为什么asyncio的run_in_executor阻止龙卷风的get处理程序？

Question

我想在龙卷风的异步GET请求处理程序中运行一个缓慢的阻止方法（实际上是从第三方库中）。将该方法设为：

def blocking_method(uid):
    print("slow method started: ", uid)
    time.sleep(10)
    print("slow method done: ", uid)
    return "slow method ({}) result".format(uid)

此外，我更喜欢在asyncio的事件循环中运行龙卷风服务器：

if __name__ == '__main__':
    tornado.platform.asyncio.AsyncIOMainLoop().install()
    loop = asyncio.get_event_loop()
    loop.run_until_complete(make_app())
    loop.run_forever()

我知道@run_in_executor装饰器，但是它不适合我，因为我使用asyncio。要在异步协程中运行阻止方法，应使用的run_in_executor方法asyncio.get_event_loop()。这是一个示例，如何从此答案中做到这一点：

import asyncio

async def main():
    loop = asyncio.get_event_loop()
    executor = concurrent.futures.ThreadPoolExecutor(max_workers=4)
    future1 = loop.run_in_executor(executor, blocking_method, 1)
    future2 = loop.run_in_executor(executor, blocking_method, 2)
    response1 = await future1
    response2 = await future2
    print(response1)
    print(response2)

if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(main())

而且效果很好，这是先前脚本的输出：

slow method started:  1
slow method started:  2
slow method done:  2
slow method done:  1
slow method (1) result
slow method (2) result

但是，如果我在async def get龙卷风的RequestHandler方法中使用非常相同的技术：

class AsyncHandler(tornado.web.RequestHandler):

    async def get(self):
        #  simple counter to distinguish requests
        self.application.counter += 1
        in_msg = "Registered request #{}, working...".format(self.application.counter)
        print(in_msg)
        loop = asyncio.get_event_loop()
        future = loop.run_in_executor(self.application.executor,
                                      blocking_method,
                                      self.application.counter)
        result = await future
        out_msg = "Request processed, result: {}".format(result)
        print(out_msg)
        self.write(out_msg)

它阻止了处理程序的方法。换句话说，如果我http://localhost:8888/在多个浏览器选项卡中打开（让它为两个），那么我 希望两个请求并行运行，并显示以下输出：

Registered request #1, working...
slow method started:  1
Registered request #2, working...
slow method started:  2
slow method done:  1
Request processed, result: slow method (1) result
slow method done:  2
Request processed, result: slow method (2) result

但是请求因此被执行：

Registered request #1, working...
slow method started:  1
slow method done:  1
Request processed, result: slow method (1) result
Registered request #2, working...
slow method started:  2
slow method done:  2
Request processed, result: slow method (2) result

那么，我哪里错了？我应该怎么做才能允许并行执行请求处理程序？

这是描述我的问题的完整脚本：

import asyncio
import concurrent.futures
import time

import tornado.web
import tornado.platform


def blocking_method(uid):
    print("slow method started: ", uid)
    time.sleep(10)
    print("slow method done: ", uid)
    return "slow method ({}) result".format(uid)


class AsyncHandler(tornado.web.RequestHandler):

    async def get(self):
        #  simple counter to distinguish requests
        self.application.counter += 1
        in_msg = "Registered request #{}, working...".format(self.application.counter)
        print(in_msg)
        loop = asyncio.get_event_loop()
        future = loop.run_in_executor(self.application.executor,
                                      blocking_method,
                                      self.application.counter)
        result = await future
        out_msg = "Request processed, result: {}".format(result)
        print(out_msg)
        self.write(out_msg)

async def make_app():
    handlers = [(r"/", AsyncHandler)]
    app = tornado.web.Application(handlers, debug=True)
    app.executor = concurrent.futures.ThreadPoolExecutor(max_workers=4)
    app.counter = 0
    app.listen(8888)

if __name__ == '__main__':
    tornado.platform.asyncio.AsyncIOMainLoop().install()
    loop = asyncio.get_event_loop()
    loop.run_until_complete(make_app())
    loop.run_forever()

Answer 1

浏览器将识别出您正在尝试在两个不同的选项卡中加载同一页面，并将第二个请求延迟到第一个请求完成为止。

http://www.tornadoweb.org/en/latest/faq.html#why-isn-t-this-example-with-time-sleep-running-in-parallel

• 在您的网址中添加一些内容，以使其具有唯一性。而不是HTTP：//本地主机：8888在两个标签，负载的http：//本地主机：8888 / X = 1？在一个和HTTP：//本地主机：8888 / x = 2时的其他。
• 使用两种不同的浏览器。例如，即使在Chrome选项卡中加载了相同的URL，Firefox也将能够加载该URL。