线程池Queue的有关问题

#coding=utf-8
from __future__ import with_statement
from BeautifulSoup import BeautifulSoup
import urllib2
from threading import Thread
from Queue import Queue
import time
import socket
socket.setdefaulttimeout(5)

class Fetcher:#把操作封到一个类里面，从网上搜得例子
    def __init__(self,th_num):
        self.opener = urllib2.build_opener(urllib2.HTTPHandler)
        self.lock = Lock() #线程锁
        self.q_req = Queue() #任务队列
        self.q_ans = Queue() #完成队列
        self.urls = []#返回抓取页面中的url
        self.th_num = th_num
        for i in range(th_num):#抓取线程
            t = Thread(target=self.thread_get)
            t.setDaemon(True)
            t.start()
        for i in range(th_num):#处理线程
            t = Thread(target=self.thread_put)
            t.setDaemon(True)
            t.start()
        
 
    def join(self): #解构时需等待两个队列完成
        time.sleep(0.5)
        print '=====================im done'
        self.q_req.join()
        self.q_ans.join()
 
    def push(self,req):
        self.q_req.put(req)
    
    def thread_put(self):
        while True:
            try:
                if not self.q_ans.empty():
                    url = self.q_ans.get()
                    self.urls.extend(url)
                    self.q_ans.task_done()
            except Queue.empty,qe:
                print qe,'Queue=========='
                continue
            except Exception ,e:
                print e,'other,excp========'
                continue

    def thread_get(self):
        print 'i am starting------'
        while  True:
            try:
                if self.q_req.empty():
                    continue
                req = self.q_req.get()
            except Queue.empty,qe:
                print 'enmpty-----------'
                continue
            urls = []
            ans = ''
            try:
                ans = self.opener.open(req).read()
                soup = BeautifulSoup(ans)
                for a in soup.findAll('a'):
                    try:
                        if a['href'].startswith('http'):
                            urls.append(a['href'])
                    except KeyError, e:
                        print e ,'=======================KeyError=in=soup=findAll'
                        continue
                    except Exception,ex:
                        print ex,'========================Exception=in=soup=findAll'
                        continue   
                self.q_ans.put(urls)
                self.q_req.task_done()                
            except UnicodeEncodeError, ue:
                print 'unicode----------------------wrong'
                print ue
                print req
                continue
            except urllib2.URLError, ue:
                print 'conn-----------rufuse'
                print ue
                print req
                continue
            except Exception, what:
                print 'other--exception----------in- threadget----'
                print what
                print req
                continue
            time.sleep(0.1) # don't spam
        print 'get=========='
 
def run(links,th_num=10):
    f = Fetcher(th_num)
    for url in links:
        f.push(url)
    f.join()
    return f.urls 

if __name__ == "__main__":
    links = ['http://kingdowin.com/',]
    deep = 2#抓取页面的深度
    while deep > 0:
        urls = run(links)
        deep -= 1
        links = urls
        print links
    print "Exiting Main Thread"