如何在aiohttp中从处理程序运行异步进程

Question

I'm trying to understand how to run an asynchronous process from coroutine handler within aioweb framework. Here is an example of code:

def process(request):
    # this function can do some calc based on given request
    # e.g. fetch/process some data and store it in DB
    # but http handler don't need to wait for its completion

async def handle(request):
    # process request
    process(request) ### THIS SHOULD RUN ASYNCHRONOUSLY

    # create response
    response_data = {'status': 'ok'}

    # Build JSON response
    body = json.dumps(response_data).encode('utf-8')
    return web.Response(body=body, content_type="application/json")

def main():
    loop = asyncio.get_event_loop()
    app = web.Application(loop=loop)
    app.router.add_route('GET', '/', handle)

    server = loop.create_server(app.make_handler(), '127.0.0.1', 8000)
    print("Server started at http://127.0.0.1:8000")
    loop.run_until_complete(server)
    try:
       loop.run_forever()
    except KeyboardInterrupt:
       pass

if __name__ == '__main__':
   main()

I want to run process function asynchronously from the handler. Can someone provide an example how I can achieve that. I'm struggle to understand how I can pass/use main event loop within a handler and pass it around to another function which by itself can run async process within it.

Answer 1

I guess you should define your existing process function as a coroutine ( async def should do the job to wrap your function as a coroutine) and use asyncio.ensure_future in your main handle function.

async def process(request):
    # Do your stuff without having anything to return

async def handle(request):
    asyncio.ensure_future(process(request))
    body = json.dumps({'status': 'ok'}).encode('utf-8')
    return web.Response(body=body, content_type="application/json")

According to asyncio documention the ensure_future method should schedule the execution of the coroutine (the process function in your case) without blocking/waiting for a result.

I guess what you are looking for could be related to some existing posts like this one : "Fire and forget" python async/await