使用Python multiprocessing并行计算函数时结果列表为空如何解决？

我正在学习Python的multiprocessing模块，写了一段并行计算的代码，但运行后所有结果列表都是空的，求修正方法：

import multiprocessing as mp
import time

starttime = time.time()

Result_1 = []
Result_2 = []
Result_3 = []

def Calculation_1():
    numbers = list(range(0, 10000000))
    for num in numbers:
        Result_1.append(num ** 0.5)

def Calculation_2():
    numbers = list(range(0, 10000000))
    for num in numbers:
        Result_2.append(num ** 2)

def Calculation_3():
    numbers = list(range(0, 10000000))
    for num in numbers:
        Result_3.append(num ** 3)

if __name__ == "__main__":

    p1 = mp.Process(target = Calculation_1)
    p2 = mp.Process(target = Calculation_2)
    p3 = mp.Process(target = Calculation_3)
    
    p1.start()
    p2.start()
    p3.start()
    
    p1.join()
    p2.join()
    p3.join()
    
    endtime = time.time()
    print("Time =", "{:.2f}".format((endtime - starttime) * (10 ** 3)), "ms")

Python多进程的子进程拥有独立的内存空间，主进程中定义的Result_1、Result_2、Result_3列表不会被共享。子进程里的append操作只是修改了自己内存里的列表副本，主进程的原列表根本没变化，所以最终是空的。

方案1：用Queue传递结果 #

Queue是多进程安全的通信工具，子进程把计算结果存入队列，主进程再取出：

import multiprocessing as mp
import time

starttime = time.time()

def Calculation_1(queue):
    numbers = list(range(0, 10000000))
    result = []
    for num in numbers:
        result.append(num ** 0.5)
    queue.put(result)

def Calculation_2(queue):
    numbers = list(range(0, 10000000))
    result = []
    for num in numbers:
        result.append(num ** 2)
    queue.put(result)

def Calculation_3(queue):
    numbers = list(range(0, 10000000))
    result = []
    for num in numbers:
        result.append(num ** 3)
    queue.put(result)

if __name__ == "__main__":
    queue1 = mp.Queue()
    queue2 = mp.Queue()
    queue3 = mp.Queue()

    p1 = mp.Process(target=Calculation_1, args=(queue1,))
    p2 = mp.Process(target=Calculation_2, args=(queue2,))
    p3 = mp.Process(target=Calculation_3, args=(queue3,))
    
    p1.start()
    p2.start()
    p3.start()
    
    # 从队列获取结果
    Result_1 = queue1.get()
    Result_2 = queue2.get()
    Result_3 = queue3.get()
    
    p1.join()
    p2.join()
    p3.join()
    
    endtime = time.time()
    print("Time =", "{:.2f}".format((endtime - starttime) * (10 ** 3)), "ms")
    print("Result_1长度:", len(Result_1))

方案2：用Manager创建共享列表 #

Manager可以生成跨进程共享的列表对象，子进程修改的是共享列表本身：

import multiprocessing as mp
import time

starttime = time.time()

def Calculation_1(result_list):
    numbers = list(range(0, 10000000))
    for num in numbers:
        result_list.append(num ** 0.5)

def Calculation_2(result_list):
    numbers = list(range(0, 10000000))
    for num in numbers:
        result_list.append(num ** 2)

def Calculation_3(result_list):
    numbers = list(range(0, 10000000))
    for num in numbers:
        result_list.append(num ** 3)

if __name__ == "__main__":
    with mp.Manager() as manager:
        Result_1 = manager.list()
        Result_2 = manager.list()
        Result_3 = manager.list()

        p1 = mp.Process(target=Calculation_1, args=(Result_1,))
        p2 = mp.Process(target=Calculation_2, args=(Result_2,))
        p3 = mp.Process(target=Calculation_3, args=(Result_3,))
        
        p1.start()
        p2.start()
        p3.start()
        
        p1.join()
        p2.join()
        p3.join()
        
        endtime = time.time()
        print("Time =", "{:.2f}".format((endtime - starttime) * (10 ** 3)), "ms")
        print("Result_2长度:", len(Result_2))

方案3：用Pool简化代码（推荐） #

如果任务逻辑类似，用Pool可以更简洁地管理进程和获取结果：

import multiprocessing as mp
import time

starttime = time.time()

def calculation_task(func, start, end):
    numbers = list(range(start, end))
    return [func(num) for num in numbers]

if __name__ == "__main__":
    # 定义三个计算逻辑
    funcs = [lambda x: x**0.5, lambda x: x**2, lambda x: x**3]
    range_start, range_end = 0, 10000000

    with mp.Pool(processes=3) as pool:
        # 异步提交任务
        tasks = [pool.apply_async(calculation_task, args=(func, range_start, range_end)) for func in funcs]
        # 收集所有结果
        Result_1, Result_2, Result_3 = [task.get() for task in tasks]
    
    endtime = time.time()
    print("Time =", "{:.2f}".format((endtime - starttime) * (10 ** 3)), "ms")
    print("Result_3长度:", len(Result_3))

内容的提问来源于stack exchange，提问作者vnc89