Stop a python 2.7 daemon by the signal

Question

I use python 2.7.3 and daemon runner in my script. In a run(loop) method i want to sleep for the some time, but not with the such code:

while True:
    time.sleep(10)

I want wait on a some synchronizing primitive, for example multiprocessing.Event. There is my code:

# -*- coding: utf-8 -*-
import logging
from daemon import runner
import signal
import multiprocessing

import spyder_cfg

logging.basicConfig(level=logging.DEBUG, format='%(asctime)s %(name)-12s %(levelname)-8s %(message)s', datefmt='%m-%d %H:%M', filename=spyder_cfg.log_file)

class Daemon(object):     
    def __init__(self, pidfile_path):
        self.stdin_path = '/dev/null'
        self.stdout_path = '/dev/tty'
        self.stderr_path = '/dev/tty'
        self.pidfile_path = None
        self.pidfile_timeout = 5
        self.pidfile_path = pidfile_path 

    def setup_daemon_context(self, daemon_context):
        self.daemon_context = daemon_context

    def run(self):
        logging.info('Spyder service has started')
        logging.debug('event from the run() = {}'.format(self.daemon_context.stop_event))
        while not self.daemon_context.stop_event.wait(10):
            try:
                logging.info('Spyder is working...')
            except BaseException as exc:
                logging.exception(exc)
        logging.info('Spyder service has been stopped') 

    def handle_exit(self, signum, frame):
        try:
            logging.info('Spyder stopping...')
            self.daemon_context.stop_event.set()
        except BaseException as exc:
            logging.exception(exc)

if __name__ == '__main__':
    app = Daemon(spyder_cfg.pid_file)
    d = runner.DaemonRunner(app)
    d.daemon_context.working_directory = spyder_cfg.work_dir
    d.daemon_context.files_preserve = [h.stream for h in logging.root.handlers]
    d.daemon_context.signal_map = {signal.SIGUSR1: app.handle_exit} 
    d.daemon_context.stop_event = multiprocessing.Event()
    app.setup_daemon_context(d.daemon_context)
    logging.debug('event from the main = {}'.format(d.daemon_context.stop_event))
    d.do_action()

It is my log file records:

06-04 11:32 root         DEBUG    event from the main = <multiprocessing.synchronize.Event object at 0x7f0ef0930d50>
06-04 11:32 root         INFO     Spyder service has started
06-04 11:32 root         DEBUG    event from the run() = <multiprocessing.synchronize.Event object at 0x7f0ef0930d50>
06-04 11:32 root         INFO     Spyder is working...
06-04 11:32 root         INFO     Spyder stopping...

There is not 'Spyder service has been stopped' print in the log, my program hang on the set() call. While debugging i see that it hang when Event.set() call, the set method hang on semaphore while all waiting entities wake up. There is no reason if Event will be global object or threading.Event. I see this one answer, but its not good for me. Is there an alternative for wait with the timeout wait with the same behavior as multiprocessing.Event?

Answer 1

I do print stack from the signal handler and i think there is deadlock, because signal handler use same stack with the my main process and when i call Event.set(), method wait() higher on the stack...

def handle_exit(self, signum, frame):
    try:
        logging.debug('Signal handler:{}'.format(traceback.print_stack()))
    except BaseException as exc:
        logging.exception(exc)


d.do_action()
  File ".../venv/work/local/lib/python2.7/site-packages/daemon/runner.py", line 189, in do_action
    func(self)
  File ".../venv/work/local/lib/python2.7/site-packages/daemon/runner.py", line 134, in _start
    self.app.run()
  File ".../venv/work/skelet/src/spyder.py", line 32, in run
    while not self.daemon_context.stop_event.wait(10):
  File "/usr/lib/python2.7/multiprocessing/synchronize.py", line 337, in wait
    self._cond.wait(timeout)
  File "/usr/lib/python2.7/multiprocessing/synchronize.py", line 246, in wait
    self._wait_semaphore.acquire(True, timeout)
  File ".../venv/work/skelet/src/spyder.py", line 41, in handle_exit
    logging.debug('Signal handler:{}'.format(traceback.print_stack()))

that is why this fix solve the problem:

def handle_exit(self, signum, frame):  
    t = Timer(1, self.handle_exit2)  
    t.start()

def handle_exit2(self): 
    self.daemon_context.stop_event.set()