Why is controller's heart beat thread daemon set to False?

Setup:
OS: Ubuntu 22.04.3 LTS
Python: Python 3.10.12
FastChat version: 0.2.36

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I am using FastChat to run local LLMs. I am trying to run the following command:

python -m fastchat.serve.controller

I get the following logs:

2024-02-25 22:08:38 | INFO | controller | args: Namespace(host='localhost', port=21001, dispatch_method='shortest_queue', ssl=False)
2024-02-25 22:08:38 | ERROR | stderr | INFO:     Started server process [15985]
2024-02-25 22:08:38 | ERROR | stderr | INFO:     Waiting for application startup.
2024-02-25 22:08:38 | ERROR | stderr | INFO:     Application startup complete.
2024-02-25 22:08:38 | ERROR | stderr | INFO:     Uvicorn running on http://localhost:21001 (Press CTRL+C to quit)

When I interrupt the process once, I get the following logs:

2024-02-25 22:09:55 | ERROR | stderr | INFO:     Shutting down
2024-02-25 22:09:55 | ERROR | stderr | INFO:     Waiting for application shutdown.
2024-02-25 22:09:55 | ERROR | stderr | INFO:     Application shutdown complete.
2024-02-25 22:09:55 | ERROR | stderr | INFO:     Finished server process [15985]

However, the process continues to run nonetheless. I believe that this is because the heart_beat_thread defined in controller.py continues to run as daemon is set to False.

self.heart_beat_thread = threading.Thread(
    target=heart_beat_controller, args=(self,)
)

Is this an intended behavior? If so, why? Is there a better way to terminate the controller thread?

For information, here are the logs that I get when I interrupt a second time:

2024-02-25 22:10:38 | ERROR | stderr | Exception ignored in: <module 'threading' from '/usr/lib/python3.10/threading.py'>
2024-02-25 22:10:38 | ERROR | stderr | Traceback (most recent call last):
2024-02-25 22:10:38 | ERROR | stderr |   File "/usr/lib/python3.10/threading.py", line 1567, in _shutdown
2024-02-25 22:10:38 | ERROR | stderr |     lock.acquire()
2024-02-25 22:10:38 | ERROR | stderr | KeyboardInterrupt:

Start with fastchat/serve/controller.py and the fastchat.serve.controller entry point, then inspect how heart_beat_thread is created and how shutdown is handled after Uvicorn exits. Reproduce the single-interrupt behavior on the stated setup and trace the remaining thread. Done means the controller terminates cleanly after interruption, or the intended daemon behavior is documented and verified.