271

假设我们有一个用 python 编写的简单的守护进程:

def mainloop():
    while True:
        # 1. do
        # 2. some
        # 3. important
        # 4. job
        # 5. sleep

mainloop()

我们使用start-stop-daemon它来守护它,默认情况下发送SIGTERM( TERM) 信号--stop

假设当前执行的步骤是#2. 而此时我们正在发送TERM信号。

发生的情况是执行立即终止。

我发现我可以使用处理信号事件,signal.signal(signal.SIGTERM, handler)但问题是它仍然会中断当前执行并将控制权传递给handler.

所以,我的问题是 - 是否可以不中断当前执行但TERM在单独的线程中处理信号(?),以便我能够设置shutdown_flag = True以便mainloop()有机会优雅地停止?

4

9 回答 9

399

基于类的清洁使用解决方案:

import signal
import time

class GracefulKiller:
  kill_now = False
  def __init__(self):
    signal.signal(signal.SIGINT, self.exit_gracefully)
    signal.signal(signal.SIGTERM, self.exit_gracefully)

  def exit_gracefully(self, *args):
    self.kill_now = True

if __name__ == '__main__':
  killer = GracefulKiller()
  while not killer.kill_now:
    time.sleep(1)
    print("doing something in a loop ...")
   
  print("End of the program. I was killed gracefully :)")
于 2015-07-16T20:55:02.330 回答
74

首先,我不确定您是否需要第二个线程来设置shutdown_flag.
为什么不直接在 SIGTERM 处理程序中设置呢?

另一种方法是从处理程序中引发异常,该异常SIGTERM将向上传播到堆栈。假设您已经进行了适当的异常处理(例如使用with/contextmanagertry: ... finally:块),这应该是一个相当优雅的关闭,类似于Ctrl+C您的程序。

示例程序signals-test.py

#!/usr/bin/python

from time import sleep
import signal
import sys


def sigterm_handler(_signo, _stack_frame):
    # Raises SystemExit(0):
    sys.exit(0)

if sys.argv[1] == "handle_signal":
    signal.signal(signal.SIGTERM, sigterm_handler)

try:
    print "Hello"
    i = 0
    while True:
        i += 1
        print "Iteration #%i" % i
        sleep(1)
finally:
    print "Goodbye"

现在看看Ctrl+C行为:

$ ./signals-test.py default
Hello
Iteration #1
Iteration #2
Iteration #3
Iteration #4
^CGoodbye
Traceback (most recent call last):
  File "./signals-test.py", line 21, in <module>
    sleep(1)
KeyboardInterrupt
$ echo $?
1

这次我SIGTERM在 4 次迭代后发送它kill $(ps aux | grep signals-test | awk '/python/ {print $2}')

$ ./signals-test.py default
Hello
Iteration #1
Iteration #2
Iteration #3
Iteration #4
Terminated
$ echo $?
143

这次我启用我的自定义SIGTERM处理程序并发送它SIGTERM

$ ./signals-test.py handle_signal
Hello
Iteration #1
Iteration #2
Iteration #3
Iteration #4
Goodbye
$ echo $?
0
于 2014-07-04T12:45:31.310 回答
44

这是一个没有线程或类的简单示例。

import signal

run = True

def handler_stop_signals(signum, frame):
    global run
    run = False

signal.signal(signal.SIGINT, handler_stop_signals)
signal.signal(signal.SIGTERM, handler_stop_signals)

while run:
    pass # do stuff including other IO stuff
于 2017-01-19T23:21:17.793 回答
29

我认为你接近一个可能的解决方案。

mainloop在单独的线程中执行并使用属性对其进行扩展shutdown_flagsignal.signal(signal.SIGTERM, handler)可以在主线程中(而不是在单独的线程中)捕获信号。信号处理程序应设置shutdown_flag为 True 并等待线程以thread.join()

于 2013-08-29T00:08:08.890 回答
14

根据之前的答案,我创建了一个上下文管理器,可以防止 sigint 和 sigterm。

import logging
import signal
import sys


class TerminateProtected:
    """ Protect a piece of code from being killed by SIGINT or SIGTERM.
    It can still be killed by a force kill.

    Example:
        with TerminateProtected():
            run_func_1()
            run_func_2()

    Both functions will be executed even if a sigterm or sigkill has been received.
    """
    killed = False

    def _handler(self, signum, frame):
        logging.error("Received SIGINT or SIGTERM! Finishing this block, then exiting.")
        self.killed = True

    def __enter__(self):
        self.old_sigint = signal.signal(signal.SIGINT, self._handler)
        self.old_sigterm = signal.signal(signal.SIGTERM, self._handler)

    def __exit__(self, type, value, traceback):
        if self.killed:
            sys.exit(0)
        signal.signal(signal.SIGINT, self.old_sigint)
        signal.signal(signal.SIGTERM, self.old_sigterm)


if __name__ == '__main__':
    print("Try pressing ctrl+c while the sleep is running!")
    from time import sleep
    with TerminateProtected():
        sleep(10)
        print("Finished anyway!")
    print("This only prints if there was no sigint or sigterm")
于 2018-05-04T11:44:13.403 回答
6

为我找到了最简单的方法。为了清楚起见,这里有一个带有 fork 的示例,这种方式对流控制很有用。

import signal
import time
import sys
import os

def handle_exit(sig, frame):
    raise(SystemExit)

def main():
    time.sleep(120)

signal.signal(signal.SIGTERM, handle_exit)

p = os.fork()
if p == 0:
    main()
    os._exit()

try:
    os.waitpid(p, 0)
except (KeyboardInterrupt, SystemExit):
    print('exit handled')
    os.kill(p, 15)
    os.waitpid(p, 0)
于 2019-02-07T16:43:42.393 回答
0

您可以threading.Event在捕获信号时设置一个。

threading.Event使用和传递是线程安全的,可以等待,并且可以从其他地方设置和清除相同的事件。

import signal, threading

quit_event = threading.Event()
signal.signal(signal.SIGTERM, lambda *_args: quit_event.set())

while not quit_event.is_set():
    print("Working...")
于 2021-09-01T15:10:55.787 回答
0

我的代码示例如何使用signal

#! /usr/bin/env python

import signal


def ctrl_handler(signum, frm):
    print "You can't cannot kill me"


print "Installing signal handler..."
signal.signal(signal.SIGINT, ctrl_handler)
print "done"

while True:
    # do something
    pass
于 2021-05-25T14:37:24.423 回答
-1

我发现的最简单的解决方案,从上面的回答中汲取灵感是

class SignalHandler:

    def __init__(self):

        # register signal handlers
        signal.signal(signal.SIGINT, self.exit_gracefully)
        signal.signal(signal.SIGTERM, self.exit_gracefully)

        self.logger = Logger(level=ERROR)

    def exit_gracefully(self, signum, frame):
        self.logger.info('captured signal %d' % signum)
        traceback.print_stack(frame)

        ###### do your resources clean up here! ####

        raise(SystemExit)
于 2019-11-11T17:47:17.347 回答