Source code for freezer_dr.common.daemon

#!/usr/bin/env python
"""Generic deamon."""
# (c) Copyright 2016 Hewlett-Packard Development Company, L.P.
#
# Licensed 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.

from __future__ import print_function

import atexit
import logging as log
import os
import sys
import time

from signal import SIGTERM


class Daemon(object):

    """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'):
        """Instantiantion."""
        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 as e:
            sys.stderr.write("fork #1 failed: %d (%s)\n" %
                             (e.errno, e.strerror))
            log.error(e)
            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 e:
            sys.stderr.write("fork #2 failed: %d (%s)\n"
                             % (e.errno, e.strerror))
            log.error(e)
            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())
        f = file(self.pidfile, 'w+')
        f.write("%s\n" % pid)
        f.close()

    def delpid(self):
        """Delete PID file."""
        os.remove(self.pidfile)

    def start(self):
        """Start the daemon."""
        log.error("Test")
        # 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
        self.daemonize()
        self.run()

    # @todo needs some enhancement like check /proc/%pid/status if it's
    # really running or not ! may be it's killed by external process
    # the PID won't be updated !
    def status(self):
        """Check daemon status."""
        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. PID: %d \n"
            sys.stdout.write(message % (self.pidfile, pid))
            sys.exit(0)
        else:
            message = "Service not running!\n"
            sys.stdout.write(message)
            sys.exit(0)

    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

        # Try killing the daemon process
        try:
            while 1:
                os.kill(pid, SIGTERM)
                time.sleep(0.1)
        except OSError as 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().
        """