Python多处理:睡眠语句被杀?

Question

我有以下代码：

import multiprocessing, datetime
def Unit_Task_Function(Argument):
print(f"Unit of work {Argument} starting {datetime.datetime.now().strftime('%Y-%m-%d : %H-%M-%S')}")
sleep(2*random.random())
print(f"Unit of work {Argument} ending {datetime.datetime.now().strftime('%Y-%m-%d : %H-%M-%S')}")    
if __name__ == "__main__":  # Allows for the safe importing of the main module
__spec__ = "ModuleSpec(name='builtins', loader=<class '_frozen_importlib.BuiltinImporter'>)"
print(f"There are {multiprocessing.cpu_count()} CPUs on this machine")
max_para_processes_at_any_time = 5
pool = multiprocessing.Pool(max_para_processes_at_any_time)

iterable_arguments = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'M', 'N']
results = pool.map_async(Unit_Task_Function, iterable_arguments)
pool.close()
pool.join()

输出为：

In [18]: run code.py
There are 8 CPUs on this machine
Unit of work A starting 2020-01-27 : 12-26-02
Unit of work B starting 2020-01-27 : 12-26-02
Unit of work C starting 2020-01-27 : 12-26-02
Unit of work D starting 2020-01-27 : 12-26-02
Unit of work E starting 2020-01-27 : 12-26-02
Unit of work F starting 2020-01-27 : 12-26-02
Unit of work G starting 2020-01-27 : 12-26-02
Unit of work H starting 2020-01-27 : 12-26-02
Unit of work M starting 2020-01-27 : 12-26-02
Unit of work N starting 2020-01-27 : 12-26-02

为什么第二次打印声明从未完成？这与所谓的"守护进程"有关吗？如何重写代码使其工作？

Answer 1

您缺少一些导入。这会导致工作人员出现导入错误，您无法看到这些错误。导入这些：

import random
from time import sleep

而你这个输出：

There are 8 CPUs on this machine
Unit of work A starting 2020-01-27 : 18-48-21
Unit of work B starting 2020-01-27 : 18-48-21
Unit of work C starting 2020-01-27 : 18-48-21
Unit of work D starting 2020-01-27 : 18-48-21
Unit of work E starting 2020-01-27 : 18-48-21
Unit of work E ending 2020-01-27 : 18-48-21
Unit of work F starting 2020-01-27 : 18-48-21
Unit of work A ending 2020-01-27 : 18-48-22
Unit of work G starting 2020-01-27 : 18-48-22
Unit of work C ending 2020-01-27 : 18-48-22
Unit of work H starting 2020-01-27 : 18-48-22
Unit of work D ending 2020-01-27 : 18-48-22
Unit of work M starting 2020-01-27 : 18-48-22
Unit of work G ending 2020-01-27 : 18-48-22
Unit of work N starting 2020-01-27 : 18-48-22
Unit of work B ending 2020-01-27 : 18-48-22
Unit of work M ending 2020-01-27 : 18-48-23
Unit of work F ending 2020-01-27 : 18-48-23
Unit of work N ending 2020-01-27 : 18-48-24
Unit of work H ending 2020-01-27 : 18-48-24

提示：在切换到pool.map_async()之前，请先使用pool.map()查看错误消息。

或者，提供一个错误回调函数来重新引发异常：

def on_error(err):
raise err
results = pool.map_async(Unit_Task_Function, 
iterable_arguments,
error_callback=on_error)