How Can I Update Class Members In Processes?

I have looked for other questions, and this un-accepted-answered question is the only one I could find that somehow covers this issue and is not really helpful. Also, I need this t

Solution 1:

You can derive a specialized version of a Proxy class used by multiprocessing.BaseManager from a (undocumented) multiprocessing.managers.NamespaceProxy that, unlike the base class, exposes all of its methods and attributes. This is similar to @shtse8's answer to the linked duplicate question, but I'm posting a runnable answer to it here to make clear how it can be done.

from multiprocessing import Process
from multiprocessing.managers import BaseManager, NamespaceProxy
import time
import types

class MyManager(BaseManager): pass  # Avoid namespace pollution.

class Apple:
    def __init__(self, color):
        self.color = color


def Proxy(target):
    """ Create a derived NamespaceProxy class for `target`. """
    def __getattr__(self, key):
        result = self._callmethod('__getattribute__', (key,))
        if isinstance(result, types.MethodType):
            def wrapper(*args, **kwargs):
                self._callmethod(key, args)
            return wrapper
        return result

    dic = {'types': types, '__getattr__': __getattr__}
    proxy_name = target.__name__ + "Proxy"
    ProxyType = type(proxy_name, (NamespaceProxy,), dic)  # Create subclass.
    ProxyType._exposed_ = tuple(dir(target))

    return ProxyType


AppleProxy = Proxy(Apple)


def thinkAboutApple(apple):
    while True:
        print(f"apple.color: {apple.color}")
        time.sleep(1)


if __name__ == '__main__':

    MyManager.register('Apple', Apple, AppleProxy)

    manager = MyManager()
    manager.start()

    my_apple = manager.Apple("red")
    new_process = Process(target=thinkAboutApple, args=(my_apple,))
    new_process.start()

    time.sleep(2)  # Allow other process to run a short while.
    my_apple.color = "brown"  # Change shared class instance.

    time.sleep(2)  # Allow other process to run at little while longer.
    new_process.terminate()