code: # Copyright (c) 2021, NVIDIA CORPORATION. All rights reserved.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
  # Set up custom environment before nearly anything else is imported
  # NOTE: this should be the first import (no not reorder)
  from maskrcnn_benchmark.utils.env import setup_environment  # noqa F401 isort:skip
  
  import argparse
  import os
  
  import torch
  from maskrcnn_benchmark.config import cfg
  from maskrcnn_benchmark.data import make_data_loader
  from maskrcnn_benchmark.engine.inference import inference
  from maskrcnn_benchmark.modeling.detector import build_detection_model
  from maskrcnn_benchmark.utils.checkpoint import DetectronCheckpointer
  from maskrcnn_benchmark.utils.collect_env import collect_env_info
  from maskrcnn_benchmark.utils.comm import synchronize, get_rank
  from maskrcnn_benchmark.utils.logger import setup_logger
  from maskrcnn_benchmark.utils.miscellaneous import mkdir
  
  
  def main():
      parser = argparse.ArgumentParser(description="PyTorch Object Detection Inference")
      parser.add_argument(
          "--config-file",
          default="/private/home/fmassa/github/detectron.pytorch_v2/configs/e2e_faster_rcnn_R_50_C4_1x_caffe2.yaml",
          metavar="FILE",
          help="path to config file",
      )
      parser.add_argument("--local_rank", type=int, default=0)
      parser.add_argument(
          "opts",
          help="Modify config options using the command-line",
          default=None,
          nargs=argparse.REMAINDER,
      )
  
      args = parser.parse_args()
  
      num_gpus = int(os.environ["WORLD_SIZE"]) if "WORLD_SIZE" in os.environ else 1
      distributed = num_gpus > 1
  
      if distributed:
          torch.cuda.set_device(args.local_rank)
          torch.distributed.init_process_group(
              backend="nccl", init_method="env://"
          )
          synchronize()
  
      cfg.merge_from_file(args.config_file)
      cfg.merge_from_list(args.opts)
      cfg.freeze()
  
      save_dir = ""
      logger = setup_logger("maskrcnn_benchmark", save_dir, get_rank())
      logger.info("Using {} GPUs".format(num_gpus))
      logger.info(cfg)
  
      logger.info("Collecting env info (might take some time)")
      logger.info("\n" + collect_env_info())
  
      model = build_detection_model(cfg)
      model.to(cfg.MODEL.DEVICE)
  
      output_dir = cfg.OUTPUT_DIR
      checkpointer = DetectronCheckpointer(cfg, model, save_dir=output_dir)
      _ = checkpointer.load(cfg.MODEL.WEIGHT)
  
      iou_types = ("bbox",)
      if cfg.MODEL.MASK_ON:
          iou_types = iou_types + ("segm",)
      if cfg.MODEL.KEYPOINT_ON:
          iou_types = iou_types + ("keypoints",)
      output_folders = [None] * len(cfg.DATASETS.TEST)
      dataset_names = cfg.DATASETS.TEST
      if cfg.OUTPUT_DIR:
          for idx, dataset_name in enumerate(dataset_names):
              output_folder = os.path.join(cfg.OUTPUT_DIR, "inference", dataset_name)
              mkdir(output_folder)
              output_folders[idx] = output_folder
      data_loaders_val = make_data_loader(cfg, is_train=False, is_distributed=distributed)
      for output_folder, dataset_name, data_loader_val in zip(output_folders, dataset_names, data_loaders_val):
          inference(
              model,
              data_loader_val,
              dataset_name=dataset_name,
              iou_types=iou_types,
              box_only=False if cfg.MODEL.RETINANET_ON else cfg.MODEL.RPN_ONLY,
              device=cfg.MODEL.DEVICE,
              expected_results=cfg.TEST.EXPECTED_RESULTS,
              expected_results_sigma_tol=cfg.TEST.EXPECTED_RESULTS_SIGMA_TOL,
              output_folder=output_folder,
          )
          synchronize()
  
  
  if __name__ == "__main__":
      main()
  
apis: torch.distributed.init_process_group torch.cuda.set_device