Source code for catalyst.core.callbacks.optimizer

from typing import Callable, Dict, List
import logging
import warnings

from catalyst.core import registry, utils
from catalyst.core.callback import Callback, CallbackNode, CallbackOrder
from catalyst.core.runner import IRunner
from catalyst.tools.typing import Optimizer

logger = logging.getLogger(__name__)


class OptimizerCallback(Callback):
    """Optimizer callback, abstraction over optimizer step."""

    def __init__(
        self,
        metric_key: str = None,
        optimizer_key: str = None,
        accumulation_steps: int = 1,
        grad_clip_params: Dict = None,
        decouple_weight_decay: bool = True,
        loss_key: str = None,
    ):
        """
        Args:
            loss_key (str): key to get loss from ``runner.batch_metrics``
            optimizer_key (str): A key to take a optimizer in case
                there are several of them and they are in a dictionary format.
            accumulation_steps (int): number of steps before
                ``model.zero_grad()``
            grad_clip_params (dict): params for gradient clipping
            decouple_weight_decay (bool): If True - decouple weight decay
                regularization.
        """
        super().__init__(order=CallbackOrder.Optimizer, node=CallbackNode.All)
        assert metric_key is None or loss_key is None
        if loss_key is not None:
            warnings.warn(
                "OptimizerCallback: "
                "`loss_key` is now deprecated in favor `metric_key`",
                stacklevel=2,
            )
        self.metric_key: str = metric_key or loss_key or "loss"
        self.optimizer_key: str = optimizer_key

        self.accumulation_steps: int = accumulation_steps
        self._accumulation_counter: int = 0

        grad_clip_params: dict = grad_clip_params or {}
        self.grad_clip_fn = registry.GRAD_CLIPPERS.get_from_params(
            **grad_clip_params
        )

        self.decouple_weight_decay = decouple_weight_decay
        self._optimizer_wd: List[float] = [0.0]

    @staticmethod
    def grad_step(
        *,
        optimizer: Optimizer,
        optimizer_wds: List[float] = 0,
        grad_clip_fn: Callable = None,
    ) -> None:
        """Makes a gradient step for a given optimizer.

        Args:
            optimizer (Optimizer): the optimizer
            optimizer_wds (List[float]): list of weight decay parameters
                for each param group
            grad_clip_fn (Callable): function for gradient clipping
        """
        for group, wd in zip(optimizer.param_groups, optimizer_wds):
            if wd > 0:
                for param in group["params"]:
                    param.data = param.data.add(-wd * group["lr"], param.data)
            if grad_clip_fn is not None:
                grad_clip_fn(group["params"])
        optimizer.step()

    def on_stage_start(self, runner: IRunner) -> None:
        """Checks that the current stage has correct optimizer."""
        self._optimizer = runner.get_attr(
            key="optimizer", inner_key=self.optimizer_key
        )
        assert self._optimizer is not None

    def on_epoch_start(self, runner: IRunner) -> None:
        """On epoch start event.

        Args:
            runner (IRunner): current runner
        """
        if self.decouple_weight_decay:
            self._optimizer_wd = [
                group.get("weight_decay", 0.0)
                for group in self._optimizer.param_groups
            ]
            for i in range(len(self._optimizer.param_groups)):
                self._optimizer.param_groups[i]["weight_decay"] = 0.0
        else:
            self._optimizer_wd = [0.0] * len(self._optimizer.param_groups)

    def on_epoch_end(self, runner: IRunner) -> None:
        """On epoch end event.

        Args:
            runner (IRunner): current runner
        """
        if self.decouple_weight_decay:
            for i, wd in enumerate(self._optimizer_wd):
                self._optimizer.param_groups[i]["weight_decay"] = wd

        lr = self._optimizer.param_groups[0]["lr"]
        lr_name = (
            f"lr/{self.optimizer_key}"
            if self.optimizer_key is not None
            else "lr"
        )
        runner.epoch_metrics[lr_name] = lr

        momentum = utils.get_optimizer_momentum(self._optimizer)
        if momentum is not None:
            momentum_name = (
                f"momentum/{self.optimizer_key}"
                if self.optimizer_key is not None
                else "momentum"
            )
            runner.epoch_metrics[momentum_name] = momentum

    def on_batch_end(self, runner: IRunner) -> None:
        """On batch end event

        Args:
            runner (IRunner): current runner
        """
        if not runner.is_train_loader:
            return

        loss = runner.batch_metrics[self.metric_key]

        self._accumulation_counter += 1
        need_gradient_step = (
            self._accumulation_counter % self.accumulation_steps == 0
        )

        # This is very hacky check whether we have AMP optimizer and this may
        # change in future.
        # But alternative solution is to have AmpOptimizerCallback.
        # or expose another c'tor argument.
        if hasattr(self._optimizer, "_amp_stash"):
            from apex import amp

            # Need to set ``delay_unscale``
            # according to
            # https://nvidia.github.io/apex/advanced.html#gradient-accumulation-across-iterations
            delay_unscale = not need_gradient_step
            with amp.scale_loss(
                loss, self._optimizer, delay_unscale=delay_unscale
            ) as scaled_loss:
                scaled_loss.backward()
        else:
            loss.backward()

        if need_gradient_step:
            self.grad_step(
                optimizer=self._optimizer,
                optimizer_wds=self._optimizer_wd,
                grad_clip_fn=self.grad_clip_fn,
            )

            utils.maybe_recursive_call(self._optimizer, "zero_grad")
            self._accumulation_counter = 0


__all__ = ["OptimizerCallback"]