Showing a global dictionary not being shared across processes. Only test-with-manager.py passes the assertion.

test-global-with-inheritance.py

import multiprocessing


ITEM_CONTAINER = dict(a=0, b=1,)
CONTROL_CONTAINER = dict(a=0, b=1, c=2, d=3, e=4, f=5)


def _acquire_in_thread_inheritance(test, d):
    d[test] = len(d.keys())
    print(d, type(d), id(d))


def main_inheritance(d):
    processes = [
        multiprocessing.Process(target=_acquire_in_thread_inheritance, args=(item, d,))
        for item in ["c", "d", "e", "f"]
    ]
    for t in processes:
        t.daemon = True
        t.start()
    for t in processes:
        t.join()


print("Test inheritance")
print(type(ITEM_CONTAINER), id(ITEM_CONTAINER))
print(ITEM_CONTAINER)
main_inheritance(d=ITEM_CONTAINER)
#Fails
assert CONTROL_CONTAINER == ITEM_CONTAINER

test-global.py

import multiprocessing


ITEM_CONTAINER = dict(a=0, b=1,)
CONTROL_CONTAINER = dict(a=0, b=1, c=2, d=3, e=4, f=5)


def _acquire_in_thread_global(test):
    ITEM_CONTAINER[test] = len(ITEM_CONTAINER.keys())
    print(ITEM_CONTAINER, type(ITEM_CONTAINER), id(ITEM_CONTAINER))


def main_global():
    processes = [
        multiprocessing.Process(target=_acquire_in_thread_global, args=(item,))
        for item in ["c", "d", "e", "f"]
    ]
    for t in processes:
        t.daemon = True
        t.start()
    for t in processes:
        t.join()


print("Test global")
print(type(ITEM_CONTAINER), id(ITEM_CONTAINER))
print(ITEM_CONTAINER)
main_global()
#Fails
assert CONTROL_CONTAINER == ITEM_CONTAINER

test-with-manager.py

import multiprocessing


ITEM_MANAGER_CONTAINER = multiprocessing.Manager().dict(a=0, b=1,)
CONTROL_CONTAINER = dict(a=0, b=1, c=2, d=3, e=4, f=5)


def _acquire_in_thread_global_manager(test):
    ITEM_MANAGER_CONTAINER[test] = len(ITEM_MANAGER_CONTAINER.keys())
    print(ITEM_MANAGER_CONTAINER, type(ITEM_MANAGER_CONTAINER), id(ITEM_MANAGER_CONTAINER))


def main_global_manager():
    processes = [
        multiprocessing.Process(target=_acquire_in_thread_global_manager, args=(item,))
        for item in ["c", "d", "e", "f"]
    ]
    for t in processes:
        t.daemon = True
        t.start()
    for t in processes:
        t.join()


print("test with manager")
print(type(ITEM_MANAGER_CONTAINER), id(ITEM_MANAGER_CONTAINER))
print(ITEM_MANAGER_CONTAINER)
main_global_manager()
#Passes
assert CONTROL_CONTAINER == dict(ITEM_MANAGER_CONTAINER)