Uvicorn in Windows kills subprocesses on reload

[sid-38]

Uvicorn server with reload=True, would send a Ctrl+C event to other subprocesses when reloading.

# main.py
import subprocess
import uvicorn

if __name__== '__main__':
    process = subprocess.Popen(["python", "frontend.py"], shell=True)

    print("Starting uvicorn")
    uvicorn.run(
        app="uvicorn_main:app",
        port=5000,
        log_level="debug",
        reload=True
    )

# frontend.py
if __name__ == "__main__":
    while True:
        print("frontend")

# uvicorn_main.py
async def app(scope, receive, send):
    assert scope['type'] == 'http'

    await send({
        'type': 'http.response.start',
        'status': 200,
        'headers': [
            [b'content-type', b'text/plain'],
        ],
    })
    await send({
        'type': 'http.response.body',
        'body': b'Hello, world!',
    })

On making changes to the uvicorn_main.py file, uvicorn reloads and the frontend loop ends.

Uvicorn version - 0.29.0
Watchfiles version - 0.21.0
Python version - 3.12.2
OS - Windows 11 Home

[sid-38]

I believe, the reason for this could be that on reload, uvicorn does a os.kill(pid, signal.CTRL_C_EVENT) and if the pid is that of an individual process instead of a process group it leads to the CTRL+C signal being sent to everything under the terminal.

It's a bug that's been reported in the following links:

1. https://bugs.python.org/issue42962
2. GenerateConsoleCtrlEvent should not succeed when dwProcessGroupId is not a group ID microsoft/terminal#335

[Kludex]

Does this happen with uvicorn 0.28.0?

[sid-38]

Yes, it does in my tests. I believe the issue affects versions from 0.22.0. If this indeed is confirmed to be an issue, I'd love to work on it