How to implement multi-processing ?

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Hi, I tried to run face detection using multi processing I am getting below error

E:\git\opencv-dnn-demo\face_detectors>python sample.py

i am detect
i am detect
i am detect
i am detect
i am detect
i am detect
Traceback (most recent call last):
  File "sample.py", line 17, in <module>
    pool.map(fd.detect, imgs)
  File "C:\Anaconda3\lib\multiprocessing\pool.py", line 260, in map
    return self._map_async(func, iterable, mapstar, chunksize).get()
  File "C:\Anaconda3\lib\multiprocessing\pool.py", line 608, in get
    raise self._value
  File "C:\Anaconda3\lib\multiprocessing\pool.py", line 119, in worker
    result = (True, func(*args, **kwds))
  File "C:\Anaconda3\lib\multiprocessing\pool.py", line 44, in mapstar
    return list(map(*args))
  File "E:\git\opencv-dnn-demo\face_detectors\yolov2.py", line 34, in detect
    detections = self.net.forward()
cv2.error: OpenCV(3.4.3) C:\projects\opencv-python\opencv\modules\dnn\src\dnn.cpp:841: error: (-215:Assertion failed) memHosts.find(lp) == memHosts.end() in function 'cv::dnn::experimental_dnn_34_v7::BlobManager::addHost'

What was the issue sorry I new to CV and Yolo