Mac 64 位中的多处理运行时错误 freeze_support()

Question

我正在尝试在 MacOS 上学习线程和多处理。我无法启动这些进程，python 给出了以下错误消息。

错误

运行时错误： 已尝试在 当前进程已完成其引导阶段。

    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. 

我的代码： parallel_processing.py

import multiprocessing
import time

start= time.perf_counter()

def do_something():
    print('sleeping 1 sec....')
    time.sleep(1)
    return('done sleeping...')

# do_something()
p1 = multiprocessing.Process(target = do_something)
p2 = multiprocessing.Process(target = do_something)

p1.start()
p2.start()

finish= time.perf_counter()

print(f'finished in {finish-start} seconds')

Answer 1

您似乎可以通过将代码放入块 if __name__ == '__main__' 来解决此问题。例如：

import multiprocessing as mp
import time

def do_something():
...
      
if __name__ == '__main__':
  p1 = mp.Process(target=do_something)
  p2 = mp.Process(target=do_something)

  p1.start()
  p2.start()
  ...

我不确定这是由于最近的 macOS 更新或 python 造成的，但它似乎与操作系统如何创建新线程有关，即 forking 与 spwaning。详情请见this blog post。