Queue

Tornado的tornado.queue模塊為基于協(xié)程的應(yīng)用程序?qū)崿F(xiàn)了一個(gè)異步生產(chǎn)者/消費(fèi)者模式的隊(duì)列。這與python標(biāo)準(zhǔn)庫為多線程環(huán)境實(shí)現(xiàn)的queue模塊類似。

一個(gè)協(xié)程執(zhí)行到y(tǒng)ieldqueue.get會(huì)暫停，直到隊(duì)列中有條目。如果queue有上限，一個(gè)協(xié)程執(zhí)行yieldqueue.put將會(huì)暫停，直到隊(duì)列中有空閑的位置。

在一個(gè)queue內(nèi)部維護(hù)了一個(gè)未完成任務(wù)的引用計(jì)數(shù)，每調(diào)用一次put操作便會(huì)增加引用計(jì)數(shù)，而調(diào)用task_done操作將會(huì)減少引用計(jì)數(shù)。

下面是一個(gè)簡單的web爬蟲的例子：

最開始，queue只包含一個(gè)基準(zhǔn)url。當(dāng)一個(gè)worker從中取出一個(gè)url后，它會(huì)從對應(yīng)的頁面中解析中所包含的url并將其放入隊(duì)列，然后調(diào)用task_done減少引用計(jì)數(shù)一次。

最后，worker會(huì)取出一個(gè)url，而這個(gè)url頁面中的所有url都已經(jīng)被處理過了，這時(shí)隊(duì)列中也沒有url了。這時(shí)調(diào)用task_done會(huì)將引用計(jì)數(shù)減少至0.

這樣,在main協(xié)程里，join操作將會(huì)解除掛起并結(jié)束主協(xié)程。

這個(gè)爬蟲使用了HTMLParse來解析html頁面。

import timefrom datetime import timedeltatry: from HTMLParser import HTMLParser from urlparse import urljoin, urldefragexcept ImportError: from html.parser import HTMLParser from urllib.parse import urljoin, urldefragfrom tornado import httpclient, gen, ioloop, queuesbase_url = 'http://www.tornadoweb.org/en/stable/'concurrency = 10@gen.coroutinedef get_links_from_url(url): """Download the page at `url` and parse it for links. Returned links have had the fragment after `#` removed, and have been made absolute so, e.g. the URL 'gen.html#tornado.gen.coroutine' becomes 'http://www.tornadoweb.org/en/stable/gen.html'. """ try:  response = yield httpclient.AsyncHTTPClient().fetch(url)  print('fetched %s' % url)  html = response.body if isinstance(response.body, str) /   else response.body.decode()  urls = [urljoin(url, remove_fragment(new_url))    for new_url in get_links(html)] except Exception as e:  print('Exception: %s %s' % (e, url))  raise gen.Return([]) raise gen.Return(urls)#用于從一個(gè)包含片段的url中提取中真正的url.def remove_fragment(url):   pure_url, frag = urldefrag(url) return pure_urldef get_links(html): class URLSeeker(HTMLParser):  def __init__(self):   HTMLParser.__init__(self)   self.urls = []	#從所有a標(biāo)簽中提取中href屬性。  def handle_starttag(self, tag, attrs):   href = dict(attrs).get('href')   if href and tag == 'a':    self.urls.append(href) url_seeker = URLSeeker() url_seeker.feed(html) return url_seeker.urls@gen.coroutinedef main(): q = queues.Queue() start = time.time() fetching, fetched = set(), set() @gen.coroutine def fetch_url():  current_url = yield q.get()  try:   if current_url in fetching:    return   print('fetching %s' % current_url)   fetching.add(current_url)   urls = yield get_links_from_url(current_url)   fetched.add(current_url)   for new_url in urls:    # Only follow links beneath the base URL    if new_url.startswith(base_url):     yield q.put(new_url)  finally:   q.task_done() @gen.coroutine def worker():  while True:   yield fetch_url() q.put(base_url) # Start workers, then wait for the work queue to be empty. for _ in range(concurrency):  worker() yield q.join(timeout=timedelta(seconds=300)) assert fetching == fetched print('Done in %d seconds, fetched %s URLs.' % (  time.time() - start, len(fetched)))if __name__ == '__main__': import logging logging.basicConfig() io_loop = ioloop.IOLoop.current() io_loop.run_sync(main)