如何优雅地处理SIGTERM信号？

Question

让我们假设我们有一个用python编写的这样一个简单的守护进程:

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

mainloop()

然后我们使用start-stop-daemon默认的send SIGTERM(TERM)信号进行守护--stop.

我们假设当前执行的步骤是#2.在这个时刻,我们正在发送TERM信号.

会发生什么是执行立即终止.

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

所以,我的问题是-它可以不中断当前执行,但处理TERM(？)在独立的线程信号,使我能够设置shutdown_flag = True,使mainloop()有机会停止正常？

Answer 1

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,signum, frame):
    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 :)"

Answer 2

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处理程序中设置它？

另一种方法是从SIGTERM处理程序引发异常,该异常将在堆栈中向上传播.假设你有适当的异常处理(例如使用with/ contextmanager和try: ... finally:块),这应该是一个相当优雅的关闭,类似于Ctrl-C你的程序.

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

Answer 3

我认为你接近可能的解决方案.

mainloop在单独的线程中执行并使用属性扩展它shutdown_flag.信号可以signal.signal(signal.SIGTERM, handler)在主线程中捕获(而不是在单独的线程中).信号处理程序应设置shutdown_flag为True并等待线程结束thread.join()

Answer 4

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

Answer 5

基于之前的答案,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")

Answer 6

为我找到了最简单的方法。这里有一个使用 fork 的例子，为了清楚起见，这种方式对于流量控制很有用。

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, signal.SIGTERM)
    os.waitpid(p, 0)