Python Signal Handling

Taken from https://docs.python.org/3/library/signal.html

Sidenote: Do not put this in a file called signal.py. Otherwise we override the module name. The following will happen (https://stackoverflow.com/a/66055075):

$ python /tmp/signal.py
Traceback (most recent call last):
File "/tmp/signal.py", line 2, in <module>
  import signal
File "/private/tmp/signal.py", line 3, in <module>
  from signal import SIGINT
ImportError: cannot import name 'SIGINT' from partially initialized module 'signal' (most likely due to a circular import) (/private/tmp/signal.py)

--

import time
import signal


def sigterm_handler(signal_num, stack_frame):
    '''Default kill signal | Graceful termination'''
    print('Terminating')
    exit(0)

def sigint_handler(signal_num, stack_frame):
    '''If someone presses ctrl-c'''
    print("Ctrl-C'ed by user.")
    exit(0)

def run_default_behavior(signal_num=None, stack_frame=None):
    print('main() executing')
    while True:
        print('still main()')
        time.sleep(2)

def wait_on_signal(signal_num=None, stack_frame=None):
    print('pausing')
    signal.pause()


signal.signal(signal.SIGTERM, sigterm_handler)
signal.signal(signal.SIGINT, sigint_handler)
signal.signal(signal.SIGUSR1, run_default_behavior)
signal.signal(signal.SIGUSR2, wait_on_signal)

run_default_behavior()

Triggering it

$ kill -SIGUSR2 "$(ps -ef | grep -v grep | grep python | grep signal_test | awk '{ print $2 }')"
$ kill -SIGUSR1 "$(ps -ef | grep -v grep | grep python | grep signal_test | awk '{ print $2 }')"

# graceful termination
$ kill "$(ps -ef | grep -v grep | grep python | grep signal_test | awk '{ print $2 }')" 
$ kill -SIGTERM"$(ps -ef | grep -v grep | grep python | grep signal_test | awk '{ print $2 }')" 


# or ctrl-c
$ kill -SIGINT "$(ps -ef | grep -v grep | grep python | grep signal_test | awk '{ print $2 }')" 

Output

$ python /tmp/signal_test.py
Still running...
pausing
running sync
Still running...
Still running...
SIGTERM received exiting
$ python /tmp/signal_test.py
SIGINT received exiting