生产者消费者模式的多线程小爬虫， 写完后进程居然都没开始？？最后才发现pages队列太小。

def main():
    base_url = '/////////'
    pages = Queue(300)
    detail_pages = Queue(100000)
    imgs = Queue(100000)
    for x in range(0, 540):
        url = base_url.format(x)
        pages.put(url)
    for x in range(5):
        Producer(pages, detail_pages, imgs).start()
    for x in range(20):
        Producer_2(pages, detail_pages, imgs).start()
    for x in range(20):
        Consumer(pages, detail_pages, imgs).start()