Python:为什么一个进程即使在它完成了它的运行()之后也会保持活动。

Question

我有一个多处理程序，它启动了一组进程。这些程序的run()部分如下所示：

def run(self):
    self.prep()
    self._prn('Started with PID {pid}'.format(pid=self.pid))
    while True:
        job = self._queue.get()
        if job is None: break
        self.do_work(**job)
    self._prn('Received spindown signal.')

( _prn方法简单地将进程的名称放在前面，如下所示：)

def _prn(self, *args, **kwargs):
    print('{nam}({pid}):'.format(nam=self.name, pid=self.pid), end='')
    print(*args, **kwargs)

作业参数是通过将数据块推入队列发送的。

因此，在完成时，我将几个None推入队列中，然后看到这个过程--全部打印出Received spindown signal.。

然而，出于莫名其妙的原因，即使我看到一个进程已经发出了Received spindown signal消息，他们仍然活着！(也就是说，他们的.is_alive()方法一直在返回True)

这是我使用的轮询代码：

while len(workers) > 0:
    still_alives = []
    for w in workers:
        if w.is_alive():
            still_alives.append(w)
        else:
            prn('    {nam} trying to join...'.format(nam=w.name))
            w.join()
            prn('    {nam} joined.'.format(nam=w.name))
    prn('  Still alive:', ' '.join((w.name for w in still_alives)))
    workers = still_alives
    time.sleep(10)

这是我看到的输出的摘录：

Main:  Still alive: Querier-0 Querier-2 Querier-3 Querier-4 Querier-6 Querier-7 Querier-9 Querier-10
Querier-9:Received spindown signal.
Querier-4:Received spindown signal.
Main::    Querier-4 trying to join...
Main::    Querier-4 joined.
Main::    Querier-9 trying to join...
Main::    Querier-9 joined.
Main::  Still alive: Querier-0 Querier-2 Querier-3 Querier-6 Querier-7 Querier-10
Querier-3:Received spindown signal.
Querier-10:Received spindown signal.
Querier-6:Received spindown signal.
Main::  Still alive: Querier-0 Querier-2 Querier-3 Querier-6 Querier-7 Querier-10
Main::  Still alive: Querier-0 Querier-2 Querier-3 Querier-6 Querier-7 Querier-10
Querier-0:Received spindown signal.
Main::  Still alive: Querier-0 Querier-2 Querier-3 Querier-6 Querier-7 Querier-10
Main::  Still alive: Querier-0 Querier-2 Querier-3 Querier-6 Querier-7 Querier-10

如您所见，Querier-4和-9死得很好。但是Querier-3，-10，-6和-0从未死过！

这里发生什么事情？

Answer 1

尝试检查来自双方的队列；如果队列不是空的，则进程不会终止。

而且，在调试一些多处理问题时，我发现这个链接非常方便。