Unable to update nested dictionary value in multiprocessing's manager.dict()

问题

I am trying to update a key in a nested dictionary of multiprocessing module's manager.dict() but not able to do so. It doesn't update the value and doesn't throw any error too.

Code:

import time
import random
from multiprocessing import Pool, Manager

def spammer_task(d, token, repeat):
    success = 0
    fail = 0
    while success+fail<repeat:
        time.sleep(random.random()*2.0)
        if (random.random()*100)>98.0:
            fail+=1
        else:
            success+=1
        d[token] = {
            'status': 'ongoing',
            'fail': fail,
            'success': success,
            'repeat': repeat
        }
    print d[token]['status']
    d[token]['status'] = 'complete'
    return

p = Pool()
m = Manager()
d = m.dict()

p.apply_async(spammer_task (d, 'abc', 5))
print d

Output:

ongoing

{'abc': {'status': 'ongoing', 'fail': 0, 'repeat': 5, 'success': 5}}

My expectations are that as soon as while loop ends, it should make d['abc']['status'] = complete. But on final print it prints its status as 'ongoing' only.

回答1:

not sure why, but the Manager DictProxy object cant seems to handle mutating a nested part. this code works:

import time
import random
from multiprocessing import Pool, Manager

def spammer_task(d, token, repeat):
    success = 0
    fail = 0
    while success+fail<repeat:
        time.sleep(random.random()*2.0)
        if (random.random()*100)>98.0:
            fail+=1
        else:
            success+=1
        d[token] = {
            'status': 'ongoing',
            'fail': fail,
            'success': success,
            'repeat': repeat,
        }
    print d[token]['status']
    foo = d[token]
    foo['status'] = 'complete'
    d[token] = foo
    return

p = Pool()
m = Manager()
d = m.dict()

p.apply_async(spammer_task(d, 'abc', 5))
print d

回答2:

Looks like this issue remains per code below:

import multiprocessing, sys;

if __name__ == '__main__':

print(sys.version);

mpd = multiprocessing.Manager().dict();
mpd['prcss'] = {'q' : 'queue_1', 'ctlg' : 'ctlg_1' };

# update 1 - doesn't work!
mpd['prcss'].update( { 'name': 'concfun_1'} );
print('Result of failed update 1:', mpd['prcss']);

# update 2 - doesn't work!
mpd['prcss']['name'] = 'concfun_1';
print('Result of failed update 2:', mpd['prcss']);

# update 3 - works!
mpd_prcss = mpd['prcss'];
mpd_prcss['name'] = 'concfun_1';
mpd['prcss'] = mpd_prcss;
print('Result of successful update 3:', mpd['prcss']);

---

Output:

3.6.1 (v3.6.1:69c0db5, Mar 21 2017, 17:54:52) [MSC v.1900 32 bit (Intel)]

Result of failed update 1: {'q': 'queue_1', 'ctlg': 'ctlg_1'}

Result of failed update 2: {'q': 'queue_1', 'ctlg': 'ctlg_1'}

Result of successful update 3: {'q': 'queue_1', 'ctlg': 'ctlg_1', 'name': 'concfun_1'}

来源：https://stackoverflow.com/questions/37510076/unable-to-update-nested-dictionary-value-in-multiprocessings-manager-dict