A daemon process class in python

In everbright task schedule project, we need some daemon process to do certain work, here is a example of daemon class:

#encoding=utf-8
#!/usr/bin/env python

import sys, os, time, atexit
from signal import SIGTERM 
Basedir='/home/ronglian/project/taskschedule'
class Daemon:
    """
    A generic daemon class.
    
    Usage: subclass the Daemon class and override the run() method
    """
    def __init__(self, pidfile, stderr=Basedir+'/logs/deamon_err.log', stdout=Basedir+'/logs/deamon_out.log', stdin='/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().
        """

Here is a example how to use the class, need to rewrite the run function in parent calss:

#encoding=utf-8

import sys, time
from daemon import Daemon
import dbaction
import Task
import getdependency
from  tslogging import GlobalLogging as Logging

class sys_sync_task_mgr(Daemon):
    def __init__(self,temppath,starttime,frequency):
        Daemon.__init__(self,temppath)
        self.starttime = starttime
        self.frequency = frequency

    def run(self):

        
        while True:
            tasknolist= self.get_task_list()
            
            if len(tasknolist['sys_task']) > 0:
                if time.ctime()>self.starttime:
                    Logging.getLog().info('Available system task list:%s'%(str(tasknolist['sys_task'])))
                    try:
                        for taskno in tasknolist['sys_task']:
                            Logging.getLog().info('Start running system task:%s'%str(taskno))
                            task = Task.sys_sync_task(taskno)
                            task.task_run()
                    except Exception, ex:
                        print 'hello'
                        Logging.getLog().error( "Exception in class: 'sys_sync_task_mgr' function:'run' :"+str(ex))
                else:
                    print 'hello'
                    Logging.getLog().warn('Time to run the tasks still not reach.')
            time.sleep(self.frequency)
    def get_task_list(self):
        tasklist = getdependency.task_dependency([],3,1).get_executable_task()
        return tasklist

#main function        
if __name__ == "__main__":
    daemon = sys_sync_task_mgr('/tmp/daemon_sys_sync_task_mgr.pid',time.ctime(),20)
    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)