Add a graceful shutdown period to allow tasks to complete.

[Dreamsorcerer]

When the server is shutting down gracefully, it should wait on pending tasks before running the application shutdown/cleanup steps and cancelling all remaining tasks.

This helps ensure that tasks have a chance to finish writing to a DB, handlers can finish responding to clients etc.

[Dreamsorcerer]

I did also want to allow a KeyboardInterrupt to cancel the pending tasks immediately and then continue with the cleanup steps, but didn't manage to figure out how to make that work.

I did write the test for it though, if anyone wants to try it:

    def test_shutdown_interrupt(self, aiohttp_unused_port: Callable[[], int]) -> None:
        port = aiohttp_unused_port()
        finished = cleanup_run = False
        async def task() -> None:
            nonlocal finished
            await asyncio.sleep(2)
            finished = True

        async def cleanup(app: web.Application) -> None:
            nonlocal cleanup_run
            cleanup_run = True

        async def test(sess: ClientSession) -> None:
            # Ensure we are in the middle of shutdown (waiting for task()).
            await asyncio.sleep(1)
            # Trigger another KeyboardInterrupt.
            assert finished == False
            async with sess.get(f"http://localhost:{port}/stop") as resp:
                pass

        try:
            t = self.run_app(port, 3, task, test, cleanup=cleanup)
        except KeyboardInterrupt:
            pytest.fail("Keyboard interrupt was propogated.")

        assert finished is False
        assert t.done()
        assert t.cancelled()
        assert cleanup_run is True

[codecov]

Codecov Report

Merging #7188 (69c08d8) into master (4635161) will decrease coverage by 0.08%.
The diff coverage is 99.30%.

@@            Coverage Diff             @@
##           master    #7188      +/-   ##
==========================================
- Coverage   97.37%   97.30%   -0.08%     
==========================================
  Files         106      106              
  Lines       31093    31244     +151     
  Branches     3875     3890      +15     
==========================================
+ Hits        30278    30402     +124     
- Misses        613      639      +26     
- Partials      202      203       +1     

Flag	Coverage Δ
CI-GHA	97.20% <99.30%> (-0.08%)	⬇️
OS-Linux	96.86% <99.30%> (-0.08%)	⬇️
OS-Windows	95.27% <99.30%> (-0.08%)	⬇️
OS-macOS	96.43% <99.30%> (-0.08%)	⬇️
Py-3.10.9	96.95% <97.91%> (-0.08%)	⬇️
Py-3.11.0	95.52% <96.52%> (-0.08%)	⬇️
Py-3.7.15	96.68% <98.61%> (-0.08%)	⬇️
Py-3.7.9	95.16% <98.61%> (-0.08%)	⬇️
Py-3.8.10	95.06% <98.61%> (-0.08%)	⬇️
Py-3.8.15	?
Py-3.8.16	96.57% <98.61%> (-0.08%)	⬇️
Py-3.9.13	95.06% <99.30%> (-0.07%)	⬇️
Py-3.9.16	96.59% <99.30%> (-0.07%)	⬇️
Py-pypy7.3.11	94.10% <98.61%> (-0.09%)	⬇️
VM-macos	96.43% <99.30%> (-0.08%)	⬇️
VM-ubuntu	96.86% <99.30%> (-0.08%)	⬇️
VM-windows	95.27% <99.30%> (-0.08%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
tests/test_run_app.py	97.84% <99.23%> (+0.52%)	⬆️
aiohttp/test_utils.py	99.69% <100.00%> (ø)
aiohttp/web_fileresponse.py	99.29% <100.00%> (ø)
aiohttp/web_runner.py	97.85% <100.00%> (+0.09%)	⬆️
aiohttp/web_protocol.py	85.79% <0.00%> (-4.83%)	⬇️
tests/test_client_ws_functional.py	97.59% <0.00%> (-0.65%)	⬇️
tests/test_client_functional.py	98.45% <0.00%> (-0.39%)	⬇️
aiohttp/http_writer.py	99.15% <0.00%> (-0.01%)	⬇️
aiohttp/client.py	94.16% <0.00%> (ø)
aiohttp/worker.py	94.44% <0.00%> (ø)
... and 34 more

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[Dreamsorcerer]

The Windows test is making me crazy, I don't see how that assertion can be failing unless Windows is needing several seconds to make a local request...

[Dreamsorcerer]

Seems that it takes over 4 seconds on Windows for the request to complete when the server rejects the connection...
On other platforms it raises the connector error immediately.

[patchback]

Backport to 3.9: 💔 cherry-picking failed — conflicts found

❌ Failed to cleanly apply edd49b5 on top of patchback/backports/3.9/edd49b5c445b1b325e483a70bdf2635d6b72f64f/pr-7188

Backporting merged PR #7188 into master

1. Ensure you have a local repo clone of your fork. Unless you cloned it
   from the upstream, this would be your origin remote.
2. Make sure you have an upstream repo added as a remote too. In these
   instructions you'll refer to it by the name upstream. If you don't
   have it, here's how you can add it:

   $ git remote add upstream https://github.com/aio-libs/aiohttp.git

3. Ensure you have the latest copy of upstream and prepare a branch
   that will hold the backported code:

   $ git fetch upstream
   $ git checkout -b patchback/backports/3.9/edd49b5c445b1b325e483a70bdf2635d6b72f64f/pr-7188 upstream/3.9

4. Now, cherry-pick PR Add a graceful shutdown period to allow tasks to complete. #7188 contents into that branch:

   $ git cherry-pick -x edd49b5c445b1b325e483a70bdf2635d6b72f64f

   If it'll yell at you with something like fatal: Commit edd49b5c445b1b325e483a70bdf2635d6b72f64f is a merge but no -m option was given., add -m 1 as follows intead:

   $ git cherry-pick -m1 -x edd49b5c445b1b325e483a70bdf2635d6b72f64f

5. At this point, you'll probably encounter some merge conflicts. You must
   resolve them in to preserve the patch from PR Add a graceful shutdown period to allow tasks to complete. #7188 as close to the
   original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/3.9/edd49b5c445b1b325e483a70bdf2635d6b72f64f/pr-7188

7. Create a PR, ensure that the CI is green. If it's not — update it so that
   the tests and any other checks pass. This is it!
   Now relax and wait for the maintainers to process your pull request
   when they have some cycles to do reviews. Don't worry — they'll tell you if
   any improvements are necessary when the time comes!

🤖 @patchback
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