Python 守护程序线程似乎无法在后台运行答案

【问题标题】：Python daemon threads seems not work in backgroundPython 守护程序线程似乎无法在后台运行
【发布时间】：2019-09-25 19:00:41
【问题描述】：

我从https://www.bogotobogo.com/python/Multithread/python_multithreading_Daemon_join_method_threads.php 中获取了一段代码并添加了三行代码，期望它可以运行一个删除任何名为 'Tested' 的文件的守护进程。它在开始时工作，但如果在运行守护进程时（我猜它做到了），我使用“触摸测试”从命令行（在 GNU/linux 中）创建一个新文件，什么也没有发生。我读过它，但如果真的线程守护进程在后台工作，我应该做错了。

import threading
import time
import logging
import os
logging.basicConfig(level=logging.DEBUG,
                    format='(%(threadName)-9s) %(message)s',)

def n():
    logging.debug('Starting')
    logging.debug('Exiting')

def d():
    logging.debug('Starting')
    #  I expected these three following lines keep running in the background and delete any new file named 'Test'

    while True:
        if os.path.isfile('test'):
            os.remove ('test')

    time.sleep(5)
    logging.debug('Exiting')

if __name__ == '__main__':

    t = threading.Thread(name='non-daemon', target=n)
    d = threading.Thread(name='daemon', target=d)
    d.setDaemon(True)

    d.start()
    t.start()

【问题讨论】：

我猜主程序退出了。因为您没有将线程重新加入主线程..尝试将其重新加入主线程
但是加入等待所有加入的线程都完成了。我想要一个线程“永远”运行。我的问题是为什么里面的代码不起作用
你可以尝试将睡眠功能移到 while true 块下吗？
Yatish，我解决了问题：d.setDaemon(True) 不起作用。我用 d.setDaemon = True 替换这条指令，效果很好。谢谢
我也试过 d = threading.Thread(name='daemon', target=d, daemon = True) 但不起作用。

标签： python python-3.x python-multithreading python-daemon

【解决方案1】：

一旦主线程退出，守护线程就会被杀死（参见上面的文档this）：

ForceBru:~ forcebru$ cat test.py
import threading
import time

def daemon():
    print('Daemon started')
    i = 0
    while True:
        print('Daemon running:', i)
        i += 1

d = threading.Thread(target=daemon, daemon=True)
d.start()
print('Started daemon!')
time.sleep(0.01)
print('Main thread is exiting. See if the daemon thread exits too')
ForceBru:~ forcebru$ python3 test.py
Daemon started
Daemon running: 0
Daemon running: 1
Daemon running: 2
Daemon running: 3
Started daemon!
Daemon running: 4
Daemon running: 5
Daemon running: 6
Daemon running: 7
Daemon running: 8
Daemon running: 9
Daemon running: 10
Daemon running: 11
<snip>
Daemon running: 1508
Daemon running: 1509
Daemon running: 1510
Main thread is exiting. See if the daemon thread exits too
Fatal Python error: could not acquire lock for <_io.BufferedWriter name='<stdout>'> at interpreter shutdown, possibly due to daemon threads

Thread 0x0000700008819000 (most recent call first):
  File "test.py", line 8 in daemon
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py", line 865 in run
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py", line 917 in _bootstrap_inner
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py", line 885 in _bootstrap

Current thread 0x0000000104ea95c0 (most recent call first):
Abort trap: 6
ForceBru:~ forcebru$

你不一定会得到错误，但还是看看它说了什么：

Fatal Python error: could not acquire lock for <_io.BufferedWriter name='<stdout>'> at interpreter shutdown, possibly due to daemon threads

因此，Python 试图在守护线程仍在运行时自行关闭。因此，您的脚本实际上退出了，因为根据文档：

...当只剩下守护线程时，整个 Python 程序退出

【讨论】：