```concurrent.futures.ProcessPoolExecutor``` may lead to wrong embedding ?

[DachuanZhao]

I notice that this module use concurrent.futures.ProcessPoolExecutor instead of joblib when generating random walk , according to https://joblib.readthedocs.io/en/latest/auto_examples/parallel_random_state.html#sphx-glr-download-auto-examples-parallel-random-state-py and https://stackoverflow.com/questions/49847794/child-processes-generating-same-random-numbers-as-parent-process , I'm not sure whether concurrent.futures.ProcessPoolExecutor may lead to wrong embedding ...... So I open this issue for discuss ......