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Use PidfdChildWatcher by default when available (home-assistant#87951)
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This is a backport from cpython 3.12

https://docs.python.org/3/library/asyncio-policy.html
> PidfdChildWatcher is a “Goldilocks” child watcher implementation. It doesn’t require signals or threads, doesn’t interfere with any processes launched outside the event loop, and scales linearly with the number of subprocesses launched by the event loop. The main disadvantage is that pidfds are specific to Linux, and only work on recent (5.3+) kernels.

python/cpython#98024
There are some additional fixes in cpython 3.12
in python/cpython#94184
when there is no event loop running in the main thread
but this is not a problem we have
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bdraco authored and AlePerla committed Feb 17, 2023
1 parent 5c1af53 commit 638c431
Showing 1 changed file with 35 additions and 0 deletions.
35 changes: 35 additions & 0 deletions homeassistant/runner.py
Original file line number Diff line number Diff line change
Expand Up @@ -2,8 +2,10 @@
from __future__ import annotations

import asyncio
from asyncio import events
import dataclasses
import logging
import os
import threading
import traceback
from typing import Any
Expand Down Expand Up @@ -49,13 +51,46 @@ class RuntimeConfig:
open_ui: bool = False


def can_use_pidfd() -> bool:
"""Check if pidfd_open is available.
Back ported from cpython 3.12
"""
if not hasattr(os, "pidfd_open"):
return False
try:
pid = os.getpid()
os.close(os.pidfd_open(pid, 0)) # pylint: disable=no-member
except OSError:
# blocked by security policy like SECCOMP
return False
return True


class HassEventLoopPolicy(asyncio.DefaultEventLoopPolicy):
"""Event loop policy for Home Assistant."""

def __init__(self, debug: bool) -> None:
"""Init the event loop policy."""
super().__init__()
self.debug = debug
self._watcher: asyncio.AbstractChildWatcher | None = None

def _init_watcher(self) -> None:
"""Initialize the watcher for child processes.
Back ported from cpython 3.12
"""
with events._lock: # type: ignore[attr-defined] # pylint: disable=protected-access
if self._watcher is None: # pragma: no branch
if can_use_pidfd():
self._watcher = asyncio.PidfdChildWatcher()
else:
self._watcher = asyncio.ThreadedChildWatcher()
if threading.current_thread() is threading.main_thread():
self._watcher.attach_loop(
self._local._loop # type: ignore[attr-defined] # pylint: disable=protected-access
)

@property
def loop_name(self) -> str:
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