuntimeWarning,
)
scheduler = {k: v for k, v in scheduler.items() if k in supported_keys}
if "scheduler" not in scheduler:
raise MisconfigurationException(
'The lr scheduler dict must have the key "scheduler" with its item being an lr scheduler'
)
if "interval" in scheduler and scheduler["interval"] not in ("step", "epoch"):
raise MisconfigurationException(
'The "interval" key in lr scheduler dict must be "step" or "epoch"'
f' but is "{scheduler["interval"]}"'
)
scheduler["reduce_on_plateau"] = scheduler.get(
"reduce_on_plateau", isinstance(scheduler["scheduler"], optim.lr_scheduler.ReduceLROnPlateau)
)
if scheduler["reduce_on_plateau"] and scheduler.get("monitor", None) is None:
raise MisconfigurationException(
"The lr scheduler dict must include a monitor when a `ReduceLROnPlateau` scheduler is used."
' For example: {"optimizer": optimizer, "lr_scheduler":'
' {"scheduler": scheduler, "monitor": "your_loss"}}'
)
is_one_cycle = isinstance(scheduler["scheduler"], optim.lr_scheduler.OneCycleLR)
if is_one_cycle and scheduler.get("interval", "epoch") == "epoch":
rank_zero_warn(
"A `OneCycleLR` scheduler is using 'interval': 'epoch'."
" Are you sure you didn't mean 'interval': 'step'?",
category=RuntimeWarning,
)
config = LRSchedulerConfig(**scheduler)
elif isinstance(scheduler, ReduceLROnPlateau):
if monitor is None:
raise MisconfigurationException(
"`configure_optimizers` must include a monitor when a `ReduceLROnPlateau`"
" scheduler is used. For example:"
' {"optimizer": optimizer, "lr_scheduler": scheduler, "monitor": "metric_to_track"}'
)
config = LRSchedulerConfig(scheduler, reduce_on_plateau=True, monitor=monitor)
else:
config = LRSchedulerConfig(scheduler)
lr_scheduler_configs.append(config)
return lr_scheduler_configs
def _configure_schedulers_manual_opt(schedulers: list) -> List[LRSchedulerConfig]:
"""Convert each scheduler into `LRSchedulerConfig` structure with relevant information, when using manual
optimization."""
lr_scheduler_configs = []
for scheduler in schedulers:
if isinstance(scheduler, dict):
# interval is not in this list even though the user needs to manually call the scheduler because
# the `LearningRateMonitor` callback needs to check its value to know when to log the learning rate
invalid_keys = {"frequency", "reduce_on_plateau", "monitor", "strict"}
keys_to_warn = [k for k in scheduler.keys() if k in invalid_keys]
if keys_to_warn:
rank_zero_warn(
f"The lr scheduler dict contains the key(s) {keys_to_warn}, but the keys will be ignored."
" You need to call `lr_scheduler.step()` manually in manual optimization.",
category=RuntimeWarning,
)
config = LRSchedulerConfig(**{key: scheduler[key] for key in scheduler if key not in invalid_keys})
else:
config = LRSchedulerConfig(scheduler)
lr_scheduler_configs.append(config)
return lr_scheduler_configs
def _validate_scheduler_api(lr_scheduler_configs: List[LRSchedulerConfig], model: "pl.LightningModule") -> None:
for config in lr_scheduler_configs:
scheduler = config.scheduler
if not isinstance(scheduler, _Stateful):
raise TypeError(
f"The provided lr scheduler `{scheduler.__class__.__name__}` is invalid."
" It should have `state_dict` and `load_state_dict` methods defined."
)
if not isinstance(scheduler, LRSchedulerTypeTuple) and not is_overridden("lr_scheduler_step", model):
raise MisconfigurationException(
f"The provided lr scheduler `{scheduler.__class__.__name__}` doesn't follow PyTorch's LRScheduler"
" API. You should override the `LightningModule.lr_scheduler_step` hook with your own logic if"
" you are using a custom LR scheduler."
)
def _set_scheduler_opt_idx(optimizers: List[Optimizer], lr_scheduler_configs: List[LRSchedulerConfig]) -> None:
for config in lr_scheduler_configs:
for opt_idx, opt in enumerate(optimizers):
if config.scheduler.optimizer is opt:
if config.opt_idx is not None and config.opt_idx != opt_idx:
raise MisconfigurationException(
"`opt_idx` set inside scheduler config does not match with the index"
" of the respective optimizer returned from `configure_optimizers`."
)
config.opt_idx = opt_idx
break
else:
raise MisconfigurationException(
"Some schedulers are attached with an optimizer that wasn't returned from `configure_optimizers`."
)
def _validate_optim_conf(optim_conf: Dict[str, Any]) -> None:
valid_keys = {"optimizer", "lr_scheduler", "frequency", "monitor"}
extra_keys = optim_conf.keys() - valid_keys
if extra_keys:
rank_zero_warn(
f"Found unsupported keys in the optimizer configuration: {set(extra_keys)}", category=RuntimeWarning
)
class _MockOptimizer(Optimizer):
"""The `_MockOptimizer` will be used inplace of an optimizer in the event that `None` is returned from
`configure_optimizers`."""
def __init__(self) -> None:
super().__init__([torch.zeros(1)], {})
def add_param_group(self, param_group: Dict[Any, Any]) -> None:
pass # Do Nothing
def load_state_dict(self, state_dict: Dict[Any, Any]) -> None:
pass # Do Nothing
def state_dict(self) -> Dict[str, Any]:
return {} # Return Empty
def step(self, closure: Optional[Callable] = None) -> None:
if closure is not None:
closure()
def zero_grad(self, set_to_none: Optional[bool] = False) -> None:
pass # Do Nothing
def __repr__(self) -> str:
return "No Optimizer"
