recursion - Python 3.4 multiprocessing recursive Pool.map()

Question

I'm developing with Python 3.4 on Ubuntu 14.04. I was trying to do recursive Pool.map(). After I invoke g(), it hangs there and never returns.

import multiprocessing as mp

pool = mp.Pool()

def d(x):
    return x / 2.0


def f(x):
    w = pool.map(d, x)
    return w

def g():
    v = pool.map(f, [[1, 2], [3, 4]])

    print(v)

Answer 1

From the documentation:

Note that the methods of the pool object should only be called by the process which created the pool.

You break that rule when you call pool.map() inside f(). Additionally, if you try to have the child process create their own pool, you'll get an assertion error:

AssertionError: daemonic processes are not allowed to have children