normal result :
$ python test.py
{'p1': 1, 'p2': 1, 'p3': 1, 'p4': 1}

run with tracing :
$ python -mtrace --trackcalls test.py
{}

It seems that the foo and save functions that multiprocess should call are not called.

#!/usr/bin/env python
import multiprocessing, sys, trace
from functools import partial

num_list = ['p1', 'p2', 'p3', 'p4']

def foo(name):
    print(name+'\n')
    return name
def save(result, shared):
    print('a\n')
    shared.results[result] = 1

def mm():
    manager = multiprocessing.Manager()
    shared = manager.dict()
    shared.results = dict()

    clbk = partial(save, shared=shared)

    pool = multiprocessing.Pool(processes=2)
    serial_pool = multiprocessing.Pool(1)

    for name in num_list:
        serial_pool.apply_async(foo, args=[name], callback=clbk)

    pool.close()
    pool.join()

    print(shared.results)

mm()