# -*- coding: utf-8 -*-
#
# Copyright (C) 2006 Edgewall Software
# All rights reserved.
#
# This software is licensed as described in the file COPYING, which
# you should have received as part of this distribution. The terms
# are also available at http://trac.edgewall.org/wiki/TracLicense.
#
# This software consists of voluntary contributions made by many
# individuals. For the exact contribution history, see the revision
# history and logs, available at http://trac.edgewall.org/log/.

import atexit
import errno
import os
import sys

def daemonize(pidfile=None, progname=None, stdin='/dev/null',
              stdout='/dev/null', stderr='/dev/null', umask=022):
    """Fork a daemon process."""

    if pidfile:
        # Check whether the pid file already exists and refers to a still
        # process running
        pidfile = os.path.abspath(pidfile)
        if os.path.exists(pidfile):
            fileobj = open(pidfile)
            try:
                try:
                    pid = int(fileobj.read())
                except ValueError:
                    sys.exit('Invalid PID in file %s' % pidfile)
            finally:
                fileobj.close()

            try: # signal the process to see if it is still running
                os.kill(pid, 0)
                if not progname:
                    progname = os.path.basename(sys.argv[0])
                sys.exit('%s is already running with pid %s' % (progname, pid))
            except OSError, e:
                if e.errno != errno.ESRCH:
                    raise

    # Perform first fork
    pid = os.fork()
    if pid > 0:
        sys.exit(0) # exit first parent

    # Decouple from parent environment
    os.chdir('/')
    os.umask(umask)
    os.setsid()

    # Perform second fork
    pid = os.fork()
    if pid > 0:
        sys.exit(0) # exit second parent

    # The process is now daemonized, redirect standard file descriptors
    for stream in sys.stdout, sys.stderr:
        stream.flush()
    stdin = open(stdin, 'r')
    stdout = open(stdout, 'a+')
    stderr = open(stderr, 'a+', 0)
    os.dup2(stdin.fileno(), sys.stdin.fileno())
    os.dup2(stdout.fileno(), sys.stdout.fileno())
    os.dup2(stderr.fileno(), sys.stderr.fileno())

    if pidfile:
        # Create/update the pid file, and register a hook to remove it when the
        # process exits
        fileobj = open(pidfile, 'w')
        try:
            fileobj.write(str(os.getpid()))
        finally:
            fileobj.close()
        def remove_pidfile():
            if os.path.exists(pidfile):
                   os.remove(pidfile)
        atexit.register(remove_pidfile)