Proste demony uniksowe w Pythonie
22 March 2009
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Dość często zachodzi potrzeba napisania jakiegoś uniksowego demona, aplikacji działającej w tle i np. przetwarzającej dane, lub wykonującej jakieś czynności porządkowe. W Pythonie mamy wiele rozwiązań umożliwiających tworzenie różnego rodzaju demonów. Jednym z prostszych i poręcznych jest klasa napisana przez Sandera Marechala. Jego rozwiązanie opiera się na klasie Daemon implementującą wszystkiche potrzebne metody. Klasa ta dziedziczona jest przez naszą klasę konkretnego demona. Oto klasa Daemon:
#!/usr/bin/env python
import sys, os, time, atexit
from signal import SIGTERM
class Daemon:
"""
A generic daemon class.
Usage: subclass the Daemon class and override the run() method
"""
def __init__(self, pidfile, stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'):
self.stdin = stdin
self.stdout = stdout
self.stderr = stderr
self.pidfile = pidfile
def daemonize(self):
"""
do the UNIX double-fork magic, see Stevens' "Advanced
Programming in the UNIX Environment" for details (ISBN 0201563177)
http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
"""
try:
pid = os.fork()
if pid > 0:
# exit first parent
sys.exit(0)
except OSError, e:
sys.stderr.write("fork #1 failed: %d (%s)
" % (e.errno, e.strerror))
sys.exit(1)
# decouple from parent environment
os.chdir("/")
os.setsid()
os.umask(0)
# do second fork
try:
pid = os.fork()
if pid > 0:
# exit from second parent
sys.exit(0)
except OSError, e:
sys.stderr.write("fork #2 failed: %d (%s)
" % (e.errno, e.strerror))
sys.exit(1)
# redirect standard file descriptors
sys.stdout.flush()
sys.stderr.flush()
si = file(self.stdin, 'r')
so = file(self.stdout, 'a+')
se = file(self.stderr, 'a+', 0)
os.dup2(si.fileno(), sys.stdin.fileno())
os.dup2(so.fileno(), sys.stdout.fileno())
os.dup2(se.fileno(), sys.stderr.fileno())
# write pidfile
atexit.register(self.delpid)
pid = str(os.getpid())
file(self.pidfile,'w+').write("%s
" % pid)
def delpid(self):
os.remove(self.pidfile)
def start(self):
"""
Start the daemon
"""
# Check for a pidfile to see if the daemon already runs
try:
pf = file(self.pidfile,'r')
pid = int(pf.read().strip())
pf.close()
except IOError:
pid = None
if pid:
message = "pidfile %s already exist. Daemon already running?
"
sys.stderr.write(message % self.pidfile)
sys.exit(1)
# Start the daemon
self.daemonize()
self.run()
def stop(self):
"""
Stop the daemon
"""
# Get the pid from the pidfile
try:
pf = file(self.pidfile,'r')
pid = int(pf.read().strip())
pf.close()
except IOError:
pid = None
if not pid:
message = "pidfile %s does not exist. Daemon not running?
"
sys.stderr.write(message % self.pidfile)
return # not an error in a restart
# Try killing the daemon process
try:
while 1:
os.kill(pid, SIGTERM)
time.sleep(0.1)
except OSError, err:
err = str(err)
if err.find("No such process") > 0:
if os.path.exists(self.pidfile):
os.remove(self.pidfile)
else:
print str(err)
sys.exit(1)
def restart(self):
"""
Restart the daemon
"""
self.stop()
self.start()
def run(self):
"""
You should override this method when you subclass Daemon. It will be called after the process has been
daemonized by start() or restart().
"""
#!/usr/bin/env python
import sys, time
from daemon import Daemon
class MyDaemon(Daemon):
def run(self):
while True:
# tutaj nasz kod
time.sleep(1)
if __name__ == "__main__":
daemon = MyDaemon('/tmp/daemon-example.pid')
if len(sys.argv) == 2:
if 'start' == sys.argv[1]:
daemon.start()
elif 'stop' == sys.argv[1]:
daemon.stop()
elif 'restart' == sys.argv[1]:
daemon.restart()
else:
print "Unknown command"
sys.exit(2)
sys.exit(0)
else:
print "usage: %s start|stop|restart" % sys.argv[0]
sys.exit(2)
#!/usr/bin/env python
import sys, time
import sqlite3
from datetime import datetime
from statgrab import *
from daemon import Daemon
class MyDaemon(Daemon):
def run(self):
sg_init()
conn = sqlite3.connect('/tmp/grabstat')
c = conn.cursor()
while True:
now = str(datetime.now())
avg_load = sg_get_load_stats()
c.execute('INSERT INTO grabs_avgload (m1, m5, m15, time) VALUES ("%s", "%s", "%s", "%s")' % (avg_load['min1'], avg_load['min5'], avg_load['min15'], now))
fs_io = sg_get_disk_io_stats()
if len(fs_io) > 0:
for i in fs_io:
c.execute('INSERT INTO grabs_fsio (disk_name, write_bytes, read_bytes, time) VALUES ("%s", "%s", "%s", "%s")' % (i['disk_name'], i['write_bytes'], i['read_bytes'], now))
fs = sg_get_fs_stats()
if len(fs) > 0:
for i in fs:
c.execute('INSERT INTO grabs_fs (device, used, avail, size, time) VALUES ("%s", "%s", "%s", "%s", "%s")' % (i['device_name'], i['used'], i['avail'], i['size'], now))
memory = sg_get_mem_stats()
c.execute('INSERT INTO grabs_memory (total, free, used, time) VALUES ("%s", "%s", "%s", "%s")' % (memory['total'], memory['free'], memory['used'], now))
net_io = sg_get_network_io_stats()
if len(net_io) > 0:
for i in net_io:
c.execute('INSERT INTO grabs_netio (interface_name, ipackets, time) VALUES ("%s", "%s", "%s")' % (i['interface_name'], i['ipackets'], now))
conn.commit()
time.sleep(120)
if __name__ == "__main__":
daemon = MyDaemon('/tmp/stats.pid')
if len(sys.argv) == 2:
if 'start' == sys.argv[1]:
daemon.start()
elif 'stop' == sys.argv[1]:
daemon.stop()
elif 'restart' == sys.argv[1]:
daemon.restart()
else:
print "Unknown command"
sys.exit(2)
sys.exit(0)
else:
print "usage: %s start|stop|restart" % sys.argv[0]
sys.exit(2)
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