uvicorn signal handling issue after uvicorn >= 0.29

[cquike]

I have an issue with the following code that starts and stops uvicorn programatically:

import sys
import signal
import time
import uvicorn
from multiprocessing import Process

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

def launch_uvicorn() :
    uvicorn.run(app, port=5000, log_level="info")

def terminate_uvicorn() :
    my_process.terminate()

def signal_handler(sig, frame):
    terminate_uvicorn()
    sys.exit(128 + sig)

my_process = None

if __name__ == "__main__":

    signal.signal(signal.SIGTERM, signal_handler)
    signal.signal(signal.SIGINT, signal_handler)

    my_process = Process(target=launch_uvicorn)
    my_process.start()

    print("Uvicorn started")
    time.sleep(5)
    print("Terminating server")
    terminate_uvicorn()

The idea is that the application is responsible of starting the uvicorn process as a child process and then stops it either before the parent process finishes or when it receives a signal. Before uvicorn 0.29 that worked fine. However from 0.29 onwards I get the following error:

Terminating server
INFO:     Shutting down
INFO:     Finished server process [109748]
Process Process-1:
Traceback (most recent call last):
  File "/usr/lib64/python3.12/multiprocessing/process.py", line 314, in _bootstrap
    self.run()
  File "/usr/lib64/python3.12/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/var/tmp/test_uvicorn.py", line 11, in launch_uvicorn
    uvicorn.run(app, port=5000, log_level="info")
  File "/var/tmp/test_env/lib64/python3.12/site-packages/uvicorn/main.py", line 575, in run
    server.run()
  File "/var/tmp/test_env/lib64/python3.12/site-packages/uvicorn/server.py", line 65, in run
    return asyncio.run(self.serve(sockets=sockets))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/asyncio/runners.py", line 194, in run
    return runner.run(main)
           ^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/asyncio/base_events.py", line 687, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File "/var/tmp/test_env/lib64/python3.12/site-packages/uvicorn/server.py", line 68, in serve
    with self.capture_signals():
  File "/usr/lib64/python3.12/contextlib.py", line 144, in __exit__
    next(self.gen)
  File "/var/tmp/test_env/lib64/python3.12/site-packages/uvicorn/server.py", line 328, in capture_signals
    signal.raise_signal(captured_signal)
  File "/var/tmp/test_uvicorn.py", line 17, in signal_handler
    terminate_uvicorn()
  File "/var/tmp/test_uvicorn.py", line 14, in terminate_uvicorn
    my_process.terminate()
  File "/usr/lib64/python3.12/multiprocessing/process.py", line 133, in terminate
    self._popen.terminate()
    ^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'terminate'

I am not sure whether that is a bug or the intended behaviour. As I understand it the child process will inherit the signal handlers from the parent, so I don't know whether in uvicorn it is simply not possible to have a process that has already its own signal handling,

I was able to workaround the issue by registering the signals after the uvicorn process starts:

    my_process = Process(target=launch_uvicorn)
    my_process.start()
    signal.signal(signal.SIGTERM, signal_handler)
    signal.signal(signal.SIGINT, signal_handler)

However there is a (albeit small) potential race condition if a signal is delivered after the uvicorn process starts and before the signals are registered.

So is this a bug in uvicorn or am I doing something wrong? There is a similar discussion already #2368 but I am not sure it is about the same thing.