从Flask路由进行Python异步调用

Question

我想在每次执行Flask路由时执行一个异步函数。为什么abar函数从不执行？

import asyncio
from flask import Flask

async def abar(a):
    print(a)

loop = asyncio.get_event_loop()
app = Flask(__name__)

@app.route("/")
def notify():
    asyncio.ensure_future(abar("abar"), loop=loop)
    return "OK"

if __name__ == "__main__":
    app.run(debug=False, use_reloader=False)
    loop.run_forever()

我还尝试将阻塞调用放在单独的线程中。但是它仍然没有调用该abar函数。

import asyncio
from threading import Thread
from flask import Flask

async def abar(a):
    print(a)

app = Flask(__name__)

def start_worker(loop):
    asyncio.set_event_loop(loop)
    try:
        loop.run_forever()
    finally:
        loop.close()

worker_loop = asyncio.new_event_loop()
worker = Thread(target=start_worker, args=(worker_loop,))

@app.route("/")
def notify():
    asyncio.ensure_future(abar("abar"), loop=worker_loop)
    return "OK"

if __name__ == "__main__":
    worker.start()
    app.run(debug=False, use_reloader=False)

Answer 1

你可以将一些异步功能整合到Flask应用中，而不必完全将其转换为异步。

import asyncio
from flask import Flask

async def abar(a):
    print(a)

loop = asyncio.get_event_loop()
app = Flask(__name__)

@app.route("/")
def notify():
    loop.run_until_complete(abar("abar"))
    return "OK"

if __name__ == "__main__":
    app.run(debug=False, use_reloader=False)

这将阻止Flask响应，直到异步函数返回为止，但是它仍然允许你做一些聪明的事情。我已经使用此模式使用aiohttp并行执行许多外部请求，然后在完成它们之后，我回到传统的flask中进行数据处理和模板渲染。

import aiohttp
import asyncio
import async_timeout
from flask import Flask

loop = asyncio.get_event_loop()
app = Flask(__name__)

async def fetch(url):
    async with aiohttp.ClientSession() as session, async_timeout.timeout(10):
        async with session.get(url) as response:
            return await response.text()

def fight(responses):
    return "Why can't we all just get along?"

@app.route("/")
def index():
    # perform multiple async requests concurrently
    responses = loop.run_until_complete(asyncio.gather(
        fetch("https://google.com/"),
        fetch("https://bing.com/"),
        fetch("https://duckduckgo.com"),
        fetch("http://www.dogpile.com"),
    ))

    # do something with the results
    return fight(responses)

if __name__ == "__main__":
    app.run(debug=False, use_reloader=False)