Avoid subprocess memory copy when c library supports posix_spawn (#87958)

* use posix spawn on alpine

* Avoid subprocess memory copy when c library supports posix_spawn

By default python 3.10 will use the fork() which has to
copy all the memory of the parent process (in our case
this can be huge since Home Assistant core can use
hundreds of megabytes of RAM). By using posix_spawn
this is avoided.

In python 3.11 vfork will also be available
https://github.com/python/cpython/issues/80004#issuecomment-1093810689
https://github.com/python/cpython/pull/11671 but we won't
always be able to use it and posix_spawn is considered safer
https://bugzilla.kernel.org/show_bug.cgi?id=215813#c14

The subprocess library doesn't know about musl though
even though it supports posix_spawn https://git.musl-libc.org/cgit/musl/log/src/process/posix_spawn.c
so we have to teach it since it only has checks for glibc
1b736838e6/Lib/subprocess.py (L745)

The constant is documented as being able to be flipped here:
https://docs.python.org/3/library/subprocess.html#disabling-use-of-vfork-or-posix-spawn

* Avoid subprocess memory copy when c library supports posix_spawn

By default python 3.10 will use the fork() which has to
copy memory of the parent process (in our case
this can be huge since Home Assistant core can use
hundreds of megabytes of RAM). By using posix_spawn
this is avoided and subprocess creation does not
get discernibly slow the larger the Home Assistant
python process grows.

In python 3.11 vfork will also be available
https://github.com/python/cpython/issues/80004#issuecomment-1093810689
https://github.com/python/cpython/pull/11671 but we won't
always be able to use it and posix_spawn is considered safer
https://bugzilla.kernel.org/show_bug.cgi?id=215813#c14

The subprocess library doesn't know about musl though
even though it supports posix_spawn https://git.musl-libc.org/cgit/musl/log/src/process/posix_spawn.c
so we have to teach it since it only has checks for glibc
1b736838e6/Lib/subprocess.py (L745)

The constant is documented as being able to be flipped here:
https://docs.python.org/3/library/subprocess.html#disabling-use-of-vfork-or-posix-spawn

* missed some

* adjust more tests

* coverage

homeassistant/runner.py

@@ -6,6 +6,7 @@ from asyncio import events
 import dataclasses
 import logging
 import os
+import subprocess
 import threading
 import traceback
 from typing import Any
@@ -28,6 +29,7 @@ from .util.thread import deadlock_safe_shutdown
 #
 MAX_EXECUTOR_WORKERS = 64
 TASK_CANCELATION_TIMEOUT = 5
+ALPINE_RELEASE_FILE = "/etc/alpine-release"
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -153,8 +155,22 @@ async def setup_and_run_hass(runtime_config: RuntimeConfig) -> int:
     return await hass.async_run()
 
 
+def _enable_posix_spawn() -> None:
+    """Enable posix_spawn on Alpine Linux."""
+    # pylint: disable=protected-access
+    if subprocess._USE_POSIX_SPAWN:
+        return
+
+    # The subprocess module does not know about Alpine Linux/musl
+    # and will use fork() instead of posix_spawn() which significantly
+    # less efficient. This is a workaround to force posix_spawn()
+    # on Alpine Linux which is supported by musl.
+    subprocess._USE_POSIX_SPAWN = os.path.exists(ALPINE_RELEASE_FILE)
+
+
 def run(runtime_config: RuntimeConfig) -> int:
     """Run Home Assistant."""
+    _enable_posix_spawn()
     asyncio.set_event_loop_policy(HassEventLoopPolicy(runtime_config.debug))
     # Backport of cpython 3.9 asyncio.run with a _cancel_all_tasks that times out
     loop = asyncio.new_event_loop()