摘要：譯者說于年月日發(fā)布，該版本正式支持的關(guān)鍵字，并且用舊版本編譯同樣可以使用這兩個(gè)關(guān)鍵字，這無疑是一種進(jìn)步。其次，這是最后一個(gè)支持和的版本了，在后續(xù)的版本了會(huì)移除對(duì)它們的兼容。

Tornado 4.3于2015年11月6日發(fā)布，該版本正式支持Python3.5的async/await關(guān)鍵字，并且用舊版本CPython編譯Tornado同樣可以使用這兩個(gè)關(guān)鍵字，這無疑是一種進(jìn)步。其次，這是最后一個(gè)支持Python2.6和Python3.2的版本了，在后續(xù)的版本了會(huì)移除對(duì)它們的兼容。現(xiàn)在網(wǎng)絡(luò)上還沒有Tornado4.3的中文文檔，所以為了讓更多的朋友能接觸并學(xué)習(xí)到它，我開始了這個(gè)翻譯項(xiàng)目，希望感興趣的小伙伴可以一起參與翻譯，項(xiàng)目地址是tornado-zh on Github，翻譯好的文檔在Read the Docs上直接可以看到。歡迎Issues or PR。

Tornado的 tornado.queues 模塊實(shí)現(xiàn)了異步生產(chǎn)者/消費(fèi)者模式的協(xié)程, 類似于通過Python 標(biāo)準(zhǔn)庫(kù)的 queue實(shí)現(xiàn)線程模式.

一個(gè)yield Queue.get 的協(xié)程直到隊(duì)列中有值的時(shí)候才會(huì)暫停. 如果隊(duì)列設(shè)置了最大長(zhǎng)度yield Queue.put 的協(xié)程直到隊(duì)列中有空間才會(huì)暫停.

一個(gè)Queue從0開始對(duì)完成的任務(wù)進(jìn)行計(jì)數(shù). Queue.put 加計(jì)數(shù);Queue.task_done減少計(jì)數(shù).

這里的網(wǎng)絡(luò)爬蟲的例子, 隊(duì)列開始的時(shí)候只包含base_url. 當(dāng)一個(gè)worker抓取到一個(gè)頁(yè)面它會(huì)解析鏈接并把它添加到隊(duì)列中, 然后調(diào)用Queue.task_done 減少計(jì)數(shù)一次. 最后, 當(dāng)一個(gè)worker抓取到的頁(yè)面URL都是之前抓取到過的并且隊(duì)列中沒有任務(wù)了.于是worker調(diào)用 Queue.task_done 把計(jì)數(shù)減到0. 等待 Queue.join 的主協(xié)程取消暫停并且完成.

    import time
    from datetime import timedelta
    
    try:
        from HTMLParser import HTMLParser
        from urlparse import urljoin, urldefrag
    except ImportError:
        from html.parser import HTMLParser
        from urllib.parse import urljoin, urldefrag
    
    from tornado import httpclient, gen, ioloop, queues
    
    base_url = "http://www.tornadoweb.org/en/stable/"
    concurrency = 10
    
    
    @gen.coroutine
    def 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)
    
    
    def remove_fragment(url):
        pure_url, frag = urldefrag(url)
        return pure_url
    
    
    def get_links(html):
        class URLSeeker(HTMLParser):
            def __init__(self):
                HTMLParser.__init__(self)
                self.urls = []
    
            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.coroutine
    def 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)