The Manager().dict() seems to work fine when the value is just a value but not when the value is a list. Is there a way to share a list between processes using a Manager()?
from multiprocessing import Process, Manager
def add(c):
for i in range(1000):
c['a'][0] += 1
c['a'][1] += 2
d = Manager().dict()
d['a'] = [0,0]
p = Process(target=add, args=(d,))
p.start()
p.join()
print(d)
Output:
{1: [0, 0]}
Solved thanks @Dale Song
It seems you must do it somewhat indirectly... assign values to a temporary list and then assign the temporary list to the dictionary, weird.
from multiprocessing import Process, Array, Manager
def test(dict,m,val):
for i in range(1000):
m[0] +=1
m[1] +=2
dict[val] = m
if __name__ == '__main__':
d = Manager().dict()
l = [0,0]
d['a'] = l
p = Process(target=test, args=(d,l,'a'))
p.start()
p.join()
print(d)
Output:
{'a': [1000, 2000]}
Another (much faster) way:
Using shared memory and multiprocessing.Array()
from multiprocessing import Process, Manager,Array
d = {}
d['a'] = Array('i', [0,0])
def add_array(c,val):
for i in range(1000):
c[val][0] +=1
c[val][1] +=2
p = Process(target=add_array, args=(d,'a', ))
p.start()
p.join()
print([d['a'][0],d['a'][1]])
Output:
[1000, 2000]
https://docs.python.org/2/library/multiprocessing.html#multiprocessing.Array https://docs.python.org/2/library/array.html #typecodes
