Uvicorn workers don't shutdown on Ctrl+C when running as a gunicorn worker inside Docker and no TTY

[kajic]

I have been investigating an issue where Uvicorn workers don't shutdown when you issue a Ctrl+C, if you run them as Gunicorn workers inside Docker without a TTY. This StackOverflow issue which I created today describes the situation in some detail:
https://stackoverflow.com/questions/79139077/how-do-you-make-gunicorn-forward-sigint-to-uvicorn-when-running-inside-docker

I've been reading through Gunicorn's arbiter.py, workers/base.py and Uvicorn's workers.py, and I'm getting closer to understanding what's going on, if not why the implementation is what it is.

First, when running without a TTY:
When gunicorn receives a SIGINT, it sends a SIGQUIT to its workers.
(gunicorn/arbiter.py:handle_int calls stop(False), and stop() sends SIGQUIT when graceful=False.)

In uvicorn/workers.py:_install_sigquit_handler, Uvicorn register's as callback gunicorn/workers/base.py:handle_exit for SIGQUIT.
Interestingly, these two issues are referenced in _install_sigquit_handler.
- #1116
- benoitc/gunicorn#2604

Here I found it strange that Gunicorn doesn't forward the SIGINT, but forwards a SIGQUIT instead.

Anyway, when uvicorn receives SIGQUIT, the registered handle_exit() callback just sets self.alive=False.
I'm not sure how self.alive affects the lifecycle of a worker, but from here on nothing much happens until Gunicorn's --graceful-timeout has elapsed, and then it sends a SIGKILL to the Uvicorn workers, and prints an error like "Worker (pid:8) was sent SIGKILL! Perhaps out of memory?".

When instead you run Gunicorn+Uvicorn with a TTY, using docker run -it ..., and press Ctrl+C, mostly everything happens as before, but now (before Gunicorn receives SIGINT) uvicorn/server.py:handle_exit receives SIGINT first, and it is able to shutdown successfully.

I still haven't been able to figure out why Uvicorn is able to receive SIGINT when there is a TTY, but not otherwise, or why it is even able to receive the SIGINT before Gunicorn does. I'd be curious to know, but assuming this discrepancy is expected, I also don't understand why _install_sigquit_handler registers handle_exit as the callback, which doesn't seem to do much more than set self.alive=False, instead of, perhaps, using handle_quit as the callback, which (I tried) does properly shutdown the workers.

Sorry for the long post, but I thought I'd share my investigation in case someone with a better understanding of signal handling in Uvicorn can elaborate on why Uvicorn is able to receive SIGINT with a TTY, but not without, and why _install_sigquit_handler uses handle_exit instead of handle_quit to handle SIGQUIT.

Thanks for your time!