rc_daemon.py

#!/usr/bin/env python
#
# Raspberry Pi Internet Radio Remote Control Class
# $Id: rc_daemon.py,v 1.7 2015/10/31 15:40:05 bob Exp $
# 
# Author : Sander Marechal
# Website http://www.jejik.com/articles/2007/02/a_simple_unix_linux_daemon_in_python/
#
# Adapted by Bob Rathbone for the Internet Radio
# Site   : http://www.bobrathbone.com
#
# This is the daemon class for the PiFace CAD remote control
#
# License: GNU V3, See https://www.gnu.org/copyleft/gpl.html
#
# Disclaimer: Software is provided as is and absolutly no warranties are implied or given.
#             The authors shall not be liable for any loss or damage however caused.
#

import sys, os, time, atexit
from signal import SIGKILL 
from signal import SIGHUP 

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: 
			self.ppid = os.getpid() 
			pid = os.fork() 
			if pid > 0:
				# exit first parent
				sys.exit(0) 
		except OSError, e: 
			sys.stderr.write("fork #1 failed: %d (%s)\n" % (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)\n" % (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\n" % pid)
	
	def delpid(self):
		os.remove(self.pidfile)

	def start(self):
		"""
		Start the daemon
		"""
		self.begin(True)

	def nodaemon(self):
		"""
		Start the program in foreground
		Test purposes only
		"""
		try:
			self.begin(False)
		except KeyboardInterrupt:
			pid = os.getpid()
			print "\nStopping remote control pid",pid
			os.kill(pid, SIGKILL)
 
	def begin(self,daemonize):
		"""
		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?\n"
			sys.stderr.write(message % self.pidfile)
			sys.exit(1)
		
		# Start the daemon
		if daemonize:
			self.daemonize()
		else:
			print "remote control running pid", os.getpid()

		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?\n"
			sys.stderr.write(message % self.pidfile)
			return # not an error in a restart

		# Stop lircd and irexec
		try:
			pid1 = int(self.exec_cmd("pidof lircd"))
			os.kill(pid1, SIGKILL)
		except OSError, err:
			print str(err)
		except ValueError:
			print "lircd not running"
		
		# Try killing the daemon process	
		try:
			cpid = int(self.exec_cmd("pgrep -P " + str(pid)))
			os.kill(cpid, SIGHUP)
			if os.path.exists(self.pidfile):
				os.remove(self.pidfile)
			os.kill(pid, SIGKILL)
			sys.exit(0)

		except ValueError, err:
			print "Remote control daemon not running"
			os.remove(self.pidfile)

		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 status(self):
		"""
		Status
		"""

	def flash(self):
		"""
		Flash activity LED
		"""


	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().
		"""

	# Execute system command
	def exec_cmd(self,cmd):
		p = os.popen(cmd)
		result = p.readline().rstrip('\n')
		return result

### End ###