loky and pyinstaller test issues

test.py

#!/usr/bin/env python

import argparse
import numpy as np

from multiprocessing import freeze_support
from joblib import Parallel, delayed, parallel_backend

# this works
backend1 = 'threading'
backend2 = 'multiprocessing'

# This doesn't work
backend3 = 'loky'

backends = [backend1, backend2, backend3]

def buildArgsParser():

    p = argparse.ArgumentParser()

    #####################
    # Required arguments
    #####################

    required = p.add_argument_group('Required arguments')

    required.add_argument('input', metavar='input',
                          help='Path of the image file to denoise.')

    required.add_argument('output', metavar='output',
                          help='Path for the saved denoised file.')

    return p


def main():
    parser = buildArgsParser()
    args = parser.parse_args()
    out = estimate_from_dwis()


def estimate_from_dwis( ncores=-1, verbose=0):
    data = np.ones(100)
    ranger = range(100)

    print('Entering inner loop')
    for backend in backends:
        with parallel_backend(backend):
            output = Parallel(n_jobs=ncores, verbose=verbose)(delayed(_inner)(data[i]) for i in ranger)
        print('Inner loop finished for backend {}'.format(backend))


def _inner(data):
    return data


if __name__ == "__main__":
    freeze_support()
    main()

When running with python test.py aa aa, works as expected. When frozen with pyinstaller, it triggers joblib/loky#236
Example (needs pyinstaller and not latest setuptools somehow):

Tested on ubuntu 16.04 with pyinstaller 3.6 and python 3.7 from conda

pip install setuptools==44 pyinstaller joblib numpy

pyinstaller test.py --onefile
./dist/test aa aa