I’m trying to create a way to pass a dataclass object to several different child processes using the Multiprocessing module. Right now I’ve tried:

import queue
from multiprocessing import Process, Queue, Manager
from multiprocessing.managers import BaseManager, NamespaceProxy

class TestManager(BaseManager):
    pass

class Test:
    def __init__(self):
        self.a = []
        self.b = []
        self.c = []

class TestProxy(NamespaceProxy):
    # We need to expose the same __dunder__ methods as NamespaceProxy,
    # in addition to the b method.
    _exposed_ = ('__getattribute__', '__setattr__', '__delattr__')


def popManager(queue, manager, i):
    manager.a.append(i)
    manager.b.append(i+1)
    manager.c.append(i**2)
    queue.put(True)


def managerParent():
    processes = []
    queues = []
    TestManager.register("Test", Test, TestProxy)
    with TestManager() as manager:
        t = manager.Test()
        for i in range(10):
            queues.append(Queue())
            processes.append(
                Process(target=popManager, args=(queues[i], t, i))
            )

        [p.start() for p in processes]
        print("started!")
        while True:
            try:
                [q.get(timeout=0.2) for i, q in enumerate(queues)]
                break
            except queue.Empty:
                print(f"Processes still running!")
        
        print(t.a, t.a, t.c)

if __name__ == "__main__":
    managerParent()

which runs just fine, but the list instances are all empty. It outputs

[] [] []

where I’d like it to output something like

[0, 1, 2, ... 9], [1, 2, 3, ..., 10], [0, 1, 4, ..., 81]