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Date: Thu, 03 Oct 2013 19:25:46 +0100
From: MRAB <python@mrabarnett.plus.com>
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To: python-list@python.org
Subject: Re: Why didn't my threads exit correctly ?
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On 03/10/2013 18:37, 李洛 wrote:
> Hi list,
> I write an example script using threading as follow.
> It look like hang when the list l_ip is empty. And any suggestion with
> debug over the threading in Python ?
>
>    1 #!/usr/bin/env python
>    2 # -*- coding: utf-8 -*-
>    3 import re
>    4 import os
>    5 import threading
>    6 from Queue import Queue
>    7 from time import sleep
>    8
>    9 l_ip = []
>   10 l_result = []
>   11 result = re.compile(r"[1-3] received")
>   12
>   13 class ping(threading.Thread):
>   14     """ """
>   15     def __init__(self, l_ip, l_result):
>   16         threading.Thread.__init__(self)
>   17         self.l_ip = l_ip
>   18         #self.l_result = l_result
>   19
>   20     def run(self):
>   21         """ """
>   22         while True:
>   23             try:
>   24                 ip = self.l_ip.pop()
>   25             except IndexError as e:
>   26                 print e
>   27                 break
>   28             ping_out = os.popen(''.join(['ping -q -c3 ',ip]), 'r')
>   29             print 'Ping ip:%s' % ip
>   30             while True:
>   31                 line = ping_out.readline()
>   32                 if not line: break
>   33                 if result.findall(line):
>   34                     l_result.append(ip)
>   35                     break
>   36
>   37 queue = Queue()
>   38
>   39 for i in range(1,110):
>   40     l_ip.append(''.join(['192.168.1.', str(i)]))
>   41 for i in xrange(10):
>   42     t = ping(l_ip, l_result)
>   43     t.start()
>   44     queue.put(t)
>   45 queue.join()
>   46 print "Result will go here."
>   47 for i in l_result:
>   48     print 'IP %s is OK' % i
>
queue.join() will block until the queue is empty, which is never is!

You're putting the workers in the queue, whereas the normal way of
doing it is to put them into a list, the inputs into a queue, and the
outputs into another queue. The workers then 'get' from the input
queue, do some processing, and 'put' to the output queue.