Answer of www.zhihu.com/question/51772677

future-demo.py

from tornado import httpclient, gen, ioloop, concurrent

def fetch(urlList, minRequire):
    resultList = []

    @gen.coroutine
    def _fetch():
        fetchList = [httpclient.AsyncHTTPClient().fetch(url) for url in urlList]
        yieldList = [concurrent.Future() for i in range(minRequire)]
        def callback(f):
            for yieldFuture in yieldList:
                if not yieldFuture.done():
                    print('Fetcheded: %s' % f.result().effective_url)
                    yieldFuture.set_result(f.result().body)
                    break
        for fetchFuture in fetchList:
            fetchFuture.add_done_callback(callback)
        for yieldFuture in yieldList:
            r = yield yieldFuture
            resultList.append(r)
    ioloop.IOLoop.current().run_sync(_fetch)
    return resultList

if __name__ == '__main__':
    urlList = ['http://127.0.0.1:5000/%s' % i for i in range(5)]
    r = fetch(urlList, 3)
    print(r)