python 如何优雅地退出子进程

主进程产生子进程，子进程进入永久循环模式。当主进程要求子进程退出时，如何能安全地退出子进程呢？

参考一些代码，我写了这个例子。运行之后，用kill pid试试。pid是主进程的pid。当然子进程的也没问题。

1）如果kill pid为子进程的pid，当所有子进程都kill掉了，主进程就关闭了。这也是我们想要的结果。

2）如果kill pid为主进程的pid，主进程向子进程发送退出信号，然后等全部子进程关闭后退出。

保证了主进程在所有子进程退出之后退出。

#!/usr/bin/python2.7
#-*- coding: UTF-8 -*-
# graceful_exit_event.py
#   UTF-8 without BOM
#
# refer:
#   http://stackoverflow.com/questions/26414704/how-does-a-python-process-exit-gracefully-after-receiving-sigterm-while-waiting?rq=1
#
# init created: 2016-07-13
# last updated: 2016-07-13
#
#######################################################################
import os, sys, signal, time, multiprocessing


class GracefulExitException(Exception):
    pass


def signal_handler(signum, frame):
    raise GracefulExitException()


class GracefulExitEvent(object):
    def __init__(self, num_workers):
        self.exit_event = multiprocessing.Event()
        pass

    def is_stop(self):
        return self.exit_event.is_set()

    def notify_stop(self):
        self.exit_event.set()


def worker_proc(gee):
    print "worker(%d) start ..." % os.getpid()
    try:
        while not gee.is_stop():
            # do task job here
            print ".",
            time.sleep(1)
        else:
            print ""
            print "worker process(%d) got exit event." % os.getpid()
            print "worker process(%d) do cleanup..." % os.getpid()
            time.sleep(1)
            print "[%d] 3" % os.getpid()
            time.sleep(1)
            print "[%d] 2" % os.getpid()
            time.sleep(1)
            print "[%d] 1" % os.getpid()

    except GracefulExitException:
        print "worker(%d) got GracefulExitException" % os.getpid()
    finally:
        print "worker(%d) exit." % os.getpid()
        sys.exit(0)


#######################################################################
if __name__ == "__main__":
    print "main process(%d) start" % os.getpid()

    # Use signal handler to throw exception which can be caught
    # by worker process to allow graceful exit.
    signal.signal(signal.SIGTERM, signal_handler)
    
    gee = GracefulExitEvent(1)

    # Start some workers process and run forever
    workers = []

    for i in range(0, 10):
        wp = multiprocessing.Process(target=worker_proc, args=(gee,))
        wp.start()
        workers.append(wp)

    try:
        for wp in workers:
            wp.join()
    except GracefulExitException:
        print "main process(%d) got GracefulExitException" % os.getpid()
        gee.notify_stop()

        for wp in workers:
            wp.join()
        pass

    # last message
    print "main process(%d) exit." % os.getpid()
    sys.exit(0)