Detailed explanation of Python daemon and script singleton execution

#!/usr/bin/env python 
#coding: utf-8 
import sys, os 
  
'''将当前进程fork为一个守护进程 
  注意：如果你的守护进程是由inetd启动的，不要这样做！inetd完成了 
  所有需要做的事情，包括重定向标准文件描述符，需要做的事情只有chdir()和umask()了 
'''
  
def daemonize (stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'): 
   #重定向标准文件描述符（默认情况下定向到/dev/null） 
  try:  
    pid = os.fork()  
     #父进程(会话组头领进程)退出，这意味着一个非会话组头领进程永远不能重新获得控制终端。 
    if pid > 0: 
      sys.exit(0)  #父进程退出 
  except OSError, e:  
    sys.stderr.write ("fork #1 failed: (%d) %s\n" % (e.errno, e.strerror) ) 
    sys.exit(1) 
  
   #从母体环境脱离 
  os.chdir("/") #chdir确认进程不保持任何目录于使用状态，否则不能umount一个文件系统。也可以改变到对于守护程序运行重要的文件所在目录 
  os.umask(0)  #调用umask(0)以便拥有对于写的任何东西的完全控制，因为有时不知道继承了什么样的umask。 
  os.setsid()  #setsid调用成功后，进程成为新的会话组长和新的进程组长，并与原来的登录会话和进程组脱离。 
  
   #执行第二次fork 
  try:  
    pid = os.fork()  
    if pid > 0: 
      sys.exit(0)  #第二个父进程退出 
  except OSError, e:  
    sys.stderr.write ("fork #2 failed: (%d) %s\n" % (e.errno, e.strerror) ) 
    sys.exit(1) 
  
   #进程已经是守护进程了，重定向标准文件描述符 
  
  for f in sys.stdout, sys.stderr: f.flush() 
  si = open(stdin, 'r') 
  so = open(stdout, 'a+') 
  se = open(stderr, 'a+', 0) 
  os.dup2(si.fileno(), sys.stdin.fileno())  #dup2函数原子化关闭和复制文件描述符 
  os.dup2(so.fileno(), sys.stdout.fileno()) 
  os.dup2(se.fileno(), sys.stderr.fileno()) 
  
#示例函数：每秒打印一个数字和时间戳 
def main(): 
  import time 
  sys.stdout.write('Daemon started with pid %d\n' % os.getpid()) 
  sys.stdout.write('Daemon stdout output\n') 
  sys.stderr.write('Daemon stderr output\n') 
  c = 0
  while True: 
    sys.stdout.write('%d: %s\n' %(c, time.ctime())) 
    sys.stdout.flush() 
    c = c+1
    time.sleep(1) 
  
if __name__ == "__main__": 
   daemonize('/dev/null','/tmp/daemon_stdout.log','/tmp/daemon_error.log') 
   main()

#!/usr/bin/env python 
#coding: utf-8 
  
#python模拟linux的守护进程 
  
import sys, os, time, atexit, string 
from signal import SIGTERM 
  
class Daemon: 
 def __init__(self, pidfile, stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'): 
   #需要获取调试信息，改为stdin='/dev/stdin', stdout='/dev/stdout', stderr='/dev/stderr'，以root身份运行。 
  self.stdin = stdin 
  self.stdout = stdout 
  self.stderr = stderr 
  self.pidfile = pidfile 
   
 def _daemonize(self): 
  try: 
   pid = os.fork()  #第一次fork，生成子进程，脱离父进程 
   if pid > 0: 
    sys.exit(0)   #退出主进程 
  except OSError, e: 
   sys.stderr.write('fork #1 failed: %d (%s)\n' % (e.errno, e.strerror)) 
   sys.exit(1) 
   
  os.chdir("/")   #修改工作目录 
  os.setsid()    #设置新的会话连接 
  os.umask(0)    #重新设置文件创建权限 
   
  try: 
   pid = os.fork() #第二次fork，禁止进程打开终端 
   if pid > 0: 
    sys.exit(0) 
  except OSError, e: 
   sys.stderr.write('fork #2 failed: %d (%s)\n' % (e.errno, e.strerror)) 
   sys.exit(1) 
   
   #重定向文件描述符 
  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()) 
   
   #注册退出函数，根据文件pid判断是否存在进程 
  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): 
   #检查pid文件是否存在以探测是否存在进程 
  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) 
    
  #启动监控 
  self._daemonize() 
  self._run() 
  
 def stop(self): 
  #从pid文件中获取pid 
  try: 
   pf = file(self.pidfile,'r') 
   pid = int(pf.read().strip()) 
   pf.close() 
  except IOError: 
   pid = None
   
  if not pid:  #重启不报错 
   message = 'pidfile %s does not exist. Daemon not running!\n'
   sys.stderr.write(message % self.pidfile) 
   return
  
   #杀进程 
  try: 
   while 1: 
    os.kill(pid, SIGTERM) 
    time.sleep(0.1) 
    #os.system('hadoop-daemon.sh stop datanode') 
    #os.system('hadoop-daemon.sh stop tasktracker') 
    #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): 
  self.stop() 
  self.start() 
  
 def _run(self): 
  """ run your fun"""
  while True: 
   #fp=open('/tmp/result','a+') 
   #fp.write('Hello World\n') 
   sys.stdout.write('%s:hello world\n' % (time.ctime(),)) 
   sys.stdout.flush()  
   time.sleep(2) 
    
  
if __name__ == '__main__': 
  daemon = Daemon('/tmp/watch_process.pid', stdout = '/tmp/watch_stdout.log') 
  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)

class MyDaemon(Daemon):
  def run(self):
    while True:
      fp=open('/tmp/run.log','a+')
      fp.write('Hello World\n')
      time.sleep(1)

#/bin/sh
while true
do
 count=`ps -ef | grep "daemonclass.py" | grep -v "grep"`
 if [ "$?" != "0" ]; then
   daemonclass.py start
 fi
 sleep 2
done

#!/usr/bin/env python
#coding: utf-8
import fcntl, sys, time, os
pidfile = 0
  
def ApplicationInstance():
  global pidfile
  pidfile = open(os.path.realpath(__file__), "r")
  try:
    fcntl.flock(pidfile, fcntl.LOCK_EX | fcntl.LOCK_NB) #创建一个排他锁,并且所被锁住其他进程不会阻塞
  except:
    print "another instance is running..."
    sys.exit(1)
  
if __name__ == "__main__":
  ApplicationInstance()
  while True:
    print 'running...'
    time.sleep(1)

#!/usr/bin/env python
#coding: utf-8
import fcntl, sys, time
pidfile = 0
  
def ApplicationInstance():
  global pidfile
  pidfile = open("instance.pid", "w")
  try:
    fcntl.lockf(pidfile, fcntl.LOCK_EX | fcntl.LOCK_NB) #创建一个排他锁,并且所被锁住其他进程不会阻塞
  except IOError:
    print "another instance is running..."
    sys.exit(0)
  
if __name__ == "__main__":
  ApplicationInstance()
  while True:
    print 'running...'
    time.sleep(1)

#!/usr/bin/env python
#coding: utf-8
import time, os, sys
import signal
  
pidfile = '/tmp/process.pid'
  
def sig_handler(sig, frame):
  if os.path.exists(pidfile):
    os.remove(pidfile)
  sys.exit(0)
  
def ApplicationInstance():
  signal.signal(signal.SIGTERM, sig_handler)
  signal.signal(signal.SIGINT, sig_handler)
  signal.signal(signal.SIGQUIT, sig_handler)
  
  try:
   pf = file(pidfile, 'r')
   pid = int(pf.read().strip())
   pf.close()
  except IOError:
   pid = None
   
  if pid:
   sys.stdout.write('instance is running...\n')
   sys.exit(0)
  
  file(pidfile, 'w+').write('%s\n' % os.getpid())
  
if __name__ == "__main__":
  ApplicationInstance()
  while True:
    print 'running...'
    time.sleep(1)

#!/usr/bin/env python
#coding: utf-8
import time, commands, signal, sys
  
def sig_handler(sig, frame):
  if os.path.exists("/tmp/test"):
    os.rmdir("/tmp/test")
  sys.exit(0)
  
def ApplicationInstance():
  signal.signal(signal.SIGTERM, sig_handler)
  signal.signal(signal.SIGINT, sig_handler)
  signal.signal(signal.SIGQUIT, sig_handler)
  if commands.getstatusoutput("mkdir /tmp/test")[0]:
    print "instance is running..."
    sys.exit(0)
  
if __name__ == "__main__":
  ApplicationInstance()
  while True:
    print 'running...'
    time.sleep(1)

import os
import os.path
import time
   
   
#class used to handle one application instance mechanism
class ApplicationInstance:
   
  #specify the file used to save the application instance pid
  def __init__( self, pid_file ):
    self.pid_file = pid_file
    self.check()
    self.startApplication()
   
  #check if the current application is already running
  def check( self ):
    #check if the pidfile exists
    if not os.path.isfile( self.pid_file ):
      return
    #read the pid from the file
    pid = 0
    try:
      file = open( self.pid_file, 'rt' )
      data = file.read()
      file.close()
      pid = int( data )
    except:
      pass
    #check if the process with specified by pid exists
    if 0 == pid:
      return
   
    try:
      os.kill( pid, 0 )  #this will raise an exception if the pid is not valid
    except:
      return
   
    #exit the application
    print "The application is already running..."
    exit(0) #exit raise an exception so don't put it in a try/except block
   
  #called when the single instance starts to save it's pid
  def startApplication( self ):
    file = open( self.pid_file, 'wt' )
    file.write( str( os.getpid() ) )
    file.close()
   
  #called when the single instance exit ( remove pid file )
  def exitApplication( self ):
    try:
      os.remove( self.pid_file )
    except:
      pass
   
   
if __name__ == '__main__':
  #create application instance
  appInstance = ApplicationInstance( '/tmp/myapp.pid' )
   
  #do something here
  print "Start MyApp"
  time.sleep(5)  #sleep 5 seconds
  print "End MyApp"
   
  #remove pid file
  appInstance.exitApplication()

#!/usr/bin/env python
#coding: utf-8
import socket, time, sys
  
  
def ApplicationInstance():
  try:  
    global s
    s = socket.socket()
    host = socket.gethostname()
    s.bind((host, 60123))
  except:
    print "instance is running..."
    sys.exit(0)
  
if __name__ == "__main__":
  ApplicationInstance()
  while True:
    print 'running...'
    time.sleep(1)

#!/usr/bin/env python
#coding: utf-8
import socket, time, sys
import functools
  
#使用装饰器实现
def ApplicationInstance(func):
  @functools.wraps(func)
  def fun(*args,**kwargs):
    import socket
    try:
      global s
      s = socket.socket()
      host = socket.gethostname()
      s.bind((host, 60123))
    except:
      print('already has an instance...')
      return None
    return func(*args,**kwargs)
  return fun
  
@ApplicationInstance
def main():
  while True:
    print 'running...'
    time.sleep(1)
  
if __name__ == "__main__":
  main()