Force quit does not cancel on-going tasks

[vxgmichel]

I've seen several related issues, but here's a very simple way to reproduce the fact that the "force quit" feature does not cancel on-going tasks as I expected:

import asyncio
from starlette.applications import Starlette
from starlette.routing import Route


async def homepage(request):
    while True:
        await asyncio.sleep(1)


app = Starlette(debug=True, routes=[Route('/', homepage)])

Run the app:

$ uvicorn main:app
INFO:     Started server process [99431]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

Run a client in another term:

$ curl http://127.0.0.1:8000

Try to stop the server with several ctrl+c (it won't stop):

^CINFO:     Shutting down
INFO:     Waiting for connections to close. (CTRL+C to force quit)
^C^C^C^C^C^C^C^C^C^C^C

Using --timeout-graceful-shutdown does work, but I would still expect to be able to force the cancelling of on-going requests.

Is it a bug or the expected behavior?

[vxgmichel]

As far as I can tell, this behavior is related to this code:

uvicorn/uvicorn/server.py

Lines 296 to 312 in b7241e1

	async def _wait_tasks_to_complete(self) -> None:
	# Wait for existing connections to finish sending responses.
	if self.server_state.connections and not self.force_exit:
	msg = "Waiting for connections to close. (CTRL+C to force quit)"
	logger.info(msg)
	while self.server_state.connections and not self.force_exit:
	await asyncio.sleep(0.1)
	# Wait for existing tasks to complete.
	if self.server_state.tasks and not self.force_exit:
	msg = "Waiting for background tasks to complete. (CTRL+C to force quit)"
	logger.info(msg)
	while self.server_state.tasks and not self.force_exit:
	await asyncio.sleep(0.1)
	for server in self.servers:
	await server.wait_closed()

Note how self.force_exit skips the waiting for existing tasks and connections, but there is still the await server.wait_closed() at the end that will block, waiting for socket transport to close.

The graceful shutdown timeout is not affected by this issue because the whole _wait_tasks_to_complete method is wrapped in a wait_for:

uvicorn/uvicorn/server.py

Lines 277 to 280 in b7241e1

	await asyncio.wait_for(
	self._wait_tasks_to_complete(),
	timeout=self.config.timeout_graceful_shutdown,
	)

[Kludex]

I understand your point, but it runs as expected.

[Kludex]

And that's why we added the timeout graceful flag.

[vxgmichel]

But isn't it weird that the graceful shutdown timeout and the forced exit do not behave the same?

My intuition would have been that hitting ctrl+c a second time would be the same as shortening the graceful shutdown timeout to "right now".

Plus the _wait_tasks_to_complete code seems to points to this direction too: having force_exit set to True means we're skipping the waiting for existing tasks and connections, but for some reasons we do not skip the server.wait_closed() operation.