accelerator.py

# Copyright 2021 The HuggingFace Team. All rights reserved.
#
# 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 contextlib
import inspect
import math
import os
import re
import shutil
import sys
import warnings
from collections import OrderedDict
from contextlib import contextmanager
from functools import partial
from typing import Any, Callable, List, Optional, Union

import torch
import torch.utils.hooks as hooks

from .checkpointing import load_accelerator_state, load_custom_state, save_accelerator_state, save_custom_state
from .data_loader import DataLoaderDispatcher, prepare_data_loader, skip_first_batches
from .logging import get_logger
from .optimizer import AcceleratedOptimizer
from .scheduler import AcceleratedScheduler
from .state import AcceleratorState, GradientState, PartialState, parse_flag_from_env
from .tracking import LOGGER_TYPE_TO_CLASS, GeneralTracker, filter_trackers
from .utils import (
    MODEL_NAME,
    DeepSpeedPlugin,
    DistributedDataParallelKwargs,
    DistributedType,
    DynamoBackend,
    FP8RecipeKwargs,
    FullyShardedDataParallelPlugin,
    GradientAccumulationPlugin,
    GradScalerKwargs,
    InitProcessGroupKwargs,
    KwargsHandler,
    LoggerType,
    MegatronLMPlugin,
    PrecisionType,
    ProjectConfiguration,
    RNGType,
    TorchDynamoPlugin,
    compare_versions,
    convert_model,
    convert_outputs_to_fp32,
    extract_model_from_parallel,
    gather,
    get_pretty_name,
    has_transformer_engine_layers,
    is_bf16_available,
    is_deepspeed_available,
    is_fp8_available,
    is_megatron_lm_available,
    is_torch_version,
    is_tpu_available,
    pad_across_processes,
    parse_choice_from_env,
    recursively_apply,
    reduce,
    release_memory,
    save,
    wait_for_everyone,
)


if is_deepspeed_available():
    import deepspeed

    from .utils import (
        DeepSpeedEngineWrapper,
        DeepSpeedOptimizerWrapper,
        DeepSpeedSchedulerWrapper,
        DummyOptim,
        DummyScheduler,
    )

if is_fp8_available():
    import transformer_engine.common.recipe as te_recipe
    from transformer_engine.pytorch import fp8_autocast


if is_megatron_lm_available():
    from .utils import (
        MegatronEngine,
        MegatronLMDummyDataLoader,
        MegatronLMDummyScheduler,
        MegatronLMOptimizerWrapper,
        MegatronLMSchedulerWrapper,
        megatron_lm_initialize,
        megatron_lm_prepare_data_loader,
        megatron_lm_prepare_model,
        megatron_lm_prepare_optimizer,
        megatron_lm_prepare_scheduler,
    )

if is_torch_version(">", "1.10.0"):
    from torch.distributed.algorithms.join import Join


if is_tpu_available(check_device=False):
    import torch_xla.distributed.xla_multiprocessing as xmp


try:
    from torch.optim.lr_scheduler import LRScheduler
except ImportError:
    from torch.optim.lr_scheduler import _LRScheduler as LRScheduler

logger = get_logger(__name__)


class Accelerator:
    """
    Creates an instance of an accelerator for distributed training (on multi-GPU, TPU) or mixed precision training.

    Args:
        device_placement (`bool`, *optional*, defaults to `True`):
            Whether or not the accelerator should put objects on device (tensors yielded by the dataloader, model,
            etc...).
        split_batches (`bool`, *optional*, defaults to `False`):
            Whether or not the accelerator should split the batches yielded by the dataloaders across the devices. If
            `True` the actual batch size used will be the same on any kind of distributed processes, but it must be a
            round multiple of the `num_processes` you are using. If `False`, actual batch size used will be the one set
            in your script multiplied by the number of processes.
        mixed_precision (`str`, *optional*):
            Whether or not to use mixed precision training. Choose from 'no','fp16','bf16 or 'fp8'. Will default to the
            value in the environment variable `ACCELERATE_MIXED_PRECISION`, which will use the default value in the
            accelerate config of the current system or the flag passed with the `accelerate.launch` command. 'fp16'
            requires pytorch 1.6 or higher. 'bf16' requires pytorch 1.10 or higher. 'fp8' requires the installation of
            transformers-engine.
        gradient_accumulation_steps (`int`, *optional*, default to 1):
            The number of steps that should pass before gradients are accumulated. A number > 1 should be combined with
            `Accelerator.accumulate`. If not passed, will default to the value in the environment variable
            `ACCELERATE_GRADIENT_ACCUMULATION_STEPS`. Can also be configured through a `GradientAccumulationPlugin`.
        cpu (`bool`, *optional*):
            Whether or not to force the script to execute on CPU. Will ignore GPU available if set to `True` and force
            the execution on one process only.
        deepspeed_plugin (`DeepSpeedPlugin`, *optional*):
            Tweak your DeepSpeed related args using this argument. This argument is optional and can be configured
            directly using *accelerate config*
        fsdp_plugin (`FullyShardedDataParallelPlugin`, *optional*):
            Tweak your FSDP related args using this argument. This argument is optional and can be configured directly
            using *accelerate config*
        megatron_lm_plugin (`MegatronLMPlugin`, *optional*):
            Tweak your MegatronLM related args using this argument. This argument is optional and can be configured
            directly using *accelerate config*
        rng_types (list of `str` or [`~utils.RNGType`]):
            The list of random number generators to synchronize at the beginning of each iteration in your prepared
            dataloaders. Should be one or several of:

            - `"torch"`: the base torch random number generator
            - `"cuda"`: the CUDA random number generator (GPU only)
            - `"xla"`: the XLA random number generator (TPU only)
            - `"generator"`: the `torch.Generator` of the sampler (or batch sampler if there is no sampler in your
              dataloader) or of the iterable dataset (if it exists) if the underlying dataset is of that type.

            Will default to `["torch"]` for PyTorch versions <=1.5.1 and `["generator"]` for PyTorch versions >= 1.6.
        log_with (list of `str`, [`~utils.LoggerType`] or [`~tracking.GeneralTracker`], *optional*):
            A list of loggers to be setup for experiment tracking. Should be one or several of:

            - `"all"`
            - `"tensorboard"`
            - `"wandb"`
            - `"comet_ml"`
            If `"all"` is selected, will pick up all available trackers in the environment and initialize them. Can
            also accept implementations of `GeneralTracker` for custom trackers, and can be combined with `"all"`.
        project_config (`ProjectConfiguration`, *optional*):
            A configuration for how saving the state can be handled.
        project_dir (`str`, `os.PathLike`, *optional*):
            A path to a directory for storing data such as logs of locally-compatible loggers and potentially saved
            checkpoints.
        dispatch_batches (`bool`, *optional*):
            If set to `True`, the dataloader prepared by the Accelerator is only iterated through on the main process
            and then the batches are split and broadcast to each process. Will default to `True` for `DataLoader` whose
            underlying dataset is an `IterableDataset`, `False` otherwise.
        even_batches (`bool`, *optional*, defaults to `True`):
            If set to `True`, in cases where the total batch size across all processes does not exactly divide the
            dataset, samples at the start of the dataset will be duplicated so the batch can be divided equally among
            all workers.
        step_scheduler_with_optimizer (`bool`, *optional`, defaults to `True`):
            Set `True` if the learning rate scheduler is stepped at the same time as the optimizer, `False` if only
            done under certain circumstances (at the end of each epoch, for instance).
        kwargs_handlers (`List[KwargHandler]`, *optional*)
            A list of `KwargHandler` to customize how the objects related to distributed training or mixed precision
            are created. See [kwargs](kwargs) for more information.
        dynamo_backend (`str` or `DynamoBackend`, *optional*, defaults to `"no"`):
            Set to one of the possible dynamo backends to optimize your training with torch dynamo.
        gradient_accumulation_plugin (`GradientAccumulationPlugin`, *optional*):
            A configuration for how gradient accumulation should be handled, if more tweaking than just the
            `gradient_accumulation_steps` is needed.

    **Available attributes:**

        - **device** (`torch.device`) -- The device to use.
        - **distributed_type** ([`~utils.DistributedType`]) -- The distributed training configuration.
        - **local_process_index** (`int`) -- The process index on the current machine.
        - **mixed_precision** (`str`) -- The configured mixed precision mode.
        - **num_processes** (`int`) -- The total number of processes used for training.
        - **optimizer_step_was_skipped** (`bool`) -- Whether or not the optimizer update was skipped (because of
          gradient overflow in mixed precision), in which
        case the learning rate should not be changed.
        - **process_index** (`int`) -- The overall index of the current process among all processes.
        - **state** ([`~state.AcceleratorState`]) -- The distributed setup state.
        - **sync_gradients** (`bool`) -- Whether the gradients are currently being synced across all processes.
        - **use_distributed** (`bool`) -- Whether the current configuration is for distributed training.
    """

    def __init__(
        self,
        device_placement: bool = True,
        split_batches: bool = False,
        mixed_precision: Union[PrecisionType, str] = None,
        gradient_accumulation_steps: int = 1,
        cpu: bool = False,
        deepspeed_plugin: DeepSpeedPlugin = None,
        fsdp_plugin: FullyShardedDataParallelPlugin = None,
        megatron_lm_plugin: MegatronLMPlugin = None,
        rng_types: Optional[List[Union[str, RNGType]]] = None,
        log_with: Optional[List[Union[str, LoggerType, GeneralTracker]]] = None,
        project_dir: Optional[Union[str, os.PathLike]] = None,
        project_config: Optional[ProjectConfiguration] = None,
        logging_dir: Optional[Union[str, os.PathLike]] = None,
        gradient_accumulation_plugin: Optional[GradientAccumulationPlugin] = None,
        dispatch_batches: Optional[bool] = None,
        even_batches: bool = True,
        step_scheduler_with_optimizer: bool = True,
        kwargs_handlers: Optional[List[KwargsHandler]] = None,
        dynamo_backend: Union[DynamoBackend, str] = None,
    ):
        if project_config is not None:
            self.project_configuration = project_config
        else:
            self.project_configuration = ProjectConfiguration(project_dir=project_dir)

        if logging_dir is not None:
            warnings.warn(
                "`logging_dir` is deprecated and will be removed in version 0.18.0 of 🤗 Accelerate. Use `project_dir` instead.",
                FutureWarning,
            )
            self.project_configuration.logging_dir = logging_dir
        if project_dir is not None and self.project_dir is None:
            self.project_configuration.project_dir = project_dir
        if mixed_precision is not None:
            mixed_precision = str(mixed_precision)
            if mixed_precision not in PrecisionType:
                raise ValueError(
                    f"Unknown mixed_precision mode: {mixed_precision}. Choose between {PrecisionType.list()}"
                )

        dynamo_plugin = TorchDynamoPlugin() if dynamo_backend is None else TorchDynamoPlugin(backend=dynamo_backend)

        if deepspeed_plugin is None:  # init from env variables
            deepspeed_plugin = (
                DeepSpeedPlugin() if os.environ.get("ACCELERATE_USE_DEEPSPEED", "false") == "true" else None
            )
        else:
            assert isinstance(
                deepspeed_plugin, DeepSpeedPlugin
            ), "`deepspeed_plugin` must be an `accelerate.utils.DeepSpeedPlugin` object."
            os.environ["ACCELERATE_USE_DEEPSPEED"] = "true"  # use DeepSpeed if plugin is provided
        if deepspeed_plugin:
            if not is_deepspeed_available():
                raise ImportError("DeepSpeed is not installed => run `pip install deepspeed` or build it from source.")
            if compare_versions("deepspeed", "<", "0.6.5"):
                raise ImportError("DeepSpeed version must be >= 0.6.5. Please update DeepSpeed.")

            mixed_precision = (
                os.environ.get("ACCELERATE_MIXED_PRECISION", "no") if mixed_precision is None else mixed_precision
            )
            deepspeed_plugin.set_mixed_precision(mixed_precision)
            deepspeed_plugin.set_deepspeed_weakref()

        if os.environ.get("ACCELERATE_USE_FSDP", "false") == "true" or isinstance(
            fsdp_plugin, FullyShardedDataParallelPlugin
        ):
            if is_torch_version("<", "1.12.0"):
                raise ValueError("FSDP requires PyTorch >= 1.12.0")

        if fsdp_plugin is None:  # init from env variables
            fsdp_plugin = (
                FullyShardedDataParallelPlugin() if os.environ.get("ACCELERATE_USE_FSDP", "false") == "true" else None
            )
        else:
            if not isinstance(fsdp_plugin, FullyShardedDataParallelPlugin):
                raise TypeError("`fsdp_plugin` must be a FullyShardedDataParallelPlugin object.")
            os.environ["ACCELERATE_USE_FSDP"] = "true"  # use FSDP if plugin is provided

        if megatron_lm_plugin is None:  # init from env variables
            megatron_lm_plugin = (
                MegatronLMPlugin() if os.environ.get("ACCELERATE_USE_MEGATRON_LM", "false") == "true" else None
            )
        else:
            if not isinstance(megatron_lm_plugin, MegatronLMPlugin):
                raise TypeError("`megatron_lm_plugin` must be a MegatronLMPlugin object.")
            os.environ["ACCELERATE_USE_MEGATRON_LM"] = "true"  # use MegatronLM if plugin is provided

        if megatron_lm_plugin:
            if not is_megatron_lm_available():
                raise ImportError("Megatron is not installed. please build it from source.")

        # Kwargs handlers
        self.ddp_handler = None
        self.scaler_handler = None
        self.init_handler = None
        self.fp8_recipe_handler = None
        if kwargs_handlers is not None:
            for handler in kwargs_handlers:
                assert isinstance(
                    handler, KwargsHandler
                ), f"Unsupported kwargs handler passed: {handler}, must be one that inherits `accelerate.utils.KwargsHandler`."
                if isinstance(handler, DistributedDataParallelKwargs):
                    if self.ddp_handler is not None:
                        raise ValueError("You can only pass one `DistributedDataParallelKwargs` in `kwargs_handler`.")
                    else:
                        self.ddp_handler = handler
                elif isinstance(handler, GradScalerKwargs):
                    if self.scaler_handler is not None:
                        raise ValueError("You can only pass one `GradScalerKwargs` in `kwargs_handler`.")
                    else:
                        self.scaler_handler = handler
                elif isinstance(handler, InitProcessGroupKwargs):
                    if self.init_handler is not None:
                        raise ValueError("You can only pass one `InitProcessGroupKwargs` in `kwargs_handler`.")
                    else:
                        self.init_handler = handler
                elif isinstance(handler, FP8RecipeKwargs):
                    if self.fp8_recipe_handler is not None:
                        raise ValueError("You can only pass one `FP8RecipeKwargs` in `kwargs_handler`.")
                    else:
                        self.fp8_recipe_handler = handler

        kwargs = self.init_handler.to_kwargs() if self.init_handler is not None else {}
        self.state = AcceleratorState(
            mixed_precision=mixed_precision,
            cpu=cpu,
            dynamo_plugin=dynamo_plugin,
            deepspeed_plugin=deepspeed_plugin,
            fsdp_plugin=fsdp_plugin,
            megatron_lm_plugin=megatron_lm_plugin,
            _from_accelerator=True,
            **kwargs,
        )

        if self.state.distributed_type == DistributedType.TPU:
            if gradient_accumulation_plugin.num_steps != 1:
                raise ValueError(
                    "Gradient accumulation is not supported on TPU. Please set `gradient_accumulation_steps` to 1 and don't pass in a `GradientAccumulationPlugin` object."
                )

        trackers = filter_trackers(log_with, self.logging_dir)
        if len(trackers) < 1 and log_with is not None:
            warnings.warn(f"`log_with={log_with}` was passed but no supported trackers are currently installed.")
        self.log_with = trackers

        if (
            (mixed_precision != "bf16")
            and getattr(self.state, "downcast_bfloat", False)
            and (self.state.distributedType != DistributedType.TPU)
        ):
            raise ValueError("Can only use `downcast_bf16` when using `mixed_precision='bf16'` and on a TPU")

        if gradient_accumulation_plugin is not None:
            if gradient_accumulation_steps != 1:
                raise ValueError(
                    "You can only pass one of `gradient_accumulation_steps` and `gradient_accumulation_plugin`. Please only pass in the created `GradientAccumulationPlugin` object."
                )
        else:
            gradient_accumulation_steps = int(
                parse_choice_from_env("ACCELERATE_GRADIENT_ACCUMULATION_STEPS", gradient_accumulation_steps)
            )
            gradient_accumulation_plugin = GradientAccumulationPlugin(num_steps=gradient_accumulation_steps)
        self.gradient_state = GradientState(
            gradient_accumulation_plugin=gradient_accumulation_plugin,
        )

        self.device_placement = device_placement
        self.split_batches = split_batches
        self.dispatch_batches = dispatch_batches
        if dispatch_batches is True and is_torch_version("<", "1.8.0"):
            raise ImportError(
                "Using `DataLoaderDispatcher` requires PyTorch 1.8.0 minimum. You have {torch.__version__}."
            )
        self.even_batches = even_batches
        self.step_scheduler_with_optimizer = step_scheduler_with_optimizer

        # Mixed precision attributes
        self.scaler = None
        self.native_amp = False
        err = "{mode} mixed precision requires {requirement}"
        if (
            self.state.mixed_precision == "fp16"
            and self.device.type != "cpu"
            and self.distributed_type not in (DistributedType.DEEPSPEED, DistributedType.MEGATRON_LM)
        ):
            self.native_amp = True
            if not torch.cuda.is_available() and not parse_flag_from_env("ACCELERATE_USE_MPS_DEVICE"):
                raise ValueError(err.format(mode="fp16", requirement="a GPU"))
            kwargs = self.scaler_handler.to_kwargs() if self.scaler_handler is not None else {}
            if self.distributed_type == DistributedType.FSDP:
                from torch.distributed.fsdp.sharded_grad_scaler import ShardedGradScaler

                self.scaler = ShardedGradScaler(**kwargs)
            else:
                self.scaler = torch.cuda.amp.GradScaler(**kwargs)
        elif self.state.mixed_precision == "bf16" and self.distributed_type not in (
            DistributedType.DEEPSPEED,
            DistributedType.MEGATRON_LM,
        ):
            if self.device.type == "cpu":
                self.native_amp = is_torch_version(">=", "1.10")
            else:
                self.native_amp = is_bf16_available(True)
            if mixed_precision == "bf16" and not self.native_amp and not is_tpu_available():
                raise ValueError(err.format(mode="bf16", requirement="PyTorch >= 1.10 and a supported device."))

        # Start of internal step tracking
        self.step = 0

        # Internal references to the training objects
        self._optimizers = []
        self._models = []
        self._schedulers = []
        self._dataloaders = []
        self._custom_objects = []

        # Hooks
        self._load_model_state_pre_hook = OrderedDict()
        self._save_model_state_pre_hook = OrderedDict()

        # RNG Types
        self.rng_types = rng_types
        if self.rng_types is None:
            self.rng_types = ["generator"]

    @property
    def use_distributed(self):
        """
        Whether the Accelerator is configured for distributed training
        """
        return self.state.use_distributed

    @property
    def distributed_type(self):
        return self.state.distributed_type

    @property
    def num_processes(self):
        return self.state.num_processes

    @property
    def process_index(self):
        return self.state.process_index

    @property
    def local_process_index(self):
        return self.state.local_process_index

    @property
    def device(self):
        return self.state.device

    @property
    def project_dir(self):
        return self.project_configuration.project_dir

    @property
    def logging_dir(self):
        return self.project_configuration.logging_dir

    @property
    def save_iteration(self):
        return self.project_configuration.iteration

    @property
    def is_main_process(self):
        """True for one process only."""
        return self.state.is_main_process

    @property
    def is_local_main_process(self):
        """True for one process per server."""
        return self.state.is_local_main_process

    @property
    def use_fp16(self):
        warnings.warn(
            "The `use_fp16` property is deprecated and will be removed in version 1.0 of Accelerate use "
            "`Accelerator.mixed_precision == 'fp16'` instead.",
            FutureWarning,
        )
        return self.mixed_precision != "no"

    @property
    def is_last_process(self):
        return self.process_index == self.num_processes - 1

    @property
    def mixed_precision(self):
        return self.state.mixed_precision

    def on_main_process(self, function: Callable[..., Any] = None):
        """
        A decorator that will run the decorated function on the main process only. Can also be called using the
        `PartialState` class.

        Args:
            function (`Callable`): The function to decorate.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()


        >>> @accelerator.on_main_process
        ... def print_something():
        ...     print("This will be printed by process 0 only.")


        >>> print_something()
        "This will be printed by process 0 only"
        ```
        """
        # For times when the `Accelerator` object itself utilizes this decorator.
        if function is None:
            if "Accelerator." in self.__qualname__:
                function = self
            else:
                raise ValueError(
                    "The `on_main_process` decorator must be called with a function on an instantiated `Accelerator` object."
                )

        def _inner(*args, **kwargs):
            return PartialState().on_main_process(function)(*args, **kwargs)

        return _inner

    def on_local_main_process(self, function: Callable[..., Any] = None):
        """
        A decorator that will run the decorated function on the local main process only. Can also be called using the
        `PartialState` class.

        Args:
            function (`Callable`): The function to decorate.

        Example:
        ```python
        # Assume we have 2 servers with 4 processes each.
        from accelerate import Accelerator

        accelerator = Accelerator()


        @accelerator.on_local_main_process
        def print_something():
            print("This will be printed by process 0 only on each server.")


        print_something()
        # On server 1:
        "This will be printed by process 0 only"
        # On server 2:
        "This will be printed by process 0 only"
        ```
        """
        # For times when the `Accelerator` object itself utilizes this decorator.
        if function is None:
            if "Accelerator." in self.__qualname__:
                function = self
            else:
                raise ValueError(
                    "The `on_local_main_process` decorator must be called with a function on an instantiated `Accelerator` object."
                )

        def _inner(*args, **kwargs):
            return PartialState().on_local_main_process(function)(*args, **kwargs)

        return _inner

    def on_last_process(self, function: Callable[..., Any]):
        """
        A decorator that will run the decorated function on the last process only. Can also be called using the
        `PartialState` class.

        Args:
            function (`Callable`): The function to decorate.

        Example:
        ```python
        # Assume we have 4 processes.
        from accelerate import Accelerator

        accelerator = Accelerator()


        @accelerator.on_last_process
        def print_something():
            print(f"Printed on process {accelerator.process_index}")


        print_something()
        "Printed on process 3"
        ```
        """
        # For times when the `Accelerator` object itself utilizes this decorator.
        if function is None:
            if "Accelerator." in self.__qualname__:
                function = self
            else:
                raise ValueError(
                    "The `on_last_process` decorator must be called with a function on an instantiated `Accelerator` object."
                )

        def _inner(*args, **kwargs):
            return PartialState().on_last_process(function)(*args, **kwargs)

        return _inner

    def on_process(self, function: Callable[..., Any] = None, process_index: int = None):
        """
        A decorator that will run the decorated function on a given process index only. Can also be called using the
        `PartialState` class.

        Args:
            function (`Callable`, `optional`):
                The function to decorate.
            process_index (`int`, `optional`):
                The index of the process on which to run the function.

        Example:
        ```python
        # Assume we have 4 processes.
        from accelerate import Accelerator

        accelerator = Accelerator()


        @accelerator.on_process(process_index=2)
        def print_something():
            print(f"Printed on process {accelerator.process_index}")


        print_something()
        "Printed on process 2"
        ```
        """
        # Initial construction of the decorator.
        if (self is not None) and (process_index is not None) and (function is None):
            return partial(self.on_process, process_index=process_index)
        # For times when the `Accelerator` object itself utilizes this decorator.
        if function is None:
            if "Accelerator." in self.__qualname__:
                function = self
            else:
                raise ValueError(
                    "The `on_main_process` decorator must be called with a function on an instantiated `Accelerator` object."
                )

        def _inner(*args, **kwargs):
            return PartialState().on_process(function, process_index)(*args, **kwargs)

        return _inner

    def on_local_process(self, function: Callable[..., Any] = None, local_process_index: int = None):
        """
        A decorator that will run the decorated function on a given local process index only. Can also be called using
        the `PartialState` class.

        Args:
            function (`Callable`, *optional*):
                The function to decorate.
            local_process_index (`int`, *optional*):
                The index of the local process on which to run the function.

        Example:
        ```python
        # Assume we have 2 servers with 4 processes each.
        from accelerate import Accelerator

        accelerator = Accelerator()


        @accelerator.on_local_process(local_process_index=2)
        def print_something():
            print(f"Printed on process {accelerator.local_process_index}")


        print_something()
        # On server 1:
        "Printed on process 2"
        # On server 2:
        "Printed on process 2"
        ```
        """
        # Initial construction of the decorator.
        if (self is not None) and (local_process_index is not None) and (function is None):
            return partial(self.on_local_process, local_process_index=local_process_index)
        # For times when the `Accelerator` object itself utilizes this decorator.
        if function is None:
            if "Accelerator." in self.__qualname__:
                function = self
            else:
                raise ValueError(
                    "The `on_main_process` decorator must be called with a function on an instantiated `Accelerator` object."
                )

        def _inner(*args, **kwargs):
            return PartialState().on_local_process(function, local_process_index)(*args, **kwargs)

        return _inner

    @contextmanager
    def main_process_first(self):
        """
        Lets the main process go first inside a with block.

        The other processes will enter the with block after the main process exits.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> with accelerator.main_process_first():
        ...     # This will be printed first by process 0 then in a seemingly
        ...     # random order by the other processes.
        ...     print(f"This will be printed by process {accelerator.process_index}")
        ```
        """
        yield self.state.main_process_first()

    @contextmanager
    def local_main_process_first(self):
        """
        Lets the local main process go inside a with block.

        The other processes will enter the with block after the main process exits.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> with accelerator.local_main_process_first():
        ...     # This will be printed first by local process 0 then in a seemingly
        ...     # random order by the other processes.
        ...     print(f"This will be printed by process {accelerator.local_process_index}")
        ```
        """
        yield self.state.local_main_process_first()

    @contextmanager
    def no_sync(self, model):
        """
        A context manager to disable gradient synchronizations across DDP processes by calling
        `torch.nn.parallel.DistributedDataParallel.no_sync`.

        If `model` is not in DDP, this context manager does nothing

        Args:
            model (`torch.nn.Module`):
                PyTorch Module that was prepared with `Accelerator.prepare`

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> dataloader, model, optimizer = accelerator.prepare(dataloader, model, optimizer)
        >>> input_a = next(iter(dataloader))
        >>> input_b = next(iter(dataloader))

        >>> with accelerator.no_sync():
        ...     outputs = model(input_a)
        ...     loss = loss_func(outputs)
        ...     accelerator.backward(loss)
        ...     # No synchronization across processes, only accumulate gradients
        >>> outputs = model(input_b)
        >>> accelerator.backward(loss)
        >>> # Synchronization across all processes
        >>> optimizer.step()
        >>> optimizer.zero_grad()
        ```
        """
        context = contextlib.nullcontext
        if self.use_distributed:
            context = getattr(model, "no_sync", context)

        with context():
            yield

    def _do_sync(self):
        "Sets the right `sync_gradients` context and either resets or increases `self.step`"
        if self.gradient_state.end_of_dataloader:
            self.step = 0
            self.gradient_state._set_sync_gradients(True)
        else:
            self.step += 1
            self.gradient_state._set_sync_gradients((self.step % self.gradient_state.num_steps) == 0)

    @property
    def sync_gradients(self):
        return self.gradient_state.sync_gradients

    @property
    def gradient_accumulation_steps(self):
        return self.gradient_state.num_steps

    @contextmanager
    def accumulate(self, model):
        """
        A context manager that will lightly wrap around and perform gradient accumulation automatically

        Args:
            model (`torch.nn.Module`):
                PyTorch Module that was prepared with `Accelerator.prepare`

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator(gradient_accumulation_steps=1)
        >>> dataloader, model, optimizer, scheduler = accelerator.prepare(dataloader, model, optimizer, scheduler)

        >>> with accelerator.accumulate(model):
        ...     for input, output in dataloader:
        ...         outputs = model(input)
        ...         loss = loss_func(outputs)
        ...         loss.backward()
        ...         optimizer.step()
        ...         scheduler.step()
        ...         optimizer.zero_grad()
        ```
        """
        self._do_sync()
        if self.sync_gradients:
            context = contextlib.nullcontext
        else:
            context = self.no_sync

        with context(model):
            yield

    @contextmanager
    def join_uneven_inputs(self, joinables, even_batches=None):
        """
        A context manager that facilitates distributed training or evaluation on uneven inputs, which acts as a wrapper
        around `torch.distributed.algorithms.join`. This is useful when the total batch size does not evenly divide the
        length of the dataset.

        Args:
            joinables (`List[torch.distributed.algorithms.Joinable]`):
                A list of models or optimizers that subclass `torch.distributed.algorithms.Joinable`. Most commonly, a
                PyTorch Module that was prepared with `Accelerator.prepare` for DistributedDataParallel training.
            even_batches (`bool`, *optional*)
                If set, this will override the value of `even_batches` set in the `Accelerator`. If it is not provided,
                the default `Accelerator` value wil be used.

        <Tip warning={true}>

        `join_uneven_inputs` is only supported for Distributed Data Parallel training on multiple GPUs. For any other
        configuration, this method will have no effect.

        </Tip>

        <Tip warning={true}>

        Overidding `even_batches` will not affect iterable-style data loaders.

        </Tip>

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator(even_batches=True)
        >>> ddp_model, optimizer, dataloader = accelerator.prepare(model, optimizer, dataloader)

        >>> with accelerator.join_uneven_inputs([ddp_model], even_batches=False):
        ...     for input, output in dataloader:
        ...         outputs = model(input)
        ...         loss = loss_func(outputs)
        ...         loss.backward()
        ...         optimizer.step()
        ...         optimizer.zero_grad()
        ```
        """
        if is_torch_version("<", "1.10.0"):
            raise ValueError(f"Joining uneven inputs requires PyTorch >= 1.10.0, You have {torch.__version__}.")

        if self.distributed_type == DistributedType.MULTI_GPU:
            dl_even_batches_values = []

            if even_batches is not None:
                iterable_dl_seen = False
                # override value in batch sampler for map-style datasets
                for dl_idx, dl in enumerate(self._dataloaders):
                    if isinstance(dl, DataLoaderDispatcher):
                        iterable_dl_seen = True
                        continue
                    dl_even_batches_values.append((dl_idx, dl.batch_sampler.even_batches))
                    dl.batch_sampler.even_batches = even_batches

                if iterable_dl_seen:
                    warnings.warn(
                        "Overridding even_batches is only supported for map-style datasets, yet some dataloaders given were iterable"
                    )
            else:
                even_batches = self.even_batches

            enable_join = False if even_batches else True
            try:
                with Join(joinables, enable=enable_join, throw_on_early_termination=False):
                    yield
            finally:
                # reset any batch samplers that have been modified
                for dl_idx, even_batches_value in dl_even_batches_values:
                    self._dataloaders[dl_idx].batch_sampler.even_batches = even_batches_value
        else:
            # Even when disabled, Join expects models to subclass Joinable, so skip entirely for single process runs
            if self.distributed_type != DistributedType.NO:
                warnings.warn(
                    "Joining uneven inputs is only supported for multi-GPU training, as a result `join_uneven_inputs` will have no effect."
                )

            with contextlib.nullcontext(joinables):
                yield

    def print(self, *args, **kwargs):
        """
        Drop in replacement of `print()` to only print once per server.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> accelerator.print("Hello world!")
        ```
        """
        self.state.print(*args, **kwargs)

    def _prepare_one(self, obj, first_pass=False, device_placement=None):
        # First pass of preparation: DataLoader, model, optimizer
        if first_pass:
            if isinstance(obj, torch.utils.data.DataLoader):
                return self.prepare_data_loader(obj, device_placement=device_placement)
            elif isinstance(obj, torch.nn.Module):
                return self.prepare_model(obj, device_placement=device_placement)
            elif isinstance(obj, torch.optim.Optimizer):
                optimizer = self.prepare_optimizer(obj, device_placement=device_placement)
                return optimizer
        # Second pass of preparation: LR scheduler (which need the full list of optimizers)
        elif isinstance(obj, LRScheduler):
            scheduler = self.prepare_scheduler(obj)
            return scheduler
        # Return the unprocessed object if previous criteria was not met
        return obj

    def _prepare_fsdp(self, *args):
        result = []
        for obj in args:
            if isinstance(obj, torch.nn.Module):
                model = obj
                break
        optimizers = []

        self._schedulers = []
        self._models = []
        intermediate_result = []
        for obj in args:
            if isinstance(obj, torch.optim.Optimizer):
                if len(obj.param_groups) > 1:
                    logger.warning(
                        "FSDP Warning: When using FSDP, several parameter groups will be conflated into "
                        "a single one due to nested module wrapping and parameter flattening."
                    )
                try:
                    optimizer = obj.optimizer.__class__(model.parameters(), **obj.optimizer.defaults)
                except TypeError:
                    if "differentiable" in obj.optimizer.defaults:
                        # https://github.com/huggingface/accelerate/issues/801
                        defaults = {k: v for k, v in obj.optimizer.defaults.items() if k != "differentiable"}
                        optimizer = obj.optimizer.__class__(model.parameters(), **defaults)
                    else:
                        raise
                obj = self.prepare_optimizer(optimizer)
                optimizers.append(obj)
            elif isinstance(obj, torch.nn.Module):
                self._models.append(obj)
            intermediate_result.append(obj)

        for obj in intermediate_result:
            if isinstance(obj, AcceleratedScheduler):
                obj.optimizer = optimizers
                for i, opt in enumerate(self._optimizers):
                    if getattr(obj.scheduler, "optimizer", None) == opt.optimizer:
                        obj.scheduler.optimizer = optimizers[i]
                        obj.optimizers = [optimizers[i]]
                        break
                self._schedulers.append(obj)
            result.append(obj)
        self._optimizers = optimizers
        return tuple(result)

    def prepare(self, *args, device_placement=None):
        """
        Prepare all objects passed in `args` for distributed training and mixed precision, then return them in the same
        order.

        Args:
            *args (list of objects):
                Any of the following type of objects:

                - `torch.utils.data.DataLoader`: PyTorch Dataloader
                - `torch.nn.Module`: PyTorch Module
                - `torch.optim.Optimizer`: PyTorch Optimizer
                - `torch.optim.lr_scheduler.LRScheduler`: PyTorch LR Scheduler

            device_placement (`List[bool]`, *optional*):
                Used to customize whether automatic device placement should be performed for each object passed. Needs
                to be a list of the same length as `args`.

        <Tip>

          You don't need to prepare a model if you only use it for inference without any kind of mixed precision

        </Tip>

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> # Assume a model, optimizer, data_loader and scheduler are defined
        >>> model, optimizer, data_loader, scheduler = accelerator.prepare(model, optimizer, data_loader, scheduler)
        ```
        """
        if device_placement is None:
            device_placement = [None for _ in args]
        elif self.distributed_type in (DistributedType.DEEPSPEED, DistributedType.MEGATRON_LM):
            raise ValueError("You can't customize device placements with DeepSpeed or Megatron-LM.")
        elif len(device_placement) != len(args):
            raise ValueError(
                f"`device_placement` should be a list with {len(args)} elements (the number of objects passed)."
            )

        if self.distributed_type == DistributedType.FSDP:
            model_count = 0
            optimizer_present = False
            for obj in args:
                if isinstance(obj, torch.nn.Module):
                    model_count += 1
                if isinstance(obj, torch.optim.Optimizer):
                    optimizer_present = True
            if model_count > 1 and optimizer_present:
                raise ValueError(
                    "For FSDP to work with multiple models (>1), "
                    "prepare must be called for all the models before optimizers are created. "
                    "Then pass the optimizers to the prepare call in the same order as corresponding models."
                )
            elif model_count == 1 and optimizer_present:
                logger.warning(
                    "FSDP Warning: When using FSDP, "
                    "it is efficient and recommended to call prepare for the model before creating the optimizer"
                )

        # On TPUs, putting the model on the XLA device will create new parameters, so the corresponding optimizer will
        # have parameters disconnected from the model (so no training :-( ).
        # If the model and optimizer have parameters on different devices we raise an error.
        if self.distributed_type == DistributedType.TPU:
            model_device, optimizer_device = self._get_devices()
            if model_device is not None and optimizer_device is not None and model_device != optimizer_device:
                raise ValueError(
                    "The model and the optimizer parameters are not on the same device, which probably means you "
                    "created an optimizer around your model **before** putting on the device. Make sure the line "
                    "model.to(device) is before the optimizer creation in your script or remove it entirely and use "
                    "the flag default value for `device_placement` in your `Accelerator` to let it handle that "
                    "part for you."
                )

        # If we're dealing with device placement, this deals with that by...
        tpu_should_fix_optimizer = self.device_placement and self.distributed_type == DistributedType.TPU
        if tpu_should_fix_optimizer or self.mixed_precision == "fp8":
            # 1. grabbing old model parameters
            old_named_params = self._get_named_parameters(*args)

        if self.distributed_type == DistributedType.DEEPSPEED:
            result = self._prepare_deepspeed(*args)
        elif self.distributed_type == DistributedType.MEGATRON_LM:
            result = self._prepare_megatron_lm(*args)
        else:
            result = tuple(
                self._prepare_one(obj, first_pass=True, device_placement=d) for obj, d in zip(args, device_placement)
            )
            result = tuple(self._prepare_one(obj, device_placement=d) for obj, d in zip(result, device_placement))

        if tpu_should_fix_optimizer or self.mixed_precision == "fp8":
            # 2. grabbing new model parameters
            new_named_params = self._get_named_parameters(*result)
            # 3. building a map from the first to the second
            mapping = {p: new_named_params[n] for n, p in old_named_params.items()}
            # 4. using that map to update the parameters of the optimizer
            for obj in result:
                if isinstance(obj, torch.optim.Optimizer):
                    obj._switch_parameters(mapping)

        if self.distributed_type == DistributedType.FSDP and model_count == 1 and optimizer_present:
            result = self._prepare_fsdp(*result)

        return result if len(result) > 1 else result[0]

    def prepare_model(self, model: torch.nn.Module, device_placement=None):
        """
        Prepares a PyTorch model for training in any distributed setup. It is recommended to use
        [`Accelerator.prepare`] instead.

        Args:
            model (`torch.nn.Module`):
                A PyTorch model to prepare. You don't need to prepare a model if it is used only for inference without
                any kind of mixed precision
            device_placement (`bool`, *optional*):
                Whether or not to place the model on the proper device. Will default to `self.device_placement`.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> # Assume a model is defined
        >>> model = accelerator.prepare_model(model)
        ```
        """
        if device_placement is None:
            device_placement = self.device_placement and self.distributed_type != DistributedType.FSDP
        self._models.append(model)
        # We check only for models loaded with `accelerate`

        # Checks if any of the child module has the attribute `hf_device_map`.
        has_hf_device_map = False
        for m in model.modules():
            if hasattr(m, "hf_device_map"):
                has_hf_device_map = True
                break

        if getattr(model, "is_loaded_in_8bit", False) and getattr(model, "hf_device_map", False):
            model_devices = set(model.hf_device_map.values())
            if len(model_devices) > 1:
                raise ValueError(
                    "You can't train a model that has been loaded in 8-bit precision on multiple devices."
                )

            current_device_index = list(model_devices)[0]
            if torch.device(current_device_index) != self.device:
                # if on the first device (GPU 0) we don't care
                if (self.device.index is not None) or (current_device_index != 0):
                    raise ValueError(
                        "You can't train a model that has been loaded in 8-bit precision on a different device than the one "
                        "you're training on. Make sure you loaded the model on the correct device using for example `device_map={'':torch.cuda.current_device()}"
                    )

            if "cpu" in model_devices or "disk" in model_devices:
                raise ValueError(
                    "You can't train a model that has been loaded in 8-bit precision with CPU or disk offload."
                )
        elif device_placement and not has_hf_device_map:
            model = model.to(self.device)

        if self.distributed_type == DistributedType.MULTI_GPU:
            if any(p.requires_grad for p in model.parameters()):
                kwargs = self.ddp_handler.to_kwargs() if self.ddp_handler is not None else {}
                model = torch.nn.parallel.DistributedDataParallel(
                    model, device_ids=[self.local_process_index], output_device=self.local_process_index, **kwargs
                )
        elif self.distributed_type == DistributedType.FSDP:
            from torch.distributed.fsdp.fully_sharded_data_parallel import FullyShardedDataParallel as FSDP

            # Check if the model is already a FSDP model due to `Manual Wrapping` and if so,
            # don't wrap it again
            if type(model) != FSDP:
                self.state.fsdp_plugin.set_auto_wrap_policy(model)
                fsdp_plugin = self.state.fsdp_plugin
                kwargs = {
                    "sharding_strategy": fsdp_plugin.sharding_strategy,
                    "cpu_offload": fsdp_plugin.cpu_offload,
                    "auto_wrap_policy": fsdp_plugin.auto_wrap_policy,
                    "backward_prefetch": fsdp_plugin.backward_prefetch,
                    "mixed_precision": fsdp_plugin.mixed_precision_policy,
                    "ignored_modules": fsdp_plugin.ignored_modules,
                    "device_id": self.device,
                }
                signature = inspect.signature(FSDP.__init__).parameters.keys()
                if "limit_all_gathers" in signature:
                    kwargs["limit_all_gathers"] = fsdp_plugin.limit_all_gathers
                if "use_orig_params" in signature:
                    kwargs["use_orig_params"] = fsdp_plugin.use_orig_params
                model = FSDP(model, **kwargs)
            self._models[-1] = model
        elif self.distributed_type == DistributedType.MULTI_CPU:
            kwargs = self.ddp_handler.to_kwargs() if self.ddp_handler is not None else {}
            model = torch.nn.parallel.DistributedDataParallel(model, **kwargs)
        if self.native_amp:
            model._original_forward = model.forward
            if self.mixed_precision == "fp16" and is_torch_version(">=", "1.10"):
                model.forward = torch.cuda.amp.autocast(dtype=torch.float16)(model.forward)
            elif self.mixed_precision == "bf16" and self.distributed_type != DistributedType.TPU:
                model.forward = torch.autocast(device_type=self.device.type, dtype=torch.bfloat16)(model.forward)
            else:
                model.forward = torch.cuda.amp.autocast()(model.forward)
            model.forward = convert_outputs_to_fp32(model.forward)
        elif self.mixed_precision == "fp8":
            if not has_transformer_engine_layers(model):
                with torch.no_grad():
                    convert_model(model)
                model._converted_to_transformer_engine = True
            model._original_forward = model.forward

            kwargs = self.fp8_recipe_handler.to_kwargs() if self.fp8_recipe_handler is not None else {}
            if "fp8_format" in kwargs:
                kwargs["fp8_format"] = getattr(te_recipe.Format, kwargs["fp8_format"])
            fp8_recipe = te_recipe.DelayedScaling(**kwargs)
            fp8_enabled = torch.cuda.get_device_capability()[0] >= 9
            if not fp8_enabled:
                logger.warn(
                    f"The current device has compute capability of {torch.cuda.get_device_capability()} which is "
                    "insufficient for FP8 mixed precision training (requires a GPU Hopper or higher, compute "
                    "capability of 9 or higher). Will use FP16 instead."
                )
            model.forward = fp8_autocast(enabled=fp8_enabled, fp8_recipe=fp8_recipe)(model.forward)
        if self.distributed_type == DistributedType.TPU and self.state.fork_launched:
            model = xmp.MpModelWrapper(model).to(self.device)
        # torch.compile should be called last.
        if self.state.dynamo_plugin.backend != DynamoBackend.NO:
            if not hasattr(torch, "compile"):
                raise ValueError("Using torch.compile requires PyTorch 2.0 or higher.")
            model = torch.compile(model, **self.state.dynamo_plugin.to_kwargs())
        return model

    def _prepare_deepspeed(self, *args):
        deepspeed_plugin = self.state.deepspeed_plugin

        is_dataloader_present = any(isinstance(obj, torch.utils.data.DataLoader) for obj in args)
        if deepspeed_plugin.deepspeed_config["train_micro_batch_size_per_gpu"] == "auto" or is_dataloader_present:
            result = [
                self._prepare_one(obj, first_pass=True) if isinstance(obj, torch.utils.data.DataLoader) else obj
                for obj in args
            ]

            batch_sizes = [obj.batch_size for obj in args if hasattr(obj, "batch_size")]
            if self.split_batches:
                batch_sizes = [batch_size // self.num_processes for batch_size in batch_sizes]
            if len(batch_sizes) == 0:
                raise ValueError(
                    "When using DeepSpeed `accelerate.prepare()` requires you to pass at least one of training or evaluation dataloaders "
                    "or alternatively set an integer value in `train_micro_batch_size_per_gpu` in the deepspeed config file"
                    "or assign integer value to `AcceleratorState().deepspeed_plugin.deepspeed_config['train_micro_batch_size_per_gpu']`."
                )

            batch_size_per_device = min(batch_sizes) if deepspeed_plugin.is_train_batch_min else max(batch_sizes)
            if len(batch_sizes) > 1:
                logger.info(
                    "Since you passed both train and evaluation dataloader, `is_train_batch_min` (here "
                    f"{deepspeed_plugin.is_train_batch_min} will decide the `train_batch_size` ({batch_size_per_device})."
                )
        else:
            batch_size_per_device = deepspeed_plugin.deepspeed_config["train_micro_batch_size_per_gpu"]
            result = [obj for obj in args]

        if self.gradient_accumulation_steps != deepspeed_plugin.deepspeed_config["gradient_accumulation_steps"]:
            logger.info(
                f"Updating DeepSpeed's gradient accumulation steps to {self.gradient_accumulation_steps} from "
                f"{deepspeed_plugin.deepspeed_config['gradient_accumulation_steps']}."
            )
            deepspeed_plugin.deepspeed_config["gradient_accumulation_steps"] = self.gradient_accumulation_steps
        config_kwargs = {
            "train_micro_batch_size_per_gpu": batch_size_per_device,
            "train_batch_size": batch_size_per_device
            * deepspeed_plugin.deepspeed_config["gradient_accumulation_steps"]
            * self.num_processes,
            "gradient_clipping": 1.0,
            "zero_optimization.stage3_gather_16bit_weights_on_model_save": False,
        }

        model = None
        optimizer = None
        scheduler = None
        for obj in result:
            if isinstance(obj, torch.nn.Module):
                model = obj
            elif isinstance(obj, (torch.optim.Optimizer, DummyOptim)):
                optimizer = obj
            elif (isinstance(obj, (LRScheduler, DummyScheduler))) or (
                type(obj).__name__ in deepspeed.runtime.lr_schedules.VALID_LR_SCHEDULES
            ):
                scheduler = obj

        if optimizer is not None:
            if "optimizer" in deepspeed_plugin.deepspeed_config and not isinstance(optimizer, (DummyOptim)):
                raise ValueError(
                    "You cannot specify an optimizer in the config file and in the code at the same time. "
                    "Please remove the optimizer from the config file or "
                    "create `accelerate.utils.DummyOptim` in the code."
                )
            elif "optimizer" not in deepspeed_plugin.deepspeed_config and isinstance(optimizer, (DummyOptim)):
                raise ValueError(
                    "You cannot create a `DummyOptim` without specifying an optimizer in the config file."
                )

            if isinstance(optimizer, (torch.optim.Optimizer)):
                deepspeed_plugin.deepspeed_config["zero_allow_untested_optimizer"] = True

        if scheduler is not None:
            if "scheduler" in deepspeed_plugin.deepspeed_config and not isinstance(scheduler, (DummyScheduler)):
                raise ValueError(
                    "You cannot specify a scheduler in the config file and in the code at the same time. "
                    "Please remove the scheduler from the config file or "
                    "create `accelerate.utils.DummyScheduler` in the code."
                )
            elif "scheduler" not in deepspeed_plugin.deepspeed_config and isinstance(scheduler, (DummyScheduler)):
                raise ValueError(
                    "You cannot create a `DummyScheduler` without specifying a scheduler in the config file."
                )

        if optimizer is not None and scheduler is not None:
            if isinstance(optimizer, (DummyOptim)) and not isinstance(scheduler, (DummyScheduler)):
                raise ValueError(
                    "You can only specify `accelerate.utils.DummyScheduler` in the code when using "
                    "`accelerate.utils.DummyOptim`."
                )

        if model is not None:
            if hasattr(model, "config"):
                hidden_size = (
                    max(model.config.hidden_sizes)
                    if getattr(model.config, "hidden_sizes", None)
                    else getattr(model.config, "hidden_size", None)
                )
                if hidden_size is not None:
                    config_kwargs.update(
                        {
                            "zero_optimization.reduce_bucket_size": hidden_size * hidden_size,
                            "zero_optimization.stage3_prefetch_bucket_size": 0.9 * hidden_size * hidden_size,
                            "zero_optimization.stage3_param_persistence_threshold": 10 * hidden_size,
                        }
                    )

            if isinstance(optimizer, (DummyOptim)):
                config_kwargs.update(
                    {"optimizer.params.lr": optimizer.lr, "optimizer.params.weight_decay": optimizer.weight_decay}
                )
            if isinstance(scheduler, (DummyScheduler)):
                config_kwargs.update(
                    {
                        "scheduler.params.warmup_min_lr": 0,
                        "scheduler.params.warmup_max_lr": scheduler.optimizer.lr,
                        "scheduler.params.warmup_num_steps": scheduler.warmup_num_steps,
                    }
                )
                if scheduler.total_num_steps is not None:
                    config_kwargs["scheduler.params.total_num_steps"] = (
                        math.ceil(scheduler.total_num_steps / self.num_processes)
                        if not self.split_batches
                        else scheduler.total_num_steps
                    )
            deepspeed_plugin.deepspeed_config_process(must_match=False, **config_kwargs)
            self.deepspeed_config = deepspeed_plugin.deepspeed_config
            kwargs = dict(model=model, config_params=self.deepspeed_config)
            if optimizer is not None:
                if isinstance(optimizer, (DummyOptim)):
                    kwargs["model_parameters"] = optimizer.params
                else:
                    kwargs["optimizer"] = optimizer
                    if scheduler is not None:
                        if type(scheduler).__name__ in deepspeed.runtime.lr_schedules.VALID_LR_SCHEDULES:
                            kwargs["lr_scheduler"] = scheduler

            engine, optimizer, _, lr_scheduler = deepspeed.initialize(**kwargs)
            if optimizer is not None:
                optimizer = DeepSpeedOptimizerWrapper(optimizer)
            if scheduler is not None:
                if lr_scheduler is None:
                    scheduler = AcceleratedScheduler(
                        scheduler,
                        optimizer,
                        step_with_optimizer=self.step_scheduler_with_optimizer,
                        split_batches=self.split_batches,
                    )
                else:
                    scheduler = DeepSpeedSchedulerWrapper(lr_scheduler, optimizer)

            for i in range(len(result)):
                if isinstance(result[i], torch.nn.Module):
                    result[i] = engine
                elif isinstance(result[i], (torch.optim.Optimizer, DummyOptim)):
                    result[i] = optimizer
                elif (isinstance(result[i], (LRScheduler, DummyScheduler))) or (
                    type(result[i]).__name__ in deepspeed.runtime.lr_schedules.VALID_LR_SCHEDULES
                ):
                    result[i] = scheduler
            # pointing for deepspeed_engine_wrapped.backward()
            self.deepspeed_engine_wrapped = DeepSpeedEngineWrapper(engine)
            self._models.append(engine)
            if optimizer is not None:
                self._optimizers.append(optimizer)
            if scheduler is not None:
                self._schedulers.append(scheduler)
            if len(self._models) > 1:
                raise AssertionError(
                    "You can't use same `Accelerator()` instance with multiple models when using DeepSpeed"
                )
        return tuple(result)

    def _prepare_megatron_lm(self, *args):
        megatron_lm_plugin = self.state.megatron_lm_plugin
        if not megatron_lm_plugin.megatron_dataset_flag:
            batch_sizes = [obj.batch_size for obj in args if hasattr(obj, "batch_size")]
            if len(batch_sizes) == 0:
                raise ValueError(
                    "You must specify a training or evaluation dataloader in `accelerate.prepare()` when using Megatron-LM."
                )

            micro_batch_size = min(batch_sizes) if megatron_lm_plugin.is_train_batch_min else max(batch_sizes)
            if len(batch_sizes) > 1:
                logger.info(
                    "Since you passed both train and evaluation dataloader, `is_train_batch_min` (here "
                    f"{megatron_lm_plugin.is_train_batch_min} will decide the `train_batch_size` ({micro_batch_size})."
                )
        else:
            for obj in args:
                if isinstance(obj, MegatronLMDummyDataLoader):
                    micro_batch_size = obj.dataset_args["micro_batch_size"]
                    break

        dp_degree = self.num_processes // (megatron_lm_plugin.tp_degree * megatron_lm_plugin.pp_degree)
        megatron_lm_plugin.set_training_args(micro_batch_size, dp_degree)

        model = None
        optimizer = None
        scheduler = None
        is_dummy_scheduler = False
        batch_data = None
        for obj in args:
            if isinstance(obj, torch.utils.data.DataLoader) and batch_data is None:
                batch_data = next(iter(obj))
            if isinstance(obj, torch.nn.Module):
                model = obj
            elif isinstance(obj, (torch.optim.Optimizer)):
                optimizer = obj
            elif isinstance(obj, (LRScheduler, MegatronLMDummyScheduler)):
                scheduler = obj

        if model is not None:
            megatron_lm_plugin.set_network_size_args(model, batch_data)
        if optimizer is not None:
            megatron_lm_plugin.set_optimizer_type(optimizer)
        if scheduler is not None:
            is_dummy_scheduler = isinstance(scheduler, MegatronLMDummyScheduler)
            if not is_dummy_scheduler:
                raise ValueError(
                    "You can't use a custom scheduler with Megatron-LM. Please use the `accelerate.utils.MegatronLMDummyScheduler` instead."
                )
            megatron_lm_plugin.set_scheduler_args(scheduler)

        # initialize megatron-lm
        megatron_lm_initialize(self, args_defaults=megatron_lm_plugin.megatron_lm_default_args)
        counter = 0
        result = []
        for obj in args:
            if isinstance(obj, torch.utils.data.DataLoader):
                result.append(megatron_lm_prepare_data_loader(self, obj))
                counter += 1
            elif isinstance(obj, MegatronLMDummyDataLoader):
                if counter == 0:
                    obj.set_megatron_data_args()
                    dataloaders = megatron_lm_prepare_data_loader(self, obj)
                result.append(dataloaders[counter])
                counter += 1
            else:
                result.append(obj)

        if model is not None:
            model = megatron_lm_prepare_model(self)
        if optimizer is not None:
            optimizer = megatron_lm_prepare_optimizer(self, model)
        if scheduler is not None:
            scheduler = megatron_lm_prepare_scheduler(self, optimizer, scheduler)

        if model is not None:
            model = MegatronEngine(self, model, optimizer, scheduler)
        if optimizer is not None:
            optimizer = MegatronLMOptimizerWrapper(optimizer)
        if scheduler is not None:
            scheduler = MegatronLMSchedulerWrapper(scheduler, optimizer)

        for i in range(len(result)):
            if isinstance(result[i], torch.nn.Module):
                result[i] = model
            elif isinstance(result[i], torch.optim.Optimizer):
                result[i] = optimizer
            elif isinstance(result[i], MegatronLMDummyScheduler):
                result[i] = scheduler
        if model is not None:
            self._models.append(model)
        if optimizer is not None:
            self._optimizers.append(optimizer)
        if scheduler is not None:
            self._schedulers.append(scheduler)
        if len(self._models) > 1:
            raise AssertionError(
                "You can't use same `Accelerator()` instance with multiple models when using Megatron-LM"
            )
        return tuple(result)

    def prepare_data_loader(self, data_loader: torch.utils.data.DataLoader, device_placement=None):
        """
        Prepares a PyTorch DataLoader for training in any distributed setup. It is recommended to use
        [`Accelerator.prepare`] instead.

        Args:
            data_loader (`torch.utils.data.DataLoader`):
                A vanilla PyTorch DataLoader to prepare
            device_placement (`bool`, *optional*):
                Whether or not to place the batches on the proper device in the prepared dataloader. Will default to
                `self.device_placement`.

        Example:

        ```python
        >>> import torch
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> data_loader = torch.utils.data.DataLoader(...)
        >>> data_loader = accelerator.prepare_data_loader(data_loader, device_placement=True)
        ```
        """
        if device_placement is None:
            device_placement = self.device_placement if self.distributed_type != DistributedType.TPU else False
        prepared_data_loader = prepare_data_loader(
            data_loader,
            self.device,
            num_processes=self.num_processes,
            process_index=self.process_index,
            split_batches=self.split_batches,
            put_on_device=device_placement,
            rng_types=self.rng_types.copy(),
            dispatch_batches=self.dispatch_batches,
            even_batches=self.even_batches,
        )
        self._dataloaders.append(prepared_data_loader)
        return prepared_data_loader

    def prepare_optimizer(self, optimizer: torch.optim.Optimizer, device_placement=None):
        """
        Prepares a PyTorch Optimizer for training in any distributed setup. It is recommended to use
        [`Accelerator.prepare`] instead.

        Args:
            optimizer (`torch.optim.Optimizer`):
                A vanilla PyTorch optimizer to prepare
            device_placement (`bool`, *optional*):
                Whether or not to place the optimizer on the proper device. Will default to `self.device_placement`.

        Example:

        ```python
        >>> import torch
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> optimizer = torch.optim.Adam(...)
        >>> optimizer = accelerator.prepare_optimizer(optimizer, device_placement=True)
        ```
        """
        if device_placement is None:
            device_placement = self.device_placement
        optimizer = AcceleratedOptimizer(optimizer, device_placement=device_placement, scaler=self.scaler)
        self._optimizers.append(optimizer)
        return optimizer

    def prepare_scheduler(self, scheduler: LRScheduler):
        """
        Prepares a PyTorch Scheduler for training in any distributed setup. It is recommended to use
        [`Accelerator.prepare`] instead.

        Args:
            scheduler (`torch.optim.lr_scheduler.LRScheduler`):
                A vanilla PyTorch scheduler to prepare

        Example:

        ```python
        >>> import torch
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> optimizer = torch.optim.Adam(...)
        >>> scheduler = torch.optim.lr_scheduler.LambdaLR(optimizer, ...)
        >>> scheduler = accelerator.prepare_scheduler(scheduler)
        ```
        """
        # We try to find the optimizer associated with `scheduler`, the default is the full list.
        optimizer = self._optimizers
        for opt in self._optimizers:
            if getattr(scheduler, "optimizer", None) == opt.optimizer:
                optimizer = opt
                break
        scheduler = AcceleratedScheduler(
            scheduler,
            optimizer,
            step_with_optimizer=self.step_scheduler_with_optimizer,
            split_batches=self.split_batches,
        )
        self._schedulers.append(scheduler)
        return scheduler

    def backward(self, loss, **kwargs):
        """
        Scales the gradients in accordance to the `GradientAccumulationPlugin` and calls the correct `backward()` based
        on the configuration.

        Should be used in lieu of `loss.backward()`.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator(gradient_accumulation_steps=2)
        >>> outputs = model(inputs)
        >>> loss = loss_fn(outputs, labels)
        >>> accelerator.backward(loss)
        ```
        """
        if self.distributed_type != DistributedType.DEEPSPEED:
            # deepspeed handles loss scaling by gradient_accumulation_steps in its `backward`
            loss = loss / self.gradient_accumulation_steps
        if self.distributed_type == DistributedType.DEEPSPEED:
            self.deepspeed_engine_wrapped.backward(loss, **kwargs)
        elif self.distributed_type == DistributedType.MEGATRON_LM:
            return
        elif self.scaler is not None:
            self.scaler.scale(loss).backward(**kwargs)
        else:
            loss.backward(**kwargs)

    def unscale_gradients(self, optimizer=None):
        """
        Unscale the gradients in mixed precision training with AMP. This is a noop in all other settings.

        Likely should be called through [`Accelerator.clip_grad_norm_`] or [`Accelerator.clip_grad_value_`]

        Args:
            optimizer (`torch.optim.Optimizer` or `List[torch.optim.Optimizer]`, *optional*):
                The optimizer(s) for which to unscale gradients. If not set, will unscale gradients on all optimizers
                that were passed to [`~Accelerator.prepare`].

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> model, optimizer = accelerator.prepare(model, optimizer)
        >>> outputs = model(inputs)
        >>> loss = loss_fn(outputs, labels)
        >>> accelerator.backward(loss)
        >>> accelerator.unscale_gradients(optimizer=optimizer)
        ```
        """
        if self.native_amp and self.mixed_precision == "fp16":
            if optimizer is None:
                # TODO: this unscales all optimizers where we should only unscale the one where parameters are.
                optimizer = self._optimizers
            elif not isinstance(optimizer, (tuple, list)):
                optimizer = [optimizer]
            for opt in optimizer:
                while isinstance(opt, AcceleratedOptimizer):
                    opt = opt.optimizer
                self.scaler.unscale_(opt)

    def clip_grad_norm_(self, parameters, max_norm, norm_type=2):
        """
        Should be used in place of `torch.nn.utils.clip_grad_norm_`.

        Returns:
            `torch.Tensor`: Total norm of the parameter gradients (viewed as a single vector).

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator(gradient_accumulation_steps=2)
        >>> dataloader, model, optimizer, scheduler = accelerator.prepare(dataloader, model, optimizer, scheduler)

        >>> for input, target in dataloader:
        ...     optimizer.zero_grad()
        ...     output = model(input)
        ...     loss = loss_func(output, target)
        ...     accelerator.backward(loss)
        ...     if accelerator.sync_gradients:
        ...         accelerator.clip_grad_norm_(model.parameters(), max_grad_norm)
        ...     optimizer.step()
        ```
        """
        if self.distributed_type == DistributedType.FSDP:
            self.unscale_gradients()
            parameters = [p for p in parameters]
            for model in self._models:
                if parameters == [p for p in model.parameters()]:
                    return model.clip_grad_norm_(max_norm, norm_type)
        elif self.distributed_type == DistributedType.DEEPSPEED:
            # `accelerator.backward(loss)` is doing that automatically. Therefore, its implementation is not needed
            # We cannot return the gradient norm because DeepSpeed does it.
            return None
        self.unscale_gradients()
        return torch.nn.utils.clip_grad_norm_(parameters, max_norm, norm_type=norm_type)

    def clip_grad_value_(self, parameters, clip_value):
        """
        Should be used in place of `torch.nn.utils.clip_grad_value_`.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator(gradient_accumulation_steps=2)
        >>> dataloader, model, optimizer, scheduler = accelerator.prepare(dataloader, model, optimizer, scheduler)

        >>> for input, target in dataloader:
        ...     optimizer.zero_grad()
        ...     output = model(input)
        ...     loss = loss_func(output, target)
        ...     accelerator.backward(loss)
        ...     if accelerator.sync_gradients:
        ...         accelerator.clip_grad_value_(model.parameters(), clip_value)
        ...     optimizer.step()
        ```
        """
        if self.distributed_type in [DistributedType.DEEPSPEED, DistributedType.FSDP]:
            raise Exception("DeepSpeed and FSDP  do not support `clip_grad_value_`. Use `clip_grad_norm_` instead.")
        self.unscale_gradients()
        torch.nn.utils.clip_grad_value_(parameters, clip_value)

    def gather(self, tensor):
        """
        Gather the values in *tensor* across all processes and concatenate them on the first dimension. Useful to
        regroup the predictions from all processes when doing evaluation.

        Note:
            This gather happens in all processes.

        Args:
            tensor (`torch.Tensor`, or a nested tuple/list/dictionary of `torch.Tensor`):
                The tensors to gather across all processes.

        Returns:
            `torch.Tensor`, or a nested tuple/list/dictionary of `torch.Tensor`: The gathered tensor(s). Note that the
            first dimension of the result is *num_processes* multiplied by the first dimension of the input tensors.

        Example:

        ```python
        >>> # Assuming four processes
        >>> import torch
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> process_tensor = torch.tensor([accelerator.process_index])
        >>> gathered_tensor = accelerator.gather(process_tensor)
        >>> gathered_tensor
        tensor([0, 1, 2, 3])
        ```
        """
        return gather(tensor)

    def gather_for_metrics(self, tensor):
        """
        Gathers `tensor` and potentially drops duplicates in the last batch if on a distributed system. Should be used
        for gathering the inputs and targets for metric calculation.

        Args:
            tensor (`torch.Tensor`, or a nested tuple/list/dictionary of `torch.Tensor`):
                The tensors for calculating metrics across all processes.

        Example:

        ```python
        >>> # Assuming two processes, with a batch size of 5 on a dataset with 9 samples
        >>> import torch
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> dataloader = torch.utils.data.DataLoader(range(9), batch_size=5)
        >>> dataloader = accelerator.prepare(dataloader)
        >>> batch = next(iter(dataloader))
        >>> gathered_items = accelerator.gather_for_metrics(batch)
        >>> len(gathered_items)
        9
        ```
        """
        tensor = self.gather(tensor)
        if self.use_distributed:
            if self.gradient_state.remainder == -1:
                logger.info(
                    "The used dataset had no length, returning gathered tensors. You should drop the remainder yourself."
                )
                return tensor
            try:
                # Then see if we're on the last batch of our eval dataloader
                if self.gradient_state.end_of_dataloader and self.gradient_state.remainder > 0:
                    # Last batch needs to be truncated on distributed systems as it contains additional samples
                    def _adjust_samples(tensor):
                        return tensor[: self.gradient_state.remainder]

                    return recursively_apply(_adjust_samples, tensor)
                else:
                    # Not at the end of the dataloader, no need to adjust the tensors
                    return tensor
            except Exception:
                # Dataset had no length or raised an error
                return tensor
        return tensor

    def reduce(self, tensor, reduction="sum"):
        """
        Reduce the values in *tensor* across all processes based on *reduction*.

        Note:
            All processes get the reduced value.

        Args:
            tensor (`torch.Tensor`, or a nested tuple/list/dictionary of `torch.Tensor`):
                The tensors to reduce across all processes.
            reduction (`str`, *optional*, defaults to "sum"):
                A reduction type, can be one of 'sum', 'mean', or 'none'. If 'none', will not perform any operation.

        Returns:
            `torch.Tensor`, or a nested tuple/list/dictionary of `torch.Tensor`:
                The reduced tensor(s).

        Example:

        ```python
        >>> # Assuming two processes
        >>> import torch
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> process_tensor = torch.arange(accelerator.num_processes) + 1 + (2 * accelerator.process_index)
        >>> process_tensor = process_tensor.to(accelerator.device)
        >>> reduced_tensor = accelerator.reduce(process_tensor, reduction="sum")
        >>> reduced_tensor
        tensor([4, 6])
        ```
        """
        return reduce(tensor, reduction)

    def pad_across_processes(self, tensor, dim=0, pad_index=0, pad_first=False):
        """
        Recursively pad the tensors in a nested list/tuple/dictionary of tensors from all devices to the same size so
        they can safely be gathered.

        Args:
            tensor (nested list/tuple/dictionary of `torch.Tensor`):
                The data to gather.
            dim (`int`, *optional*, defaults to 0):
                The dimension on which to pad.
            pad_index (`int`, *optional*, defaults to 0):
                The value with which to pad.
            pad_first (`bool`, *optional*, defaults to `False`):
                Whether to pad at the beginning or the end.

        Returns:
            `torch.Tensor`, or a nested tuple/list/dictionary of `torch.Tensor`:
                The padded tensor(s).

        Example:

        ```python
        >>> # Assuming two processes, with the first processes having a tensor of size 1 and the second of size 2
        >>> import torch
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> process_tensor = torch.arange(accelerator.process_index + 1).to(accelerator.device)
        >>> padded_tensor = accelerator.pad_across_processes(process_tensor)
        >>> padded_tensor.shape
        torch.Size([2])
        ```
        """
        return pad_across_processes(tensor, dim=dim, pad_index=pad_index, pad_first=pad_first)

    def unwrap_model(self, model, keep_fp32_wrapper: bool = True):
        """
        Unwraps the `model` from the additional layer possible added by [`~Accelerator.prepare`]. Useful before saving
        the model.

        Args:
            model (`torch.nn.Module`):
                The model to unwrap.
            keep_fp32_wrapper (`bool`, *optional*, defaults to `True`):
                Whether to not remove the mixed precision hook if it was added.

        Returns:
            `torch.nn.Module`: The unwrapped model.

        Example:

        ```python
        >>> # Assuming two GPU processes
        >>> from torch.nn.parallel import DistributedDataParallel
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> model = accelerator.prepare(MyModel())
        >>> print(model.__class__.__name__)
        DistributedDataParallel

        >>> model = accelerator.unwrap_model(model)
        >>> print(model.__class__.__name__)
        MyModel
        ```
        """
        return extract_model_from_parallel(model, keep_fp32_wrapper)

    def wait_for_everyone(self):
        """
        Will stop the execution of the current process until every other process has reached that point (so this does
        nothing when the script is only run in one process). Useful to do before saving a model.

        Example:

        ```python
        >>> # Assuming two GPU processes
        >>> import time
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> if accelerator.is_main_process:
        ...     time.sleep(2)
        >>> else:
        ...     print("I'm waiting for the main process to finish its sleep...")
        >>> accelerator.wait_for_everyone()
        >>> # Should print on every process at the same time
        >>> print("Everyone is here")
        ```
        """
        wait_for_everyone()

    @on_main_process
    def init_trackers(self, project_name: str, config: Optional[dict] = None, init_kwargs: Optional[dict] = {}):
        """
        Initializes a run for all trackers stored in `self.log_with`, potentially with starting configurations

        Args:
            project_name (`str`):
                The name of the project. All trackers will save their data based on this
            config (`dict`, *optional*):
                Optional starting configuration to be logged.
            init_kwargs (`dict`, *optional*):
                A nested dictionary of kwargs to be passed to a specific tracker's `__init__` function. Should be
                formatted like so:
                ```python
                {"wandb": {"tags": ["tag_a", "tag_b"]}}
                ```

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator(log_with="tensorboard")
        >>> accelerator.init_trackers(
        ...     project_name="my_project",
        ...     config={"learning_rate": 0.001, "batch_size": 32},
        ...     init_kwargs={"tensorboard": {"flush_secs": 60}},
        ... )
        ```
        """
        self.trackers = []
        for tracker in self.log_with:
            if issubclass(type(tracker), GeneralTracker):
                # Custom trackers are already initialized
                self.trackers.append(tracker)
            else:
                tracker_init = LOGGER_TYPE_TO_CLASS[str(tracker)]
                if getattr(tracker_init, "requires_logging_directory"):
                    # We can skip this check since it was done in `__init__`
                    self.trackers.append(
                        tracker_init(project_name, self.logging_dir, **init_kwargs.get(str(tracker), {}))
                    )
                else:
                    self.trackers.append(tracker_init(project_name, **init_kwargs.get(str(tracker), {})))
        if config is not None:
            for tracker in self.trackers:
                tracker.store_init_configuration(config)

    def get_tracker(self, name: str, unwrap: bool = False):
        """
        Returns a `tracker` from `self.trackers` based on `name` on the main process only.

        Args:
            name (`str`):
                The name of a tracker, corresponding to the `.name` property.
            unwrap (`bool`):
                Whether to return the internal tracking mechanism or to return the wrapped tracker instead
                (recommended).

        Returns:
            `GeneralTracker`: The tracker corresponding to `name` if it exists.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator(log_with="tensorboard")
        >>> accelerator.init_trackers("my_project")
        >>> tensorboard_tracker = accelerator.get_tracker("tensorboard")
        ```
        """
        if len(getattr(self, "trackers", [])) > 0:
            for tracker in self.trackers:
                if tracker.name == name:
                    return tracker.tracker if unwrap else tracker
            raise ValueError(f"{name} is not an available tracker stored inside the `Accelerator`.")
        # Handle tracker only made on main process
        return GeneralTracker(_blank=True)

    @on_main_process
    def log(self, values: dict, step: Optional[int] = None, log_kwargs: Optional[dict] = {}):
        """
        Logs `values` to all stored trackers in `self.trackers` on the main process only.

        Args:
            values (`dict`):
                Values should be a dictionary-like object containing only types `int`, `float`, or `str`.
            step (`int`, *optional*):
                The run step. If included, the log will be affiliated with this step.
            log_kwargs (`dict`, *optional*):
                A nested dictionary of kwargs to be passed to a specific tracker's `log` function. Should be formatted
                like so:
                ```python
                {"wandb": {"tags": ["tag_a", "tag_b"]}}
                ```

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator(log_with="tensorboard")
        >>> accelerator.init_trackers("my_project")
        >>> accelerator.log({"loss": 0.5, "accuracy": 0.9})
        ```
        """
        for tracker in self.trackers:
            tracker.log(values, step=step, **log_kwargs.get(tracker.name, {}))

    @on_main_process
    def end_training(self):
        """
        Runs any special end training behaviors, such as stopping trackers on the main process only. Should always be
        called at the end of your script if using experiment tracking.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator(log_with="tensorboard")
        >>> accelerator.init_trackers("my_project")
        >>> # Do training
        >>> accelerator.end_training()
        ```
        """
        for tracker in self.trackers:
            tracker.finish()

    def save(self, obj, f):
        """
        Save the object passed to disk once per machine. Use in place of `torch.save`.

        Args:
            obj (`object`): The object to save.
            f (`str` or `os.PathLike`): Where to save the content of `obj`.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> arr = [0, 1, 2, 3]
        >>> accelerator.save(arr, "array.pkl")
        ```
        """
        save(obj, f)

    def register_save_state_pre_hook(self, hook: Callable[..., None]) -> hooks.RemovableHandle:
        """
        Registers a pre hook to be run before `save_checkpoint` is called in [`Accelerator.save_state`].

        Args:
            hook (`Callable`):
                A function to be called in [`Accelerator.save_state`] before `save_checkpoint`.

        The hook should have the following signature:

        `hook(models: List[torch.nn.Module], weights: List[Dict[str, torch.Tensor]], input_dir: str) -> None`

        The `models` argument are the models as saved in the accelerator state under `accelerator._models`, `weigths`
        argument are the state dicts of the `models`, and the `input_dir` argument is the `input_dir` argument passed
        to [`Accelerator.load_state`].

        <Tip>

        Should only be used in conjunction with [`Accelerator.register_load_state_pre_hook`]. Can be useful to save
        configurations in addition to model weights. Can also be used to overwrite model saving with a customized
        method. In this case, make sure to remove already loaded weights from the weights list.

        </Tip>

        Returns:
            `torch.utils.hooks.RemovableHandle`: a handle that can be used to remove the added hook by calling
            `handle.remove()`
        """
        handle = hooks.RemovableHandle(self._save_model_state_pre_hook)
        self._save_model_state_pre_hook[handle.id] = hook
        return handle

    def save_state(self, output_dir: str = None, **save_model_func_kwargs):
        """
        Saves the current states of the model, optimizer, scaler, RNG generators, and registered objects to a folder.

        If a `ProjectConfiguration` was passed to the `Accelerator` object with `automatic_checkpoint_naming` enabled
        then checkpoints will be saved to `self.project_dir/checkpoints`. If the number of current saves is greater
        than `total_limit` then the oldest save is deleted. Each checkpoint is saved in seperate folders named
        `checkpoint_<iteration>`.

        Otherwise they are just saved to `output_dir`.

        <Tip>

        Should only be used when wanting to save a checkpoint during training and restoring the state in the same
        environment.

        </Tip>

        Args:
            output_dir (`str` or `os.PathLike`):
                The name of the folder to save all relevant weights and states.
            save_model_func_kwargs (`dict`, *optional*):
                Additional keyword arguments for saving model which can be passed to the underlying save function, such
                as optional arguments for DeepSpeed's `save_checkpoint` function.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> model, optimizer, lr_scheduler = ...
        >>> model, optimizer, lr_scheduler = accelerator.prepare(model, optimizer, lr_scheduler)
        >>> accelerator.save_state(output_dir="my_checkpoint")
        ```
        """
        if self.project_configuration.automatic_checkpoint_naming:
            output_dir = os.path.join(self.project_dir, "checkpoints")
        os.makedirs(output_dir, exist_ok=True)
        if self.project_configuration.automatic_checkpoint_naming:
            folders = [os.path.join(output_dir, folder) for folder in os.listdir(output_dir)]
            if self.project_configuration.total_limit is not None and (
                len(folders) + 1 > self.project_configuration.total_limit
            ):

                def _inner(folder):
                    return list(map(int, re.findall(r"[\/]?([0-9]+)(?=[^\/]*$)", folder)))[0]

                folders.sort(key=_inner)
                logger.warning(
                    f"Deleting {len(folders) + 1 - self.project_configuration.total_limit} checkpoints to make room for new checkpoint."
                )
                for folder in folders[: len(folders) + 1 - self.project_configuration.total_limit]:
                    shutil.rmtree(folder)
            output_dir = os.path.join(output_dir, f"checkpoint_{self.save_iteration}")
            if os.path.exists(output_dir):
                raise ValueError(
                    f"Checkpoint directory {output_dir} ({self.save_iteration}) already exists. Please manually override `self.save_iteration` with what iteration to start with."
                )
        os.makedirs(output_dir, exist_ok=True)
        logger.info(f"Saving current state to {output_dir}")

        # Save the models taking care of FSDP and DeepSpeed nuances
        weights = []
        for i, model in enumerate(self._models):
            if self.distributed_type == DistributedType.FSDP:
                logger.info("Saving FSDP model")
                self.state.fsdp_plugin.save_model(self, model, output_dir, i)
                logger.info(f"FSDP Model saved to output dir {output_dir}")
            elif self.distributed_type == DistributedType.DEEPSPEED:
                logger.info("Saving DeepSpeed Model and Optimizer")
                ckpt_id = f"{MODEL_NAME}" if i == 0 else f"{MODEL_NAME}_{i}"
                model.save_checkpoint(output_dir, ckpt_id, **save_model_func_kwargs)
                logger.info(f"DeepSpeed Model and Optimizer saved to output dir {os.path.join(output_dir, ckpt_id)}")
            elif self.distributed_type == DistributedType.MEGATRON_LM:
                logger.info("Saving Megatron-LM Model, Optimizer and Scheduler")
                model.save_checkpoint(output_dir)
                logger.info(f"Megatron-LM Model , Optimizer and Scheduler saved to output dir {output_dir}")
            else:
                weights.append(self.get_state_dict(model, unwrap=False))

        # Save the optimizers taking care of FSDP and DeepSpeed nuances
        optimizers = []
        if self.distributed_type == DistributedType.FSDP:
            for opt in self._optimizers:
                logger.info("Saving FSDP Optimizer")
                self.state.fsdp_plugin.save_optimizer(self, opt, self._models[i], output_dir, i)
                logger.info(f"FSDP Optimizer saved to output dir {output_dir}")
        elif self.distributed_type not in [DistributedType.DEEPSPEED, DistributedType.MEGATRON_LM]:
            optimizers = self._optimizers

        # Save the lr schedulers taking care of DeepSpeed nuances
        schedulers = []
        if self.distributed_type == DistributedType.DEEPSPEED:
            for i, scheduler in enumerate(self._schedulers):
                if isinstance(scheduler, DeepSpeedSchedulerWrapper):
                    continue
                schedulers.append(scheduler)
        elif self.distributed_type not in [DistributedType.MEGATRON_LM]:
            schedulers = self._schedulers

        # Call model loading hooks that might have been registered with
        # accelerator.register_model_state_hook
        for hook in self._save_model_state_pre_hook.values():
            hook(self._models, weights, output_dir)

        save_location = save_accelerator_state(
            output_dir, weights, optimizers, schedulers, self.state.process_index, self.scaler
        )
        for i, obj in enumerate(self._custom_objects):
            save_custom_state(obj, output_dir, i)
        self.project_configuration.iteration += 1
        return save_location

    def register_load_state_pre_hook(self, hook: Callable[..., None]) -> hooks.RemovableHandle:
        """
        Registers a pre hook to be run before [`load_checkpoint`] is called in [`Accelerator.load_state`].

        Args:
            hook (`Callable`):
                A function to be called in [`Accelerator.load_state`] before `load_checkpoint`.

        The hook should have the following signature:

        `hook(models: List[torch.nn.Module], input_dir: str) -> None`

        The `models` argument are the models as saved in the accelerator state under `accelerator._models`, and the
        `input_dir` argument is the `input_dir` argument passed to [`Accelerator.load_state`].

        <Tip>

        Should only be used in conjunction with [`Accelerator.register_save_state_pre_hook`]. Can be useful to load
        configurations in addition to model weights. Can also be used to overwrite model loading with a customized
        method. In this case, make sure to remove already loaded models from the models list.

        </Tip>

        Returns:
            `torch.utils.hooks.RemovableHandle`: a handle that can be used to remove the added hook by calling
            `handle.remove()`
        """
        handle = hooks.RemovableHandle(self._load_model_state_pre_hook)
        self._load_model_state_pre_hook[handle.id] = hook
        return handle

    def load_state(self, input_dir: str, **load_model_func_kwargs):
        """
        Loads the current states of the model, optimizer, scaler, RNG generators, and registered objects.

        <Tip>

        Should only be used in conjunction with [`Accelerator.save_state`].

        </Tip>

        Args:
            input_dir (`str` or `os.PathLike`):
                The name of the folder all relevant weights and states were saved in.
            load_model_func_kwargs (`dict`, *optional*):
                Additional keyword arguments for loading model which can be passed to the underlying load function,
                such as optional arguments for DeepSpeed's `load_checkpoint` function.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> model, optimizer, lr_scheduler = ...
        >>> model, optimizer, lr_scheduler = accelerator.prepare(model, optimizer, lr_scheduler)
        >>> accelerator.load_state("my_checkpoint")
        ```
        """
        # Check if folder exists
        input_dir = os.path.expanduser(input_dir)
        if not os.path.isdir(input_dir):
            raise ValueError(f"Tried to find {input_dir} but folder does not exist")
        logger.info(f"Loading states from {input_dir}")

        # Load the models taking care of FSDP and DeepSpeed nuances
        models = []
        for i, model in enumerate(self._models):
            if self.distributed_type == DistributedType.FSDP:
                logger.info("Loading FSDP model")
                self.state.fsdp_plugin.load_model(self, model, input_dir, i)
                logger.info(f"FSDP Model loaded from input dir {input_dir}")
            elif self.distributed_type == DistributedType.DEEPSPEED:
                logger.info("Loading DeepSpeed Model and Optimizer")
                ckpt_id = f"{MODEL_NAME}" if i == 0 else f"{MODEL_NAME}_{i}"
                model.load_checkpoint(input_dir, ckpt_id, **load_model_func_kwargs)
                logger.info(f"DeepSpeed Model and Optimizer loaded from input dir {os.path.join(input_dir, ckpt_id)}")
            elif self.distributed_type == DistributedType.MEGATRON_LM:
                logger.info("Loading Megatron-LM Model, Optimizer and Scheduler")
                model.load_checkpoint(input_dir)
                logger.info(f"Megatron-LM Model , Optimizer and Scheduler loaded from input dir {input_dir}")
            else:
                models.append(model)

        # Load the optimizers taking care of FSDP and DeepSpeed nuances
        optimizers = []
        if self.distributed_type == DistributedType.FSDP:
            for i, opt in enumerate(self._optimizers):
                logger.info("Loading FSDP Optimizer")
                self.state.fsdp_plugin.load_optimizer(self, opt, self._models[i], input_dir, i)
                logger.info(f"FSDP Optimizer loaded from input dir {input_dir}")
        elif self.distributed_type not in [DistributedType.DEEPSPEED, DistributedType.MEGATRON_LM]:
            optimizers = self._optimizers

        # Load the lr schedulers taking care of DeepSpeed nuances
        schedulers = []
        if self.distributed_type == DistributedType.DEEPSPEED:
            for i, scheduler in enumerate(self._schedulers):
                if isinstance(scheduler, DeepSpeedSchedulerWrapper):
                    continue
                schedulers.append(scheduler)
        elif self.distributed_type not in [DistributedType.MEGATRON_LM]:
            schedulers = self._schedulers

        # Call model loading hooks that might have been registered with
        # accelerator.register_model_state_hook
        for hook in self._load_model_state_pre_hook.values():
            hook(models, input_dir)

        load_accelerator_state(
            input_dir, models, optimizers, schedulers, self.state.process_index, self.scaler, **load_model_func_kwargs
        )
        custom_checkpoints = [f for f in os.listdir(input_dir) if "custom_checkpoint" in f]
        if len(custom_checkpoints) != len(self._custom_objects):
            err = "Warning! Number of found checkpoints does not match the number of registered objects:"
            err += f"\n\tFound checkpoints: {len(custom_checkpoints)}"
            err += f"\n\tRegistered objects: {len(self._custom_objects)}\nSkipping."
            logger.warning(err)
        else:
            logger.info(f"Loading in {len(custom_checkpoints)} custom states")
            for index, obj in enumerate(self._custom_objects):
                load_custom_state(obj, input_dir, index)

    def free_memory(self):
        """
        Will release all references to the internal objects stored and call the garbage collector. You should call this
        method between two trainings with different models/optimizers.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> model, optimizer, scheduler = ...
        >>> model, optimizer, scheduler = accelerator.prepare(model, optimizer, scheduler)
        >>> accelerator.free_memory()
        >>> del model, optimizer, scheduler
        ```
        """
        self._schedulers = []
        self._optimizers = []
        self._models = []
        self._dataloaders = []
        self.deepspeed_engine_wrapped = None
        release_memory()

    def clear(self):
        """
        Alias for [`Accelerate.free_memory`], releases all references to the internal objects stored and call the
        garbage collector. You should call this method between two trainings with different models/optimizers.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> model, optimizer, scheduler = ...
        >>> model, optimizer, scheduler = accelerator.prepare(model, optimizer, scheduler)
        >>> accelerator.free_memory()
        >>> del model, optimizer, scheduler
        ```
        """
        self.free_memory()

    def _get_named_parameters(self, *args):
        named_parameters = {}
        for obj in args:
            if isinstance(obj, torch.nn.Module):
                obj = extract_model_from_parallel(obj)
                named_parameters.update({n: p for n, p in obj.named_parameters()})
        return named_parameters

    def _get_devices(self, *args):
        model_device = None
        optimizer_device = None
        for obj in args:
            # Loop through model parameters and stop at the first once we have its device.
            if isinstance(obj, torch.nn.Module):
                for param in obj.parameters():
                    model_device = param.device
                    break
            # Loop through optimizer parameters groups and stop at the first once we have its device.
            if isinstance(obj, torch.optim.Optimizer):
                for param_group in obj.param_groups:
                    if len(param_group["params"]) > 0:
                        optimizer_device = param_group["params"][0].device
                        break
        return (model_device, optimizer_device)

    def get_state_dict(self, model, unwrap=True):
        """
        Returns the state dictionary of a model sent through [`Accelerator.prepare`] potentially without full
        precision.

        Args:
            model (`torch.nn.Module`):
                A PyTorch model sent through [`Accelerator.prepare`]
            unwrap (`bool`, *optional*, defaults to `True`):
                Whether to return the original underlying state_dict of `model` or to return the wrapped state_dict

        Returns:
            `dict`: The state dictionary of the model potentially without full precision.

        Example:

        ```python
        >>> import torch
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> net = torch.nn.Linear(2, 2)
        >>> net = accelerator.prepare(net)
        >>> state_dict = accelerator.get_state_dict(net)
        ```
        """
        is_zero_3 = False
        if self.distributed_type == DistributedType.DEEPSPEED:
            is_zero_3 = self.deepspeed_config["zero_optimization"]["stage"] == 3

        if is_zero_3:
            if model.zero_gather_16bit_weights_on_model_save():
                state_dict = model._zero3_consolidated_16bit_state_dict()
            else:
                raise ValueError(
                    "Cannot get 16bit model weights because `stage3_gather_16bit_weights_on_model_save` in DeepSpeed config is False. "
                    "To save the model weights in 16bit, set `stage3_gather_16bit_weights_on_model_save` to True in DeepSpeed config file or "
                    "set `zero3_save_16bit_model` to True when using `accelerate config`. "
                    "To save the full checkpoint, run `model.save_checkpoint(save_dir)` and use `zero_to_fp32.py` to recover weights."
                )
        else:
            if unwrap:
                model = self.unwrap_model(model)
            state_dict = model.state_dict()

        if state_dict is not None:
            for k in state_dict:
                if state_dict[k].dtype == torch.float16:
                    state_dict[k] = state_dict[k].float()

        return state_dict

    def register_for_checkpointing(self, *objects):
        """
        Makes note of `objects` and will save or load them in during `save_state` or `load_state`.

        These should be utilized when the state is being loaded or saved in the same script. It is not designed to be
        used in different scripts.

        <Tip>

        Every `object` must have a `load_state_dict` and `state_dict` function to be stored.

        </Tip>

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> # Assume `CustomObject` has a `state_dict` and `load_state_dict` function.
        >>> obj = CustomObject()
        >>> accelerator.register_for_checkpointing(obj)
        >>> accelerator.save_state("checkpoint.pt")
        ```
        """
        invalid_objects = []
        for obj in objects:
            if not hasattr(obj, "state_dict") or not hasattr(obj, "load_state_dict"):
                invalid_objects.append(obj)
        if len(invalid_objects) > 0:
            err = "All `objects` must include a `state_dict` and `load_state_dict` function to be stored. The following inputs are invalid:"
            for index, obj in enumerate(invalid_objects):
                err += f"\n\t- Item at index {index}, `{get_pretty_name(obj)}`"
            raise ValueError(err)
        self._custom_objects.extend(objects)

    @contextmanager
    def autocast(self):
        """
        Will apply automatic mixed-precision inside the block inside this context manager, if it is enabled. Nothing
        different will happen otherwise.

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator(mixed_precision="fp16")
        >>> with accelerator.autocast():
        ...     train()
        ```
        """
        if self.native_amp:
            if self.mixed_precision == "fp16" and is_torch_version(">=", "1.10"):
                autocast_context = torch.cuda.amp.autocast(dtype=torch.float16)
            elif self.mixed_precision == "bf16":
                if self.distributed_type in [DistributedType.NO, DistributedType.MULTI_CPU, DistributedType.MULTI_GPU]:
                    autocast_context = torch.autocast(dtype=torch.bfloat16, device_type=self.device.type)
            else:
                autocast_context = torch.cuda.amp.autocast()

            autocast_context.__enter__()
            yield
            autocast_context.__exit__(*sys.exc_info())
        else:
            yield

    @property
    def optimizer_step_was_skipped(self):
        """
        Whether or not the optimizer update was skipped (because of gradient overflow in mixed precision), in which
        case the learning rate should not be changed.
        """
        for optimizer in self._optimizers:
            if optimizer.step_was_skipped:
                return True
        return False

    def skip_first_batches(self, dataloader, num_batches: int = 0):
        """
        Creates a new `torch.utils.data.DataLoader` that will efficiently skip the first `num_batches`.

        Args:
            dataloader (`torch.utils.data.DataLoader`): The data loader in which to skip batches.
            num_batches (`int`, *optional*, defaults to 0): The number of batches to skip

        Example:

        ```python
        >>> from accelerate import Accelerator

        >>> accelerator = Accelerator()
        >>> dataloader, model, optimizer, scheduler = accelerator.prepare(dataloader, model, optimizer, scheduler)

        >>> for input, target in accelerator.skip_first_batches(dataloader, num_batches=2):
        ...     optimizer.zero_grad()
        ...     output = model(input)
        ...     loss = loss_func(output, target)
        ...     accelerator.backward(loss)
        ...     optimizer.step()
        ```
        """
        return skip_first_batches(dataloader, num_batches=num_batches)