CTRL^C doesn't work while startup in progress

[levsh]

Checklist

• The bug is reproducible against the latest release or master.
• There are no similar issues or pull requests to fix it yet.

Describe the bug

Hi!

ctrl^c doesn't work until on_startup function completes. This happens because install_signal_handlers call before startup

Steps to reproduce the bug

import asyncio

import uvicorn
from fastapi import FastAPI

async def on_startup():
    for _ in range(10):
        await asyncio.sleep(1)

app = FastAPI(on_startup=[on_startup])

if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=5000, log_level="info")

Expected behavior

No response

Actual behavior

No response

Debugging material

No response

Environment

uvicorn - 0.16.0
python - 3.8.6

Additional context

No response

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[msenol86]

This happens to me too. This is my solution:

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


@app.on_event("startup")
async def startup_event():
    import signal
    signal.signal(signal.SIGINT, receive_signal)
    # startup tasks

[tomchristie]

This is probably a reasonable behaviour?

I'd assume that a sensible approach would be that we always allow the startup to run to completion, but then exit (and run shutdown) if we've been interrupted.

[jmwielandt]

This is probably a reasonable behaviour?

I'd assume that a sensible approach would be that we always allow the startup to run to completion, but then exit (and run shutdown) if we've been interrupted.

@tomchristie Hi, I'm having this problem. Imagine you had the wrong config and need to stop the program ASAP.
Ctrl-C doesn't work for any endpoint btw, uvicorn is waiting them to finish before ending the process.

Ctrl-C is mainly for development, where you can't discard a mistake or just a test of a while True: pass. With this, devs are forced to use htop or the task manager to end python.

[Birch-san]

This is probably a reasonable behaviour?

@tomchristie

the problem is that the thing the application may be doing on startup, is downloaing a giant file.

I was launching ialacol's uvicorn server, and on startup it began downloading a 4GB LLM checkpoint. the default model wasn't one I wished to use, so I tried to interrupt it in order to change the CLI args.
I tried to stop it by sending a Ctrl C to uvicorn, but nothing happened. the interrupt was buffered and only serviced after the download completed.