File size: 26,491 Bytes
938e515
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
# Copyright (c) Facebook, Inc. and its affiliates.
import itertools
import logging
import numpy as np
import operator
import pickle
from collections import OrderedDict, defaultdict
from typing import Any, Callable, Dict, List, Optional, Union
import torch
import torch.utils.data as torchdata
from tabulate import tabulate
from termcolor import colored

from detectron2.config import configurable
from detectron2.structures import BoxMode
from detectron2.utils.comm import get_world_size
from detectron2.utils.env import seed_all_rng
from detectron2.utils.file_io import PathManager
from detectron2.utils.logger import _log_api_usage, log_first_n

from .catalog import DatasetCatalog, MetadataCatalog
from .common import AspectRatioGroupedDataset, DatasetFromList, MapDataset, ToIterableDataset
from .dataset_mapper import DatasetMapper
from .detection_utils import check_metadata_consistency
from .samplers import (
    InferenceSampler,
    RandomSubsetTrainingSampler,
    RepeatFactorTrainingSampler,
    TrainingSampler,
)

"""
This file contains the default logic to build a dataloader for training or testing.
"""

__all__ = [
    "build_batch_data_loader",
    "build_detection_train_loader",
    "build_detection_test_loader",
    "get_detection_dataset_dicts",
    "load_proposals_into_dataset",
    "print_instances_class_histogram",
]


def filter_images_with_only_crowd_annotations(dataset_dicts):
    """
    Filter out images with none annotations or only crowd annotations
    (i.e., images without non-crowd annotations).
    A common training-time preprocessing on COCO dataset.

    Args:
        dataset_dicts (list[dict]): annotations in Detectron2 Dataset format.

    Returns:
        list[dict]: the same format, but filtered.
    """
    num_before = len(dataset_dicts)

    def valid(anns):
        for ann in anns:
            if ann.get("iscrowd", 0) == 0:
                return True
        return False

    dataset_dicts = [x for x in dataset_dicts if valid(x["annotations"])]
    num_after = len(dataset_dicts)
    logger = logging.getLogger(__name__)
    logger.info(
        "Removed {} images with no usable annotations. {} images left.".format(
            num_before - num_after, num_after
        )
    )
    return dataset_dicts


def filter_images_with_few_keypoints(dataset_dicts, min_keypoints_per_image):
    """
    Filter out images with too few number of keypoints.

    Args:
        dataset_dicts (list[dict]): annotations in Detectron2 Dataset format.

    Returns:
        list[dict]: the same format as dataset_dicts, but filtered.
    """
    num_before = len(dataset_dicts)

    def visible_keypoints_in_image(dic):
        # Each keypoints field has the format [x1, y1, v1, ...], where v is visibility
        annotations = dic["annotations"]
        return sum(
            (np.array(ann["keypoints"][2::3]) > 0).sum()
            for ann in annotations
            if "keypoints" in ann
        )

    dataset_dicts = [
        x for x in dataset_dicts if visible_keypoints_in_image(x) >= min_keypoints_per_image
    ]
    num_after = len(dataset_dicts)
    logger = logging.getLogger(__name__)
    logger.info(
        "Removed {} images with fewer than {} keypoints.".format(
            num_before - num_after, min_keypoints_per_image
        )
    )
    return dataset_dicts


def load_proposals_into_dataset(dataset_dicts, proposal_file):
    """
    Load precomputed object proposals into the dataset.

    The proposal file should be a pickled dict with the following keys:

    - "ids": list[int] or list[str], the image ids
    - "boxes": list[np.ndarray], each is an Nx4 array of boxes corresponding to the image id
    - "objectness_logits": list[np.ndarray], each is an N sized array of objectness scores
      corresponding to the boxes.
    - "bbox_mode": the BoxMode of the boxes array. Defaults to ``BoxMode.XYXY_ABS``.

    Args:
        dataset_dicts (list[dict]): annotations in Detectron2 Dataset format.
        proposal_file (str): file path of pre-computed proposals, in pkl format.

    Returns:
        list[dict]: the same format as dataset_dicts, but added proposal field.
    """
    logger = logging.getLogger(__name__)
    logger.info("Loading proposals from: {}".format(proposal_file))

    with PathManager.open(proposal_file, "rb") as f:
        proposals = pickle.load(f, encoding="latin1")

    # Rename the key names in D1 proposal files
    rename_keys = {"indexes": "ids", "scores": "objectness_logits"}
    for key in rename_keys:
        if key in proposals:
            proposals[rename_keys[key]] = proposals.pop(key)

    # Fetch the indexes of all proposals that are in the dataset
    # Convert image_id to str since they could be int.
    img_ids = set({str(record["image_id"]) for record in dataset_dicts})
    id_to_index = {str(id): i for i, id in enumerate(proposals["ids"]) if str(id) in img_ids}

    # Assuming default bbox_mode of precomputed proposals are 'XYXY_ABS'
    bbox_mode = BoxMode(proposals["bbox_mode"]) if "bbox_mode" in proposals else BoxMode.XYXY_ABS

    for record in dataset_dicts:
        # Get the index of the proposal
        i = id_to_index[str(record["image_id"])]

        boxes = proposals["boxes"][i]
        objectness_logits = proposals["objectness_logits"][i]
        # Sort the proposals in descending order of the scores
        inds = objectness_logits.argsort()[::-1]
        record["proposal_boxes"] = boxes[inds]
        record["proposal_objectness_logits"] = objectness_logits[inds]
        record["proposal_bbox_mode"] = bbox_mode

    return dataset_dicts


def print_instances_class_histogram(dataset_dicts, class_names):
    """
    Args:
        dataset_dicts (list[dict]): list of dataset dicts.
        class_names (list[str]): list of class names (zero-indexed).
    """
    num_classes = len(class_names)
    hist_bins = np.arange(num_classes + 1)
    histogram = np.zeros((num_classes,), dtype=int)
    for entry in dataset_dicts:
        annos = entry["annotations"]
        classes = np.asarray(
            [x["category_id"] for x in annos if not x.get("iscrowd", 0)], dtype=int
        )
        if len(classes):
            assert classes.min() >= 0, f"Got an invalid category_id={classes.min()}"
            assert (
                classes.max() < num_classes
            ), f"Got an invalid category_id={classes.max()} for a dataset of {num_classes} classes"
        histogram += np.histogram(classes, bins=hist_bins)[0]

    N_COLS = min(6, len(class_names) * 2)

    def short_name(x):
        # make long class names shorter. useful for lvis
        if len(x) > 13:
            return x[:11] + ".."
        return x

    data = list(
        itertools.chain(*[[short_name(class_names[i]), int(v)] for i, v in enumerate(histogram)])
    )
    total_num_instances = sum(data[1::2])
    data.extend([None] * (N_COLS - (len(data) % N_COLS)))
    if num_classes > 1:
        data.extend(["total", total_num_instances])
    data = itertools.zip_longest(*[data[i::N_COLS] for i in range(N_COLS)])
    table = tabulate(
        data,
        headers=["category", "#instances"] * (N_COLS // 2),
        tablefmt="pipe",
        numalign="left",
        stralign="center",
    )
    log_first_n(
        logging.INFO,
        "Distribution of instances among all {} categories:\n".format(num_classes)
        + colored(table, "cyan"),
        key="message",
    )


def get_detection_dataset_dicts(
    names,
    filter_empty=True,
    min_keypoints=0,
    proposal_files=None,
    check_consistency=True,
):
    """
    Load and prepare dataset dicts for instance detection/segmentation and semantic segmentation.

    Args:
        names (str or list[str]): a dataset name or a list of dataset names
        filter_empty (bool): whether to filter out images without instance annotations
        min_keypoints (int): filter out images with fewer keypoints than
            `min_keypoints`. Set to 0 to do nothing.
        proposal_files (list[str]): if given, a list of object proposal files
            that match each dataset in `names`.
        check_consistency (bool): whether to check if datasets have consistent metadata.

    Returns:
        list[dict]: a list of dicts following the standard dataset dict format.
    """
    if isinstance(names, str):
        names = [names]
    assert len(names), names

    available_datasets = DatasetCatalog.keys()
    names_set = set(names)
    if not names_set.issubset(available_datasets):
        logger = logging.getLogger(__name__)
        logger.warning(
            "The following dataset names are not registered in the DatasetCatalog: "
            f"{names_set - available_datasets}. "
            f"Available datasets are {available_datasets}"
        )

    dataset_dicts = [DatasetCatalog.get(dataset_name) for dataset_name in names]

    if isinstance(dataset_dicts[0], torchdata.Dataset):
        if len(dataset_dicts) > 1:
            # ConcatDataset does not work for iterable style dataset.
            # We could support concat for iterable as well, but it's often
            # not a good idea to concat iterables anyway.
            return torchdata.ConcatDataset(dataset_dicts)
        return dataset_dicts[0]

    for dataset_name, dicts in zip(names, dataset_dicts):
        assert len(dicts), "Dataset '{}' is empty!".format(dataset_name)

    if proposal_files is not None:
        assert len(names) == len(proposal_files)
        # load precomputed proposals from proposal files
        dataset_dicts = [
            load_proposals_into_dataset(dataset_i_dicts, proposal_file)
            for dataset_i_dicts, proposal_file in zip(dataset_dicts, proposal_files)
        ]

    dataset_dicts = list(itertools.chain.from_iterable(dataset_dicts))

    has_instances = "annotations" in dataset_dicts[0]
    if filter_empty and has_instances:
        dataset_dicts = filter_images_with_only_crowd_annotations(dataset_dicts)
    if min_keypoints > 0 and has_instances:
        dataset_dicts = filter_images_with_few_keypoints(dataset_dicts, min_keypoints)

    if check_consistency and has_instances:
        try:
            class_names = MetadataCatalog.get(names[0]).thing_classes
            check_metadata_consistency("thing_classes", names)
            print_instances_class_histogram(dataset_dicts, class_names)
        except AttributeError:  # class names are not available for this dataset
            pass

    assert len(dataset_dicts), "No valid data found in {}.".format(",".join(names))
    return dataset_dicts


def build_batch_data_loader(
    dataset,
    sampler,
    total_batch_size,
    *,
    aspect_ratio_grouping=False,
    num_workers=0,
    collate_fn=None,
    drop_last: bool = True,
    single_gpu_batch_size=None,
    seed=None,
    **kwargs,
):
    """
    Build a batched dataloader. The main differences from `torch.utils.data.DataLoader` are:
    1. support aspect ratio grouping options
    2. use no "batch collation", because this is common for detection training

    Args:
        dataset (torch.utils.data.Dataset): a pytorch map-style or iterable dataset.
        sampler (torch.utils.data.sampler.Sampler or None): a sampler that produces indices.
            Must be provided iff. ``dataset`` is a map-style dataset.
        total_batch_size, aspect_ratio_grouping, num_workers, collate_fn: see
            :func:`build_detection_train_loader`.
        single_gpu_batch_size: You can specify either `single_gpu_batch_size` or `total_batch_size`.
            `single_gpu_batch_size` specifies the batch size that will be used for each gpu/process.
            `total_batch_size` allows you to specify the total aggregate batch size across gpus.
            It is an error to supply a value for both.
        drop_last (bool): if ``True``, the dataloader will drop incomplete batches.

    Returns:
        iterable[list]. Length of each list is the batch size of the current
            GPU. Each element in the list comes from the dataset.
    """
    if single_gpu_batch_size:
        if total_batch_size:
            raise ValueError(
                """total_batch_size and single_gpu_batch_size are mutually incompatible.
                Please specify only one. """
            )
        batch_size = single_gpu_batch_size
    else:
        world_size = get_world_size()
        assert (
            total_batch_size > 0 and total_batch_size % world_size == 0
        ), "Total batch size ({}) must be divisible by the number of gpus ({}).".format(
            total_batch_size, world_size
        )
        batch_size = total_batch_size // world_size
    logger = logging.getLogger(__name__)
    logger.info("Making batched data loader with batch_size=%d", batch_size)

    if isinstance(dataset, torchdata.IterableDataset):
        assert sampler is None, "sampler must be None if dataset is IterableDataset"
    else:
        dataset = ToIterableDataset(dataset, sampler, shard_chunk_size=batch_size)

    generator = None
    if seed is not None:
        generator = torch.Generator()
        generator.manual_seed(seed)

    if aspect_ratio_grouping:
        assert drop_last, "Aspect ratio grouping will drop incomplete batches."
        data_loader = torchdata.DataLoader(
            dataset,
            num_workers=num_workers,
            collate_fn=operator.itemgetter(0),  # don't batch, but yield individual elements
            worker_init_fn=worker_init_reset_seed,
            generator=generator,
            **kwargs
        )  # yield individual mapped dict
        data_loader = AspectRatioGroupedDataset(data_loader, batch_size)
        if collate_fn is None:
            return data_loader
        return MapDataset(data_loader, collate_fn)
    else:
        return torchdata.DataLoader(
            dataset,
            batch_size=batch_size,
            drop_last=drop_last,
            num_workers=num_workers,
            collate_fn=trivial_batch_collator if collate_fn is None else collate_fn,
            worker_init_fn=worker_init_reset_seed,
            generator=generator,
            **kwargs
        )


def _get_train_datasets_repeat_factors(cfg) -> Dict[str, float]:
    repeat_factors = cfg.DATASETS.TRAIN_REPEAT_FACTOR
    assert all(len(tup) == 2 for tup in repeat_factors)
    name_to_weight = defaultdict(lambda: 1, dict(repeat_factors))
    # The sampling weights map should only contain datasets in train config
    unrecognized = set(name_to_weight.keys()) - set(cfg.DATASETS.TRAIN)
    assert not unrecognized, f"unrecognized datasets: {unrecognized}"
    logger = logging.getLogger(__name__)
    logger.info(f"Found repeat factors: {list(name_to_weight.items())}")

    # pyre-fixme[7]: Expected `Dict[str, float]` but got `DefaultDict[typing.Any, int]`.
    return name_to_weight


def _build_weighted_sampler(cfg, enable_category_balance=False):
    dataset_repeat_factors = _get_train_datasets_repeat_factors(cfg)
    # OrderedDict to guarantee order of values() consistent with repeat factors
    dataset_name_to_dicts = OrderedDict(
        {
            name: get_detection_dataset_dicts(
                [name],
                filter_empty=cfg.DATALOADER.FILTER_EMPTY_ANNOTATIONS,
                min_keypoints=cfg.MODEL.ROI_KEYPOINT_HEAD.MIN_KEYPOINTS_PER_IMAGE
                if cfg.MODEL.KEYPOINT_ON
                else 0,
                proposal_files=cfg.DATASETS.PROPOSAL_FILES_TRAIN
                if cfg.MODEL.LOAD_PROPOSALS
                else None,
            )
            for name in cfg.DATASETS.TRAIN
        }
    )
    # Repeat factor for every sample in the dataset
    repeat_factors = [
        [dataset_repeat_factors[dsname]] * len(dataset_name_to_dicts[dsname])
        for dsname in cfg.DATASETS.TRAIN
    ]

    repeat_factors = list(itertools.chain.from_iterable(repeat_factors))

    repeat_factors = torch.tensor(repeat_factors)
    logger = logging.getLogger(__name__)
    if enable_category_balance:
        """
        1. Calculate repeat factors using category frequency for each dataset and then merge them.
        2. Element wise dot producting the dataset frequency repeat factors with
            the category frequency repeat factors gives the final repeat factors.
        """
        category_repeat_factors = [
            RepeatFactorTrainingSampler.repeat_factors_from_category_frequency(
                dataset_dict, cfg.DATALOADER.REPEAT_THRESHOLD
            )
            for dataset_dict in dataset_name_to_dicts.values()
        ]
        # flatten the category repeat factors from all datasets
        category_repeat_factors = list(itertools.chain.from_iterable(category_repeat_factors))
        category_repeat_factors = torch.tensor(category_repeat_factors)
        repeat_factors = torch.mul(category_repeat_factors, repeat_factors)
        repeat_factors = repeat_factors / torch.min(repeat_factors)
        logger.info(
            "Using WeightedCategoryTrainingSampler with repeat_factors={}".format(
                cfg.DATASETS.TRAIN_REPEAT_FACTOR
            )
        )
    else:
        logger.info(
            "Using WeightedTrainingSampler with repeat_factors={}".format(
                cfg.DATASETS.TRAIN_REPEAT_FACTOR
            )
        )

    sampler = RepeatFactorTrainingSampler(repeat_factors)
    return sampler


def _train_loader_from_config(cfg, mapper=None, *, dataset=None, sampler=None):
    if dataset is None:
        dataset = get_detection_dataset_dicts(
            cfg.DATASETS.TRAIN,
            filter_empty=cfg.DATALOADER.FILTER_EMPTY_ANNOTATIONS,
            min_keypoints=cfg.MODEL.ROI_KEYPOINT_HEAD.MIN_KEYPOINTS_PER_IMAGE
            if cfg.MODEL.KEYPOINT_ON
            else 0,
            proposal_files=cfg.DATASETS.PROPOSAL_FILES_TRAIN if cfg.MODEL.LOAD_PROPOSALS else None,
        )
        _log_api_usage("dataset." + cfg.DATASETS.TRAIN[0])

    if mapper is None:
        mapper = DatasetMapper(cfg, True)

    if sampler is None:
        sampler_name = cfg.DATALOADER.SAMPLER_TRAIN
        logger = logging.getLogger(__name__)
        if isinstance(dataset, torchdata.IterableDataset):
            logger.info("Not using any sampler since the dataset is IterableDataset.")
            sampler = None
        else:
            logger.info("Using training sampler {}".format(sampler_name))
            if sampler_name == "TrainingSampler":
                sampler = TrainingSampler(len(dataset))
            elif sampler_name == "RepeatFactorTrainingSampler":
                repeat_factors = RepeatFactorTrainingSampler.repeat_factors_from_category_frequency(
                    dataset, cfg.DATALOADER.REPEAT_THRESHOLD
                )
                sampler = RepeatFactorTrainingSampler(repeat_factors)
            elif sampler_name == "RandomSubsetTrainingSampler":
                sampler = RandomSubsetTrainingSampler(
                    len(dataset), cfg.DATALOADER.RANDOM_SUBSET_RATIO
                )
            elif sampler_name == "WeightedTrainingSampler":
                sampler = _build_weighted_sampler(cfg)
            elif sampler_name == "WeightedCategoryTrainingSampler":
                sampler = _build_weighted_sampler(cfg, enable_category_balance=True)
            else:
                raise ValueError("Unknown training sampler: {}".format(sampler_name))

    return {
        "dataset": dataset,
        "sampler": sampler,
        "mapper": mapper,
        "total_batch_size": cfg.SOLVER.IMS_PER_BATCH,
        "aspect_ratio_grouping": cfg.DATALOADER.ASPECT_RATIO_GROUPING,
        "num_workers": cfg.DATALOADER.NUM_WORKERS,
    }


@configurable(from_config=_train_loader_from_config)
def build_detection_train_loader(
    dataset,
    *,
    mapper,
    sampler=None,
    total_batch_size,
    aspect_ratio_grouping=True,
    num_workers=0,
    collate_fn=None,
    **kwargs
):
    """
    Build a dataloader for object detection with some default features.

    Args:
        dataset (list or torch.utils.data.Dataset): a list of dataset dicts,
            or a pytorch dataset (either map-style or iterable). It can be obtained
            by using :func:`DatasetCatalog.get` or :func:`get_detection_dataset_dicts`.
        mapper (callable): a callable which takes a sample (dict) from dataset and
            returns the format to be consumed by the model.
            When using cfg, the default choice is ``DatasetMapper(cfg, is_train=True)``.
        sampler (torch.utils.data.sampler.Sampler or None): a sampler that produces
            indices to be applied on ``dataset``.
            If ``dataset`` is map-style, the default sampler is a :class:`TrainingSampler`,
            which coordinates an infinite random shuffle sequence across all workers.
            Sampler must be None if ``dataset`` is iterable.
        total_batch_size (int): total batch size across all workers.
        aspect_ratio_grouping (bool): whether to group images with similar
            aspect ratio for efficiency. When enabled, it requires each
            element in dataset be a dict with keys "width" and "height".
        num_workers (int): number of parallel data loading workers
        collate_fn: a function that determines how to do batching, same as the argument of
            `torch.utils.data.DataLoader`. Defaults to do no collation and return a list of
            data. No collation is OK for small batch size and simple data structures.
            If your batch size is large and each sample contains too many small tensors,
            it's more efficient to collate them in data loader.

    Returns:
        torch.utils.data.DataLoader:
            a dataloader. Each output from it is a ``list[mapped_element]`` of length
            ``total_batch_size / num_workers``, where ``mapped_element`` is produced
            by the ``mapper``.
    """
    if isinstance(dataset, list):
        dataset = DatasetFromList(dataset, copy=False)
    if mapper is not None:
        dataset = MapDataset(dataset, mapper)

    if isinstance(dataset, torchdata.IterableDataset):
        assert sampler is None, "sampler must be None if dataset is IterableDataset"
    else:
        if sampler is None:
            sampler = TrainingSampler(len(dataset))
        assert isinstance(sampler, torchdata.Sampler), f"Expect a Sampler but got {type(sampler)}"
    return build_batch_data_loader(
        dataset,
        sampler,
        total_batch_size,
        aspect_ratio_grouping=aspect_ratio_grouping,
        num_workers=num_workers,
        collate_fn=collate_fn,
        **kwargs
    )


def _test_loader_from_config(cfg, dataset_name, mapper=None):
    """
    Uses the given `dataset_name` argument (instead of the names in cfg), because the
    standard practice is to evaluate each test set individually (not combining them).
    """
    if isinstance(dataset_name, str):
        dataset_name = [dataset_name]

    dataset = get_detection_dataset_dicts(
        dataset_name,
        filter_empty=False,
        proposal_files=[
            cfg.DATASETS.PROPOSAL_FILES_TEST[list(cfg.DATASETS.TEST).index(x)] for x in dataset_name
        ]
        if cfg.MODEL.LOAD_PROPOSALS
        else None,
    )
    if mapper is None:
        mapper = DatasetMapper(cfg, False)
    return {
        "dataset": dataset,
        "mapper": mapper,
        "num_workers": cfg.DATALOADER.NUM_WORKERS,
        "sampler": InferenceSampler(len(dataset))
        if not isinstance(dataset, torchdata.IterableDataset)
        else None,
    }


@configurable(from_config=_test_loader_from_config)
def build_detection_test_loader(
    dataset: Union[List[Any], torchdata.Dataset],
    *,
    mapper: Callable[[Dict[str, Any]], Any],
    sampler: Optional[torchdata.Sampler] = None,
    batch_size: int = 1,
    num_workers: int = 0,
    collate_fn: Optional[Callable[[List[Any]], Any]] = None,
) -> torchdata.DataLoader:
    """
    Similar to `build_detection_train_loader`, with default batch size = 1,
    and sampler = :class:`InferenceSampler`. This sampler coordinates all workers
    to produce the exact set of all samples.

    Args:
        dataset: a list of dataset dicts,
            or a pytorch dataset (either map-style or iterable). They can be obtained
            by using :func:`DatasetCatalog.get` or :func:`get_detection_dataset_dicts`.
        mapper: a callable which takes a sample (dict) from dataset
           and returns the format to be consumed by the model.
           When using cfg, the default choice is ``DatasetMapper(cfg, is_train=False)``.
        sampler: a sampler that produces
            indices to be applied on ``dataset``. Default to :class:`InferenceSampler`,
            which splits the dataset across all workers. Sampler must be None
            if `dataset` is iterable.
        batch_size: the batch size of the data loader to be created.
            Default to 1 image per worker since this is the standard when reporting
            inference time in papers.
        num_workers: number of parallel data loading workers
        collate_fn: same as the argument of `torch.utils.data.DataLoader`.
            Defaults to do no collation and return a list of data.

    Returns:
        DataLoader: a torch DataLoader, that loads the given detection
        dataset, with test-time transformation and batching.

    Examples:
    ::
        data_loader = build_detection_test_loader(
            DatasetRegistry.get("my_test"),
            mapper=DatasetMapper(...))

        # or, instantiate with a CfgNode:
        data_loader = build_detection_test_loader(cfg, "my_test")
    """
    if isinstance(dataset, list):
        dataset = DatasetFromList(dataset, copy=False)
    if mapper is not None:
        dataset = MapDataset(dataset, mapper)
    if isinstance(dataset, torchdata.IterableDataset):
        assert sampler is None, "sampler must be None if dataset is IterableDataset"
    else:
        if sampler is None:
            sampler = InferenceSampler(len(dataset))
    return torchdata.DataLoader(
        dataset,
        batch_size=batch_size,
        sampler=sampler,
        drop_last=False,
        num_workers=num_workers,
        collate_fn=trivial_batch_collator if collate_fn is None else collate_fn,
    )


def trivial_batch_collator(batch):
    """
    A batch collator that does nothing.
    """
    return batch


def worker_init_reset_seed(worker_id):
    initial_seed = torch.initial_seed() % 2**31
    seed_all_rng(initial_seed + worker_id)