Question

我想在tornado的异步GET请求处理程序中运行一个慢速阻塞方法（实际上来自第三方库）。让方法只是：

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tornado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，但它不适合我，因为我使用asyncio。要在异步协同程序中运行阻止方法，我应该使用run_in_executor asyncio.get_event_loop()方法。以下是this答案：

的示例

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())

它完美无缺，这里是前一个脚本的输出：

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

但是如果我在龙卷风的RequestHandler的async def get方法中使用相同的技术：

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)

它会阻止处理程序的方法。换句话说，如果我在几个浏览器标签中打开http://localhost:8888/（让它为两个），那么我期望两个请求并行工作，输出如下：

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

但请求已执行因此：

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？我该怎么做才能允许并行执行请求处理程序？

以下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

浏览器会识别您正在尝试在两个不同的标签页中加载相同的页面，并将第二个请求延迟到第一个请求完成。

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

在您的网址上添加一些内容，使其独一无二。在两个标签中代替http://localhost:8888，而在一个标签中加载http://localhost:8888/?x=1，在另一个标签中加载http://localhost:8888/?x=2。
使用两种不同的浏览器。例如，即使在Chrome标签页中加载相同的网址，Firefox也可以加载网址。

为什么asyncio的run_in_executor会阻止龙卷风的获取处理程序？

1 个答案: