[Python] child process signal control

child_process

import os
import signal
import time
import sys

pid = os.getpid()
received = False


def signal_usr1(signum, frame):
    "Callback invoked when a signal is received"
    global received
    received = True
    print('CHILD {:>6}: Received USR1'.format(pid))
    sys.stdout.flush()


print('CHILD {:>6}: Setting up signal handler'.format(pid))
sys.stdout.flush()
signal.signal(signal.SIGUSR1, signal_usr1)
print('CHILD {:>6}: Pausing to wait for signal'.format(pid))
sys.stdout.flush()
time.sleep(3)

if not received:
    print('CHILD {:>6}: Never received signal'.format(pid))

output_eg

PARENT      : Pausing before sending signal...
CHILD   8117: Setting up signal handler
CHILD   8117: Pausing to wait for signal
PARENT      : Signaling child
CHILD   8117: Received USR1

parent

import os
import signal
import subprocess
import time
import sys

proc = subprocess.Popen(['python3', 'child_process.py'])
print('PARENT      : Pausing before sending signal...')
sys.stdout.flush()
time.sleep(1)
print('PARENT      : Signaling child')
sys.stdout.flush()
os.kill(proc.pid, signal.SIGUSR1)    # !! here it rocks !!