Dataset not support Multiprocessing

I install the mxnet using cmake, and when the following code cannot work

        if self._num_workers > 0:
            self._worker_pool = multiprocessing.Pool(
                self._num_workers, initializer=_worker_initializer, initargs=[self._dataset])

from the gluoncv/data/ class, however, the pip installed mxnet can work.

I wonder if I forget some flags in the CMakeLists.txt . anyone have met this problem ?