Python多进程中GlobalCount全局变量无法同步问题求助

我在代码里声明了全局变量GlobalCount，用multiprocessing启动process()方法每秒对它自增，断点查看自增操作正常，但并行发送GETSTATUS请求获取其值时，返回结果始终为0。请问哪里操作错误？

问题代码 #

import multiprocessing
import socket
import time

from multiprocessing import Value

# globals
GlobalCount = Value('i', 0)  # 'i' stands for integer

def main():

    server_ip = "127.0.0.1"
    server_port = 2222

    # Create a UDP socket
    server_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    server_address = (server_ip, server_port)
    server_socket.bind(server_address)

    response = ""

    print("UDP server is listening on {}:{}".format(*server_address))

    while True:
        
        # Receive data from the client
        data, client_address = server_socket.recvfrom(256)

        if data:

            data_str = data.decode('utf-8') 
            arrayParams = data_str.split(';')

            if arrayParams[0] == "PROCESS":

                server_socket.sendto(response.encode(), client_address)

                # Start the process in parallel
                training_process = multiprocessing.Process(target=process)
                training_process.start()

            elif arrayParams[0] == "GETSTATUS":
                current_value = GlobalCount.value
                response = str(current_value) # here GlobalCount is always 0
                server_socket.sendto(response.encode(), client_address)

            else:
                print("")

def process():

    for i in range(100):
        
        with GlobalCount.get_lock():  # Ensure thread-safety when updating the value
            GlobalCount.value += 1
        time.sleep(1)

# Execute at start
if __name__ == '__main__':
    main()

问题核心是多进程启动机制导致共享变量被重复初始化：

• 在Windows系统下，multiprocessing.Process采用spawn方式创建子进程，会重新导入主模块。你的GlobalCount定义在模块全局作用域，子进程启动时会重新执行这行代码，生成新的Value实例——子进程修改的是自己的副本，主进程的GlobalCount始终是初始值0。
• 即便在Unix/Linux系统（用fork机制），虽然能继承父进程变量，但将共享变量显式传入子进程是更安全、跨平台的写法。

修改步骤 #

1. 将GlobalCount的初始化移到main()函数内部，避免子进程重新初始化。
2. 启动子进程时，将GlobalCount作为参数传入process()函数，确保子进程操作的是同一个共享对象。

修改后的代码 #

import multiprocessing
import socket
import time

from multiprocessing import Value

def main():
    # 将共享变量移到main内部，避免子进程重复初始化
    GlobalCount = Value('i', 0)  # 'i' stands for integer

    server_ip = "127.0.0.1"
    server_port = 2222

    server_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    server_address = (server_ip, server_port)
    server_socket.bind(server_address)

    response = ""

    print("UDP server is listening on {}:{}".format(*server_address))

    while True:
        data, client_address = server_socket.recvfrom(256)

        if data:
            data_str = data.decode('utf-8') 
            arrayParams = data_str.split(';')

            if arrayParams[0] == "PROCESS":
                server_socket.sendto(response.encode(), client_address)
                # 启动子进程时传入共享变量
                training_process = multiprocessing.Process(target=process, args=(GlobalCount,))
                training_process.start()

            elif arrayParams[0] == "GETSTATUS":
                current_value = GlobalCount.value
                response = str(current_value)
                server_socket.sendto(response.encode(), client_address)

            else:
                print("")

# 修改process函数，接收传入的共享变量
def process(GlobalCount):
    for i in range(100):
        with GlobalCount.get_lock():
            GlobalCount.value += 1
        time.sleep(1)

if __name__ == '__main__':
    main()

补充说明 #

• multiprocessing.Value本身是进程安全的共享对象，但必须保证所有进程操作的是同一个实例。
• 上述修改兼容Windows、Unix/Linux所有平台，避免了系统机制差异带来的问题。

内容的提问来源于stack exchange，提问作者Jaume