AssertionError: Default process group is not initialized

detectron2遇到问题：

Traceback (most recent call last):
  File "projects/SparseRCNN/train_net.py", line 143, in <module>
    args=(args,),
  File "/home/ubuntu/bigdisk/part2/SparseR-CNN/detectron2/engine/launch.py", line 62, in launch
    main_func(*args)
  File "projects/SparseRCNN/train_net.py", line 131, in main
    return trainer.train()
  File "/home/ubuntu/bigdisk/part2/SparseR-CNN/detectron2/engine/defaults.py", line 419, in train
    super().train(self.start_iter, self.max_iter)
  File "/home/ubuntu/bigdisk/part2/SparseR-CNN/detectron2/engine/train_loop.py", line 134, in train
    self.run_step()
  File "/home/ubuntu/bigdisk/part2/SparseR-CNN/detectron2/engine/defaults.py", line 429, in run_step
    self._trainer.run_step()
  File "/home/ubuntu/bigdisk/part2/SparseR-CNN/detectron2/engine/train_loop.py", line 228, in run_step
    loss_dict = self.model(data)
  File "/home/ubuntu/anaconda3/envs/sparse/lib/python3.6/site-packages/torch/nn/modules/module.py", line 722, in _call_impl
    result = self.forward(*input, **kwargs)
  File "/home/ubuntu/bigdisk/part2/SparseR-CNN/projects/SparseRCNN/sparsercnn/detector.py", line 121, in forward
    src = self.backbone(images.tensor)
  File "/home/ubuntu/anaconda3/envs/sparse/lib/python3.6/site-packages/torch/nn/modules/module.py", line 722, in _call_impl
    result = self.forward(*input, **kwargs)
  File "/home/ubuntu/bigdisk/part2/SparseR-CNN/detectron2/modeling/backbone/fpn.py", line 127, in forward
    bottom_up_features = self.bottom_up(x)
  File "/home/ubuntu/anaconda3/envs/sparse/lib/python3.6/site-packages/torch/nn/modules/module.py", line 722, in _call_impl
    result = self.forward(*input, **kwargs)
  File "/home/ubuntu/bigdisk/part2/SparseR-CNN/detectron2/modeling/backbone/resnet.py", line 434, in forward
    x = self.stem(x)
  File "/home/ubuntu/anaconda3/envs/sparse/lib/python3.6/site-packages/torch/nn/modules/module.py", line 722, in _call_impl
    result = self.forward(*input, **kwargs)
  File "/home/ubuntu/bigdisk/part2/SparseR-CNN/detectron2/modeling/backbone/resnet.py", line 356, in forward
    x = self.conv1(x)
  File "/home/ubuntu/anaconda3/envs/sparse/lib/python3.6/site-packages/torch/nn/modules/module.py", line 722, in _call_impl
    result = self.forward(*input, **kwargs)
  File "/home/ubuntu/bigdisk/part2/SparseR-CNN/detectron2/layers/wrappers.py", line 80, in forward
    x = self.norm(x)
  File "/home/ubuntu/anaconda3/envs/sparse/lib/python3.6/site-packages/torch/nn/modules/module.py", line 722, in _call_impl
    result = self.forward(*input, **kwargs)
  File "/home/ubuntu/anaconda3/envs/sparse/lib/python3.6/site-packages/torch/nn/modules/batchnorm.py", line 493, in forward
    world_size = torch.distributed.get_world_size(process_group)
  File "/home/ubuntu/anaconda3/envs/sparse/lib/python3.6/site-packages/torch/distributed/distributed_c10d.py", line 620, in get_world_size
    return _get_group_size(group)
  File "/home/ubuntu/anaconda3/envs/sparse/lib/python3.6/site-packages/torch/distributed/distributed_c10d.py", line 219, in _get_group_size
    _check_default_pg()
  File "/home/ubuntu/anaconda3/envs/sparse/lib/python3.6/site-packages/torch/distributed/distributed_c10d.py", line 210, in _check_default_pg
    "Default process group is not initialized"
AssertionError: Default process group is not initialized

解决方法：

vi detectron2/engine/launch.py

修改

if world_size > 1:

为

if world_size >= 1: