Tornado使用-队列Queue

1.tornado队列的特点
和python标准队列queue相比，tornado的队列Queue支持异步

2.Queue常用方法
Queue.get()
会暂停，直到queue中有元素

Queue.put()
对有最大长度限制的队列，会暂停，直到队列有空闲空间

Queue.task_done()
对每一个get元素，紧接着调用task_done()，表示这个任务执行完毕

Queue.join()
等待，直到所有任务都执行完毕，即所有元素都调用了task_done()

3.示例
给出一个地址http://www.tornadoweb.org/en/stable/，分析页面中所有以这个url为前缀的链接，
并依次访问，解析，直到找出所有的url

  1 #!/usr/bin/env python
  2 
  3 import time
  4 from datetime import timedelta
  5 
  6 try:
  7     from HTMLParser import HTMLParser
  8     from urlparse import urljoin, urldefrag
  9 except ImportError:
 10     from html.parser import HTMLParser
 11     from urllib.parse import urljoin, urldefrag
 12 
 13 from tornado import httpclient, gen, ioloop, queues
 14 
 15 base_url = 'http://www.tornadoweb.org/en/stable/'
 16 concurrency = 10
 17 
 18 
 19 @gen.coroutine
 20 def get_links_from_url(url):
 21     """Download the page at `url` and parse it for links.
 22 
 23     Returned links have had the fragment after `#` removed, and have been made
 24     absolute so, e.g. the URL 'gen.html#tornado.gen.coroutine' becomes
 25     'http://www.tornadoweb.org/en/stable/gen.html'.
 26     """
 27     try:
 28         response = yield httpclient.AsyncHTTPClient().fetch(url)
 29         print('fetched %s' % url)
 30 
 31         html = response.body if isinstance(response.body, str) \
 32             else response.body.decode()
 33         urls = [urljoin(url, remove_fragment(new_url))
 34                 for new_url in get_links(html)]
 35     except Exception as e:
 36         print('Exception: %s %s' % (e, url))
 37         raise gen.Return([])
 38 
 39     raise gen.Return(urls)
 40 
 41 
 42 def remove_fragment(url):
 43     pure_url, frag = urldefrag(url)
 44     return pure_url
 45 
 46 
 47 def get_links(html):
 48     class URLSeeker(HTMLParser):
 49         def __init__(self):
 50             HTMLParser.__init__(self)
 51             self.urls = []
 52 
 53         def handle_starttag(self, tag, attrs):
 54             href = dict(attrs).get('href')
 55             if href and tag == 'a':
 56                 self.urls.append(href)
 57 
 58     url_seeker = URLSeeker()
 59     url_seeker.feed(html)
 60     return url_seeker.urls
 61 
 62 
 63 @gen.coroutine
 64 def main():
 65     q = queues.Queue()
 66     start = time.time()
 67     fetching, fetched = set(), set()
 68 
 69     @gen.coroutine
 70     def fetch_url():
 71         current_url = yield q.get()
 72         try:
 73             if current_url in fetching:
 74                 return
 75 
 76             print('fetching %s' % current_url)
 77             fetching.add(current_url)
 78             urls = yield get_links_from_url(current_url)
 79             fetched.add(current_url)
 80 
 81             for new_url in urls:
 82                 # Only follow links beneath the base URL
 83                 if new_url.startswith(base_url):
 84                     yield q.put(new_url)
 85 
 86         finally:
 87             q.task_done()
 88 
 89     @gen.coroutine
 90     def worker():
 91         while True:
 92             yield fetch_url()
 93 
 94     q.put(base_url)
 95 
 96     # Start workers, then wait for the work queue to be empty.
 97     for _ in range(concurrency):
 98         worker()
 99     yield q.join(timeout=timedelta(seconds=300))
100     assert fetching == fetched
101     print('Done in %d seconds, fetched %s URLs.' % (
102         time.time() - start, len(fetched)))
103 
104 
105 if __name__ == '__main__':
106     import logging
107     logging.basicConfig()
108     io_loop = ioloop.IOLoop.current()
109     io_loop.run_sync(main)

posted on 2020-12-22 09:50 画入新雪阅读(451) 评论(0) 编辑收藏举报