stuck at 0% when excute python demo_large_image.py

[heheguoqushi]

My envirements are:
Ubuntu18.0
GCC5.5.0
CUDA10.0
Python3.7
Pytorch==1.2.0
Torchvision==0.4
mmcv==0.4.3
I have Installed as the offical docs
when I excute python demo_large_image.py
it stuck at 0% for more than 10 mins， I think a 1M picture shoud not be slow as that.

(AerialDetection) txy@robot:~/AerialDetection$ python demo_large_image.py
loading annotations into memory...
Done (t=0.00s)
creating index...
index created!
0%| | 0/4 [00:00<?, ?it/s]

please help me. Thanks!