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# Copyright (c) OpenMMLab. All rights reserved.
import math
import torch
from torch.utils.data import DistributedSampler as _DistributedSampler
from mmdet.core.utils import sync_random_seed
from mmdet.utils import get_device
class DistributedSampler(_DistributedSampler):
def __init__(self,
dataset,
num_replicas=None,
rank=None,
shuffle=True,
seed=0):
super().__init__(
dataset, num_replicas=num_replicas, rank=rank, shuffle=shuffle)
# In distributed sampling, different ranks should sample
# non-overlapped data in the dataset. Therefore, this function
# is used to make sure that each rank shuffles the data indices
# in the same order based on the same seed. Then different ranks
# could use different indices to select non-overlapped data from the
# same data list.
device = get_device()
self.seed = sync_random_seed(seed, device)
def __iter__(self):
# deterministically shuffle based on epoch
if self.shuffle:
g = torch.Generator()
# When :attr:`shuffle=True`, this ensures all replicas
# use a different random ordering for each epoch.
# Otherwise, the next iteration of this sampler will
# yield the same ordering.
g.manual_seed(self.epoch + self.seed)
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
# in case that indices is shorter than half of total_size
indices = (indices *
math.ceil(self.total_size / len(indices)))[:self.total_size]
assert len(indices) == self.total_size
# subsample
indices = indices[self.rank:self.total_size:self.num_replicas]
assert len(indices) == self.num_samples
return iter(indices)
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