Simple Python fire & forget skeleton useful to launch heavy tasks as background processes

fire-and-forget.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

'''
- Requirements:
    + python-daemon==2.2.3
'''

from __future__ import absolute_import, division, print_function, unicode_literals
import argparse
import daemon
import errno
import os
import signal
import sys
import time
from lockfile import pidlockfile


###############################################################################
## TASK
###############################################################################

def task(options):
    sys.stdout.write('Starting task execution...\n')
    print(options)
    time.sleep(10)
    sys.stdout.write('Gracefully stopping task execution...\n')


###############################################################################
## FIRE & FORGET
###############################################################################

def fire_and_forget(options):
    if options.pidfile is not None:
        pid = pidlockfile.read_pid_from_pidfile(options.pidfile)
        if pid is not None and is_pid_running(pid):
            sys.stderr.write("PID {} in pidfile '{}' is already running.\n".format(
                pid, options.pidfile))
            sys.exit(1)
        pidlockfile.remove_existing_pidfile(options.pidfile)

    with daemon.DaemonContext(
            pidfile=\
                pidlockfile.PIDLockFile(options.pidfile) \
                if options.pidfile is not None else None,
            detach_process=False if options.nodetach else True,
            stdout=sys.stdout if options.nodetach else None,
            stderr=sys.stderr if options.nodetach else None):
        if options.timeout > 0:
            signal.signal(signal.SIGALRM, sigalrm_handler)
            signal.alarm(options.timeout)

        task(options)

    if options.pidfile is not None:
        pidlockfile.remove_existing_pidfile(options.pidfile)


def sigalrm_handler(signum, frame):
    sys.stderr.write('Abruptly stopping due to SIGALRM event.\n')
    sys.exit(1)


def is_pid_running(pid):
    try:
        os.kill(pid, signal.SIG_DFL)
    except OSError as e:
        if e.errno == errno.ESRCH:
            return False
    return True


###############################################################################
## MAIN
###############################################################################

def main():
    parser = argparse.ArgumentParser()

    parser.add_argument(
        '--pidfile', type=str, default=None)
    parser.add_argument(
        '--timeout', type=int, default=300)
    parser.add_argument(
        '--nodetach', action='store_const', const=True, default=False)
    parser.add_argument(
        '--foo', type=str, default=None)
    parser.add_argument(
        '--bar', type=str, default=None)

    fire_and_forget(parser.parse_args())


if __name__ == '__main__':
    main()