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[QUESTION] Would expect this simple example to behave asynchronously but it doesn't

See original GitHub issue

Description

I’m probably not understanding the asynchronous concept correctly in FastAPI.

I’m accessing the root endpoint of the following app from two clients at the same time. I’d expect FastAPI to print Started twice:

from fastapi import FastAPI
import asyncio

app = FastAPI()

@app.get("/")
async def read_root():
    print('Started')
    await asyncio.sleep(5)
    print('Finished')
    return {"Hello": "World"}

Instead I get the following, which looks very much non asynchronous:

Started
Finished
INFO: ('127.0.0.1', 49655) - "GET / HTTP/1.1" 200
Started
Finished
INFO: ('127.0.0.1', 49655) - "GET / HTTP/1.1" 200

What am I missing?

Issue Analytics

State:
Created 4 years ago
Comments:6 (4 by maintainers)

Top GitHub Comments

2reactions

euri10commented, Oct 15, 2019

sorry misread you explain what you want and you’re right it should do that

I guess when you state that you used 2 clients at the same time, maybe that was not enough at the same time, no idea how you proceeded to launch concurrent requests

See this log launching 10 concurrent requests with

ab -n 10 -c 10 http://localhost:8000/

/home/lotsos/.local/share/virtualenvs/rapidfastapitest-s8GpZJ_e/bin/python /home/lotsos/PycharmProjects/rapidfastapitest/625_asyn_question.py
email-validator not installed, email fields will be treated as str.
To install, run: pip install email-validator
INFO: Started server process [7007]
INFO: Waiting for application startup.
INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
2019-10-15 11:02:49,713 625_asyn_question DEBUG    Started
2019-10-15 11:02:54,713 625_asyn_question DEBUG    Finished
INFO: ('127.0.0.1', 47518) - "GET / HTTP/1.0" 200
2019-10-15 11:02:54,718 625_asyn_question DEBUG    Started
2019-10-15 11:02:54,719 625_asyn_question DEBUG    Started
2019-10-15 11:02:54,719 625_asyn_question DEBUG    Started
2019-10-15 11:02:54,720 625_asyn_question DEBUG    Started
2019-10-15 11:02:54,720 625_asyn_question DEBUG    Started
2019-10-15 11:02:54,720 625_asyn_question DEBUG    Started
2019-10-15 11:02:54,721 625_asyn_question DEBUG    Started
2019-10-15 11:02:54,721 625_asyn_question DEBUG    Started
2019-10-15 11:02:54,721 625_asyn_question DEBUG    Started
2019-10-15 11:02:59,719 625_asyn_question DEBUG    Finished
INFO: ('127.0.0.1', 47520) - "GET / HTTP/1.0" 200
2019-10-15 11:02:59,720 625_asyn_question DEBUG    Finished
INFO: ('127.0.0.1', 47522) - "GET / HTTP/1.0" 200
2019-10-15 11:02:59,720 625_asyn_question DEBUG    Finished
INFO: ('127.0.0.1', 47524) - "GET / HTTP/1.0" 200
2019-10-15 11:02:59,721 625_asyn_question DEBUG    Finished
INFO: ('127.0.0.1', 47526) - "GET / HTTP/1.0" 200
2019-10-15 11:02:59,721 625_asyn_question DEBUG    Finished
INFO: ('127.0.0.1', 47528) - "GET / HTTP/1.0" 200
2019-10-15 11:02:59,722 625_asyn_question DEBUG    Finished
INFO: ('127.0.0.1', 47530) - "GET / HTTP/1.0" 200
2019-10-15 11:02:59,722 625_asyn_question DEBUG    Finished
INFO: ('127.0.0.1', 47532) - "GET / HTTP/1.0" 200
2019-10-15 11:02:59,723 625_asyn_question DEBUG    Finished
INFO: ('127.0.0.1', 47534) - "GET / HTTP/1.0" 200
2019-10-15 11:02:59,724 625_asyn_question DEBUG    Finished
INFO: ('127.0.0.1', 47536) - "GET / HTTP/1.0" 200

snippet used

import uvicorn
from fastapi import FastAPI
import asyncio

import logging

logger: logging.Logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)

if not logger.hasHandlers():
    sh = logging.StreamHandler()
    fmt = logging.Formatter(fmt="%(asctime)s %(name)-12s %(levelname)-8s %(message)s")
    sh.setFormatter(fmt)
    logger.addHandler(sh)
    logger.propagate = False



app = FastAPI()


@app.get("/")
async def read_root():
    logger.debug('Started')
    await asyncio.sleep(5)
    logger.debug('Finished')
    return {"Hello": "World"}



if __name__ == '__main__':
    uvicorn.run("625_asyn_question:app")

1reaction

tiangolocommented, Apr 10, 2020

Thanks for the help here @euri10 ! 👏 🙇

Thanks for reporting back and closing the issue @fhennecker 👍