[PR #10464/182198fc backport][3.11] Explicitly close the socket if there is a failure in start_connection()

[patchback]

This is a backport of PR #10464 as merged into master (182198f).

What do these changes do?

Over in MagicStack/uvloop#653 in issue is described where after upgrading from aiohttp 3.9.5 -> 3.10.5 (but same thing on 3.11.11), under certain conditions where exceptions are raised at the right/wrong time, continued use of aiohttp can result in File descriptor 2877 is used by transport errors.

I've been able to repro with a small script (gist) that starts/stops/cancels many connections repeatedly. I can repro on at least Ubuntu 24 x86, aiohttp 3.11.11 and uvloop 0.21.0. This fix resolves the errors in my repro script.

I was unable to produce a detailed end-to-end explanation for what's happening here, but I do know that we enter the error state when an exception is thrown while inside of uvloop's create_connection function, here:

https://github.com/MagicStack/uvloop/blob/7bb12a174884b2ec8b3162a08564e5fb8a5c6b39/uvloop/loop.pyx#L2066

In that case, if sock.close() is not called (this pr changes that), uvloop seems to erroneously hold on to a ref to the transport when the underlying file descriptor has been relinquished to the os.

It feels like at its core a bug in uvloop, however this at least works around it in aiohttp.

Are there changes in behavior for the user?

No... Aside from this error not reproducing.

Is it a substantial burden for the maintainers to support this?

Unless I've made a mistake (it is a very small change though), I think this is a pure bug fix.

Related issue number

MagicStack/uvloop#653

Checklist

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[codspeed-hq]

CodSpeed Performance Report

Merging #10477 will not alter performance

_{Comparing patchback/backports/3.11/182198fccae2d71b857a0f26b18e7317fd6cff4f/pr-10464 (38f368e) with 3.11 (79c5093)}

Summary

✅ 48 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.08%. Comparing base (79c5093) to head (38f368e).
Report is 1 commits behind head on 3.11.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             3.11   #10477   +/-   ##
=======================================
  Coverage   98.08%   98.08%           
=======================================
  Files         123      123           
  Lines       37342    37354   +12     
  Branches     4503     4507    +4     
=======================================
+ Hits        36628    36640   +12     
  Misses        538      538           
  Partials      176      176           

Flag	Coverage Δ
CI-GHA	97.97% <100.00%> (+<0.01%)	⬆️
OS-Linux	97.67% <100.00%> (+<0.01%)	⬆️
OS-Windows	94.73% <100.00%> (+<0.01%)	⬆️
OS-macOS	96.81% <100.00%> (+<0.01%)	⬆️
Py-3.10.11	96.66% <100.00%> (+<0.01%)	⬆️
Py-3.10.16	97.18% <100.00%> (-0.06%)	⬇️
Py-3.11.11	97.31% <100.00%> (-0.01%)	⬇️
Py-3.11.9	96.74% <100.00%> (+<0.01%)	⬆️
Py-3.12.8	96.58% <100.00%> (-0.01%)	⬇️
Py-3.12.9	97.72% <100.00%> (+<0.01%)	⬆️
Py-3.13.1	96.58% <100.00%> (-0.01%)	⬇️
Py-3.13.2	97.71% <100.00%> (+<0.01%)	⬆️
Py-3.9.13	96.57% <92.30%> (-0.01%)	⬇️
Py-3.9.21	97.14% <92.30%> (+<0.01%)	⬆️
Py-pypy7.3.16	96.72% <92.30%> (+<0.01%)	⬆️
VM-macos	96.81% <100.00%> (+<0.01%)	⬆️
VM-ubuntu	97.67% <100.00%> (+<0.01%)	⬆️
VM-windows	94.73% <100.00%> (+<0.01%)	⬆️

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