Python 多进程报错问题

Python 多进程报错问题

windows环境下代码如下

import multiprocessing
import os
import time

def show_info(name, age):
    print(name, age)

    # 以元组方式传参
sub_process = multiprocessing.Process(target=show_info, args=("李四", 20))
sub_process.start()
# 以字典方式传参
sub2_process = multiprocessing.Process(target=show_info, kwargs={"name": "张三", "age": 40})
sub2_process.start()
# 以两种方式传参
sub3_process = multiprocessing.Process(target=show_info, args=("王五",), kwargs={"age": 60})
sub3_process.start()

运行会报如下错误

RuntimeError: 
        An attempt has been made to start a new process before the
        current process has finished its bootstrapping phase.

        This probably means that you are not using fork to start your
        child processes and you have forgotten to use the proper idiom
        in the main module:

            if __name__ == '__main__':
                freeze_support()
                ...

        The "freeze_support()" line can be omitted if the program
        is not going to be frozen to produce an executable.

　　加上 if __name__ == '__main__'   后，错误消失

import multiprocessing
def show_info(name, age):
    print(name, age)
if __name__ == '__main__':
    # 以元组方式传参
    sub_process = multiprocessing.Process(target=show_info, args=("李四", 20))
    sub_process.start()
    # 以字典方式传参
    sub2_process = multiprocessing.Process(target=show_info, kwargs={"name": "张三", "age": 40})
    sub2_process.start()
    # 以两种方式传参
    sub3_process = multiprocessing.Process(target=show_info, args=("王五",), kwargs={"age": 60})
    sub3_process.start()

但是在linux和mac环境下，不加 if __name__ == '__main__'   是可以正常运行的，这是为什么呢？

请你们自己去思考哦。

小细节：windows创建多进程，会默认把当前文件全部代码copy一份，放在其他创建出来的进程里面去执行，就形成了无限递归。

而且进程之前不共享全局变量。每个进程里面都有自己的一份儿全局变量