…eter is finalizing (#40649)

Backport of #40447 to v1.75.x.
---
This PR changes the logic of `shutdown_grpc_aio` to skip
`_actual_aio_shutdown` python interpreter is already [being
finalized](https://docs.python.org/3.14/glossary.html#term-interpreter-shutdown)
(cleaning up resources, destroying objects, preparing for program exit,
etc). `_actual_aio_shutdown` involves `PollerCompletionQueue` shutdown,
followed by core
[`grpc_shutdown`](https://grpc.github.io/grpc/core/grpc_8h.html#a35f55253e80714c17f4f3a0657e06f1b)
API call.

Reasoning:
1. During finalizations, in come cases resources we're accessing may
already be freed, and the order is not deterministic. Some of the
resources being unloaded prior the `_actual_aio_shutdown` call:
`_global_aio_state`, `AsyncIOEngine` enum, or even python libraries like
`sys`. This leads to errors like `AttributeError: 'NoneType' object has
no attribute 'POLLER'`.
2. `PollerCompletionQueue.shutdown()` will try to wait on its poller
thread to finish gracefully. In py3.14, `PythonFinalizationError` is
raised when `Thread.join()` is called during finalization. I think the
logic here is similar to (1): these threads may have already been
deallocated.

Note that in some cases users were able to prevent
`_actual_aio_shutdown` from being called by manually calling
`init_grpc_aio` prior to initializing any grpc objects. This resulted in
an incorrect positive refcount, which prevents `_actual_aio_shutdown`
from being run. Before the above finalization check was added this
side-effect was sometimes misused to avoid deadlock on finialization
(#22365).

This PR:
- Fixes #39520
- Fixes #22365
- Fixes #38679
- Fixes #33342
- Fixes #36655

#40726)

Backport of #40403 to v1.75.x.
---
This PR enables Python 3.14 in all the different tests - Basic tests
(Native Python tests), Bazel tests and Distrib tests to build Python
3.14 artifacts. In addition, it also updates all the public facing
METADATA versions.

## Distribtests
Required pre-requisite changes to enable 3.14 artifacts are covered in
#40289 .

## Bazel tests
Enabling Python 3.14 required updating the rules_python version to a
more recent version that supports 3.14. This was done in #40602

## Basic tests
The following errors were caught by the Basic tests when running via
Python 3.14 and resolved in this PR:

### 1) No running event loop for AsyncIO when run outside an async
function
```
Traceback (most recent call last):
  File "src/python/grpcio/grpc/_cython/_cygrpc/aio/common.pyx.pxi", line 184, in grpc._cython.cygrpc.get_working_loop
RuntimeError: no running event loop
```
This was caught by the
`tests_aio.unit.outside_init_test.TestOutsideInit` and
`tests_aio.unit.init_test.TestInit` tests, and was also previously
reported in #39507 with the root cause.

Following some investigation, the fix is being worked on by @sergiitk in
PR #40293. In order to parallelize the fix and this PR, these 2 tests
are currently being skipped for Python 3.14 and above.

### 2) Pickling error from the `multiprocessing` library
```
_pickle.PicklingError: Can't pickle <function _test_well_known_types at 0x7f3937eee610>: it's not the same object as tests.unit._dynamic_stubs_test._test_well_known_types
when serializing dict item '_target'
when serializing multiprocessing.context.Process state
when serializing multiprocessing.context.Process object
```
This was caught by the `tests.unit._dynamic_stubs_test.DynamicStubTest`
which runs test cases in a subprocess using the `multiprocessing`
library.
Error root cause:
- The default start method of multiprocessing in linux has changed to
`forkserver` instead of `fork` from Python 3.14.
- `forkserver` has a few extra restrictions for picklability as compared
to `fork` (Ref: [Python
Docs](https://docs.python.org/3.14/library/multiprocessing.html#the-spawn-and-forkserver-start-methods))
- All the [test case
functions](https://github.com/grpc/grpc/blob/0243842d5d10f624bf8f09f45026dd300805502f/src/python/grpcio_tests/tests/unit/_dynamic_stubs_test.py#L115)
in the DynamicStubTest that are provided as `target` to the
`multiprocessing.Process` use decorators. This causes problems when
pickling them.

Hence to resolve this, we manually set the 'start method' of
`multiprocessing` to use the `fork` start method.

… changes (#40758)

Backport of #40750 to v1.75.x.
---
> [!IMPORTANT]
> **This fix is only needed to support the use of grpc.aio outside of a
running event loop.** This approach is [strongly
discouraged](https://docs.python.org/3.14/library/asyncio-policy.html#asyncio-policies)
by Python, and will be deprecated in future gRPC releases.
>
> Please use the
[asyncio.run()](https://docs.python.org/3.14/library/asyncio-runner.html#asyncio.run)
function or the
[asyncio.Runner](https://docs.python.org/3.14/library/asyncio-runner.html#asyncio.Runner).
If you see this in Python REPL, use the dedicated [asyncio
REPL](https://docs.python.org/3/library/asyncio.html#asyncio-cli) by
running `python -m asyncio`.

This PR handles the following [asyncio behavioral
changes](https://docs.python.org/3.14/whatsnew/3.14.html#id11)
introduced in python3.14:
-
[asyncio.get_event_loop()](https://docs.python.org/3.14/library/asyncio-eventloop.html#asyncio.get_event_loop)
now raises a `RuntimeError` if there is no current event loop, and no
longer implicitly creates an event loop.
-
[Deprecations](https://docs.python.org/3.14/whatsnew/3.14.html#deprecated):
[asyncio.get_event_loop_policy()](https://docs.python.org/3.14/library/asyncio-policy.html#asyncio.get_event_loop_policy),
[asyncio.AbstractEventLoopPolicy](https://docs.python.org/3.14/library/asyncio-policy.html#asyncio.AbstractEventLoopPolicy),
[asyncio.DefaultEventLoopPolicy](https://docs.python.org/3.14/library/asyncio-policy.html#asyncio.DefaultEventLoopPolicy).
Note that this PR preserves the existing behavior and does not migrate
off of [asyncio policy
system](https://docs.python.org/3.14/library/asyncio-policy.html) yet.
This will be done separately, see #39518.

To support 3.14, this PR:
1. Fixes #39507 by handling the call to deprecated
`asyncio.get_event_loop_policy()` when calling `new_event_loop()`. This
was necessary because all warnings were elevated to errors within the
context manager, and the newly deprecated policy caused an unhandled
exception.
2. Handles the `BaseDefaultEventLoopPolicy.get_event_loop()` behavior
change.
[Before](https://github.com/python/cpython/blob/v3.13.7/Lib/asyncio/events.py#L695)
python 3.14, it would only throw `RuntimeError` when there's no loop in
non-main threads.
[After](https://github.com/python/cpython/blob/v3.14.0rc3/Lib/asyncio/events.py#L714)
python 3.14, it removes the special handling of the main thread. This PR
preserves preserves the pre-3.14 grpc.aio behavior for 3.14.

Co-authored-by: Sergii Tkachenko <[email protected]>

Change was created by the release automation script. See go/grpc-release

…rden install script (#40772)

Backport of #40769 to v1.75.x.
---
Composer sha sum updated, see https://composer.github.io/pubkeys.html

> Installer Checksum (SHA-384)
`ed0feb545ba87161262f2d45a633e34f591ebb3381f2e0063c345ebea4d228dd0043083717770234ec00c5a9f9593792`
> Last Updated: 2025-09-18

Also hardens the install script.

Co-authored-by: Sergii Tkachenko <[email protected]>