thread_per_async.py

import asyncio
import threading

from tornado.ioloop import IOLoop
from tornado.web import Application, RequestHandler


def asyncrazy(func, *args):
    """run a stand-alone async function synchronously with a thread"""
    result = None

    def wrapper():
        nonlocal result
        loop = asyncio.SelectorEventLoop()
        asyncio.set_event_loop(loop)
        result = loop.run_until_complete(func(*args))

    thr = threading.Thread(target=wrapper)
    thr.start()
    thr.join()
    return result


async def aio_func(msg):
    print("started async...")
    await asyncio.sleep(2)
    print("still going", flush=True)
    await asyncio.sleep(2)
    print("async done", flush=True)
    return "async %s!" % msg


class MainHandler(RequestHandler):
    def get(self):
        msg = self.get_argument("msg")
        resp = asyncrazy(aio_func, msg)
        self.set_header("Content-Type", "text/plain")
        self.write(resp.encode() + b"\n")


if __name__ == "__main__":
    app = Application([('/', MainHandler)])
    app.listen(8080)
    print("listening on port 8080", flush=True)
    IOLoop.current().start()