无法在龙卷风中对期货调用 result()

问题描述

我想使用 python 库 tornado(4.2 版)执行一些异步 HTTP 请求.但是我不能强制未来完成(使用 result())，因为我得到一个异常:DummyFuture 不支持结果阻塞".

I want to do some asynchronous HTTP-requests using the python library tornado (version 4.2). I can however not force a future to complete (using result()) since I get an Exception: "DummyFuture does not support blocking for results".

我有 python 3.4.3，因此未来的支持应该是标准库的一部分.concurrent.py 的文档说:

I have python 3.4.3 therefore future support should be part of the standard library. The documentation of concurrent.py says:

Tornado 将使用 concurrent.futures.Future(如果可用)；否则它将使用在此模块中定义的兼容类.

下面提供了我正在尝试做的最小示例:

A minimal example for what I am trying to do is provided below:

from tornado.httpclient import AsyncHTTPClient;

future = AsyncHTTPClient().fetch("http://google.com")
future.result()

如果我正确理解我的问题，它会发生，因为以某种方式没有使用 concurrent.futures.Future 的导入.tornado 中的相关代码似乎在 concurrent.py 中，但我在理解问题究竟出在哪里方面并没有真正取得进展.

If I understand my problem correctly it occurs because the import of concurrent.futures.Future somehow is not used. The relevant code in tornado appears to be in concurrent.py but I am not really making progress on understanding where exactly the problem lies.

推荐答案

尝试创建另一个Future并使用add_done_callback:

Try to create another Future and use add_done_callback:

来自 Tornado 文档

from tornado.concurrent import Future

def async_fetch_future(url):
    http_client = AsyncHTTPClient()
    my_future = Future()
    fetch_future = http_client.fetch(url)
    fetch_future.add_done_callback(
        lambda f: my_future.set_result(f.result()))
    return my_future

但是你仍然需要用ioloop解决未来，就像这样:

But you still need solve the future with the ioloop, like this:

# -*- coding: utf-8 -*-
from tornado.concurrent import Future
from tornado.httpclient import AsyncHTTPClient
from tornado.ioloop import IOLoop


def async_fetch_future():
    http_client = AsyncHTTPClient()
    my_future = Future()
    fetch_future = http_client.fetch('http://www.google.com')
    fetch_future.add_done_callback(
        lambda f: my_future.set_result(f.result()))
    return my_future

response = IOLoop.current().run_sync(async_fetch_future)

print(response.body)

另一种方法是使用 tornado.gen.coroutine 装饰器，如下所示:

Another way to this, is using tornado.gen.coroutinedecorator, like this:

# -*- coding: utf-8 -*-
from tornado.gen import coroutine
from tornado.httpclient import AsyncHTTPClient
from tornado.ioloop import IOLoop


@coroutine
def async_fetch_future():
    http_client = AsyncHTTPClient()
    fetch_result = yield http_client.fetch('http://www.google.com')
    return fetch_result

result = IOLoop.current().run_sync(async_fetch_future)

print(result.body)

coroutine 装饰器使函数返回一个 Future.

coroutine decorator causes the function to return a Future.

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