多线程的小爬虫，测试后发现有三条内容重复了 40 多次？

import requests
from bs4 import BeautifulSoup
import threading

url_num = 0
url_list = ['http://ubuntuforums.org/forumdisplay.php?f=333',]
for x in range(1, 50):
    url_num += 1
    raw_url = 'http://ubuntuforums.org/forumdisplay.php?f=333&page=%d' % url_num
    url_list.append(raw_url)

class MyThread(threading.Thread):
    def __init__(self, func, args, name=""):
        threading.Thread.__init__(self)
        self.func = func
        self.args = args
        self.name = name
    def run(self):
        apply(self.func, self.args)

def running(url):
    # lock.acquire()
    html = requests.get(url)
    if html.status_code == 200:
        html_text = html.text

    soup = BeautifulSoup(html_text)
    with open('/home/zhg/Pictures/cao.txt', 'a+') as f:
        for link in soup.find_all('a', 'title'):
            s = 'http://ubuntuforums.org/' + str(link.get('href')) + ' ' + str(link.get_text().encode('utf-8'))
            f.writelines(s)
            f.writelines('\n')
    # lock.release()

if __name__ == '__main__':
    thread_list = [ MyThread(running, (url, ), running.__name__) for url in url_list ]
    for t in thread_list:
        t.setDaemon(True)
        t.start()
    for i in thread_list:
        i.join()
    print "process ended"

    with open('/home/zhg/Pictures/cao.txt', 'r') as f:
        f_list = f.readlines()
        set_list = set(f_list)
    for x in set_list:
        if f_list.count(x) > 1:
            print "the <%s> has found <%d>" % (x, f_list.count(x))

而且如何加锁的话运行速率和直接用for循环不用多线程一样，这是为什么？

---

额，这个问题解决了，问题留着给其他人参考。
数据在存储到文件之前没有去重复，而爬数据的网页上有置顶的文章，所以爬了50多页，三条置顶的文章出现了40多次。
我还以为是没加锁的关系。