multiprocessing.freeze_support() #运行该语句后，将检查子进程是否为frozen executable中的fake forked process，如是，将运行命令行指定的代码并退出。如果要将脚本打包为exe可执行文件，必须首先执行该语句。

One needs to call this function straight after the if __name__ == '__main__' line of the main module. For example:

from multiprocessing import Process, freeze_support

def f():
    print('hello world!')

if __name__ == '__main__':
    freeze_support()
    Process(target=f).start()

内部原理：

The reason is lack of fork() on Windows (which is not entirely true). Because of this, on Windows the fork is simulated by creating a new process in which code, which on Linux is being run in child process, is being run. As the code is to be run in technically unrelated process, it has to be delivered there before it can be run. The way it's being delivered is first it's being pickled and then sent through the pipe from the original process to the new one. In addition this new process is being informed it has to run the code passed by pipe, by passing --multiprocessing-fork command line argument to it. If you take a look at implementation of freeze_support() function its task is to check if the process it's being run in is supposed to run code passed by pipe or not.

参考链接：https://zhuanlan.zhihu.com/p/46798399

multiprocessing — Process-based parallelism — Python 3.10.2 documentation

python - multiprocessing.freeze_support() - Stack Overflow