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import platform
import random
from functools import partial
from typing import Optional, Union
import numpy as np
from mmcv.runner import get_dist_info
from mmcv.utils import Registry, build_from_cfg
from torch.utils.data import DataLoader
from torch.utils.data.dataset import Dataset
import torch
from torch.utils.data import DistributedSampler as _DistributedSampler
class DistributedSampler(_DistributedSampler):
def __init__(self,
dataset,
num_replicas=None,
rank=None,
shuffle=True,
round_up=True):
super().__init__(dataset, num_replicas=num_replicas, rank=rank)
self.shuffle = shuffle
self.round_up = round_up
if self.round_up:
self.total_size = self.num_samples * self.num_replicas
else:
self.total_size = len(self.dataset)
def __iter__(self):
# deterministically shuffle based on epoch
if self.shuffle:
g = torch.Generator()
g.manual_seed(self.epoch)
indices = torch.randperm(len(self.dataset), generator=g).tolist()
else:
indices = torch.arange(len(self.dataset)).tolist()
# add extra samples to make it evenly divisible
if self.round_up:
indices = (
indices *
int(self.total_size / len(indices) + 1))[:self.total_size]
assert len(indices) == self.total_size
# subsample
indices = indices[self.rank:self.total_size:self.num_replicas]
if self.round_up:
assert len(indices) == self.num_samples
return iter(indices)
def build_dataloader(dataset: Dataset,
samples_per_gpu: int,
workers_per_gpu: int,
num_gpus: Optional[int] = 1,
dist: Optional[bool] = True,
shuffle: Optional[bool] = True,
round_up: Optional[bool] = True,
seed: Optional[Union[int, None]] = None,
persistent_workers: Optional[bool] = True,
**kwargs):
"""Build PyTorch DataLoader.
In distributed training, each GPU/process has a dataloader.
In non-distributed training, there is only one dataloader for all GPUs.
Args:
dataset (:obj:`Dataset`): A PyTorch dataset.
samples_per_gpu (int): Number of training samples on each GPU, i.e.,
batch size of each GPU.
workers_per_gpu (int): How many subprocesses to use for data loading
for each GPU.
num_gpus (int, optional): Number of GPUs. Only used in non-distributed
training.
dist (bool, optional): Distributed training/test or not. Default: True.
shuffle (bool, optional): Whether to shuffle the data at every epoch.
Default: True.
round_up (bool, optional): Whether to round up the length of dataset by
adding extra samples to make it evenly divisible. Default: True.
persistent_workers (bool): If True, the data loader will not shutdown
the worker processes after a dataset has been consumed once.
This allows to maintain the workers Dataset instances alive.
The argument also has effect in PyTorch>=1.7.0.
Default: True
kwargs: any keyword argument to be used to initialize DataLoader
Returns:
DataLoader: A PyTorch dataloader.
"""
rank, world_size = get_dist_info()
if dist:
sampler = DistributedSampler(
dataset, world_size, rank, shuffle=shuffle, round_up=round_up)
shuffle = False
batch_size = samples_per_gpu
num_workers = workers_per_gpu
else:
sampler = None
batch_size = num_gpus * samples_per_gpu
num_workers = num_gpus * workers_per_gpu
init_fn = partial(
worker_init_fn, num_workers=num_workers, rank=rank,
seed=seed) if seed is not None else None
data_loader = DataLoader(
dataset,
batch_size=batch_size,
sampler=sampler,
num_workers=num_workers,
pin_memory=False,
shuffle=shuffle,
worker_init_fn=init_fn,
persistent_workers=persistent_workers,
**kwargs)
return data_loader
def worker_init_fn(worker_id: int, num_workers: int, rank: int, seed: int):
"""Init random seed for each worker."""
# The seed of each worker equals to
# num_worker * rank + worker_id + user_seed
worker_seed = num_workers * rank + worker_id + seed
np.random.seed(worker_seed)
random.seed(worker_seed)
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