How to process SIGTERM signal gracefully?

Let's assume we have such a trivial daemon written in python:

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

    mainloop()

and we daemonize it using start-stop-daemon which by default sends SIGTERM (TERM) signal on --stop.

Let's suppose the current step performed is #2. And at this very moment we're sending TERM signal.

What happens is that the execution terminates immediately.

I've found that I can handle the signal event using signal.signal(signal.SIGTERM, handler) but the thing is that it still interrupts the current execution and passes the control to handler.

So, my question is - is it possible to not interrupt the current execution but handle the TERM signal in a separated thread (?) so that I was able to set shutdown_flag = True so that mainloop() had a chance to stop gracefully?

A class based clean to use solution:

    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 True:
        time.sleep(1)
        print("doing something in a loop ...")
        if killer.kill_now:
          break

      print "End of the program. I was killed gracefully :)"

From: stackoverflow.com/q/18499497

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