I'm using the famous code referenced here or here to do a daemon in Python, like this:
import sys, daemon
class test(daemon.Daemon):
def run(self):
self.db = somedb.connect() # connect to a DB
self.blah = 127
with open('blah0.txt', 'w') as f:
f.write(self.blah)
# doing lots of things here, modifying self.blah
def before_stop(self):
self.db.close() # properly close the DB (sync to disk, etc.)
with open('blah1.txt', 'w') as f:
f.write(self.blah)
daemon = test(pidfile='_.pid')
if 'start' == sys.argv[1]:
daemon.start()
elif 'stop' == sys.argv[1]:
daemon.before_stop() # AttributeError: test instance has no attribute 'blah'
daemon.stop()
The problem is that when calling ./myscript.py stop and thus daemon.before_stop(), there is no reference anymore to self.blah!
AttributeError: test instance has no attribute 'blah'
Thus with this daemonization method, it's impossible to have access to the daemon's variables before stopping the daemon...
Question: how to have access to the daemon class' variables just before:
stopping with ./myscript.py stop
being stopped with SIGTERM
(being killed?)
EDIT: solved, and here is a working daemon code with a quit() method.
The Daemon code sends a SIGTERM signal to the daemon process to ask it to stop. If you want that something is run by the daemon process itself, it must be run from a signal handler or from an atexit.register called method.
The daemonize method already installs such a method, just call beforestop from there:
# this one could be either in a subclass or in a modified base daemeon class
def delpid(self):
if hasattr(self, 'before_stop'):
self.before_stop()
os.remove(self.pidfile)
# this one should be in subclass
def before_stop(self):
self.db.close() # properly close the DB (sync to disk, etc.)
with open('blah1.txt', 'w') as f:
f.write(self.blah)
But that is not enough! The Python Standard Library documentation says about atexit:
The functions registered via this module are not called when the program is killed by a signal not handled by Python
As the process is expected to receive a SIGTERM signal, you have to install a handler. As shown in one active state recipe, it is damned simple: just ask the program to stop if it receives the signal:
...
from signal import signal, SIGTERM
...
atexit.register(self.delpid)
signal(SIGTERM, lambda signum, stack_frame: exit(1))