# Copyright (c) 2024, NVIDIA CORPORATION. All rights reserved.

"""Input/output checkpointing."""

from enum import Enum, auto
from logging import getLogger
import os
import random
import shutil
import sys
import threading
from pathlib import Path

import numpy as np
from time import time

import torch

from megatron.core import mpu, tensor_parallel, dist_checkpointing
from megatron.core.dist_checkpointing.mapping import ShardedObject
from megatron.core.dist_checkpointing.serialization import get_default_load_sharded_strategy
from megatron.core.dist_checkpointing.state_dict_transformation import (
     prepare_state_dict_for_save,
     recreate_state_dict_after_load,
     )
from megatron.core.dist_checkpointing.strategies.fully_parallel import \
    FullyParallelSaveStrategyWrapper, FullyParallelLoadStrategyWrapper
from megatron.core.num_microbatches_calculator import update_num_microbatches
from megatron.core.utils import is_float8tensor
from .async_utils import schedule_async_save
from .global_vars import get_args, get_one_logger
from .utils import unwrap_model, print_rank_0, append_to_progress_log, is_last_rank
from ..core.dist_checkpointing.serialization import \
    get_default_save_sharded_strategy
from .one_logger_utils import on_save_checkpoint_start, on_save_checkpoint_success

# [ModelOpt]: Import
try:
    from modelopt.torch.opt.plugins import (
        save_modelopt_state,
        save_sharded_modelopt_state,
        restore_modelopt_state,
        restore_sharded_modelopt_state,
    )
    has_nvidia_modelopt = True
except Exception:
    has_nvidia_modelopt = False

_CHECKPOINT_VERSION = None

logger = getLogger(__name__)
_NON_PERSISTENT_CKPT_SUBDIR = 'non_persistent'

def set_checkpoint_version(value):
    global _CHECKPOINT_VERSION
    if _CHECKPOINT_VERSION is not None:
        assert _CHECKPOINT_VERSION == value, \
            "checkpoint versions do not match"
    _CHECKPOINT_VERSION = value


def get_checkpoint_version():
    global _CHECKPOINT_VERSION
    return _CHECKPOINT_VERSION


def check_checkpoint_args(checkpoint_args):
    """Ensure fixed arguments for a model are the same for the input
    arguments and the one retrieved from checkpoint."""
    args = get_args()

    def _compare(arg_name, old_arg_name=None, default=None):
        if old_arg_name is not None:
            ckpt_arg_name = old_arg_name
        else:
            ckpt_arg_name = arg_name
        if default is not None:
            checkpoint_value = getattr(checkpoint_args, ckpt_arg_name, default)
        else:
            checkpoint_value = getattr(checkpoint_args, ckpt_arg_name)
        args_value = getattr(args, arg_name)
        error_message = '{} value from checkpoint ({}) is not equal to the ' \
                        'input argument value ({}).'.format(
                            arg_name, checkpoint_value, args_value)
        assert checkpoint_value == args_value, error_message

    _compare('num_layers')
    _compare('hidden_size')
    _compare('num_attention_heads')
    _compare('add_position_embedding', default=True)
    if args.vocab_file:
        _compare('max_position_embeddings')
        _compare('make_vocab_size_divisible_by')
        if not args.use_dist_ckpt:
            _compare('padded_vocab_size')
        _compare('tokenizer_type')
    if args.data_parallel_random_init:
        _compare('data_parallel_random_init')
    if get_checkpoint_version() < 3.0:
        _compare('tensor_model_parallel_size',
                 old_arg_name='model_parallel_size')
    if get_checkpoint_version() >= 3.0 and not args.use_dist_ckpt:
        _compare('tensor_model_parallel_size')
        _compare('pipeline_model_parallel_size')


def ensure_directory_exists(filename, check_parent=True):
    """Build filename's path if it does not already exists."""
    dirname = os.path.dirname(filename) if check_parent else filename
    os.makedirs(dirname, exist_ok=True)


def get_checkpoint_name(checkpoints_path, iteration, release=False,
                        pipeline_parallel=None,
                        tensor_rank=None, pipeline_rank=None,
                        expert_parallel=None, expert_rank=None,
                        return_base_dir=False, basename="model_optim_rng.pt"):
    """Determine the directory name for this rank's checkpoint."""
    if release:
        directory = 'release'
    else:
        directory = 'iter_{:07d}'.format(iteration)
    if return_base_dir:
        common_path = os.path.join(checkpoints_path, directory)
        return common_path

    # Use both the tensor and pipeline MP rank.
    if pipeline_parallel is None:
        pipeline_parallel = (mpu.get_pipeline_model_parallel_world_size() > 1)
    if tensor_rank is None:
        tensor_rank = mpu.get_tensor_model_parallel_rank()
    if pipeline_rank is None:
        pipeline_rank = mpu.get_pipeline_model_parallel_rank()
    if expert_parallel is None:
        expert_parallel = (mpu.get_expert_model_parallel_world_size() > 1)
    if expert_rank is None:
        expert_rank = mpu.get_expert_model_parallel_rank()

    # Use both the tensor and pipeline MP rank. If using the distributed
    # optimizer, then the optimizer's path must additionally include the
    # data parallel rank.
    if not pipeline_parallel:
        common_path = os.path.join(checkpoints_path, directory,
                            f'mp_rank_{tensor_rank:02d}')
    else:
        common_path = os.path.join(checkpoints_path, directory,
                f'mp_rank_{tensor_rank:02d}_{pipeline_rank:03d}')

    if expert_parallel:
        common_path = common_path + f'_{expert_rank:03d}'

    return os.path.join(common_path, basename)


def get_distributed_optimizer_checkpoint_name(model_checkpoint_name):
    return os.path.join(os.path.dirname(model_checkpoint_name),
                        "distrib_optim.pt")


def find_checkpoint_rank_0(checkpoints_path, iteration, release=False):
    """Finds the checkpoint for rank 0 without knowing if we are using
    pipeline parallelism/expert parallelism or not.

    Since the checkpoint naming scheme changes if pipeline or expert
    parallelism is present, we need to look for both naming schemes if
    we don't know if the checkpoint has pipeline or expert parallelism.
    """

    # Look for checkpoint with no pipelining and no expert parallelism
    filename = get_checkpoint_name(checkpoints_path, iteration, release,
                                   pipeline_parallel=False,
                                   tensor_rank=0, pipeline_rank=0,
                                   expert_parallel=False, expert_rank=0)
    if os.path.isfile(filename):
        return filename

    # Look for checkpoint with no pipelining and expert parallelism
    filename = get_checkpoint_name(checkpoints_path, iteration, release,
                                   pipeline_parallel=False,
                                   tensor_rank=0, pipeline_rank=0,
                                   expert_parallel=True, expert_rank=0)
    if os.path.isfile(filename):
        return filename

    # Look for checkpoint with pipelining and no expert parallelism
    filename = get_checkpoint_name(checkpoints_path, iteration, release,
                                   pipeline_parallel=True,
                                   tensor_rank=0, pipeline_rank=0,
                                   expert_parallel=False, expert_rank=0)
    if os.path.isfile(filename):
        return filename

    # Look for checkpoint with pipelining and expert parallelism
    filename = get_checkpoint_name(checkpoints_path, iteration, release,
                                   pipeline_parallel=True,
                                   tensor_rank=0, pipeline_rank=0,
                                   expert_parallel=True, expert_rank=0)
    if os.path.isfile(filename):
        return filename

    # Look for a distributed checkpoint
    filename = get_checkpoint_name(checkpoints_path, iteration, release,
                                   pipeline_parallel=True,
                                   return_base_dir=True)
    if dist_checkpointing.check_is_distributed_checkpoint(filename):
        return filename

    return None


def get_checkpoint_tracker_filename(checkpoints_path):

    """Tracker file rescords the latest chckpoint during
    training to restart from."""
    return os.path.join(checkpoints_path, 'latest_checkpointed_iteration.txt')


def checkpoint_exists(checkpoints_path):
    if checkpoints_path is None:
        return False
    load_step = 'latest_checkpointed_iteration.txt'
    return os.path.exists(os.path.join(checkpoints_path, load_step))


def read_metadata(tracker_filename):
    # Read the tracker file and either set the iteration or
    # mark it as a release checkpoint.
    iteration = 0
    release = False
    with open(tracker_filename, 'r') as f:
        metastring = f.read().strip()
        try:
            iteration = int(metastring)
        except ValueError:
            release = metastring == 'release'
            if not release:
                print_rank_0('ERROR: Invalid metadata file {}. Exiting'.format(
                    tracker_filename))
                sys.exit()
    assert iteration > 0 or release, 'error parsing metadata file {}'.format(
        tracker_filename)

    # Get the max iteration retrieved across the ranks.
    if torch.distributed.is_initialized():
        iters_cuda = torch.tensor([iteration], dtype=torch.long, device='cuda')
        torch.distributed.all_reduce(iters_cuda, op=torch.distributed.ReduceOp.MAX)
        max_iter = iters_cuda[0].item()

        # We should now have all the same iteration.
        # If not, print a warning and chose the maximum
        # iteration across all ranks.
        if iteration != max_iter:
            rank = torch.distributed.get_rank()
            print('WARNING: on rank {} found iteration {} in the '
                  'metadata while max iteration across the ranks '
                  'is {}, replacing it with max iteration.'.format(
                      rank, iteration, max_iter), flush=True)
    else:
        # When loading a checkpoint outside of training (for example,
        # when editing it), we might not have torch distributed
        # initialized, in this case, just assume we have the latest
        max_iter = iteration
    return max_iter, release


def get_rng_state(use_dist_ckpt: bool = False):
    """ collect rng state across data parallel ranks """
    args = get_args()
    rng_state = {
        'random_rng_state': random.getstate(),
        'np_rng_state': np.random.get_state(),
        'torch_rng_state': torch.get_rng_state(),
        'cuda_rng_state': torch.cuda.get_rng_state(),
        'rng_tracker_states': tensor_parallel.get_cuda_rng_tracker().get_states()}

    rng_state_list = None
    if torch.distributed.is_initialized() and \
            mpu.get_data_parallel_world_size() > 1 and \
            args.data_parallel_random_init:
        rng_state_list = \
            [None for i in range(mpu.get_data_parallel_world_size())]
        torch.distributed.all_gather_object(
            rng_state_list,
            rng_state,
            group=mpu.get_data_parallel_group())
    else:
        rng_state_list = [rng_state]

    if use_dist_ckpt:
        pp_rank = mpu.get_pipeline_model_parallel_rank()
        pp_size = mpu.get_pipeline_model_parallel_world_size()
        tp_rank = mpu.get_tensor_model_parallel_rank()
        tp_size = mpu.get_tensor_model_parallel_world_size()
        rng_state_list = ShardedObject('rng_state', rng_state_list, (pp_size, tp_size), (pp_rank, tp_rank),
                                       replica_id=mpu.get_data_parallel_rank(with_context_parallel=True))

    return rng_state_list

class CheckpointType(Enum):
    LEGACY = auto()
    LOCAL = auto()
    GLOBAL = auto()

def save_checkpoint(iteration, model, optimizer, opt_param_scheduler, num_floating_point_operations_so_far,
                    checkpointing_context=None, pipeline_rank=None, expert_rank=None, tensor_rank=None, pipeline_parallel=None, expert_parallel=None, non_persistent_ckpt=False,
                    train_data_iterator=None, ft_client=None):
    """Save a model, optimizer and optionally dataloader checkpoint.

    Checkpointing context is used to persist some checkpointing state
    throughout a single job. Must be initialized externally (not used if None).

    If non_persistent_ckpt is True,
    the checkpoint will be saved with special functionality for removing old checkpoints.
    There are several types of non-persistent checkpoints:
    "global" - Saved as a standard checkpoint (e.g., on Lustre) with old checkpoints being removed.
    "local" - [TBD] Each rank saves a portion of the checkpoint locally (e.g., on SSD/ramdisk).
    "in_memory" - [TBD] A special kind of local checkpoint that avoids serialization.

    Dataloader checkpoint is only saved if the dataloader supports it. Currently this applies only
    to the Megatron Energon dataloader (multimodal) and not the built-in Megatron dataloader (text-only).
    """
    start_ckpt = time()
    args = get_args()

    # Prepare E2E metrics at start of save checkpoint
    productive_metrics = on_save_checkpoint_start(args.async_save)

    # Only rank zero of the data parallel writes to the disk.
    model = unwrap_model(model)

    # Handle non_persistent_ckpt flag. Besides overwriting `args.save` and
    # `args.use_dist_ckpt`, non-persistent global ckpt requires no additional logic
    ckpt_type = CheckpointType.GLOBAL if args.use_dist_ckpt else CheckpointType.LEGACY
    save_dir = args.save
    if non_persistent_ckpt:
        if args.non_persistent_ckpt_type == 'global':
            ckpt_type = CheckpointType.GLOBAL
            save_dir = (
                args.non_persistent_global_ckpt_dir
                if args.non_persistent_global_ckpt_dir
                else os.path.join(save_dir, _NON_PERSISTENT_CKPT_SUBDIR)
            )
            # TODO Can we ensure the previous checkpoint is saved? We don't want to allow two saves in parallel.
            cleanup_old_non_persistent_checkpoint(
                save_dir, leave_ckpt_num=1, do_async=args.async_save
            )
        elif args.non_persistent_ckpt_type == 'local':
            raise RuntimeError('LocalCheckpointManagers are not yet integrated')
            ckpt_type = CheckpointType.LOCAL
            save_dir = checkpointing_context['local_checkpoint_manager'].local_ckpt_dir
        else:
            assert False, 'Please use local or global non-persistent checkpoints' \
                f'(got: {args.non_persistent_ckpt_type})'

    ckpt_format = args.ckpt_format if ckpt_type == CheckpointType.GLOBAL else 'torch'
    print_rank_0('saving checkpoint at iteration {:7d} to {} in {} format'.format(
        iteration, save_dir, ckpt_format))

    # Collect rng state across data parallel ranks.
    rng_state = get_rng_state(ckpt_type != CheckpointType.LEGACY)

    # Checkpoint name.
    return_base_dir = (ckpt_type != CheckpointType.LEGACY)
    checkpoint_name = get_checkpoint_name(save_dir, iteration, release=False, pipeline_parallel=pipeline_parallel,
        tensor_rank=tensor_rank, pipeline_rank=pipeline_rank, expert_parallel=expert_parallel, expert_rank=expert_rank, return_base_dir=return_base_dir)

    # Save dataloader state if the dataloader supports it (currently only Megatron Energon).
    save_dataloader_state(train_data_iterator, iteration, getattr(args, "dataloader_save", None))

    # Save distributed optimizer's custom parameter state.
    if (
        args.use_distributed_optimizer
        and not args.no_save_optim
        and optimizer is not None
        and ckpt_type == CheckpointType.LEGACY
    ):
        optim_checkpoint_name = \
            get_distributed_optimizer_checkpoint_name(checkpoint_name)
        ensure_directory_exists(optim_checkpoint_name)
        optimizer.save_parameter_state(optim_checkpoint_name)

    async_save_request = None
    if args.async_save:
        if ckpt_type == CheckpointType.LEGACY:
            raise NotImplementedError('Async checkpoint save not implemented for legacy checkpoints')
        elif ckpt_type == CheckpointType.GLOBAL and args.ckpt_format != 'torch_dist':
            raise NotImplementedError(f'Async checkpoint save not implemented for {args.ckpt_format} distributed checkpoint format')

    rank = torch.distributed.get_rank() if torch.distributed.is_initialized() else 0

    # Collect args, model, RNG.
    if not torch.distributed.is_initialized() \
            or mpu.get_data_modulo_expert_parallel_rank(with_context_parallel=True) == 0 \
            or ckpt_type != CheckpointType.LEGACY:
        optim_sd_kwargs = {}
        if ckpt_type != CheckpointType.LEGACY and args.use_distributed_optimizer:
            optim_sd_kwargs['sharding_type'] = ('fully_sharded_model_space'
                                                if args.ckpt_fully_parallel_save
                                                else 'dp_zero_gather_scatter')
            print_rank_0(f'Storing distributed optimizer sharded state of type {optim_sd_kwargs["sharding_type"]}')
        state_dict = generate_state_dict(
            args,
            model,
            optimizer,
            opt_param_scheduler,
            rng_state,
            ckpt_type != CheckpointType.LEGACY,
            iteration,
            optim_sd_kwargs=optim_sd_kwargs,
        )

        if args.enable_ft_package and ft_client is not None:
            state_dict["ft_state"] = ft_client.state_dict()
        state_dict['num_floating_point_operations_so_far'] = num_floating_point_operations_so_far
        if ckpt_type == CheckpointType.GLOBAL:
            if not torch.distributed.is_initialized() or torch.distributed.get_rank() == 0:
                # TODO Handle non-empty directories (e.g., after a crash during saving).
                ensure_directory_exists(checkpoint_name, check_parent=False)
            if checkpointing_context is not None and 'save_strategy' in checkpointing_context:
                save_strategy = checkpointing_context['save_strategy']
                # Already saved once before - don't need to rerun sharding validation
                validate_sharding_integrity = not args.ckpt_assume_constant_structure
            else:
                validate_sharding_integrity = True
                save_strategy = get_default_save_sharded_strategy(args.ckpt_format)
                if args.ckpt_assume_constant_structure and args.ckpt_format == 'torch_dist':
                    save_strategy.use_cached_ckpt_structure = args.ckpt_assume_constant_structure
                if args.ckpt_fully_parallel_save:
                    save_strategy = FullyParallelSaveStrategyWrapper(save_strategy, mpu.get_data_parallel_group(with_context_parallel=True),
                                                                     args.ckpt_assume_constant_structure)
            # Store save strategy for future checkpoint saves
            if checkpointing_context is not None:
                checkpointing_context['save_strategy'] = save_strategy
            end_ckpt = time()
            logger.debug(f"rank: {rank}, takes {end_ckpt - start_ckpt} to prepare state dict for ckpt ")
            async_save_request = dist_checkpointing.save(state_dict, checkpoint_name, save_strategy,
                                                         async_sharded_save=args.async_save,
                                                         validate_access_integrity=validate_sharding_integrity)
            # [ModelOpt]: save sharded modelopt_state
            if has_nvidia_modelopt:
                save_sharded_modelopt_state(model, checkpoint_name, (args.ckpt_format, 1))
        else:
            # [ModelOpt]: Inject modelopt_state into state_dict
            if has_nvidia_modelopt:
                save_modelopt_state(model, state_dict)

            if ckpt_type == CheckpointType.LOCAL:
                state_dict_for_save = prepare_state_dict_for_save(
                    state_dict, algo=args.non_persistent_local_ckpt_algo
                )
                async_save_request = checkpointing_context['local_checkpoint_manager'].save(
                    state_dict_for_save, iteration, is_async=bool(args.async_save)
                )
            else:
                assert ckpt_type == CheckpointType.LEGACY
                # Save.
                ensure_directory_exists(checkpoint_name)
                torch.save(state_dict, checkpoint_name)
    start_misc = time()
    if not args.async_save:
        assert async_save_request is None
        # Wait so everyone is done (necessary)
        if torch.distributed.is_initialized():
            torch.distributed.barrier()

    # And update the latest iteration
    if not torch.distributed.is_initialized() \
            or torch.distributed.get_rank() == 0:
        tracker_filename = get_checkpoint_tracker_filename(save_dir)

        if ckpt_type == CheckpointType.LOCAL:
            def iter_finalize_fn():
                print_rank_0('  successfully saved local checkpoint from iteration {:7d}'
                             .format(iteration))
                if args.log_progress and args.async_save:
                    append_to_progress_log(f'Saved async local checkpoint\tIteration: {iteration}',
                                           barrier=False)
        else:
            def iter_finalize_fn():
                with open(tracker_filename, 'w') as f:
                    f.write(str(iteration))
                print_rank_0('  successfully saved checkpoint from iteration {:7d} to {}'
                             .format(iteration, args.save))
                if args.log_progress and args.async_save:
                    append_to_progress_log(f'Saved async checkpoint\tIteration: {iteration}',
                                           barrier=False)

        if args.async_save:
            assert async_save_request is not None
            async_save_request.add_finalize_fn(iter_finalize_fn)
        else:
            iter_finalize_fn()

    # Additional callback for one_logger (last rank)
    if not torch.distributed.is_initialized() \
       or is_last_rank():
        def onelogger_finalize_fn():
            on_save_checkpoint_success(productive_metrics, args.async_save)
        if args.async_save:
            assert async_save_request is not None
            async_save_request.add_finalize_fn(onelogger_finalize_fn)
        else:
            onelogger_finalize_fn()

    if args.async_save:
        schedule_async_save(async_save_request)
        print_rank_0('  scheduled an async checkpoint save at iteration {:7d} to {}' \
                     .format(iteration, save_dir))

    # Wait so everyone is done (not necessary)
    if torch.distributed.is_initialized():
        torch.distributed.barrier()

    end_misc = time()
    logger.debug(f"rank: {rank}, takes {end_misc - start_misc} to finalize ckpt save ")


def cleanup_old_non_persistent_checkpoint(save_dir, leave_ckpt_num=1, do_async=False):
    if torch.distributed.is_initialized() and torch.distributed.get_rank() != 0:
        return
    save_dir = Path(save_dir)

    iter_prefix = "iter_"
    iter_ckpts = save_dir.rglob(f'{iter_prefix}*')
    sorted_iter_ckpts = sorted(iter_ckpts, key=lambda ckpt_name: int(ckpt_name.name[len(iter_prefix):]))
    if not sorted_iter_ckpts:
        return
    rm_iter_ckpts = sorted_iter_ckpts[:-leave_ckpt_num]
    print_rank_0(f'Non-persistent checkpoints scheduled for removal: {rm_iter_ckpts}')
    print_rank_0(f'Non-persistent checkpoints to be kept: {sorted_iter_ckpts[-leave_ckpt_num:]}')

    def remove_iter_ckpts(_iter_ckpts):
        for ckpt in _iter_ckpts:
            shutil.rmtree(ckpt)
    if do_async:
        threading.Thread(target=remove_iter_ckpts, args=(rm_iter_ckpts,)).start()
    else:
        remove_iter_ckpts(rm_iter_ckpts)


def save_dataloader_state(train_iterator, iteration, dataloader_save_path):
    """Saves dataloader state if the dataloader supports it.

    Currently, this is only used by Megatron Energon dataloader (multimodal) to store its state at a
    specific iteration. The Megatron built-in dataloader (text-only) creates index files upfront
    to track its state.

    If the provided dataloader has `save_state` method, then it is called to save the state.
    Otherwise, no state is saved.

    Args:
        train_iterator (iterable): Train dataloader.
        iteration (int): Current iteration.
        dataloader_save_path (str): Path where the dataloader state is saved.
    """
    # If no dataloader or saving path is provided, then exit early.
    if train_iterator is None or dataloader_save_path is None:
        return

    # If dataloader doesn't support saving state, exit early.
    if not hasattr(train_iterator, "save_state"):
        return

    # Save dataloader state for each data parallel rank only once.
    first_rank = mpu.is_pipeline_first_stage(ignore_virtual=True) and mpu.get_tensor_model_parallel_rank() == 0
    if not first_rank:
        return

    dp_rank = mpu.get_data_parallel_rank()
    print(f"saving dataloader checkpoint at iteration {iteration} to {dataloader_save_path}")
    train_dataloader_state_dict = train_iterator.save_state()
    data_state_save_path = get_checkpoint_name(
        dataloader_save_path, iteration,
        basename=f'train_dataloader_dprank{dp_rank:03d}.pt'
    )

    torch.distributed.barrier(group=mpu.get_data_parallel_group())

    if mpu.get_data_parallel_rank() == 0:
        ensure_directory_exists(data_state_save_path)

    torch.distributed.barrier(group=mpu.get_data_parallel_group())

    dataloader_save_dict = {}
    dataloader_save_dict['dataloader_state_dict'] = train_dataloader_state_dict
    torch.save(dataloader_save_dict, data_state_save_path)


def generate_state_dict(args, model, optimizer, opt_param_scheduler,
                        rng_state, use_dist_ckpt=False, iteration=None,
                        optim_sd_kwargs=None):
    # Arguments, iteration, and model.
    state_dict = {}
    state_dict['args'] = args
    state_dict['checkpoint_version'] = 3.0
    if iteration is not None:
        state_dict['iteration'] = iteration

    if len(model) == 1:
        state_dict['model'] = (model[0].sharded_state_dict()
                               if use_dist_ckpt else
                               model[0].state_dict_for_save_checkpoint())
    else:
        for i in range(len(model)):
            mpu.set_virtual_pipeline_model_parallel_rank(i)
            state_dict['model%d' % i] = (
                model[i].sharded_state_dict()
                if use_dist_ckpt else
                model[i].state_dict_for_save_checkpoint())
    # Optimizer stuff.
    if not args.no_save_optim:
        if optimizer is not None:
            state_dict['optimizer'] = (optimizer.sharded_state_dict(state_dict, **(optim_sd_kwargs or {}))
                                       if use_dist_ckpt else
                                       optimizer.state_dict())
        if opt_param_scheduler is not None:
            state_dict['opt_param_scheduler'] = \
                opt_param_scheduler.state_dict()
    # RNG states.
    if not args.no_save_rng:
        state_dict["rng_state"] = rng_state
    return state_dict


def _transpose_first_dim(t, num_splits, num_splits_first, model):
    input_shape = t.size()
    # We use a self_attention module but the values extracted aren't
    # specific to self attention so should work for cross attention as well
    while hasattr(model, 'module'):
        model = model.module
    attention_module = model.language_model.encoder.layers[0].self_attention
    hidden_size_per_attention_head = attention_module.hidden_size_per_attention_head
    num_attention_heads_per_partition = attention_module.num_attention_heads_per_partition
    if num_splits_first:
        """[num_splits * np * hn, h]
        -->(view) [num_splits, np, hn, h]
        -->(tranpose) [np, num_splits, hn, h]
        -->(view) [np * num_splits * hn, h] """

        intermediate_shape = \
            (num_splits, num_attention_heads_per_partition,
             hidden_size_per_attention_head) + input_shape[1:]

        t = t.view(*intermediate_shape)
        t = t.transpose(0, 1).contiguous()
    else:
        """[np * hn * num_splits, h]
        -->(view) [np, hn, num_splits, h]
        -->(tranpose) [np, num_splits, hn, h]
        -->(view) [np * num_splits * hn, h] """

        intermediate_shape = \
            (num_attention_heads_per_partition,
             hidden_size_per_attention_head, num_splits) +\
             input_shape[1:]

        t = t.view(*intermediate_shape)
        t = t.transpose(1, 2).contiguous()
    t = t.view(*input_shape)

    return t


def fix_query_key_value_ordering(model, checkpoint_version):
    """Fix up query/key/value matrix ordering if checkpoint
    version is smaller than 2.0
    """
    if checkpoint_version < 2.0:
        if isinstance(model, list):
            assert len(model)==1
            model = model[0]
        for name, param in model.named_parameters():
            if name.endswith(('.query_key_value.weight', '.query_key_value.bias')):
                if checkpoint_version == 0:
                    fixed_param = _transpose_first_dim(param.data, 3, True, model)
                elif checkpoint_version == 1.0:
                    fixed_param = _transpose_first_dim(param.data, 3, False, model)
                else:
                    print_rank_0(f"Invalid checkpoint version {checkpoint_version}.")
                    sys.exit()
                param.data.copy_(fixed_param)
            if name.endswith(('.key_value.weight', '.key_value.bias')):
                if checkpoint_version == 0:
                    fixed_param = _transpose_first_dim(param.data, 2, True, model)
                elif checkpoint_version == 1.0:
                    fixed_param = _transpose_first_dim(param.data, 2, False, model)
                else:
                    print_rank_0(f"Invalid checkpoint version {checkpoint_version}.")
                    sys.exit()
                param.data.copy_(fixed_param)
        print_rank_0(" successfully fixed query-key-values ordering for"
                     " checkpoint version {}".format(checkpoint_version))


def _get_non_persistent_iteration(non_persistent_global_dir, args, checkpointing_context=None):
    if args.non_persistent_ckpt_type is None:
        return -1
    elif args.non_persistent_ckpt_type == "global":
        tracker_filename = get_checkpoint_tracker_filename(non_persistent_global_dir)
        if os.path.isfile(tracker_filename):
            iteration, release = read_metadata(tracker_filename)
            if release:
                raise RuntimeError('Non-persistent checkpoint can\'t be a release checkpoint')
        else:
            iteration = -1
            print_rank_0('WARNING: could not find the metadata file {}'.format(tracker_filename))
            print_rank_0('    will not load any non-persistent checkpoint')
        return iteration
    elif args.non_persistent_ckpt_type == "local":
        raise RuntimeError('LocalCheckpointManagers are not yet integrated')
        return checkpointing_context['local_checkpoint_manager'].get_latest_checkpoint_iteration()
    else:
        assert False, 'Please use local or global non-persistent checkpoints' \
            f'(got: {args.non_persistent_ckpt_type})'


def _load_non_persistent_base_checkpoint(
    non_persistent_global_dir,
    args,
    rank0,
    sharded_state_dict,
    non_persistent_iteration,
    checkpointing_context=None,
):
    """ Load the base state_dict from a non-persistent distributed checkpoint.
    Depending on the non_persistent_ckpt_type, different logic may be required.
    """
    assert args.non_persistent_ckpt_type is not None
    if args.non_persistent_ckpt_type == "global":
        if not rank0:
            print_rank_0(
                f'Loading from a non-persistent checkpoint (non-persistent iter {non_persistent_iteration})'
            )
        return _load_global_dist_base_checkpoint(
            non_persistent_global_dir, args, rank0, sharded_state_dict, non_persistent_iteration, False
        )
    elif args.non_persistent_ckpt_type == "local":
        raise RuntimeError('LocalCheckpointManagers are not yet integrated')
        intermediate_state_dict, checkpoint_name = checkpointing_context[
            'local_checkpoint_manager'
        ].load()
        state_dict = recreate_state_dict_after_load(
            sharded_state_dict,
            intermediate_state_dict,
            algo=args.non_persistent_local_ckpt_algo,
        )
        return state_dict, checkpoint_name, False, CheckpointType.LOCAL
    else:
        assert False, 'Please use local or global non-persistent checkpoints' \
            f'(got: {args.non_persistent_ckpt_type})'


def _load_global_dist_base_checkpoint(
    load_dir, args, rank0, sharded_state_dict, iteration, release
):
    """ Load the base state_dict from the given directory containing the global distributed checkpoint """
    if rank0:
        checkpoint_name = find_checkpoint_rank_0(load_dir, iteration, release)
        state_dict = dist_checkpointing.load_common_state_dict(checkpoint_name)
        return state_dict, checkpoint_name, release, CheckpointType.GLOBAL

    if sharded_state_dict is None:
        assert not args.auto_detect_ckpt_format and not args.use_dist_ckpt, (
            args.auto_detect_ckpt_format,
            args.use_dist_ckpt,
        )
        raise RuntimeError(
            'Detected load from a distributed checkpoint, but neither --use-dist-ckpt nor --auto-detect-ckpt-format is set.'
        )

    checkpoint_name = get_checkpoint_name(load_dir, iteration, release, return_base_dir=True)
    load_strategy = get_default_load_sharded_strategy(checkpoint_name)
    # NOTE: `args.ckpt_fully_parallel_load` applies to both persistent and non-persistent checkpoints.
    if args.ckpt_fully_parallel_load:
        load_strategy = FullyParallelLoadStrategyWrapper(
            load_strategy, mpu.get_data_parallel_group(with_context_parallel=True)
        )
    state_dict = dist_checkpointing.load(sharded_state_dict, checkpoint_name, load_strategy, strict=args.dist_ckpt_strictness)
    return state_dict, checkpoint_name, release, CheckpointType.GLOBAL


def _load_base_checkpoint(
    load_dir,
    args,
    rank0=False,
    sharded_state_dict=None,
    checkpointing_context=None,
):
    """ Load the base state_dict from the given directory

    If rank0 is true, just loads rank 0 checkpoint, ignoring arguments.
    """
    # Try to load non-persistent checkpoint first
    non_persistent_global_dir = (
        args.non_persistent_global_ckpt_dir
        if args.non_persistent_global_ckpt_dir or load_dir is None
        else os.path.join(load_dir, _NON_PERSISTENT_CKPT_SUBDIR)
    )
    non_persistent_iteration = _get_non_persistent_iteration(
        non_persistent_global_dir, args, checkpointing_context
    )
    iteration, release = -1, False
    tracker_filename = 'because load directory is not defined'
    if load_dir is not None:
        tracker_filename = get_checkpoint_tracker_filename(load_dir)
        if os.path.isfile(tracker_filename):
            iteration, release = read_metadata(tracker_filename)
    if non_persistent_iteration != -1:  # there is a non-persistent checkpoint
        if non_persistent_iteration >= iteration:
            return _load_non_persistent_base_checkpoint(
                non_persistent_global_dir,
                args,
                rank0,
                sharded_state_dict,
                non_persistent_iteration,
                checkpointing_context,
            )
        else:
            print_rank_0('WARNING: non-persistent checkpoints are older than persistent checkpoint')

    # Otherwise we are dealing with global checkpoints
    # If no tracker file, return nothing
    if iteration == -1:
        if not rank0:
            print_rank_0('WARNING: could not find the metadata file {}'.format(tracker_filename))
            print_rank_0('    will not load any checkpoints and will start from random')
        # Conditionally exit if checkpoint not found.
        if args.exit_on_missing_checkpoint:
            print_rank_0(">> '--exit-on-missing-checkpoint' set ... exiting. <<")
            if torch.distributed.is_initialized():
                torch.distributed.barrier()
            sys.exit()

        return None, "", False, None

    # Determine the type of the checkpoint
    checkpoint_name = get_checkpoint_name(load_dir, iteration, release, return_base_dir=True)
    is_dist_ckpt = dist_checkpointing.check_is_distributed_checkpoint(checkpoint_name)
    if not rank0:
        dist_infix = "distributed " if is_dist_ckpt else ""
        if release:
            print_rank_0(f' loading release {dist_infix}checkpoint from {load_dir}')
        else:
            print_rank_0(
                f' loading {dist_infix}checkpoint from {load_dir} at iteration {iteration}'
            )

    # Handle global distributed checkpoint
    if is_dist_ckpt:
        return _load_global_dist_base_checkpoint(
            load_dir, args, rank0, sharded_state_dict, iteration, release
        )
    # Handle global legacy checkpoint
    if rank0:
        checkpoint_name = find_checkpoint_rank_0(load_dir, iteration, release)
    else:
        checkpoint_name = get_checkpoint_name(load_dir, iteration, release, return_base_dir=False)
    try:
        state_dict = torch.load(checkpoint_name, map_location='cpu')
    except ModuleNotFoundError:
        from megatron.legacy.fp16_deprecated import loss_scaler

        # For backward compatibility.
        if not rank0:
            print_rank_0(' > deserializing using the old code structure ...')
        sys.modules['fp16.loss_scaler'] = sys.modules['megatron.legacy.fp16_deprecated.loss_scaler']
        sys.modules['megatron.fp16.loss_scaler'] = sys.modules[
            'megatron.legacy.fp16_deprecated.loss_scaler'
        ]
        sys.modules['megatron.model'] = sys.modules['megatron.legacy.model']
        state_dict = torch.load(checkpoint_name, map_location='cpu')
        sys.modules.pop('fp16.loss_scaler', None)
        sys.modules.pop('megatron.fp16.loss_scaler', None)
        sys.modules.pop('megatron.model', None)
    except Exception as e:
        print('could not load the checkpoint')
        print(e)
        sys.exit()

    return state_dict, checkpoint_name, release, CheckpointType.LEGACY


def load_args_from_checkpoint(
    args, load_arg='load', checkpointing_context=None
):
    """Set required arguments from the checkpoint specified in the
    arguments.

    Will overwrite arguments that have a non-None default value, but
    will leave any arguments that default to None as set.

    Returns the same args NameSpace with the new values added/updated.

    If no checkpoint is specified in args, or if the checkpoint is
    there but invalid, the arguments will not be modified

    """
    load_dir = getattr(args, load_arg)

    if load_dir is None:
        print_rank_0('No load directory specified, using provided arguments.')
        return args

    state_dict, checkpoint_name, release, ckpt_type = _load_base_checkpoint(
        load_dir,
        args,
        rank0=True,
        checkpointing_context=checkpointing_context,
    )

    # Args.
    if not state_dict:
        print_rank_0('Checkpoint not found to provide arguments, using provided arguments.')
        return args

    if 'args' not in state_dict:
        print_rank_0('Checkpoint provided does not have arguments saved, using provided arguments.')
        return args

    checkpoint_args = state_dict['args']
    checkpoint_version = state_dict.get('checkpoint_version', 0)
    args.iteration = state_dict['iteration']

    # One-off conversion for foundation models
    if hasattr(checkpoint_args, 'disable_bias_linear'):
        setattr(
            checkpoint_args, 'add_bias_linear', not getattr(checkpoint_args, 'disable_bias_linear')
        )

    def _set_arg(arg_name, old_arg_name=None, force=False):
        if not force and getattr(args, arg_name, None) is not None:
            return

        if old_arg_name is not None:
            checkpoint_value = getattr(checkpoint_args, old_arg_name, None)
        else:
            checkpoint_value = getattr(checkpoint_args, arg_name, None)

        if checkpoint_value is not None:
            print_rank_0(f"Setting {arg_name} to {checkpoint_value} from checkpoint")
            setattr(args, arg_name, checkpoint_value)
        else:
            print_rank_0(f"Checkpoint did not provide arguments {arg_name}")

    _set_arg('num_layers')
    _set_arg('hidden_size')
    _set_arg('ffn_hidden_size')
    _set_arg('seq_length')
    _set_arg('num_attention_heads')
    _set_arg('num_query_groups', force=True)
    _set_arg('group_query_attention', force=True)
    _set_arg('kv_channels')
    _set_arg('max_position_embeddings')
    _set_arg('position_embedding_type', force=True)
    _set_arg('add_position_embedding', force=True)
    _set_arg('use_rotary_position_embeddings', force=True)
    _set_arg('rotary_percent', force=True)
    _set_arg('rotary_interleaved', force=True)
    _set_arg('add_bias_linear', force=True)
    _set_arg('add_qkv_bias', force=True)
    _set_arg('swiglu', force=True)
    _set_arg('untie_embeddings_and_output_weights', force=True)
    _set_arg('apply_layernorm_1p', force=True)
    _set_arg('normalization', force=True)
    _set_arg('tokenizer_type')
    _set_arg('padded_vocab_size')
    _set_arg('apply_query_key_layer_scaling', force=True)
    if checkpoint_version < 3.0:
        _set_arg('tensor_model_parallel_size', 'model_parallel_size')
    else:
        _set_arg('tensor_model_parallel_size', force=True)
        _set_arg('pipeline_model_parallel_size', force=True)
        _set_arg('virtual_pipeline_model_parallel_size', force=True)
        _set_arg('num_layers_per_virtual_pipeline_stage')
    return args, checkpoint_args


def fix_fp8_params_lose_precision_when_loading_dist_ckpt(state_dict):
    """
    When "--fp8-param-gather" and "--use-dist-ckpt" are both enabled, the state dict read from
    dist-checkpoint loses precision (the weights read from checkpoint go through the process of
    bf16/fp16 -> fp8 -> bf16/fp16). This function is implemented to solve this problem.
    When "--fp8-param-gather" is disabled, this function doesn't modify anything.
    """
    for key in state_dict.keys():
        if key.startswith('model'):
            for _, sharded_tensor in state_dict[key].items():
                if is_float8tensor(sharded_tensor.data):
                    sharded_tensor.data = sharded_tensor.data.from_float8().cpu()


def load_checkpoint(model, optimizer, opt_param_scheduler, load_arg='load', strict=True,
                    ft_client=None, checkpointing_context=None):
    """Load a model checkpoint and return the iteration.
    strict (bool): whether to strictly enforce that the keys in
        :attr:`state_dict` of the checkpoint match the names of
        parameters and buffers in model.
    """
    args = get_args()
    load_dir = getattr(args, load_arg)

    # Finetuning directories
    pretrained_dir = getattr(args, 'pretrained_checkpoint', None)
    if pretrained_dir is not None and not checkpoint_exists(load_dir):
        print_rank_0(
            f'Checkpoint file not found in load directory {load_dir} attempting to finetune with checkpoint in {pretrained_dir}'
        )
        load_dir = pretrained_dir
        if not checkpoint_exists(load_dir):
            raise FileNotFoundError("No checkpoint found in load directory or pretrained directory")
        args.finetune = True

    model = unwrap_model(model)

    load_kwargs = {}
    is_dist_ckpt = False
    if (
        args.auto_detect_ckpt_format
        or args.use_dist_ckpt
        or args.non_persistent_save_interval is not None
    ):
        state_dict, checkpoint_name, release, ckpt_type = _load_base_checkpoint(
            load_dir,
            args,
            rank0=True,
            checkpointing_context=checkpointing_context,
        )
        if args.enable_ft_package and ft_client is not None and state_dict is not None:
            if 'ft_state' in state_dict:
                ft_client.load_state_dict(state_dict['ft_state'])
            else:
                print_rank_0("ft_state is not present in state_dict")
        is_dist_ckpt = (
            ckpt_type == CheckpointType.LOCAL
            or dist_checkpointing.check_is_distributed_checkpoint(checkpoint_name)
        )
        if is_dist_ckpt:
            ckpt_tp_pp = (
                state_dict['args'].tensor_model_parallel_size,
                state_dict['args'].pipeline_model_parallel_size,
            )
            run_tp_pp = (
                mpu.get_tensor_model_parallel_world_size(),
                mpu.get_pipeline_model_parallel_world_size(),
            )
            mismatch_msg = "(TP, PP) mismatch after resume ({} vs {} from checkpoint)".format(
                ckpt_tp_pp, run_tp_pp
            )

            # Determine if RNG state will be loaded
            if (ckpt_tp_pp == run_tp_pp and not release and not args.finetune and not args.no_load_rng
                    and not getattr(state_dict['args'], 'no_save_rng', False)):
                gen_sd_rng_state = get_rng_state(True)  # we can load the rng state
            else:
                gen_sd_rng_state = None
                if ckpt_tp_pp != run_tp_pp:
                    print_rank_0("{}: RNG state will be ignored".format(mismatch_msg))

            optim_sd_kwargs = dict(is_loading=True)
            # Determine if optimizer state will be loaded
            if (not release and not args.finetune and not args.no_load_optim
                    and not getattr(state_dict['args'], 'no_save_optim', False)):
                gen_sd_optim = optimizer
                gen_sd_opt_param_scheduler = opt_param_scheduler

                if args.use_distributed_optimizer:
                    optim_sd_kwargs['sharding_type'] = ('fully_sharded_model_space'
                                                        if getattr(state_dict['args'], 'ckpt_fully_parallel_save', False)
                                                        else 'dp_zero_gather_scatter')
                    # This is for backwards-compatibility. Can be removed once 'fully_sharded_bucket_space' loading is removed
                    for maybe_dist_opt_optim_state in (state_dict['optimizer'], *state_dict['optimizer'].values()):
                        if 'param_state_sharding_type' in maybe_dist_opt_optim_state:
                            if maybe_dist_opt_optim_state['param_state_sharding_type'] == 'fully_sharded_bucket_space':
                                print_rank_0('Detected deprecated `fully_sharded_bucket_space` DistributedOptimizer checkpoint format')
                                optim_sd_kwargs['sharding_type'] = maybe_dist_opt_optim_state['param_state_sharding_type']
                            break

                    if ckpt_tp_pp != run_tp_pp and optim_sd_kwargs['sharding_type'] != 'fully_sharded_model_space':
                        raise RuntimeError(f"{mismatch_msg}: not supported for DistributedOptimizer with sharding type {optim_sd_kwargs['sharding_type']}."
                                           f" Please use `--ckpt-fully-parallel-save` flag during checkpoint saving.")
            else:
                gen_sd_optim = None
                gen_sd_opt_param_scheduler = None
            load_kwargs['sharded_state_dict'] = generate_state_dict(args, model, gen_sd_optim, gen_sd_opt_param_scheduler,
                                                                    gen_sd_rng_state, True, optim_sd_kwargs=optim_sd_kwargs)
            # When "--fp8-param-gather" is disabled, this function doesn't modify anything.
            fix_fp8_params_lose_precision_when_loading_dist_ckpt(load_kwargs['sharded_state_dict'])

    state_dict, checkpoint_name, release, ckpt_type = _load_base_checkpoint(
        load_dir, args, rank0=False, checkpointing_context=checkpointing_context,
        **load_kwargs
    )

    if args.enable_ft_package and ft_client is not None and state_dict is not None:
        if 'ft_state' in state_dict:
            ft_client.load_state_dict(state_dict['ft_state'])
        else:
            print_rank_0("ft_state is not present in state_dict")

    # Checkpoint not loaded.
    if state_dict is None:
        # Iteration and num_floating_point_operations_so_far default to 0.
        return 0, 0

    # Set checkpoint version.
    set_checkpoint_version(state_dict.get('checkpoint_version', 0))

    # Set iteration.
    if args.finetune or release:
        iteration = 0
    else:
        try:
            iteration = state_dict['iteration']
        except KeyError:
            try:  # Backward compatible with older checkpoints
                iteration = state_dict['total_iters']
            except KeyError:
                print_rank_0('A metadata file exists but unable to load '
                             'iteration from checkpoint {}, exiting'.format(checkpoint_name))
                sys.exit()
    num_floating_point_operations_so_far = state_dict.get('num_floating_point_operations_so_far', 0)

    # Check arguments.
    assert args.consumed_train_samples == 0
    assert args.skipped_train_samples == 0
    assert args.consumed_valid_samples == 0
    if 'args' in state_dict and not args.finetune:
        checkpoint_args = state_dict['args']
        check_checkpoint_args(checkpoint_args)
        args.consumed_train_samples = getattr(checkpoint_args,
                                              'consumed_train_samples', 0)
        args.skipped_train_samples = getattr(checkpoint_args,
                                             'skipped_train_samples', 0)
        update_num_microbatches(consumed_samples=args.consumed_train_samples)
        args.consumed_valid_samples = getattr(checkpoint_args,
                                              'consumed_valid_samples', 0)
    else:
        print_rank_0('could not find arguments in the checkpoint ...')

    # [ModelOpt]: loading modelopt_state (sharded or not)
    if has_nvidia_modelopt:
        if ckpt_type == CheckpointType.LOCAL:
            raise NotImplementedError('Local checkpointing does not support model opt')
        if not args.use_dist_ckpt:
            restore_modelopt_state(model, state_dict)
        else:
            restore_sharded_modelopt_state(model, checkpoint_name)

    # Model.
    strict = False if args.retro_add_retriever else strict
    if len(model) == 1:
        model[0].load_state_dict(state_dict['model'], strict=strict)
    else:
        for i in range(len(model)):
            mpu.set_virtual_pipeline_model_parallel_rank(i)
            model[i].load_state_dict(state_dict['model%d' % i], strict=strict)

    # Fix up query/key/value matrix ordering if needed.
    checkpoint_version = get_checkpoint_version()
    print_rank_0(f' checkpoint version {checkpoint_version}')
    fix_query_key_value_ordering(model, checkpoint_version)

    # Optimizer.
    if not release and not args.finetune and not args.no_load_optim:
        try:
            # Load state dict.
            if optimizer is not None:
                optimizer.load_state_dict(state_dict['optimizer'])

            # Load distributed optimizer's custom parameter state.
            # For distributed checkpoint it's already loaded in load_state_dict above
            if args.use_distributed_optimizer and not is_dist_ckpt:
                # NOTE: this is a manual read of the tracker file.
                # This code should not be reached when reading from a non_persistent checkpoint
                assert not is_dist_ckpt
                tracker_filename = get_checkpoint_tracker_filename(load_dir)
                iteration, release = read_metadata(tracker_filename)
                model_checkpoint_name = \
                    get_checkpoint_name(load_dir, iteration, release)
                optim_checkpoint_name = \
                    get_distributed_optimizer_checkpoint_name(
                        model_checkpoint_name)
                optimizer.load_parameter_state(optim_checkpoint_name,
                                               update_legacy_format=args.ckpt_convert_update_legacy_dist_opt_format)

            # Load scheduler.
            if opt_param_scheduler is not None:
                if 'lr_scheduler' in state_dict: # backward compatbility
                    opt_param_scheduler.load_state_dict(state_dict['lr_scheduler'])
                else:
                    opt_param_scheduler.load_state_dict(state_dict['opt_param_scheduler'])
        except KeyError as e:
            print_rank_0('Unable to load optimizer from checkpoint {}. '
                         'Specify --no-load-optim or --finetune to prevent '
                         'attempting to load the optimizer state, '
                         'exiting ...'.format(checkpoint_name))
            raise e
    else:
        if (args.fp16 or args.bf16) and optimizer is not None:
            optimizer.reload_model_params()

    # rng states.
    if not release and not args.finetune and not args.no_load_rng:
        try:
            if 'rng_state' in state_dict:
                # access rng_state for data parallel rank
                if args.data_parallel_random_init:
                    rng_state = state_dict['rng_state'][mpu.get_data_parallel_rank()]
                else:
                    rng_state = state_dict['rng_state'][0]
                random.setstate(rng_state['random_rng_state'])
                np.random.set_state(rng_state['np_rng_state'])
                torch.set_rng_state(rng_state['torch_rng_state'])
                torch.cuda.set_rng_state(rng_state['cuda_rng_state'])
                # Check for empty states array
                if not rng_state['rng_tracker_states']:
                    raise KeyError
                tensor_parallel.get_cuda_rng_tracker().set_states(
                    rng_state['rng_tracker_states'])
            else:  # backward compatability
                random.setstate(state_dict['random_rng_state'])
                np.random.set_state(state_dict['np_rng_state'])
                torch.set_rng_state(state_dict['torch_rng_state'])
                torch.cuda.set_rng_state(state_dict['cuda_rng_state'])
                # Check for empty states array
                if not state_dict['rng_tracker_states']:
                    raise KeyError
                tensor_parallel.get_cuda_rng_tracker().set_states(
                    state_dict['rng_tracker_states'])
        except KeyError:
            print_rank_0('Unable to load rng state from checkpoint {}. '
                         'Specify --no-load-rng or --finetune to prevent '
                         'attempting to load the rng state, '
                         'exiting ...'.format(checkpoint_name))
            sys.exit()

    # Some utilities want to load a checkpoint without distributed being initialized
    if torch.distributed.is_initialized():
        torch.distributed.barrier()

    print_rank_0(f'  successfully loaded checkpoint from {load_dir} '
                 f'[ t {mpu.get_tensor_model_parallel_rank()}, '
                 f'p {mpu.get_pipeline_model_parallel_rank()} ] '
                 f'at iteration {iteration}')

    torch.cuda.empty_cache()
    return iteration, num_floating_point_operations_so_far


def load_biencoder_checkpoint(model, only_query_model=False,
                              only_context_model=False, custom_load_path=None):
    """
    selectively load retrieval models for indexing/retrieving
    from saved checkpoints
    """

    args = get_args()

    model = unwrap_model(model)

    load_path = custom_load_path if custom_load_path is not None else args.load

    tracker_filename = get_checkpoint_tracker_filename(load_path)
    with open(tracker_filename, 'r') as f:
        iteration = int(f.read().strip())

    checkpoint_name = get_checkpoint_name(load_path, iteration,
                                          args.use_distributed_optimizer,
                                          release=False)

    if mpu.get_data_parallel_rank() == 0:
        print('global rank {} is loading checkpoint {}'.format(
            torch.distributed.get_rank(), checkpoint_name))

    state_dict = torch.load(checkpoint_name, map_location='cpu')
    ret_state_dict = state_dict['model']

    if only_query_model:
        ret_state_dict.pop('context_model')
    if only_context_model:
        ret_state_dict.pop('query_model')

    assert len(model) == 1
    model[0].load_state_dict(ret_state_dict)
    torch.distributed.barrier()

    if mpu.get_data_parallel_rank() == 0:
        print(' successfully loaded {}'.format(checkpoint_name))

    return model
