python Class Object Sharing between Processes created using multiprocessing module

Question

How do I create the python shared object of my class which can be modified by worker processes. I created the worker processes by using multiprocessing.Process module. I have some knowledge about multiprocessing.Manager module. Can any one explain with example how to register my class in to Manager, start the manager and create the shared object of my class.

Answer 1

Here is an example:

from multiprocessing import Process, Pool
from multiprocessing.managers import BaseManager


class MySharedClass(object):
    stored_value = 0
    def get(self):
        return self.stored_value

    def set(self, new_value):
        self.stored_value = new_value
        return self.stored_value


class MyManager(BaseManager):
    pass


MyManager.register('MySharedClass', MySharedClass)

def worker ( proxy_object, i):
    proxy_object.set( proxy_object.get() + i )
    print ("id %d, sum %d" %(i, proxy_object.get()))
    return proxy_object


if __name__ == '__main__':
    manager = MyManager()
    manager.start()
    shared = manager.MySharedClass()

    pool = Pool(5)
    for i in range(33):
        pool.apply(func=worker, args=(shared, i))
    pool.close()
    pool.join()
    print "result: %d" % shared.get()

id 0, sum 0
id 1, sum 1
id 2, sum 3
...
id 31, sum 496
id 32, sum 528
result: 528

Another variant (have never use it in the real project):

from multiprocessing import Process, Pool
from multiprocessing.managers import BaseManager, NamespaceProxy


class MySharedClass(object):
    def __init__(self):
        self.stored_value = 0

    def get(self):
        return self.stored_value

    def set(self, new_value):
        self.stored_value = new_value
        return self.stored_value


class MyManager(BaseManager):
    pass

class MyProxy(NamespaceProxy):
    _exposed_ = ('__getattribute__', '__setattr__', '__delattr__')# add 'get' to use get


    #def get(self):
    #    callmethod = object.__getattribute__(self, '_callmethod')
    #    return callmethod('get')

MyManager.register('MySharedClass', MySharedClass, MyProxy)

def worker ( proxy_object, i):
    proxy_object.stored_value =  proxy_object.stored_value + i
    print ("id %d, sum %d" %(i, proxy_object.stored_value))
    return proxy_object


if __name__ == '__main__':
    manager = MyManager()
    manager.start()
    shared = manager.MySharedClass()
    print shared.stored_value

    pool = Pool(5)
    for i in range(33):
        pool.apply(func=worker, args=(shared, i))
    pool.close()
    pool.join()
    print "result: %d" % shared.stored_value