#!/usr/bin/env python

#-*- coding:utf8 -*-

# Copyright 2007 Doug Hellmann.

#

#

# All Rights Reserved

#

# Permission to use, copy, modify, and distribute this software and

# its documentation for any purpose and without fee is hereby

# granted, provided that the above copyright notice appear in all

# copies and that both that copyright notice and this permission

# notice appear in supporting documentation, and that the name of Doug

# Hellmann not be used in advertising or publicity pertaining to

# distribution of the software without specific, written prior

# permission.

#

# DOUG HELLMANN DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,

# INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN

# NO EVENT SHALL DOUG HELLMANN BE LIABLE FOR ANY SPECIAL, INDIRECT OR

# CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS

# OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,

# NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN

# CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

#

"""Fork, then send the child process a signal.

"""

__module_id__ = "$Id$"

#end_pymotw_header

import os

import signal

import time

def signal_usr1(signum, frame):

"Callback invoked when a signal is received"

pid = os.getpid()

print 'Received USR1 in process %s' % pid

print 'Forking...'

child_pid = os.fork() #子进程ID

if child_pid: #父进程

print 'PARENT: Pausing before sending signal...'

time.sleep(1)

print 'PARENT: Signaling %s' % child_pid

os.kill(child_pid, signal.SIGUSR1)

else:#子继承

print 'CHILD: Setting up signal handler'

signal.signal(signal.SIGUSR1, signal_usr1) #此处不会阻塞

print 'CHILD: Pausing to wait for signal'

time.sleep(5)

# Forking...

# PARENT: Pausing before sending signal...

# CHILD: Setting up signal handler

# CHILD: Pausing to wait for signal

# PARENT: Signaling 38700

# Received USR1 in process 38700