asfpy/daemon.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""
This is the standardized daemon library.
Usage example:
    import asfpy.daemon
    def main():
        print("hello world...")
    myprog = asfpy.daemon(main, pidfile = '/var/run/myprog.pid')
    myprog.start()
"""

import os
import sys
import atexit
import signal
import time

class Daemon:
    def __init__(self, main, pidfile = None, quiet = True):
        self.main = main
        if not pidfile:
            pidfile = sys.argv[0] if len(sys.argv) > 0 else 'generic_py'
            pidfile = "/var/run/%s.pid" % pidfile
        self.pidfile = pidfile
        self.quiet = quiet

    def daemonize(self):
        try:
            pid = os.fork()
            if pid > 0:
                # exit first parent
                sys.exit(0)
        except OSError as err:
            sys.stderr.write('fork #1 failed: {0}\n'.format(err))
            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 as err:
            sys.stderr.write('fork #2 failed: {0}\n'.format(err))
            sys.exit(1)

        # redirect standard file descriptors if need be
        if self.quiet:
            sys.stdout.flush()
            sys.stderr.flush()
            si = open(os.devnull, 'r')
            so = open(os.devnull, 'a+')
            se = open(os.devnull, 'a+')

            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())
        with open(self.pidfile,'w+') as f:
            f.write(pid + '\n')

    def delpid(self):
        os.remove(self.pidfile)

    def start(self, args = None):
        """Start the daemon."""

        # Check for a pidfile to see if the daemon already runs
        try:
            with open(self.pidfile,'r') as pf:

                pid = int(pf.read().strip())
        except IOError:
            pid = None

        if pid:
            message = "pidfile {0} already exist. " + \
                    "Daemon already running?\n"
            sys.stderr.write(message.format(self.pidfile))
            sys.exit(1)

        # Start the daemon
        self.daemonize()
        self.run(args)

    def stop(self):
        """Stop the daemon."""

        # Get the pid from the pidfile
        try:
            with open(self.pidfile,'r') as pf:
                pid = int(pf.read().strip())
        except IOError:
            pid = None

        if not pid:
            message = "pidfile {0} does not exist. " + \
                    "Daemon not running?\n"
            sys.stderr.write(message.format(self.pidfile))
            return # not an error in a restart

        # Try killing the daemon process
        print("Trying to kill")
        try:
            while 1:
                os.kill(pid, signal.SIGTERM)
                time.sleep(0.1)
        except OSError as err:
            e = str(err.args)
            if e.find("No such process") > 0:
                if os.path.exists(self.pidfile):
                    os.remove(self.pidfile)
            else:
                print (str(err.args))
                print("boo")
                sys.exit(1)
        print("killed")

    def restart(self):
        """Restart the daemon."""
        self.stop()
        self.start()

    def run(self, args = None):
        if args:
            self.main(args)
        else:
            self.main()