demeter/demeter/daemon.py

# -*- coding: utf-8 -*-
import os
import sys
import time
import atexit
import signal
  
  
class Daemon(object):
  def __init__(self, pidfile='/tmp/daemon.pid', stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'):
    self.stdin = stdin
    self.stdout = stdout
    self.stderr = stderr
    self.pidfile = pidfile
  
  def daemonize(self):
    if os.path.exists(self.pidfile):
      raise RuntimeError('Already running.')
  
    # First fork (detaches from parent)
    try:
      if os.fork() > 0:
        raise SystemExit(0)
    except OSError as e:
      raise RuntimeError('fork #1 faild: {0} ({1})\n'.format(e.errno, e.strerror))
  
    os.chdir('/')
    os.setsid()
    os.umask(0o22)
  
    # Second fork (relinquish session leadership)
    try:
      if os.fork() > 0:
        raise SystemExit(0)
    except OSError as e:
      raise RuntimeError('fork #2 faild: {0} ({1})\n'.format(e.errno, e.strerror))
  
    # Flush I/O buffers
    sys.stdout.flush()
    sys.stderr.flush()
  
    # Replace file descriptors for stdin, stdout, and stderr
    with open(self.stdin, 'rb', 0) as f:
      os.dup2(f.fileno(), sys.stdin.fileno())
    with open(self.stdout, 'ab', 0) as f:
      os.dup2(f.fileno(), sys.stdout.fileno())
    with open(self.stderr, 'ab', 0) as f:
      os.dup2(f.fileno(), sys.stderr.fileno())
  
    # Write the PID file
    with open(self.pidfile, 'w') as f:
      print(os.getpid(), file=f)
  
    # Arrange to have the PID file removed on exit/signal
    atexit.register(lambda: os.remove(self.pidfile))
  
    signal.signal(signal.SIGTERM, self.__sigterm_handler)
  
  # Signal handler for termination (required)
  @staticmethod
  def __sigterm_handler(signo, frame):
    raise SystemExit(1)
  
  def start(self):
    try:
      self.daemonize()
    except RuntimeError as e:
      print(e, file=sys.stderr)
      raise SystemExit(1)
  
    self.run()
  
  def stop(self):
    try:
      if os.path.exists(self.pidfile):
        with open(self.pidfile) as f:
          os.kill(int(f.read()), signal.SIGTERM)
      else:
        print('Not running.', file=sys.stderr)
        raise SystemExit(1)
    except OSError as e:
      if 'No such process' in str(e) and os.path.exists(self.pidfile):
        os.remove(self.pidfile)
  
  def restart(self):
    self.stop()
    self.start()
  
  def run(self):
  #继承类重写该方法
    pass