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# Copyright (c) Facebook, Inc. and its affiliates.
import copy
import itertools
import logging
import numpy as np
import pickle
import random
import torch.utils.data as data
from torch.utils.data.sampler import Sampler
from detectron2.utils.serialize import PicklableWrapper
__all__ = ["MapDataset", "DatasetFromList", "AspectRatioGroupedDataset", "ToIterableDataset"]
def _shard_iterator_dataloader_worker(iterable):
# Shard the iterable if we're currently inside pytorch dataloader worker.
worker_info = data.get_worker_info()
if worker_info is None or worker_info.num_workers == 1:
# do nothing
yield from iterable
else:
yield from itertools.islice(iterable, worker_info.id, None, worker_info.num_workers)
class _MapIterableDataset(data.IterableDataset):
"""
Map a function over elements in an IterableDataset.
Similar to pytorch's MapIterDataPipe, but support filtering when map_func
returns None.
This class is not public-facing. Will be called by `MapDataset`.
"""
def __init__(self, dataset, map_func):
self._dataset = dataset
self._map_func = PicklableWrapper(map_func) # wrap so that a lambda will work
def __len__(self):
return len(self._dataset)
def __iter__(self):
for x in map(self._map_func, self._dataset):
if x is not None:
yield x
class MapDataset(data.Dataset):
"""
Map a function over the elements in a dataset.
"""
def __init__(self, dataset, map_func):
"""
Args:
dataset: a dataset where map function is applied. Can be either
map-style or iterable dataset. When given an iterable dataset,
the returned object will also be an iterable dataset.
map_func: a callable which maps the element in dataset. map_func can
return None to skip the data (e.g. in case of errors).
How None is handled depends on the style of `dataset`.
If `dataset` is map-style, it randomly tries other elements.
If `dataset` is iterable, it skips the data and tries the next.
"""
self._dataset = dataset
self._map_func = PicklableWrapper(map_func) # wrap so that a lambda will work
self._rng = random.Random(42)
self._fallback_candidates = set(range(len(dataset)))
def __new__(cls, dataset, map_func):
is_iterable = isinstance(dataset, data.IterableDataset)
if is_iterable:
return _MapIterableDataset(dataset, map_func)
else:
return super().__new__(cls)
def __getnewargs__(self):
return self._dataset, self._map_func
def __len__(self):
return len(self._dataset)
def __getitem__(self, idx):
retry_count = 0
cur_idx = int(idx)
while True:
data = self._map_func(self._dataset[cur_idx])
if data is not None:
self._fallback_candidates.add(cur_idx)
return data
# _map_func fails for this idx, use a random new index from the pool
retry_count += 1
self._fallback_candidates.discard(cur_idx)
cur_idx = self._rng.sample(self._fallback_candidates, k=1)[0]
if retry_count >= 3:
logger = logging.getLogger(__name__)
logger.warning(
"Failed to apply `_map_func` for idx: {}, retry count: {}".format(
idx, retry_count
)
)
class DatasetFromList(data.Dataset):
"""
Wrap a list to a torch Dataset. It produces elements of the list as data.
"""
def __init__(self, lst: list, copy: bool = True, serialize: bool = True):
"""
Args:
lst (list): a list which contains elements to produce.
copy (bool): whether to deepcopy the element when producing it,
so that the result can be modified in place without affecting the
source in the list.
serialize (bool): whether to hold memory using serialized objects, when
enabled, data loader workers can use shared RAM from master
process instead of making a copy.
"""
self._lst = lst
self._copy = copy
self._serialize = serialize
def _serialize(data):
buffer = pickle.dumps(data, protocol=-1)
return np.frombuffer(buffer, dtype=np.uint8)
if self._serialize:
logger = logging.getLogger(__name__)
logger.info(
"Serializing {} elements to byte tensors and concatenating them all ...".format(
len(self._lst)
)
)
self._lst = [_serialize(x) for x in self._lst]
self._addr = np.asarray([len(x) for x in self._lst], dtype=np.int64)
self._addr = np.cumsum(self._addr)
self._lst = np.concatenate(self._lst)
logger.info("Serialized dataset takes {:.2f} MiB".format(len(self._lst) / 1024 ** 2))
def __len__(self):
if self._serialize:
return len(self._addr)
else:
return len(self._lst)
def __getitem__(self, idx):
if self._serialize:
start_addr = 0 if idx == 0 else self._addr[idx - 1].item()
end_addr = self._addr[idx].item()
bytes = memoryview(self._lst[start_addr:end_addr])
return pickle.loads(bytes)
elif self._copy:
return copy.deepcopy(self._lst[idx])
else:
return self._lst[idx]
class ToIterableDataset(data.IterableDataset):
"""
Convert an old indices-based (also called map-style) dataset
to an iterable-style dataset.
"""
def __init__(self, dataset: data.Dataset, sampler: Sampler, shard_sampler: bool = True):
"""
Args:
dataset: an old-style dataset with ``__getitem__``
sampler: a cheap iterable that produces indices to be applied on ``dataset``.
shard_sampler: whether to shard the sampler based on the current pytorch data loader
worker id. When an IterableDataset is forked by pytorch's DataLoader into multiple
workers, it is responsible for sharding its data based on worker id so that workers
don't produce identical data.
Most samplers (like our TrainingSampler) do not shard based on dataloader worker id
and this argument should be set to True. But certain samplers may be already
sharded, in that case this argument should be set to False.
"""
assert not isinstance(dataset, data.IterableDataset), dataset
assert isinstance(sampler, Sampler), sampler
self.dataset = dataset
self.sampler = sampler
self.shard_sampler = shard_sampler
def __iter__(self):
if not self.shard_sampler:
sampler = self.sampler
else:
# With map-style dataset, `DataLoader(dataset, sampler)` runs the
# sampler in main process only. But `DataLoader(ToIterableDataset(dataset, sampler))`
# will run sampler in every of the N worker. So we should only keep 1/N of the ids on
# each worker. The assumption is that sampler is cheap to iterate so it's fine to
# discard ids in workers.
sampler = _shard_iterator_dataloader_worker(self.sampler)
for idx in sampler:
yield self.dataset[idx]
def __len__(self):
return len(self.sampler)
class AspectRatioGroupedDataset(data.IterableDataset):
"""
Batch data that have similar aspect ratio together.
In this implementation, images whose aspect ratio < (or >) 1 will
be batched together.
This improves training speed because the images then need less padding
to form a batch.
It assumes the underlying dataset produces dicts with "width" and "height" keys.
It will then produce a list of original dicts with length = batch_size,
all with similar aspect ratios.
"""
def __init__(self, dataset, batch_size):
"""
Args:
dataset: an iterable. Each element must be a dict with keys
"width" and "height", which will be used to batch data.
batch_size (int):
"""
self.dataset = dataset
self.batch_size = batch_size
self._buckets = [[] for _ in range(2)]
# Hard-coded two aspect ratio groups: w > h and w < h.
# Can add support for more aspect ratio groups, but doesn't seem useful
def __iter__(self):
for d in self.dataset:
w, h = d["width"], d["height"]
bucket_id = 0 if w > h else 1
bucket = self._buckets[bucket_id]
bucket.append(d)
if len(bucket) == self.batch_size:
yield bucket[:]
del bucket[:]
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