python multiprocessing.Process.Manager not producing consistent results?
- by COpython
I've written the following code to illustrate the problem I'm seeing. I'm trying to use a Process.Manager.list() to keep track of a list and increment random indices of that list.
Each time there are 100 processes spawned, and each process increments a random index of the list by 1. Therefore, one would expect the SUM of the resulting list to be the same each time, correct? I get something between 203 and 205.
from multiprocessing import Process, Manager
import random
class MyProc(Process):
def __init__(self, A):
Process.__init__(self)
self.A = A
def run(self):
i = random.randint(0, len(self.A)-1)
self.A[i] = self.A[i] + 1
if __name__ == '__main__':
procs = []
M = Manager()
a = M.list(range(15))
print('A: {0}'.format(a))
print('sum(A) = {0}'.format(sum(a)))
for i in range(100):
procs.append(MyProc(a))
map(lambda x: x.start(), procs)
map(lambda x: x.join(), procs)
print('A: {0}'.format(a))
print('sum(A) = {0}'.format(sum(a)))
