CODEWITHSUNDEEP
python-asynciosanic
davidtgq
davidtgq

Reputation: 4000

How to wait 5 seconds (without blocking) before sending Response?

This seems to be possible because in app.Sanic.handle_request() there's this snippet:

            if isawaitable(response):
                response = await response

And this is how awaitable is checked by Python:

def isawaitable(object):
    """Return true if object can be passed to an ``await`` expression."""
    return (isinstance(object, types.CoroutineType) or
            isinstance(object, types.GeneratorType) and
                bool(object.gi_code.co_flags & CO_ITERABLE_COROUTINE) or
            isinstance(object, collections.abc.Awaitable))

I know to use async def to create an awaitable function, but I don't know how to create an awaitable HTTPResponse instance. It would really help to see an example of an awaitable response with a simple await asyncio.sleep(5) if possible.

Tried the solution by Mikhail, here's what I observed:

Full code (run by saving as test.py, then in shell python test.py and going to http://127.0.0.1:8000/api/test):

import asyncio
from sanic import Sanic
from sanic.response import HTTPResponse
from sanic.handlers import ErrorHandler


class AsyncHTTPResponse(HTTPResponse):  # make it awaitable
    def __await__(self):
        return self._coro().__await__()  # see https://stackoverflow.com/a/33420721/1113207

    async def _coro(self):
        print('Sleeping')
        await asyncio.sleep(5)
        print('Slept 5 seconds')
        return self


class CustomErrorHandler(ErrorHandler):
    def response(self, request, exception):
        return AsyncHTTPResponse(status=500)


app = Sanic(__name__, error_handler=CustomErrorHandler())


@app.get("/api/test")
async def test(request):
    return HTTPResponse(status=204)


@app.get("/api/raise500")
async def raise500(request):
    raise Exception


@app.get("/api/ret500")
async def ret500(request):
    return AsyncHTTPResponse(status=500)

if __name__ == "__main__":
    app.run()

Upvotes: 2

Views: 3364

Answers (2)

kwarunek
kwarunek

Reputation: 12577

Since Mikhail's answer is the right one, I will only discuss the further edit

  • raise500 blocks other raise500 (bug)

It does not seem to block. A simple test (added some query string to distinguish requests):

for i in `seq 2`;do curl http://127.0.0.1:8000/api/raise500&req=$i & done

From the log's datetime it looks that there is not delay (block) between requests

Sleeping
Sleeping
Slept 5 seconds
2017-11-26 01:01:49 - (network)[INFO][127.0.0.1:37310]: GET http://127.0.0.1:8000/api/raise500?req=1  500 0
Slept 5 seconds
2017-11-26 01:01:49 - (network)[INFO][127.0.0.1:37308]: GET http://127.0.0.1:8000/api/raise500?req=2  500 0
  • ret500 does not enter the asyncio.sleep() (bug)

It's because you return awaitable in awaitable function, but sanic await only for the first one:

@app.get("/api/ret500")
async def ret500(request):
    return AsyncHTTPResponse(status=500)

The handle_request does:

response = ret500(request)  # call `async def ret500` and returns awaitable
if isawaitable(response):
    response = await response  # resolve and returns another awaitable - AsyncHTTPResponse object

# note to wait 5 seconds sanic would need again await for it
# response = await response

Solutions:

  1. do not return awaitable, in other words await AsyncHTTPResponse by yourself

    @app.get("/api/ret500")
async def ret500(request):
    res = await AsyncHTTPResponse(status=500)
    return res

  2. drop ret500's async

    @app.get("/api/ret500")
def ret500(request):
    return AsyncHTTPResponse(status=500)

    Note: this technique is only valid if do not intend to call async functions in it.

Upvotes: 3

Mikhail Gerasimov
Mikhail Gerasimov

Reputation: 39546

Class that implements __await__ magic method becomes awaitable.

I didn't check if it'll work in your case, but here is example of creating awaitable custom class instance:

import asyncio
from inspect import isawaitable


class HTTPResponse:  # class we have
    pass


class AsyncHTTPResponse(HTTPResponse):  # make it awaitable
    def __await__(self):
        return self._coro().__await__()  # see https://stackoverflow.com/a/33420721/1113207

    async def _coro(self):
        await asyncio.sleep(2)
        return self


async def main():
    resp = AsyncHTTPResponse()

    if isinstance(resp, HTTPResponse):
        print('It is HTTPResponse class ...')

    if isawaitable(resp):
        print('... which is also awaitable.')

    print('Let us see how it works.')
    await resp


loop = asyncio.get_event_loop()
try:
    loop.run_until_complete(main())
finally:
    loop.run_until_complete(loop.shutdown_asyncgens())
    loop.close()

Upvotes: 3

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