multiprocessing 问题

代码：

import multiprocessing

import time

class a:

    def __init__(self) -> None:

        self.count = 0

    def aa(self,pool:'multiprocessing.pool.Pool'):

        pool.apply_async(func = self.aaa, args=(), kwds={})

        return  True

   

    def aaa(self):

        for i in range(5):

            self.count = self.count +1

            print("count" ,self.count)

            time.sleep(0.5)

        return True

if __name__ == "__main__":

    pool = multiprocessing.Pool(processes=None, initializer=None, initargs=(), maxtasksperchild=None)

    qw =a()

    qw.aa(pool)

    while True:

        print(qw.count)

        time.sleep(1)

打印结果：

0

count 1

0

count 2

count 3

0

count 4

为什么while循环里的打印结果全是零？