How to process SIGTERM signal gracefully?

Question

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?

Accepted Answer

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 not killer.kill_now:
    time.sleep(1)
    print("doing something in a loop ...")
   
  print("End of the program. I was killed gracefully :)")
```

How to process SIGTERM signal gracefully?

Solution

Problem

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