Python多进程启动时没用__name__=__main__会报错

程序demo

# -*- coding:utf-8 -*-
from multiprocessing import Pool
import os, time, random


def worker(msg):
    t_start = time.time()
    print("%s开始执行,进程号为%d" % (msg, os.getpid()))
    time.sleep(random.random() * 2)
    t_stop = time.time()
    print(msg, "执行完毕，耗时%0.2f" % (t_stop - t_start))


po = Pool(3)
for i in range(0, 10):
    po.apply_async(worker, (i,))

print("----start----")
po.close()
po.join()
print("-----end-----")

在运行多进程程序时报错如下

报错原因

python多进程 没有必需__name__="__main__"。

但windows 平台有特殊要求Since Windows has no fork, the multiprocessing module starts a new Python process and imports the calling module. If Process() gets called upon import, then this sets off an infinite succession of new processes (or until your machine runs out of resources). This is the reason for hiding calls to Process() inside

if __name__ == “__main__”
since statements inside this if-statement will not get called upon import.

windows中没有fork()函数，如果不加if __name__ == "__main__"会造成引用循环