多线程冻结

Question

我对以下代码有一点问题：

def getTextFromURL(url):
    req = pycurl.Curl()
    print "URL: "+ str(url)
    req.setopt(pycurl.URL, url)
    req.setopt(pycurl.HTTPHEADER, ["Accept:"])
    req.setopt(pycurl.CONNECTTIMEOUT, 5)
    req.setopt(pycurl.TIMEOUT, 10)
    req.setopt(pycurl.NOSIGNAL, 1)
    resultStream = StringIO.StringIO()
    req.setopt(pycurl.WRITEFUNCTION, resultStream.write)
    try: 
        req.perform()
        text = BeautifulSoup(resultStream.getvalue()).get_text()
        return text
    except BaseException as e:
        print type(e)
        return ''

def addTextToTask(newTask):
    newTask.fullText = getTextFromURL(newTask.url)
    return newTask


def createTasks(sources):
    newTasks = []
    for source in sources:
        newTask = models.Task(title = source.title, url = source.url, fullText = None)
        newTasks.append(newTask)
    pool = Pool(4)
    fullTasks = pool.map(addTextToTask, newTasks)
    pool.close()
    pool.join() 
    for fullTask in fullTasks:
        db.session.add(fullTask)
    db.session.commit()
    return True

当我调用createTasks（） - 函数时，它工作正常，少于100个源。如果我用超过100个来源调用它，它开始变慢并最终冻结。我没有收到任何错误消息。