将 defaultdict 与多处理一起使用?

问题描述

只是实验和学习，我知道如何创建一个可以通过多个进程访问的共享字典，但我不确定如何保持字典同步.我相信 defaultdict 说明了我遇到的问题.

Just experimenting and learning, and I know how to create a shared dictionary that can be accessed with multiple proceses but I'm not sure how to keep the dict synced. defaultdict, I believe, illustrates the problem I'm having.

from collections import defaultdict
from multiprocessing import Pool, Manager, Process

#test without multiprocessing
s = 'mississippi'
d = defaultdict(int)
for k in s:
    d[k] += 1

print d.items() # Success! result: [('i', 4), ('p', 2), ('s', 4), ('m', 1)]
print '*'*10, ' with multiprocessing ', '*'*10

def test(k, multi_dict):
    multi_dict[k] += 1

if __name__ == '__main__':
    pool = Pool(processes=4)
    mgr = Manager()
    multi_d = mgr.dict()
    for k in s:
        pool.apply_async(test, (k, multi_d))

    # Mark pool as closed -- no more tasks can be added.
    pool.close()

    # Wait for tasks to exit
    pool.join()

    # Output results
    print multi_d.items()  #FAIL

print '*'*10, ' with multiprocessing and process module like on python site example', '*'*10
def test2(k, multi_dict2):
    multi_dict2[k] += 1


if __name__ == '__main__':
    manager = Manager()

    multi_d2 = manager.dict()
    for k in s:
        p = Process(target=test2, args=(k, multi_d2))
    p.start()
    p.join()

    print multi_d2 #FAIL

第一个结果有效(因为它不使用 multiprocessing)，但我无法让它与 multiprocessing 一起使用.我不知道如何解决它，但我认为可能是因为它没有被同步(并在以后加入结果)或者可能是因为在 multiprocessing 我不知道如何设置 defaultdict(int) 到字典中.

The first result works(because its not using multiprocessing), but I'm having problems getting it to work with multiprocessing. I'm not sure how to solve it but I think there might be due to it not being synced(and joining the results later) or maybe because within multiprocessing I cannot figure how to set defaultdict(int) to the dictionary.

任何关于如何使它工作的帮助或建议都会很棒！

Any help or suggestions on how to get this to work would be great!

推荐答案

您可以继承 BaseManager 并注册其他类型以进行共享.在默认 AutoProxy 生成的类型不起作用的情况下，您需要提供合适的代理类型.对于defaultdict，如果只需要访问dict中已经存在的属性，可以使用DictProxy.

You can subclass BaseManager and register additional types for sharing. You need to provide a suitable proxy type in cases where the default AutoProxy-generated type does not work. For defaultdict, if you only need to access the attributes that are already present in dict, you can use DictProxy.

from multiprocessing import Pool
from multiprocessing.managers import BaseManager, DictProxy
from collections import defaultdict

class MyManager(BaseManager):
    pass

MyManager.register('defaultdict', defaultdict, DictProxy)

def test(k, multi_dict):
    multi_dict[k] += 1

if __name__ == '__main__':
    pool = Pool(processes=4)
    mgr = MyManager()
    mgr.start()
    multi_d = mgr.defaultdict(int)
    for k in 'mississippi':
        pool.apply_async(test, (k, multi_d))
    pool.close()
    pool.join()
    print multi_d.items()

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