Impossible to stop a too long job or startup event

[Xmaster6y]

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Example Code

import logging
import time

from fastapi import FastAPI

app = FastAPI()

@app.on_event("startup")
def startup_event():
    logger = logging.getLogger("uvicorn")
    logger.info("Starting up...")
    while True:
        logger.info("long process running...")
        time.sleep(1)

@app.get("/")
async def home():
    while True:
        logger.info("other long process running...")
        time.sleep(1)
    return {"success": "Welcome to the API!"}

Description

I happen to have a long startup event waiting for other microservices to set up. I noticed that it was not possible to stop the process with a usual ^C or using signals. It is really not handy when it comes to testing (manual and auto).

I looked into the lifespan part of the doc but couldn't find something similar.

To reproduce, simply run the code with uvicorn main:app --port 8000. if you can stop it, I might have other problems. Even when removing the startup infinite loop, I cannot stop the request process.

I may be missing something big, but this feels weird.

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.101.1

Pydantic Version

2.2.1

Python Version

3.9.16

Additional Context

No response

[JavierSanchezCastro]

Looking at the logs I see that this msg appears after @app.on_event("startup"), so I suppose CTRL+C is only available after "startup".

INFO: Application startup complete
INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

A possible workaround that I just tested is using "--reload" flag, which should work.

[Xmaster6y]

Thanks for the info, I am aware of the logs, but I don't really understand why it is blocked during startup.

The --reload doesn't solve my problem, seeing that this option is just there to watch file modifications.

[JavierSanchezCastro]

I think it's uvicorn side, check this Kludex/uvicorn#1301

About the --reload, I see that in Ubuntu it's not working, but does in Windows, I'm not really sure if it's uvicorn or how the system handles the signals.

[YuriiMotov]

As JavierSanchezCastro mentioned, it comes from Uvicorn (Kludex/uvicorn#1301).

The solution from here is to set the handler for SIGINT signal:

import asyncio
from contextlib import asynccontextmanager
import logging
import signal
import sys

from fastapi import FastAPI

logger = logging.getLogger("uvicorn")

def receive_signal(signalNumber, frame):
    print("Received:", signalNumber)
    sys.exit()

@asynccontextmanager
async def lifespan(app: FastAPI):
    signal.signal(signal.SIGINT, receive_signal)
    logger.info("Starting up...")
    for i in range(10):
        logger.info(f"long process running ({i})...")
        await asyncio.sleep(1)
    yield
    logger.info("Shutdown...")


app = FastAPI(lifespan=lifespan)