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。

#-*- 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
#   http://www.cnblogs.com/kaituorensheng/p/4445418.html
# init created: 2016-07-13
# last updated: 2016-07-14
#
#######################################################################
import os
import signal
import multiprocessing


class GracefulExitException(Exception):
    @staticmethod
    def sigterm_handler(signum, frame):
        raise GracefulExitException()
    pass


class GracefulExitEvent(object):
    def __init__(self):
        self.workers = []
        self.exit_event = multiprocessing.Event()

        # Use signal handler to throw exception which can be caught
        # by worker process to allow graceful exit.
        signal.signal(signal.SIGTERM, GracefulExitException.sigterm_handler)
        pass

    def reg_worker(self, wp):
        self.workers.append(wp)
        pass

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

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

    def wait_all(self):
        while True:
            try:
                for wp in self.workers:
                    wp.join()

                print "main process(%d) exit." % os.getpid()
                break
            except GracefulExitException:
                self.notify_stop()
                print "main process(%d) got GracefulExitException." % os.getpid()
            except Exception, ex:
                self.notify_stop()
                print "main process(%d) got unexpected Exception: %r" % (os.getpid(), ex)                
                break
        pass


#######################################################################
def worker_proc(gee):
    import sys, time
    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()
    except Exception, ex:
        print "Exception:", ex
    finally:
        print "worker(%d) exit." % os.getpid()
        sys.exit(0)


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

    gee = GracefulExitEvent()

    # Start some workers process and run forever
    for i in range(0, 10):
        wp = multiprocessing.Process(target=worker_proc, args=(gee,))
        wp.start()
        gee.reg_worker(wp)

    gee.wait_all()
    sys.exit(0)

需要说明的是：

如果某个进程接受 kill pid，必须在该进程函数的最外层捕获： except GracefulExitException，

同时该进程函数内部调用捕获了 except Excetion，则必须在之前捕获GracefulExitException，

即：

      (2) 必须在(3)之前。否则同时去掉(2)和(3)。

def do_some_func():
    try:
        time.sleep(10)

        blablabla

    (1) except SomeError:
        # 捕获特定的异常
        pass

    (2) except GracefulExitException:
        # 接收 kill pid
        pass

    (3) except:  # 不建议捕获默认异常, 否则必须在此之前捕获：GracefulExitException
        pass



def some_process_main(gee):

    try:

        while not gee.is_stop():
            do_some_func()

    except GracefulExitException:
        # 接收到了 kill pid, 设置中止循环
        gee.notify_stop()
        pass
    except:
        pass