捕捉 Ctrl+C/SIGINT 并在 python 中优雅地退出多进程

2022-01-12 00:00:00 python multiprocessing signals

问题描述

如何在多进程 python 程序中捕获 Ctrl+C 并优雅地退出所有进程，我需要该解决方案在 unix 和 windows 上都可以工作.我尝试了以下方法:

How do I catch a Ctrl+C in multiprocess python program and exit all processes gracefully, I need the solution to work both on unix and windows. I've tried the following:

import multiprocessing
import time
import signal
import sys

jobs = []

def worker():
    signal.signal(signal.SIGINT, signal_handler)
    while(True):
        time.sleep(1.1234)
        print "Working..."

def signal_handler(signal, frame):
    print 'You pressed Ctrl+C!'
    # for p in jobs:
    #     p.terminate()
    sys.exit(0)

if __name__ == "__main__":
    for i in range(50):
        p = multiprocessing.Process(target=worker)
        jobs.append(p)
        p.start()

它有点工作，但我认为这不是正确的解决方案.

And it's kind of working, but I don't think it's the right solution.

解决方案

先前接受的解决方案 有竞争条件，但它没有使用 map 和 async 函数.

The previously accepted solution has race conditions and it does not work with map and async functions.

multiprocessing.Pool处理Ctrl+C/SIGINT的正确方法是:

  1. 在创建进程 Pool 之前让进程忽略 SIGINT.这种方式创建的子进程继承 SIGINT 处理程序.
  2. 在创建 Pool 后，在父进程中恢复原始 SIGINT 处理程序.
  3. 使用 map_async 和 apply_async 而不是阻塞 map 和 apply.
  4. 使用超时等待结果，因为默认阻塞等待忽略所有信号.这是 Python 错误 https://bugs.python.org/issue8296.
  1. Make the process ignore SIGINT before a process Pool is created. This way created child processes inherit SIGINT handler.
  2. Restore the original SIGINT handler in the parent process after a Pool has been created.
  3. Use map_async and apply_async instead of blocking map and apply.
  4. Wait on the results with timeout because the default blocking waits to ignore all signals. This is Python bug https://bugs.python.org/issue8296.

<小时>

把它放在一起:

Putting it together:

#!/bin/env python
from __future__ import print_function

import multiprocessing
import os
import signal
import time

def run_worker(delay):
    print("In a worker process", os.getpid())
    time.sleep(delay)

def main():
    print("Initializng 2 workers")
    original_sigint_handler = signal.signal(signal.SIGINT, signal.SIG_IGN)
    pool = multiprocessing.Pool(2)
    signal.signal(signal.SIGINT, original_sigint_handler)
    try:
        print("Starting 2 jobs of 5 seconds each")
        res = pool.map_async(run_worker, [5, 5])
        print("Waiting for results")
        res.get(60) # Without the timeout this blocking call ignores all signals.
    except KeyboardInterrupt:
        print("Caught KeyboardInterrupt, terminating workers")
        pool.terminate()
    else:
        print("Normal termination")
        pool.close()
    pool.join()

if __name__ == "__main__":
    main()

正如@YakovShklarov 所指出的，在父进程中忽略信号和取消忽略信号之间有一个时间窗口，在此期间信号可能会丢失.使用 pthread_sigmask 代替在父进程中临时阻止信号的传递可以防止信号丢失，但是在 Python-2 中不可用.

As @YakovShklarov noted, there is a window of time between ignoring the signal and unignoring it in the parent process, during which the signal can be lost. Using pthread_sigmask instead to temporarily block the delivery of the signal in the parent process would prevent the signal from being lost, however, it is not available in Python-2.

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