guanlan-src/vendor/pyfastapi/anyio/_backends/_asyncio.py

from __future__ import annotations

import array
import asyncio
import concurrent.futures
import math
import os
import socket
import sys
import threading
import weakref
from asyncio import (
    AbstractEventLoop,
    CancelledError,
    all_tasks,
    create_task,
    current_task,
    get_running_loop,
    sleep,
)
from asyncio.base_events import _run_until_complete_cb  # type: ignore[attr-defined]
from collections import OrderedDict, deque
from collections.abc import (
    AsyncGenerator,
    AsyncIterator,
    Awaitable,
    Callable,
    Collection,
    Coroutine,
    Iterable,
    Sequence,
)
from concurrent.futures import Future
from contextlib import AbstractContextManager, suppress
from contextvars import Context, copy_context
from dataclasses import dataclass, field
from functools import partial, wraps
from inspect import (
    CORO_RUNNING,
    CORO_SUSPENDED,
    getcoroutinestate,
)
from io import IOBase
from os import PathLike
from queue import Queue
from signal import Signals
from socket import AddressFamily, SocketKind
from threading import Thread
from types import CodeType, TracebackType
from typing import (
    IO,
    TYPE_CHECKING,
    Any,
    Literal,
    ParamSpec,
    TypeVar,
    cast,
)
from weakref import WeakKeyDictionary

from .. import (
    CapacityLimiterStatistics,
    EventStatistics,
    LockStatistics,
    TaskInfo,
    abc,
)
from .._core._eventloop import (
    claim_worker_thread,
    set_current_async_library,
    threadlocals,
)
from .._core._exceptions import (
    BrokenResourceError,
    BusyResourceError,
    ClosedResourceError,
    EndOfStream,
    RunFinishedError,
    WouldBlock,
)
from .._core._sockets import convert_ipv6_sockaddr
from .._core._streams import create_memory_object_stream
from .._core._synchronization import (
    CapacityLimiter as BaseCapacityLimiter,
)
from .._core._synchronization import Event as BaseEvent
from .._core._synchronization import Lock as BaseLock
from .._core._synchronization import (
    ResourceGuard,
    SemaphoreStatistics,
)
from .._core._synchronization import Semaphore as BaseSemaphore
from .._core._tasks import CancelScope as BaseCancelScope
from .._core._tasks import TaskHandle
from ..abc import (
    AsyncBackend,
    IPSockAddrType,
    SocketListener,
    UDPPacketType,
    UNIXDatagramPacketType,
)
from ..abc._tasks import call_for_coroutine, get_callable_name, get_coro_name
from ..lowlevel import RunVar, _run_vars

if TYPE_CHECKING:
    from _typeshed import FileDescriptorLike

    from ..abc._eventloop import StrOrBytesPath
    from ..streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
else:
    FileDescriptorLike = object

if sys.version_info >= (3, 11):
    from asyncio import Runner
    from typing import Self, TypeVarTuple, Unpack
else:
    import contextvars
    import enum
    import signal
    from asyncio import coroutines, events, exceptions, tasks

    from exceptiongroup import BaseExceptionGroup
    from typing_extensions import Self, TypeVarTuple, Unpack

    class _State(enum.Enum):
        CREATED = "created"
        INITIALIZED = "initialized"
        CLOSED = "closed"

    class Runner:
        # Copied from CPython 3.11
        def __init__(
            self,
            *,
            debug: bool | None = None,
            loop_factory: Callable[[], AbstractEventLoop] | None = None,
        ):
            self._state = _State.CREATED
            self._debug = debug
            self._loop_factory = loop_factory
            self._loop: AbstractEventLoop | None = None
            self._context = None
            self._interrupt_count = 0
            self._set_event_loop = False

        def __enter__(self) -> Self:
            self._lazy_init()
            return self

        def __exit__(
            self,
            exc_type: type[BaseException] | None,
            exc_val: BaseException | None,
            exc_tb: TracebackType | None,
        ) -> None:
            self.close()

        def close(self) -> None:
            """Shutdown and close event loop."""
            loop = self._loop
            if self._state is not _State.INITIALIZED or loop is None:
                return
            try:
                _cancel_all_tasks(loop)
                loop.run_until_complete(loop.shutdown_asyncgens())
                if hasattr(loop, "shutdown_default_executor"):
                    loop.run_until_complete(loop.shutdown_default_executor())
                else:
                    loop.run_until_complete(_shutdown_default_executor(loop))
            finally:
                if self._set_event_loop:
                    events.set_event_loop(None)
                loop.close()
                self._loop = None
                self._state = _State.CLOSED

        def get_loop(self) -> AbstractEventLoop:
            """Return embedded event loop."""
            self._lazy_init()
            return self._loop

        def run(self, coro: Coroutine[T_Retval], *, context=None) -> T_Retval:
            """Run a coroutine inside the embedded event loop."""
            if not coroutines.iscoroutine(coro):
                raise ValueError(f"a coroutine was expected, got {coro!r}")

            if events._get_running_loop() is not None:
                # fail fast with short traceback
                raise RuntimeError(
                    "Runner.run() cannot be called from a running event loop"
                )

            self._lazy_init()

            if context is None:
                context = self._context
            task = context.run(self._loop.create_task, coro)

            if (
                threading.current_thread() is threading.main_thread()
                and signal.getsignal(signal.SIGINT) is signal.default_int_handler
            ):
                sigint_handler = partial(self._on_sigint, main_task=task)
                try:
                    signal.signal(signal.SIGINT, sigint_handler)
                except ValueError:
                    # `signal.signal` may throw if `threading.main_thread` does
                    # not support signals (e.g. embedded interpreter with signals
                    # not registered - see gh-91880)
                    sigint_handler = None
            else:
                sigint_handler = None

            self._interrupt_count = 0
            try:
                return self._loop.run_until_complete(task)
            except exceptions.CancelledError:
                if self._interrupt_count > 0:
                    uncancel = getattr(task, "uncancel", None)
                    if uncancel is not None and uncancel() == 0:
                        raise KeyboardInterrupt  # noqa: B904
                raise  # CancelledError
            finally:
                if (
                    sigint_handler is not None
                    and signal.getsignal(signal.SIGINT) is sigint_handler
                ):
                    signal.signal(signal.SIGINT, signal.default_int_handler)

        def _lazy_init(self) -> None:
            if self._state is _State.CLOSED:
                raise RuntimeError("Runner is closed")
            if self._state is _State.INITIALIZED:
                return
            if self._loop_factory is None:
                self._loop = events.new_event_loop()
                if not self._set_event_loop:
                    # Call set_event_loop only once to avoid calling
                    # attach_loop multiple times on child watchers
                    events.set_event_loop(self._loop)
                    self._set_event_loop = True
            else:
                self._loop = self._loop_factory()
            if self._debug is not None:
                self._loop.set_debug(self._debug)
            self._context = contextvars.copy_context()
            self._state = _State.INITIALIZED

        def _on_sigint(self, signum, frame, main_task: asyncio.Task) -> None:
            self._interrupt_count += 1
            if self._interrupt_count == 1 and not main_task.done():
                main_task.cancel()
                # wakeup loop if it is blocked by select() with long timeout
                self._loop.call_soon_threadsafe(lambda: None)
                return
            raise KeyboardInterrupt()

    def _cancel_all_tasks(loop: AbstractEventLoop) -> None:
        to_cancel = tasks.all_tasks(loop)
        if not to_cancel:
            return

        for task in to_cancel:
            task.cancel()

        loop.run_until_complete(tasks.gather(*to_cancel, return_exceptions=True))

        for task in to_cancel:
            if task.cancelled():
                continue
            if task.exception() is not None:
                loop.call_exception_handler(
                    {
                        "message": "unhandled exception during asyncio.run() shutdown",
                        "exception": task.exception(),
                        "task": task,
                    }
                )

    async def _shutdown_default_executor(loop: AbstractEventLoop) -> None:
        """Schedule the shutdown of the default executor."""

        def _do_shutdown(future: asyncio.futures.Future) -> None:
            try:
                loop._default_executor.shutdown(wait=True)  # type: ignore[attr-defined]
                loop.call_soon_threadsafe(future.set_result, None)
            except Exception as ex:
                loop.call_soon_threadsafe(future.set_exception, ex)

        loop._executor_shutdown_called = True
        if loop._default_executor is None:
            return
        future = loop.create_future()
        thread = threading.Thread(target=_do_shutdown, args=(future,))
        thread.start()
        try:
            await future
        finally:
            thread.join()


T_Retval = TypeVar("T_Retval")
T_co = TypeVar("T_co", covariant=True)
T_contra = TypeVar("T_contra", contravariant=True)
PosArgsT = TypeVarTuple("PosArgsT")
P = ParamSpec("P")

_root_task: RunVar[asyncio.Task[Any] | None] = RunVar("_root_task")


def find_root_task() -> asyncio.Task:
    root_task = _root_task.get(None)
    if root_task is not None and not root_task.done():
        return root_task

    # Look for a task that has been started via run_until_complete()
    for task in all_tasks():
        if task._callbacks and not task.done():
            for cb, context in task._callbacks:
                if (
                    cb is _run_until_complete_cb
                    or getattr(cb, "__module__", None) == "uvloop.loop"
                ):
                    _root_task.set(task)

                    def _unset(t: asyncio.Task[Any]) -> None:
                        if vars := _run_vars.get(t.get_loop()):
                            vars.pop(_root_task, None)

                    # Register a callback to break the task -> loop -> _run_var[loop][_root_task] -> task cycle
                    # Also run it in its own context to not create another reference.
                    # We can't use RunVar.reset() here since these are called synchronously
                    # and thus lowlevel.current_token() (which RunVar.reset() depends on) fails.
                    task.add_done_callback(_unset, context=context)
                    return task

    # Look up the topmost task in the AnyIO task tree, if possible
    task = cast(asyncio.Task, current_task())
    state = _task_states.get(task)
    if state:
        cancel_scope = state.cancel_scope
        while cancel_scope and cancel_scope._parent_scope is not None:
            cancel_scope = cancel_scope._parent_scope

        if cancel_scope is not None:
            return cast(asyncio.Task, cancel_scope._host_task)

    return task


def _task_started(task: asyncio.Task) -> bool:
    """Return ``True`` if the task has been started and has not finished."""
    # The task coro should never be None here, as we never add finished tasks to the
    # task list
    coro = task.get_coro()
    assert coro is not None
    return getcoroutinestate(coro) in (CORO_RUNNING, CORO_SUSPENDED)


#
# Timeouts and cancellation
#


def is_anyio_cancellation(exc: CancelledError) -> bool:
    # Sometimes third party frameworks catch a CancelledError and raise a new one, so as
    # a workaround we have to look at the previous ones in __context__ too for a
    # matching cancel message
    while True:
        if (
            exc.args
            and isinstance(exc.args[0], str)
            and exc.args[0].startswith("Cancelled via cancel scope ")
        ):
            return True

        if isinstance(exc.__context__, CancelledError):
            exc = exc.__context__
            continue

        return False


class CancelScope(BaseCancelScope):
    __slots__ = (
        "_active",
        "_cancel_called",
        "_cancel_handle",
        "_cancel_reason",
        "_cancelled_caught",
        "_child_scopes",
        "_deadline",
        "_host_task",
        "_parent_scope",
        "_pending_uncancellations",
        "_shield",
        "_tasks",
        "_timeout_handle",
    )

    def __new__(cls, *, deadline: float = math.inf, shield: bool = False) -> Self:
        return object.__new__(cls)

    def __init__(self, deadline: float = math.inf, shield: bool = False):
        self._deadline = deadline
        self._shield = shield
        self._parent_scope: CancelScope | None = None
        self._child_scopes: set[CancelScope] = set()
        self._cancel_called = False
        self._cancel_reason: str | None = None
        self._cancelled_caught = False
        self._active = False
        self._timeout_handle: asyncio.TimerHandle | None = None
        self._cancel_handle: asyncio.Handle | None = None
        self._tasks: set[asyncio.Task] = set()
        self._host_task: asyncio.Task | None = None
        if sys.version_info >= (3, 11):
            self._pending_uncancellations: int | None = 0
        else:
            self._pending_uncancellations = None

    def __enter__(self) -> Self:
        if self._active:
            raise RuntimeError(
                "Each CancelScope may only be used for a single 'with' block"
            )

        self._host_task = host_task = cast(asyncio.Task, current_task())
        self._tasks.add(host_task)
        try:
            task_state = _task_states[host_task]
        except KeyError:
            task_state = TaskState(None, self)
            _task_states[host_task] = task_state
        else:
            self._parent_scope = task_state.cancel_scope
            task_state.cancel_scope = self
            if self._parent_scope is not None:
                # If using an eager task factory, the parent scope may not even contain
                # the host task
                self._parent_scope._child_scopes.add(self)
                self._parent_scope._tasks.discard(host_task)

        self._timeout()
        self._active = True

        # Start cancelling the host task if the scope was cancelled before entering
        if self._cancel_called:
            self._deliver_cancellation(self)

        return self

    def __exit__(
        self,
        exc_type: type[BaseException] | None,
        exc_val: BaseException | None,
        exc_tb: TracebackType | None,
    ) -> bool:
        del exc_tb

        if not self._active:
            raise RuntimeError("This cancel scope is not active")
        if current_task() is not self._host_task:
            raise RuntimeError(
                "Attempted to exit cancel scope in a different task than it was "
                "entered in"
            )

        assert self._host_task is not None
        host_task_state = _task_states.get(self._host_task)
        if host_task_state is None or host_task_state.cancel_scope is not self:
            raise RuntimeError(
                "Attempted to exit a cancel scope that isn't the current tasks's "
                "current cancel scope"
            )

        try:
            self._active = False
            if self._timeout_handle:
                self._timeout_handle.cancel()
                self._timeout_handle = None

            self._tasks.remove(self._host_task)
            if self._parent_scope is not None:
                self._parent_scope._child_scopes.remove(self)
                self._parent_scope._tasks.add(self._host_task)

            host_task_state.cancel_scope = self._parent_scope

            # Restart the cancellation effort in the closest visible, cancelled parent
            # scope if necessary
            self._restart_cancellation_in_parent()

            # We only swallow the exception iff it was an AnyIO CancelledError, either
            # directly as exc_val or inside an exception group and there are no cancelled
            # parent cancel scopes visible to us here
            if self._cancel_called and not self._parent_cancellation_is_visible_to_us:
                # For each level-cancel() call made on the host task, call uncancel()
                while self._pending_uncancellations:
                    self._host_task.uncancel()
                    self._pending_uncancellations -= 1

                # Update cancelled_caught and check for exceptions we must not swallow
                if isinstance(exc_val, BaseExceptionGroup):
                    cancelleds_caught, remaining = exc_val.split(
                        lambda exc: (
                            isinstance(exc, CancelledError)
                            and is_anyio_cancellation(exc)
                        )
                    )

                    if cancelleds_caught is None:
                        return False

                    self._cancelled_caught = True

                    if remaining is None:
                        return True

                    context = remaining.__context__
                    try:
                        # Preserve __cause__ and __suppress_context__ by avoiding `raise
                        # ... from ...`
                        raise remaining
                    finally:
                        # Preserve __context__
                        remaining.__context__ = context
                        del context
                else:
                    if isinstance(exc_val, CancelledError) and is_anyio_cancellation(
                        exc_val
                    ):
                        self._cancelled_caught = True
                        return True
                    else:
                        return False
            else:
                if self._pending_uncancellations:
                    assert self._parent_scope is not None
                    assert self._parent_scope._pending_uncancellations is not None
                    self._parent_scope._pending_uncancellations += (
                        self._pending_uncancellations
                    )
                    self._pending_uncancellations = 0

                return False
        finally:
            self._host_task = None
            del exc_val

    @property
    def _effectively_cancelled(self) -> bool:
        cancel_scope: CancelScope | None = self
        while cancel_scope is not None:
            if cancel_scope._cancel_called:
                return True

            if cancel_scope.shield:
                return False

            cancel_scope = cancel_scope._parent_scope

        return False

    @property
    def _parent_cancellation_is_visible_to_us(self) -> bool:
        return (
            self._parent_scope is not None
            and not self.shield
            and self._parent_scope._effectively_cancelled
        )

    def _timeout(self) -> None:
        if self._deadline != math.inf:
            loop = get_running_loop()
            if loop.time() >= self._deadline:
                self.cancel("deadline exceeded")
            else:
                self._timeout_handle = loop.call_at(self._deadline, self._timeout)

    def _deliver_cancellation(self, origin: CancelScope) -> bool:
        """
        Deliver cancellation to directly contained tasks and nested cancel scopes.

        Schedule another run at the end if we still have tasks eligible for
        cancellation.

        :param origin: the cancel scope that originated the cancellation
        :return: ``True`` if the delivery needs to be retried on the next cycle

        """
        should_retry = False
        current = current_task()
        for task in self._tasks:
            # Always skip tasks that are already done (see issue #1111)
            if task.done():
                continue

            should_retry = True
            if task._must_cancel:  # type: ignore[attr-defined]
                continue

            # The task is eligible for cancellation if it has started
            if task is not current and (task is self._host_task or _task_started(task)):
                waiter = task._fut_waiter  # type: ignore[attr-defined]
                if not isinstance(waiter, asyncio.Future) or not waiter.done():
                    task.cancel(origin._cancel_reason)
                    if (
                        task is origin._host_task
                        and origin._pending_uncancellations is not None
                    ):
                        origin._pending_uncancellations += 1

        # Deliver cancellation to child scopes that aren't shielded or running their own
        # cancellation callbacks
        for scope in self._child_scopes:
            if not scope._shield and not scope.cancel_called:
                should_retry = scope._deliver_cancellation(origin) or should_retry

        # Schedule another callback if there are still tasks left
        if origin is self:
            if should_retry:
                self._cancel_handle = get_running_loop().call_soon(
                    self._deliver_cancellation, origin
                )
            else:
                self._cancel_handle = None

        return should_retry

    def _restart_cancellation_in_parent(self) -> None:
        """
        Restart the cancellation effort in the closest directly cancelled parent scope.

        """
        scope = self._parent_scope
        while scope is not None:
            if scope._cancel_called:
                if scope._cancel_handle is None:
                    scope._deliver_cancellation(scope)

                break

            # No point in looking beyond any shielded scope
            if scope._shield:
                break

            scope = scope._parent_scope

    def _reparent(self, new_parent: CancelScope) -> None:
        """
        Move this active scope from its current parent to ``new_parent``.

        Used by :meth:`TaskGroup.start` to move a task that has just called
        ``task_status.started()`` into the target task group's cancel scope.
        """
        if self._parent_scope is new_parent:
            return

        if self._parent_scope is not None:
            self._parent_scope._child_scopes.discard(self)

        self._parent_scope = new_parent
        new_parent._child_scopes.add(self)

        # If the new parent (or an ancestor) is already cancelled, (re)start the
        # delivery loop to ensure we're cancelled at next checkpoint like Trio.
        self._restart_cancellation_in_parent()

    def cancel(self, reason: str | None = None) -> None:
        if not self._cancel_called:
            if self._timeout_handle:
                self._timeout_handle.cancel()
                self._timeout_handle = None

            self._cancel_called = True
            self._cancel_reason = f"Cancelled via cancel scope {id(self):x}"
            if task := current_task():
                self._cancel_reason += f" by {task}"

            if reason:
                self._cancel_reason += f"; reason: {reason}"

            if self._host_task is not None:
                self._deliver_cancellation(self)

    @property
    def deadline(self) -> float:
        return self._deadline

    @deadline.setter
    def deadline(self, value: float) -> None:
        self._deadline = float(value)
        if self._timeout_handle is not None:
            self._timeout_handle.cancel()
            self._timeout_handle = None

        if self._active and not self._cancel_called:
            self._timeout()

    @property
    def cancel_called(self) -> bool:
        return self._cancel_called

    @property
    def cancelled_caught(self) -> bool:
        return self._cancelled_caught

    @property
    def shield(self) -> bool:
        return self._shield

    @shield.setter
    def shield(self, value: bool) -> None:
        if self._shield != value:
            self._shield = value
            if not value:
                self._restart_cancellation_in_parent()


#
# Task states
#


class TaskState:
    """
    Encapsulates auxiliary task information that cannot be added to the Task instance
    itself because there are no guarantees about its implementation.
    """

    __slots__ = "__weakref__", "cancel_scope", "parent_id"

    def __init__(self, parent_id: int | None, cancel_scope: CancelScope | None):
        self.parent_id = parent_id
        self.cancel_scope = cancel_scope


_task_states: WeakKeyDictionary[asyncio.Task, TaskState] = WeakKeyDictionary()


#
# Task groups
#


class _AsyncioTaskStatus(abc.TaskStatus[T_contra]):
    def __init__(
        self,
        future: asyncio.Future,
        parent_id: int,
        target_scope: CancelScope,
        spawn_scope: CancelScope,
    ):
        self._future = future
        self._parent_id = parent_id
        # The eventual parent scope for this spawn_scope
        # (after task_status.started() has been called)
        self._target_scope = target_scope
        # The task's own cancel scope, also held by its TaskHandle
        self._spawn_scope = spawn_scope

    def started(self, value: T_contra | None = None) -> None:
        task = cast(asyncio.Task, current_task())
        _task_states[task].parent_id = self._parent_id
        if self._future.done():
            if not self._future.cancelled():
                raise RuntimeError("called 'started' twice on the same task status")
            else:
                # Caller of start() was cancelled, nothing to reparent
                return

        self._future.set_result(value)
        self._spawn_scope._reparent(self._target_scope)


if sys.version_info >= (3, 12):
    _eager_task_factory_code: CodeType | None = asyncio.eager_task_factory.__code__
else:
    _eager_task_factory_code = None


class TaskGroup(abc.TaskGroup):
    def __init__(self) -> None:
        self.cancel_scope: CancelScope = CancelScope()
        self._entered = False
        self._exceptions: list[BaseException] = []
        self._tasks: set[asyncio.Task] = set()
        self._on_completed_fut: asyncio.Future[None] | None = None

    async def __aenter__(self) -> Self:
        if self._entered:
            raise RuntimeError("TaskGroup cannot be entered more than once")

        self._entered = True

        self.cancel_scope.__enter__()
        return self

    async def __aexit__(
        self,
        exc_type: type[BaseException] | None,
        exc_val: BaseException | None,
        exc_tb: TracebackType | None,
    ) -> bool:
        try:
            if exc_val is not None:
                self.cancel_scope.cancel()
                if not isinstance(exc_val, CancelledError):
                    self._exceptions.append(exc_val)

            loop = get_running_loop()
            try:
                if self._tasks:
                    with CancelScope() as wait_scope:
                        while self._tasks:
                            self._on_completed_fut = loop.create_future()

                            try:
                                await self._on_completed_fut
                            except CancelledError as exc:
                                # Shield the scope against further cancellation attempts,
                                # as they're not productive (#695)
                                wait_scope.shield = True
                                self.cancel_scope.cancel()

                                # Set exc_val from the cancellation exception if it was
                                # previously unset. However, we should not replace a native
                                # cancellation exception with one raise by a cancel scope.
                                if exc_val is None or (
                                    isinstance(exc_val, CancelledError)
                                    and not is_anyio_cancellation(exc)
                                ):
                                    exc_val = exc

                            self._on_completed_fut = None
                else:
                    # If there are no child tasks to wait on, run at least one checkpoint
                    # anyway
                    await AsyncIOBackend.cancel_shielded_checkpoint()

                if self._exceptions:
                    # The exception that got us here should already have been
                    # added to self._exceptions so it's ok to break exception
                    # chaining and avoid adding a "During handling of above..."
                    # for each nesting level.
                    raise BaseExceptionGroup(
                        "unhandled errors in a TaskGroup", self._exceptions
                    ) from None
                elif exc_val:
                    raise exc_val
            except BaseException as exc:
                if self.cancel_scope.__exit__(type(exc), exc, exc.__traceback__):
                    return True

                raise

            return self.cancel_scope.__exit__(exc_type, exc_val, exc_tb)
        finally:
            del exc_val, exc_tb, self._exceptions

    def _spawn(
        self,
        coro: Coroutine[Any, Any, T_co],
        name: object,
        task_status: _AsyncioTaskStatus | None = None,
    ) -> TaskHandle[T_co]:
        task_status_future = task_status._future if task_status is not None else None

        def task_done(_task: asyncio.Task) -> None:
            if sys.version_info >= (3, 14) and self.cancel_scope._host_task is not None:
                asyncio.future_discard_from_awaited_by(
                    _task, self.cancel_scope._host_task
                )

            task_state = _task_states[_task]
            assert task_state.cancel_scope is not None
            assert _task in task_state.cancel_scope._tasks
            task_state.cancel_scope._tasks.remove(_task)
            self._tasks.remove(task)
            del _task_states[_task]

            if self._on_completed_fut is not None and not self._tasks:
                try:
                    self._on_completed_fut.set_result(None)
                except asyncio.InvalidStateError:
                    pass

            try:
                exc = _task.exception()
            except CancelledError as e:
                while isinstance(e.__context__, CancelledError):
                    e = e.__context__

                exc = e

            if exc is not None:
                # The future can only be in the cancelled state if the host task was
                # cancelled, so return immediately instead of adding one more
                # CancelledError to the exceptions list
                if task_status_future is not None and task_status_future.cancelled():
                    return

                if task_status_future is None or task_status_future.done():
                    if not isinstance(exc, CancelledError):
                        self._exceptions.append(exc)

                    if not self.cancel_scope._effectively_cancelled:
                        self.cancel_scope.cancel()
                else:
                    task_status_future.set_exception(exc)
            elif task_status_future is not None and not task_status_future.done():
                task_status_future.set_exception(
                    RuntimeError("Child exited without calling task_status.started()")
                )

        if task_status_future is not None:
            parent_id = id(current_task())
            caller_state = _task_states.get(cast(asyncio.Task, current_task()))
            if caller_state is not None and caller_state.cancel_scope is not None:
                initial_scope = caller_state.cancel_scope
            else:
                # The caller is an unmanaged task (no task state)
                initial_scope = self.cancel_scope
        else:
            parent_id = id(self.cancel_scope._host_task)
            initial_scope = self.cancel_scope

        spawn_scope = task_status._spawn_scope if task_status is not None else None
        handle = TaskHandle(coro, name, cancel_scope=spawn_scope)
        loop = asyncio.get_running_loop()
        wrapper_coro = handle._run_coro()
        try:
            if (
                (factory := loop.get_task_factory())
                and getattr(factory, "__code__", None) is _eager_task_factory_code
                and (closure := getattr(factory, "__closure__", None))
            ):
                custom_task_constructor = closure[0].cell_contents
                task = custom_task_constructor(
                    wrapper_coro, loop=loop, name=handle.name
                )
            else:
                task = loop.create_task(wrapper_coro, name=handle.name)
        except BaseException:
            with suppress(BaseException):
                wrapper_coro.close()

            with suppress(BaseException):
                coro.close()

            raise

        # Make the spawned task inherit the initial cancel scope
        _task_states[task] = TaskState(parent_id=parent_id, cancel_scope=initial_scope)
        initial_scope._tasks.add(task)
        self._tasks.add(task)
        if sys.version_info >= (3, 14) and self.cancel_scope._host_task is not None:
            asyncio.future_add_to_awaited_by(task, self.cancel_scope._host_task)

        task.add_done_callback(task_done)
        return handle

    def create_task(
        self,
        coro: Coroutine[Any, Any, T_co],
        *,
        name: object = None,
        context: Context | None = None,
    ) -> TaskHandle[T_co]:
        if not isinstance(coro, Coroutine):
            raise TypeError(f"expected a coroutine, got {coro.__class__.__qualname__}")

        if not self._entered or not self.cancel_scope._active:
            coro.close()
            raise RuntimeError(
                "This task group is not active; no new tasks can be started."
            )

        final_name = get_coro_name(coro, name)

        if context is not None:
            return context.run(self._spawn, coro, name=final_name)
        else:
            return self._spawn(coro, name=final_name)

    async def start(
        self,
        func: Callable[[Unpack[PosArgsT]], Coroutine[Any, Any, T_co]],
        *args: Unpack[PosArgsT],
        name: object = None,
        return_handle: Literal[False, True] = False,
    ) -> Any:
        if not self._entered or not self.cancel_scope._active:
            raise RuntimeError(
                "This task group is not active; no new tasks can be started."
            )

        # Until task_status.started() is called, a task spawned via start() belongs to
        # the *caller's* cancel scope, not the target group's, so cancelling the group
        # does not cancel a task that hasn't reported startup yet. The
        # task_status.started() call moves the task's cancel scope to this task group's
        # cancel scope.
        #
        # The caller may be an unmanaged task (no _task_states entry), in which case
        # fall back to the group's own scope.
        future: asyncio.Future = asyncio.Future()
        final_name = get_callable_name(func, name)
        task_status: _AsyncioTaskStatus[Any] = _AsyncioTaskStatus(
            future, id(self.cancel_scope._host_task), self.cancel_scope, CancelScope()
        )
        coro = call_for_coroutine(func, args, task_status=task_status)
        handle = self._spawn(coro, final_name, task_status)

        # If the task raises an exception after sending a start value without a switch
        # point between, the task group is cancelled and this method never proceeds to
        # process the completed future. That's why we have to have a shielded cancel
        # scope here.
        try:
            await future
        except BaseException:
            if handle.status is TaskHandle.Status.PENDING:
                # Cancel the task and wait for it to exit before returning
                handle.cancel()
                with CancelScope(shield=True):
                    await handle.wait()

            raise

        if return_handle:
            handle._start_value = future.result()
            return handle
        else:
            return future.result()


#
# Threads
#

_Retval_Queue_Type = tuple[T_Retval | None, BaseException | None]


class WorkerThread(Thread):
    MAX_IDLE_TIME = 10  # seconds

    def __init__(
        self,
        root_task: asyncio.Task,
        workers: set[WorkerThread],
        idle_workers: deque[WorkerThread],
    ):
        kwargs: dict[str, Any] = {}
        if sys.version_info >= (3, 14):
            kwargs["context"] = Context()

        super().__init__(name="AnyIO worker thread", **kwargs)
        self.root_task = root_task
        self.workers = workers
        self.idle_workers = idle_workers
        self.loop = root_task._loop
        self.queue: Queue[
            tuple[Context, Callable, tuple, asyncio.Future, CancelScope] | None
        ] = Queue(2)
        self.idle_since = AsyncIOBackend.current_time()
        self.stopping = False

    def _report_result(
        self, future: asyncio.Future, result: Any, exc: BaseException | None
    ) -> None:
        self.idle_since = AsyncIOBackend.current_time()
        if not self.stopping:
            self.idle_workers.append(self)

        if not future.cancelled():
            if exc is not None:
                if isinstance(exc, StopIteration):
                    new_exc = RuntimeError("coroutine raised StopIteration")
                    new_exc.__cause__ = exc
                    exc = new_exc

                future.set_exception(exc)
            else:
                future.set_result(result)

    def run(self) -> None:
        with claim_worker_thread(AsyncIOBackend, self.loop):
            while True:
                item = self.queue.get()
                if item is None:
                    # Shutdown command received
                    return

                context, func, args, future, cancel_scope = item
                if not future.cancelled():
                    result = None
                    exception: BaseException | None = None
                    threadlocals.current_cancel_scope = cancel_scope
                    try:
                        result = context.run(func, *args)
                    except BaseException as exc:
                        exception = exc
                    finally:
                        del threadlocals.current_cancel_scope

                    try:
                        self.loop.call_soon_threadsafe(
                            self._report_result, future, result, exception
                        )
                    except RuntimeError:
                        if not self.loop.is_closed():
                            raise

                    del result, exception

                self.queue.task_done()
                del item, context, func, args, future, cancel_scope

    def stop(self, f: asyncio.Task | None = None) -> None:
        self.stopping = True
        self.queue.put_nowait(None)
        self.workers.discard(self)
        try:
            self.idle_workers.remove(self)
        except ValueError:
            pass


_threadpool_idle_workers: RunVar[deque[WorkerThread]] = RunVar(
    "_threadpool_idle_workers"
)
_threadpool_workers: RunVar[set[WorkerThread]] = RunVar("_threadpool_workers")


#
# Subprocesses
#


@dataclass(eq=False)
class StreamReaderWrapper(abc.ByteReceiveStream):
    _stream: asyncio.StreamReader

    async def receive(self, max_bytes: int = 65536) -> bytes:
        if max_bytes < 1:
            raise ValueError("max_bytes must be a positive integer")

        data = await self._stream.read(max_bytes)
        if data:
            return data
        else:
            raise EndOfStream

    async def aclose(self) -> None:
        self._stream.set_exception(ClosedResourceError())
        await AsyncIOBackend.checkpoint()


@dataclass(eq=False)
class StreamWriterWrapper(abc.ByteSendStream):
    _stream: asyncio.StreamWriter
    _closed: bool = field(init=False, default=False)

    async def send(self, item: bytes) -> None:
        await AsyncIOBackend.checkpoint_if_cancelled()
        stream_paused = self._stream._protocol._paused  # type: ignore[attr-defined]
        try:
            self._stream.write(item)
            await self._stream.drain()
        except (ConnectionResetError, BrokenPipeError, RuntimeError) as exc:
            # If closed by us and/or the peer:
            # * on stdlib, drain() raises ConnectionResetError or BrokenPipeError
            # * on uvloop and Winloop, write() eventually starts raising RuntimeError
            if self._closed:
                raise ClosedResourceError from exc
            elif self._stream.is_closing():
                raise BrokenResourceError from exc

            raise

        if not stream_paused:
            await AsyncIOBackend.cancel_shielded_checkpoint()

    async def aclose(self) -> None:
        self._closed = True
        self._stream.close()
        await AsyncIOBackend.checkpoint()


@dataclass(eq=False)
class Process(abc.Process):
    _process: asyncio.subprocess.Process
    _stdin: StreamWriterWrapper | None
    _stdout: StreamReaderWrapper | None
    _stderr: StreamReaderWrapper | None
    _exited: asyncio.Event
    _transport: asyncio.SubprocessTransport

    async def aclose(self) -> None:
        with CancelScope(shield=True) as scope:
            # We need to close the underlying pipe_transports as well to allow a
            # process blocking on full buffers to receive SIGPIPE and exit.
            if self._stdin:
                await self._stdin.aclose()
                if pipe := self._transport.get_pipe_transport(0):
                    pipe.close()
            if self._stdout:
                await self._stdout.aclose()
                if pipe := self._transport.get_pipe_transport(1):
                    pipe.close()
            if self._stderr:
                await self._stderr.aclose()
                if pipe := self._transport.get_pipe_transport(2):
                    pipe.close()

            scope.shield = False
            try:
                await self.wait()
            except BaseException:
                scope.shield = True
                # Closing the transport on asyncio also handles sending kill
                self._transport.close()
                await self.wait()
                raise

    async def wait(self) -> int:
        await self._exited.wait()
        assert self._process.returncode is not None
        return self._process.returncode

    def terminate(self) -> None:
        self._process.terminate()

    def kill(self) -> None:
        self._process.kill()

    def send_signal(self, signal: int) -> None:
        self._process.send_signal(signal)

    @property
    def pid(self) -> int:
        return self._process.pid

    @property
    def returncode(self) -> int | None:
        return self._process.returncode

    @property
    def stdin(self) -> abc.ByteSendStream | None:
        return self._stdin

    @property
    def stdout(self) -> abc.ByteReceiveStream | None:
        return self._stdout

    @property
    def stderr(self) -> abc.ByteReceiveStream | None:
        return self._stderr


def _forcibly_shutdown_process_pool_on_exit(
    workers: set[Process], _task: object
) -> None:
    """
    Forcibly shuts down worker processes belonging to this event loop."""
    child_watcher: asyncio.AbstractChildWatcher | None = None  # type: ignore[name-defined]
    if sys.version_info < (3, 12):
        try:
            child_watcher = asyncio.get_event_loop_policy().get_child_watcher()
        except NotImplementedError:
            pass

    # Close as much as possible (w/o async/await) to avoid warnings
    for process in workers.copy():
        if process.returncode is not None:
            continue

        process._stdin._stream._transport.close()  # type: ignore[union-attr]
        process._stdout._stream._transport.close()  # type: ignore[union-attr]
        process._stderr._stream._transport.close()  # type: ignore[union-attr]
        process.kill()
        if child_watcher:
            child_watcher.remove_child_handler(process.pid)


async def _shutdown_process_pool_on_exit(workers: set[abc.Process]) -> None:
    """
    Shuts down worker processes belonging to this event loop.

    NOTE: this only works when the event loop was started using asyncio.run() or
    anyio.run().

    """
    process: abc.Process
    try:
        await sleep(math.inf)
    except asyncio.CancelledError:
        workers = workers.copy()
        for process in workers:
            if process.returncode is None:
                process.kill()

        for process in workers:
            await process.aclose()


#
# Sockets and networking
#


class StreamProtocol(asyncio.Protocol):
    read_queue: deque[bytes]
    read_event: asyncio.Event
    write_event: asyncio.Event
    exception: Exception | None = None
    is_at_eof: bool = False

    def connection_made(self, transport: asyncio.BaseTransport) -> None:
        self.read_queue = deque()
        self.read_event = asyncio.Event()
        self.write_event = asyncio.Event()
        self.write_event.set()
        cast(asyncio.Transport, transport).set_write_buffer_limits(0)

    def connection_lost(self, exc: Exception | None) -> None:
        if exc:
            self.exception = exc

        self.read_event.set()
        self.write_event.set()

    def data_received(self, data: bytes) -> None:
        # ProactorEventloop sometimes sends bytearray instead of bytes
        self.read_queue.append(bytes(data))
        self.read_event.set()

    def eof_received(self) -> bool | None:
        self.is_at_eof = True
        self.read_event.set()
        return True

    def pause_writing(self) -> None:
        self.write_event = asyncio.Event()

    def resume_writing(self) -> None:
        self.write_event.set()


class DatagramProtocol(asyncio.DatagramProtocol):
    read_queue: deque[tuple[bytes, IPSockAddrType]]
    read_event: asyncio.Event
    write_event: asyncio.Event
    closed_event: asyncio.Event
    exception: Exception | None = None

    def connection_made(self, transport: asyncio.BaseTransport) -> None:
        self.read_queue = deque(maxlen=100)  # arbitrary value
        self.read_event = asyncio.Event()
        self.write_event = asyncio.Event()
        self.closed_event = asyncio.Event()
        self.write_event.set()

    def connection_lost(self, exc: Exception | None) -> None:
        self.read_event.set()
        self.write_event.set()
        self.closed_event.set()

    def datagram_received(self, data: bytes, addr: IPSockAddrType) -> None:
        addr = convert_ipv6_sockaddr(addr)
        self.read_queue.append((data, addr))
        self.read_event.set()

    def error_received(self, exc: Exception) -> None:
        self.exception = exc

    def pause_writing(self) -> None:
        self.write_event.clear()

    def resume_writing(self) -> None:
        self.write_event.set()


class SocketStream(abc.SocketStream):
    def __init__(self, transport: asyncio.Transport, protocol: StreamProtocol):
        self._transport = transport
        self._protocol = protocol
        self._receive_guard = ResourceGuard("reading from")
        self._send_guard = ResourceGuard("writing to")
        self._closed = False

    @property
    def _raw_socket(self) -> socket.socket:
        return self._transport.get_extra_info("socket")

    async def receive(self, max_bytes: int = 65536) -> bytes:
        if max_bytes < 1:
            raise ValueError("max_bytes must be a positive integer")

        with self._receive_guard:
            if (
                not self._protocol.read_event.is_set()
                and not self._transport.is_closing()
                and not self._protocol.is_at_eof
            ):
                self._transport.resume_reading()
                await self._protocol.read_event.wait()
                self._transport.pause_reading()
            else:
                await AsyncIOBackend.checkpoint()

            try:
                chunk = self._protocol.read_queue.popleft()
            except IndexError:
                if self._closed:
                    raise ClosedResourceError from None
                elif self._protocol.exception:
                    raise BrokenResourceError from self._protocol.exception
                else:
                    raise EndOfStream from None

            if len(chunk) > max_bytes:
                # Split the oversized chunk
                chunk, leftover = chunk[:max_bytes], chunk[max_bytes:]
                self._protocol.read_queue.appendleft(leftover)

            # If the read queue is empty, clear the flag so that the next call will
            # block until data is available
            if not self._protocol.read_queue:
                self._protocol.read_event.clear()

        return chunk

    async def send(self, item: bytes) -> None:
        with self._send_guard:
            await AsyncIOBackend.checkpoint()

            if self._closed:
                raise ClosedResourceError
            elif self._protocol.exception is not None:
                raise BrokenResourceError from self._protocol.exception

            try:
                self._transport.write(item)
            except RuntimeError as exc:
                if self._transport.is_closing():
                    raise BrokenResourceError from exc
                else:
                    raise

            await self._protocol.write_event.wait()

    async def send_eof(self) -> None:
        try:
            self._transport.write_eof()
        except OSError:
            pass

    async def aclose(self) -> None:
        self._closed = True
        if not self._transport.is_closing():
            try:
                self._transport.write_eof()
            except OSError:
                pass

            self._transport.close()
            await sleep(0)
            self._transport.abort()


class _RawSocketMixin:
    _receive_future: asyncio.Future | None = None
    _send_future: asyncio.Future | None = None
    _closing = False

    def __init__(self, raw_socket: socket.socket):
        self.__raw_socket = raw_socket
        self._receive_guard = ResourceGuard("reading from")
        self._send_guard = ResourceGuard("writing to")

    @property
    def _raw_socket(self) -> socket.socket:
        return self.__raw_socket

    def _wait_until_readable(self, loop: asyncio.AbstractEventLoop) -> asyncio.Future:
        def callback(f: object) -> None:
            del self._receive_future
            loop.remove_reader(self.__raw_socket)

        f = self._receive_future = asyncio.Future()
        loop.add_reader(self.__raw_socket, f.set_result, None)
        f.add_done_callback(callback)
        return f

    def _wait_until_writable(self, loop: asyncio.AbstractEventLoop) -> asyncio.Future:
        def callback(f: object) -> None:
            del self._send_future
            loop.remove_writer(self.__raw_socket)

        f = self._send_future = asyncio.Future()
        loop.add_writer(self.__raw_socket, f.set_result, None)
        f.add_done_callback(callback)
        return f

    async def aclose(self) -> None:
        if not self._closing:
            self._closing = True
            if self.__raw_socket.fileno() != -1:
                self.__raw_socket.close()

            if self._receive_future and not self._receive_future.done():
                self._receive_future.set_result(None)
            if self._send_future and not self._send_future.done():
                self._send_future.set_result(None)


class UNIXSocketStream(_RawSocketMixin, abc.UNIXSocketStream):
    async def send_eof(self) -> None:
        with self._send_guard:
            self._raw_socket.shutdown(socket.SHUT_WR)

    async def receive(self, max_bytes: int = 65536) -> bytes:
        if max_bytes < 1:
            raise ValueError("max_bytes must be a positive integer")

        loop = get_running_loop()
        await AsyncIOBackend.checkpoint()
        with self._receive_guard:
            while True:
                try:
                    data = self._raw_socket.recv(max_bytes)
                except BlockingIOError:
                    await self._wait_until_readable(loop)
                except OSError as exc:
                    if self._closing:
                        raise ClosedResourceError from None
                    else:
                        raise BrokenResourceError from exc
                else:
                    if not data:
                        raise EndOfStream

                    return data

    async def send(self, item: bytes) -> None:
        loop = get_running_loop()
        await AsyncIOBackend.checkpoint()
        with self._send_guard:
            view = memoryview(item)
            while view:
                try:
                    bytes_sent = self._raw_socket.send(view)
                except BlockingIOError:
                    await self._wait_until_writable(loop)
                except OSError as exc:
                    if self._closing:
                        raise ClosedResourceError from None
                    else:
                        raise BrokenResourceError from exc
                else:
                    view = view[bytes_sent:]

    async def receive_fds(self, msglen: int, maxfds: int) -> tuple[bytes, list[int]]:
        if not isinstance(msglen, int) or msglen < 0:
            raise ValueError("msglen must be a non-negative integer")
        if not isinstance(maxfds, int) or maxfds < 1:
            raise ValueError("maxfds must be a positive integer")

        loop = get_running_loop()
        fds = array.array("i")
        await AsyncIOBackend.checkpoint()
        with self._receive_guard:
            while True:
                try:
                    message, ancdata, _flags, _addr = self._raw_socket.recvmsg(
                        msglen, socket.CMSG_LEN(maxfds * fds.itemsize)
                    )
                except BlockingIOError:
                    await self._wait_until_readable(loop)
                except OSError as exc:
                    if self._closing:
                        raise ClosedResourceError from None
                    else:
                        raise BrokenResourceError from exc
                else:
                    if not message and not ancdata:
                        raise EndOfStream

                    break

        for cmsg_level, cmsg_type, cmsg_data in ancdata:
            if cmsg_level != socket.SOL_SOCKET or cmsg_type != socket.SCM_RIGHTS:
                raise RuntimeError(
                    f"Received unexpected ancillary data; message = {message!r}, "
                    f"cmsg_level = {cmsg_level}, cmsg_type = {cmsg_type}"
                )

            fds.frombytes(cmsg_data[: len(cmsg_data) - (len(cmsg_data) % fds.itemsize)])

        return message, list(fds)

    async def send_fds(self, message: bytes, fds: Collection[int | IOBase]) -> None:
        if not message:
            raise ValueError("message must not be empty")
        if not fds:
            raise ValueError("fds must not be empty")

        loop = get_running_loop()
        filenos: list[int] = []
        for fd in fds:
            if isinstance(fd, int):
                filenos.append(fd)
            elif isinstance(fd, IOBase):
                filenos.append(fd.fileno())

        fdarray = array.array("i", filenos)
        await AsyncIOBackend.checkpoint()
        with self._send_guard:
            while True:
                try:
                    # The ignore can be removed after mypy picks up
                    # https://github.com/python/typeshed/pull/5545
                    self._raw_socket.sendmsg(
                        [message], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, fdarray)]
                    )
                    break
                except BlockingIOError:
                    await self._wait_until_writable(loop)
                except OSError as exc:
                    if self._closing:
                        raise ClosedResourceError from None
                    else:
                        raise BrokenResourceError from exc


class TCPSocketListener(abc.SocketListener):
    _accept_scope: CancelScope | None = None
    _closed = False

    def __init__(self, raw_socket: socket.socket):
        self.__raw_socket = raw_socket
        self._loop = cast(asyncio.BaseEventLoop, get_running_loop())
        self._accept_guard = ResourceGuard("accepting connections from")

    @property
    def _raw_socket(self) -> socket.socket:
        return self.__raw_socket

    async def accept(self) -> abc.SocketStream:
        if self._closed:
            raise ClosedResourceError

        with self._accept_guard:
            await AsyncIOBackend.checkpoint()
            with CancelScope() as self._accept_scope:
                try:
                    client_sock, _addr = await self._loop.sock_accept(self._raw_socket)
                except asyncio.CancelledError:
                    # Workaround for https://bugs.python.org/issue41317
                    try:
                        self._loop.remove_reader(self._raw_socket)
                    except (ValueError, NotImplementedError):
                        pass

                    if self._closed:
                        raise ClosedResourceError from None

                    raise
                finally:
                    self._accept_scope = None

        client_sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
        transport, protocol = await self._loop.connect_accepted_socket(
            StreamProtocol, client_sock
        )
        return SocketStream(transport, protocol)

    async def aclose(self) -> None:
        if self._closed:
            return

        self._closed = True
        if self._accept_scope:
            # Workaround for https://bugs.python.org/issue41317
            try:
                self._loop.remove_reader(self._raw_socket)
            except (ValueError, NotImplementedError):
                pass

            self._accept_scope.cancel()
            await sleep(0)

        self._raw_socket.close()


class UNIXSocketListener(abc.SocketListener):
    def __init__(self, raw_socket: socket.socket):
        self.__raw_socket = raw_socket
        self._loop = get_running_loop()
        self._accept_guard = ResourceGuard("accepting connections from")
        self._closed = False

    async def accept(self) -> abc.SocketStream:
        await AsyncIOBackend.checkpoint()
        with self._accept_guard:
            while True:
                try:
                    client_sock, _ = self.__raw_socket.accept()
                    client_sock.setblocking(False)
                    return UNIXSocketStream(client_sock)
                except BlockingIOError:
                    f: asyncio.Future = asyncio.Future()
                    self._loop.add_reader(self.__raw_socket, f.set_result, None)
                    f.add_done_callback(
                        lambda _: self._loop.remove_reader(self.__raw_socket)
                    )
                    await f
                except OSError as exc:
                    if self._closed:
                        raise ClosedResourceError from None
                    else:
                        raise BrokenResourceError from exc

    async def aclose(self) -> None:
        self._closed = True
        self.__raw_socket.close()

    @property
    def _raw_socket(self) -> socket.socket:
        return self.__raw_socket


class UDPSocket(abc.UDPSocket):
    def __init__(
        self, transport: asyncio.DatagramTransport, protocol: DatagramProtocol
    ):
        self._transport = transport
        self._protocol = protocol
        self._receive_guard = ResourceGuard("reading from")
        self._send_guard = ResourceGuard("writing to")
        self._closed = False

    @property
    def _raw_socket(self) -> socket.socket:
        return self._transport.get_extra_info("socket")

    async def aclose(self) -> None:
        self._closed = True
        if not self._transport.is_closing():
            self._transport.close()

        await self._protocol.closed_event.wait()

    async def receive(self) -> tuple[bytes, IPSockAddrType]:
        with self._receive_guard:
            await AsyncIOBackend.checkpoint()

            # If the buffer is empty, ask for more data
            if not self._protocol.read_queue and not self._transport.is_closing():
                self._protocol.read_event.clear()
                await self._protocol.read_event.wait()

            try:
                return self._protocol.read_queue.popleft()
            except IndexError:
                if self._closed:
                    raise ClosedResourceError from None
                else:
                    raise BrokenResourceError from None

    async def send(self, item: UDPPacketType) -> None:
        with self._send_guard:
            await AsyncIOBackend.checkpoint()
            await self._protocol.write_event.wait()
            if self._closed:
                raise ClosedResourceError
            elif self._transport.is_closing():
                raise BrokenResourceError
            else:
                self._transport.sendto(*item)


class ConnectedUDPSocket(abc.ConnectedUDPSocket):
    def __init__(
        self, transport: asyncio.DatagramTransport, protocol: DatagramProtocol
    ):
        self._transport = transport
        self._protocol = protocol
        self._receive_guard = ResourceGuard("reading from")
        self._send_guard = ResourceGuard("writing to")
        self._closed = False

    @property
    def _raw_socket(self) -> socket.socket:
        return self._transport.get_extra_info("socket")

    async def aclose(self) -> None:
        self._closed = True
        if not self._transport.is_closing():
            self._transport.close()

        await self._protocol.closed_event.wait()

    async def receive(self) -> bytes:
        with self._receive_guard:
            await AsyncIOBackend.checkpoint()

            # If the buffer is empty, ask for more data
            if not self._protocol.read_queue and not self._transport.is_closing():
                self._protocol.read_event.clear()
                await self._protocol.read_event.wait()

            try:
                packet = self._protocol.read_queue.popleft()
            except IndexError:
                if self._closed:
                    raise ClosedResourceError from None
                else:
                    raise BrokenResourceError from None

            return packet[0]

    async def send(self, item: bytes) -> None:
        with self._send_guard:
            await AsyncIOBackend.checkpoint()
            await self._protocol.write_event.wait()
            if self._closed:
                raise ClosedResourceError
            elif self._transport.is_closing():
                raise BrokenResourceError
            else:
                self._transport.sendto(item)


class UNIXDatagramSocket(_RawSocketMixin, abc.UNIXDatagramSocket):
    async def receive(self) -> UNIXDatagramPacketType:
        loop = get_running_loop()
        await AsyncIOBackend.checkpoint()
        with self._receive_guard:
            while True:
                try:
                    data = self._raw_socket.recvfrom(65536)
                except BlockingIOError:
                    await self._wait_until_readable(loop)
                except OSError as exc:
                    if self._closing:
                        raise ClosedResourceError from None
                    else:
                        raise BrokenResourceError from exc
                else:
                    return data

    async def send(self, item: UNIXDatagramPacketType) -> None:
        loop = get_running_loop()
        await AsyncIOBackend.checkpoint()
        with self._send_guard:
            while True:
                try:
                    self._raw_socket.sendto(*item)
                except BlockingIOError:
                    await self._wait_until_writable(loop)
                except OSError as exc:
                    if self._closing:
                        raise ClosedResourceError from None
                    else:
                        raise BrokenResourceError from exc
                else:
                    return


class ConnectedUNIXDatagramSocket(_RawSocketMixin, abc.ConnectedUNIXDatagramSocket):
    async def receive(self) -> bytes:
        loop = get_running_loop()
        await AsyncIOBackend.checkpoint()
        with self._receive_guard:
            while True:
                try:
                    data = self._raw_socket.recv(65536)
                except BlockingIOError:
                    await self._wait_until_readable(loop)
                except OSError as exc:
                    if self._closing:
                        raise ClosedResourceError from None
                    else:
                        raise BrokenResourceError from exc
                else:
                    return data

    async def send(self, item: bytes) -> None:
        loop = get_running_loop()
        await AsyncIOBackend.checkpoint()
        with self._send_guard:
            while True:
                try:
                    self._raw_socket.send(item)
                except BlockingIOError:
                    await self._wait_until_writable(loop)
                except OSError as exc:
                    if self._closing:
                        raise ClosedResourceError from None
                    else:
                        raise BrokenResourceError from exc
                else:
                    return


_read_events: RunVar[dict[int, asyncio.Future[bool]]] = RunVar("read_events")
_write_events: RunVar[dict[int, asyncio.Future[bool]]] = RunVar("write_events")


#
# Synchronization
#


class Event(BaseEvent):
    __slots__ = ("_event",)

    def __new__(cls) -> Self:
        return object.__new__(cls)

    def __init__(self) -> None:
        self._event = asyncio.Event()

    def set(self) -> None:
        self._event.set()

    def is_set(self) -> bool:
        return self._event.is_set()

    async def wait(self) -> None:
        if self.is_set():
            await AsyncIOBackend.checkpoint()
        else:
            await self._event.wait()

    def statistics(self) -> EventStatistics:
        return EventStatistics(len(self._event._waiters))


class Lock(BaseLock):
    __slots__ = "_fast_acquire", "_owner_task", "_waiters"

    def __new__(cls, *, fast_acquire: bool = False) -> Self:
        return object.__new__(cls)

    def __init__(self, *, fast_acquire: bool = False) -> None:
        self._fast_acquire = fast_acquire
        self._owner_task: asyncio.Task | None = None
        self._waiters: deque[tuple[asyncio.Task, asyncio.Future]] = deque()

    async def acquire(self) -> None:
        task = cast(asyncio.Task, current_task())
        if self._owner_task is None and not self._waiters:
            await AsyncIOBackend.checkpoint_if_cancelled()
            self._owner_task = task

            # Unless on the "fast path", yield control of the event loop so that other
            # tasks can run too
            if not self._fast_acquire:
                try:
                    await AsyncIOBackend.cancel_shielded_checkpoint()
                except CancelledError:
                    self.release()
                    raise

            return

        if self._owner_task == task:
            raise RuntimeError("Attempted to acquire an already held Lock")

        fut: asyncio.Future[None] = asyncio.Future()
        item = task, fut
        self._waiters.append(item)
        try:
            await fut
        except CancelledError:
            if fut.cancelled():
                try:
                    self._waiters.remove(item)
                except ValueError:
                    pass
            else:
                self.release()

            raise

    def acquire_nowait(self) -> None:
        task = cast(asyncio.Task, current_task())
        if self._owner_task is None and not self._waiters:
            self._owner_task = task
            return

        if self._owner_task is task:
            raise RuntimeError("Attempted to acquire an already held Lock")

        raise WouldBlock

    def locked(self) -> bool:
        return self._owner_task is not None

    def release(self) -> None:
        if self._owner_task != current_task():
            raise RuntimeError("The current task is not holding this lock")

        # A cancelled waiter that already received ownership removes itself from
        # _waiters before calling release(); any cancelled waiter still queued here
        # was cancelled before being woken, so drop it.
        while self._waiters:
            task, fut = self._waiters.popleft()
            if fut.cancelled():
                continue

            self._owner_task = task
            fut.set_result(None)
            return

        self._owner_task = None

    def statistics(self) -> LockStatistics:
        task_info = AsyncIOTaskInfo(self._owner_task) if self._owner_task else None
        return LockStatistics(self.locked(), task_info, len(self._waiters))


class Semaphore(BaseSemaphore):
    __slots__ = "_fast_acquire", "_max_value", "_value", "_waiters"

    def __new__(
        cls,
        initial_value: int,
        *,
        max_value: int | None = None,
        fast_acquire: bool = False,
    ) -> Self:
        return object.__new__(cls)

    def __init__(
        self,
        initial_value: int,
        *,
        max_value: int | None = None,
        fast_acquire: bool = False,
    ):
        super().__init__(initial_value, max_value=max_value)
        self._value = initial_value
        self._max_value = max_value
        self._fast_acquire = fast_acquire
        self._waiters: deque[asyncio.Future[None]] = deque()

    async def acquire(self) -> None:
        if self._value > 0 and not self._waiters:
            await AsyncIOBackend.checkpoint_if_cancelled()
            self._value -= 1

            # Unless on the "fast path", yield control of the event loop so that other
            # tasks can run too
            if not self._fast_acquire:
                try:
                    await AsyncIOBackend.cancel_shielded_checkpoint()
                except CancelledError:
                    self.release()
                    raise

            return

        fut: asyncio.Future[None] = asyncio.Future()
        self._waiters.append(fut)
        try:
            await fut
        except CancelledError:
            if fut.cancelled():
                try:
                    self._waiters.remove(fut)
                except ValueError:
                    pass
            else:
                self.release()

            raise

    def acquire_nowait(self) -> None:
        if self._value == 0:
            raise WouldBlock

        self._value -= 1

    def release(self) -> None:
        if self._max_value is not None and self._value == self._max_value:
            raise ValueError("semaphore released too many times")

        while self._waiters:
            fut = self._waiters.popleft()
            if fut.cancelled():
                continue

            fut.set_result(None)
            return

        self._value += 1

    @property
    def value(self) -> int:
        return self._value

    @property
    def max_value(self) -> int | None:
        return self._max_value

    def statistics(self) -> SemaphoreStatistics:
        return SemaphoreStatistics(len(self._waiters))


class CapacityLimiter(BaseCapacityLimiter):
    __slots__ = "_borrowers", "_total_tokens", "_wait_queue"

    def __new__(cls, total_tokens: float) -> Self:
        return object.__new__(cls)

    def __init__(self, total_tokens: float):
        self._total_tokens: float = 0
        self._borrowers: set[Any] = set()
        self._wait_queue: OrderedDict[Any, asyncio.Event] = OrderedDict()
        self.total_tokens = total_tokens

    async def __aenter__(self) -> None:
        await self.acquire()

    async def __aexit__(
        self,
        exc_type: type[BaseException] | None,
        exc_val: BaseException | None,
        exc_tb: TracebackType | None,
    ) -> None:
        self.release()

    @property
    def total_tokens(self) -> float:
        return self._total_tokens

    @total_tokens.setter
    def total_tokens(self, value: float) -> None:
        if not isinstance(value, int) and not math.isinf(value):
            raise TypeError("total_tokens must be an int or math.inf")

        if value < 0:
            raise ValueError("total_tokens must be >= 0")

        self._total_tokens = value

        # Notify waiting tasks that they have acquired the limiter while
        # there is spare capacity.
        while self._wait_queue and len(self._borrowers) < self._total_tokens:
            borrower, event = self._wait_queue.popitem(last=False)
            self._borrowers.add(borrower)
            event.set()

    @property
    def borrowed_tokens(self) -> int:
        return len(self._borrowers)

    @property
    def available_tokens(self) -> float:
        return self._total_tokens - len(self._borrowers)

    def _notify_next_waiter(self) -> None:
        """Hand a free token to the next task in line, if any."""
        if self._wait_queue and len(self._borrowers) < self._total_tokens:
            borrower, event = self._wait_queue.popitem(last=False)
            self._borrowers.add(borrower)
            event.set()

    def acquire_nowait(self) -> None:
        self.acquire_on_behalf_of_nowait(current_task())

    def acquire_on_behalf_of_nowait(self, borrower: object) -> None:
        if borrower in self._borrowers:
            raise RuntimeError(
                "this borrower is already holding one of this CapacityLimiter's tokens"
            )

        if self._wait_queue or len(self._borrowers) >= self._total_tokens:
            raise WouldBlock

        self._borrowers.add(borrower)

    async def acquire(self) -> None:
        return await self.acquire_on_behalf_of(current_task())

    async def acquire_on_behalf_of(self, borrower: object) -> None:
        await AsyncIOBackend.checkpoint_if_cancelled()
        try:
            self.acquire_on_behalf_of_nowait(borrower)
        except WouldBlock:
            event = asyncio.Event()
            self._wait_queue[borrower] = event
            try:
                await event.wait()
            except BaseException:
                self._wait_queue.pop(borrower, None)
                if event.is_set():
                    self._borrowers.discard(borrower)
                    self._notify_next_waiter()

                raise
        else:
            try:
                await AsyncIOBackend.cancel_shielded_checkpoint()
            except BaseException:
                self.release()
                raise

    def release(self) -> None:
        self.release_on_behalf_of(current_task())

    def release_on_behalf_of(self, borrower: object) -> None:
        try:
            self._borrowers.remove(borrower)
        except KeyError:
            raise RuntimeError(
                "this borrower isn't holding any of this CapacityLimiter's tokens"
            ) from None

        self._notify_next_waiter()

    def statistics(self) -> CapacityLimiterStatistics:
        return CapacityLimiterStatistics(
            self.borrowed_tokens,
            self.total_tokens,
            tuple(self._borrowers),
            len(self._wait_queue),
        )


_default_thread_limiter: RunVar[CapacityLimiter] = RunVar("_default_thread_limiter")


#
# Operating system signals
#


class _SignalReceiver:
    def __init__(self, signals: tuple[Signals, ...]):
        self._signals = signals
        self._loop = get_running_loop()
        self._signal_queue: deque[Signals] = deque()
        self._future: asyncio.Future = asyncio.Future()
        self._handled_signals: set[Signals] = set()

    def _deliver(self, signum: Signals) -> None:
        self._signal_queue.append(signum)
        if not self._future.done():
            self._future.set_result(None)

    def __enter__(self) -> Self:
        for sig in set(self._signals):
            self._loop.add_signal_handler(sig, self._deliver, sig)
            self._handled_signals.add(sig)

        return self

    def __exit__(
        self,
        exc_type: type[BaseException] | None,
        exc_val: BaseException | None,
        exc_tb: TracebackType | None,
    ) -> None:
        for sig in self._handled_signals:
            self._loop.remove_signal_handler(sig)

    def __aiter__(self) -> _SignalReceiver:
        return self

    async def __anext__(self) -> Signals:
        await AsyncIOBackend.checkpoint()
        if not self._signal_queue:
            self._future = asyncio.Future()
            await self._future

        return self._signal_queue.popleft()


#
# Testing and debugging
#


class AsyncIOTaskInfo(TaskInfo):
    def __init__(self, task: asyncio.Task):
        task_state = _task_states.get(task)
        if task_state is None:
            parent_id = None
        else:
            parent_id = task_state.parent_id

        coro = task.get_coro()
        assert coro is not None, "created TaskInfo from a completed Task"
        super().__init__(id(task), parent_id, task.get_name(), coro)
        self._task = weakref.ref(task)

    def has_pending_cancellation(self) -> bool:
        if not (task := self._task()):
            # If the task isn't around anymore, it won't have a pending cancellation
            return False

        if task._must_cancel or (  # type: ignore[attr-defined]
            isinstance(task._fut_waiter, asyncio.Future)  # type: ignore[attr-defined]
            and task._fut_waiter.cancelled()  # type: ignore[attr-defined]
        ):
            return True

        if task_state := _task_states.get(task):
            if cancel_scope := task_state.cancel_scope:
                return cancel_scope._effectively_cancelled

        return False


class TestRunner(abc.TestRunner):
    _send_stream: MemoryObjectSendStream[tuple[Awaitable[Any], asyncio.Future[Any]]]

    def __init__(
        self,
        *,
        debug: bool | None = None,
        use_uvloop: bool = False,
        loop_factory: Callable[[], AbstractEventLoop] | None = None,
    ) -> None:
        if use_uvloop and loop_factory is None:
            if sys.platform != "win32":
                import uvloop

                loop_factory = uvloop.new_event_loop
            else:
                import winloop

                loop_factory = winloop.new_event_loop

        self._runner = Runner(debug=debug, loop_factory=loop_factory)
        self._exceptions: list[BaseException] = []
        self._runner_task: asyncio.Task | None = None

    def __enter__(self) -> Self:
        self._runner.__enter__()
        self.get_loop().set_exception_handler(self._exception_handler)
        return self

    def __exit__(
        self,
        exc_type: type[BaseException] | None,
        exc_val: BaseException | None,
        exc_tb: TracebackType | None,
    ) -> None:
        self._runner.__exit__(exc_type, exc_val, exc_tb)

    def get_loop(self) -> AbstractEventLoop:
        return self._runner.get_loop()

    def is_running(self) -> bool:
        try:
            asyncio.get_running_loop()
            return True
        except RuntimeError:
            return False

    def _exception_handler(
        self, loop: asyncio.AbstractEventLoop, context: dict[str, Any]
    ) -> None:
        if isinstance(context.get("exception"), Exception):
            self._exceptions.append(context["exception"])
        else:
            loop.default_exception_handler(context)

    def _raise_async_exceptions(self) -> None:
        # Re-raise any exceptions raised in asynchronous callbacks
        if self._exceptions:
            exceptions, self._exceptions = self._exceptions, []
            if len(exceptions) == 1:
                raise exceptions[0]
            elif exceptions:
                raise BaseExceptionGroup(
                    "Multiple exceptions occurred in asynchronous callbacks", exceptions
                )

    async def _run_tests_and_fixtures(
        self,
        receive_stream: MemoryObjectReceiveStream[
            tuple[Awaitable[T_Retval], asyncio.Future[T_Retval]]
        ],
    ) -> None:
        from _pytest.outcomes import OutcomeException

        with receive_stream, self._send_stream:
            async for coro, future in receive_stream:
                try:
                    retval = await coro
                except CancelledError as exc:
                    if not future.cancelled():
                        future.cancel(*exc.args)

                    raise
                except BaseException as exc:
                    if not future.cancelled():
                        future.set_exception(exc)

                    if not isinstance(exc, (Exception, OutcomeException)):
                        raise
                else:
                    if not future.cancelled():
                        future.set_result(retval)

    async def _call_in_runner_task(
        self,
        func: Callable[P, Awaitable[T_Retval]],
        /,
        *args: P.args,
        **kwargs: P.kwargs,
    ) -> T_Retval:
        if not self._runner_task:
            self._send_stream, receive_stream = create_memory_object_stream[
                tuple[Awaitable[Any], asyncio.Future]
            ](1)
            self._runner_task = self.get_loop().create_task(
                self._run_tests_and_fixtures(receive_stream)
            )

        coro = func(*args, **kwargs)
        future: asyncio.Future[T_Retval] = self.get_loop().create_future()
        self._send_stream.send_nowait((coro, future))
        return await future

    def run_asyncgen_fixture(
        self,
        fixture_func: Callable[..., AsyncGenerator[T_Retval, Any]],
        kwargs: dict[str, Any],
    ) -> Iterable[T_Retval]:
        asyncgen = fixture_func(**kwargs)
        fixturevalue: T_Retval = self.get_loop().run_until_complete(
            self._call_in_runner_task(asyncgen.asend, None)
        )
        self._raise_async_exceptions()

        yield fixturevalue

        try:
            self.get_loop().run_until_complete(
                self._call_in_runner_task(asyncgen.asend, None)
            )
        except StopAsyncIteration:
            self._raise_async_exceptions()
        else:
            self.get_loop().run_until_complete(asyncgen.aclose())
            raise RuntimeError("Async generator fixture did not stop")

    def run_fixture(
        self,
        fixture_func: Callable[..., Coroutine[Any, Any, T_Retval]],
        kwargs: dict[str, Any],
    ) -> T_Retval:
        retval = self.get_loop().run_until_complete(
            self._call_in_runner_task(fixture_func, **kwargs)
        )
        self._raise_async_exceptions()
        return retval

    def run_test(
        self, test_func: Callable[..., Coroutine[Any, Any, Any]], kwargs: dict[str, Any]
    ) -> None:
        from _pytest.outcomes import OutcomeException

        try:
            self.get_loop().run_until_complete(
                self._call_in_runner_task(test_func, **kwargs)
            )
        except Exception as exc:
            self._exceptions.append(exc)
        except OutcomeException:
            raise
        except BaseException:
            # A BaseException (e.g. KeyboardInterrupt, SystemExit) interrupted the event loop before
            # the test completed. Cancel _runner_task so it does not resume when the event
            # loop is re-entered during async generator fixture teardown.
            if self._runner_task is not None and not self._runner_task.done():
                self._runner_task.cancel()
                self._send_stream.close()
                try:
                    self.get_loop().run_until_complete(self._runner_task)
                except CancelledError:
                    pass
                finally:
                    self._runner_task = None
            raise
        self._raise_async_exceptions()


class _ProcessStreamProtocol(asyncio.subprocess.SubprocessStreamProtocol):
    """
    A subprocess protocol that allows us to be notified of ``process_exited``

    asyncio's own ``Process.wait()`` only resolves once every pipe transport has
    disconnected so to get same semantics as on trio and uvloop we need this.
    """

    def __init__(self) -> None:
        # Match the standard factory for asyncio.create_process
        super().__init__(limit=2**16, loop=asyncio.get_running_loop())
        self.exited = asyncio.Event()

    def process_exited(self) -> None:
        super().process_exited()
        self.exited.set()


class AsyncIOBackend(AsyncBackend):
    @classmethod
    def run(
        cls,
        func: Callable[[Unpack[PosArgsT]], Awaitable[T_Retval]],
        args: tuple[Unpack[PosArgsT]],
        kwargs: dict[str, Any],
        options: dict[str, Any],
    ) -> T_Retval:
        @wraps(func)
        async def wrapper() -> T_Retval:
            task = cast(asyncio.Task, current_task())
            task.set_name(get_callable_name(func))
            _task_states[task] = TaskState(None, None)

            try:
                return await func(*args)
            finally:
                del _task_states[task]

        debug = options.get("debug", None)
        loop_factory = options.get("loop_factory", None)
        if loop_factory is None and options.get("use_uvloop", False):
            if sys.platform != "win32":
                import uvloop

                loop_factory = uvloop.new_event_loop
            else:
                import winloop

                loop_factory = winloop.new_event_loop

        with Runner(debug=debug, loop_factory=loop_factory) as runner:
            return runner.run(wrapper())

    @classmethod
    def current_token(cls) -> object:
        return get_running_loop()

    @classmethod
    def current_time(cls) -> float:
        return get_running_loop().time()

    @classmethod
    def cancelled_exception_class(cls) -> type[BaseException]:
        return CancelledError

    @classmethod
    async def checkpoint(cls) -> None:
        await sleep(0)

    @classmethod
    async def checkpoint_if_cancelled(cls) -> None:
        task = current_task()
        if task is None:
            return

        try:
            cancel_scope = _task_states[task].cancel_scope
        except KeyError:
            return

        while cancel_scope:
            if cancel_scope.cancel_called:
                await sleep(0)
            elif cancel_scope.shield:
                break
            else:
                cancel_scope = cancel_scope._parent_scope

    @classmethod
    async def cancel_shielded_checkpoint(cls) -> None:
        with CancelScope(shield=True):
            await sleep(0)

    @classmethod
    async def sleep(cls, delay: float) -> None:
        await sleep(delay)

    @classmethod
    def create_cancel_scope(
        cls, *, deadline: float = math.inf, shield: bool = False
    ) -> CancelScope:
        return CancelScope(deadline=deadline, shield=shield)

    @classmethod
    def current_effective_deadline(cls) -> float:
        if (task := current_task()) is None:
            return math.inf

        try:
            cancel_scope = _task_states[task].cancel_scope
        except KeyError:
            return math.inf

        deadline = math.inf
        while cancel_scope:
            deadline = min(deadline, cancel_scope.deadline)
            if cancel_scope._cancel_called:
                deadline = -math.inf
                break
            elif cancel_scope.shield:
                break
            else:
                cancel_scope = cancel_scope._parent_scope

        return deadline

    @classmethod
    def create_task_group(cls) -> abc.TaskGroup:
        return TaskGroup()

    @classmethod
    def create_event(cls) -> BaseEvent:
        return Event()

    @classmethod
    def create_lock(cls, *, fast_acquire: bool) -> BaseLock:
        return Lock(fast_acquire=fast_acquire)

    @classmethod
    def create_semaphore(
        cls,
        initial_value: int,
        *,
        max_value: int | None = None,
        fast_acquire: bool = False,
    ) -> BaseSemaphore:
        return Semaphore(initial_value, max_value=max_value, fast_acquire=fast_acquire)

    @classmethod
    def create_capacity_limiter(cls, total_tokens: float) -> BaseCapacityLimiter:
        return CapacityLimiter(total_tokens)

    @classmethod
    async def run_sync_in_worker_thread(  # type: ignore[return]
        cls,
        func: Callable[[Unpack[PosArgsT]], T_Retval],
        args: tuple[Unpack[PosArgsT]],
        abandon_on_cancel: bool = False,
        limiter: BaseCapacityLimiter | None = None,
    ) -> T_Retval:
        await cls.checkpoint()

        # If this is the first run in this event loop thread, set up the necessary
        # variables
        try:
            idle_workers = _threadpool_idle_workers.get()
            workers = _threadpool_workers.get()
        except LookupError:
            idle_workers = deque()
            workers = set()
            _threadpool_idle_workers.set(idle_workers)
            _threadpool_workers.set(workers)

        async with limiter or cls.current_default_thread_limiter():
            with CancelScope(shield=not abandon_on_cancel) as scope:
                future = asyncio.Future[T_Retval]()
                root_task = find_root_task()
                if not idle_workers:
                    worker = WorkerThread(root_task, workers, idle_workers)
                    worker.start()
                    workers.add(worker)
                    root_task.add_done_callback(worker.stop, context=Context())
                else:
                    worker = idle_workers.pop()

                    # Prune any other workers that have been idle for MAX_IDLE_TIME
                    # seconds or longer
                    now = cls.current_time()
                    while idle_workers:
                        if (
                            now - idle_workers[0].idle_since
                            < WorkerThread.MAX_IDLE_TIME
                        ):
                            break

                        expired_worker = idle_workers.popleft()
                        expired_worker.root_task.remove_done_callback(
                            expired_worker.stop
                        )
                        expired_worker.stop()

                context = copy_context()
                context.run(set_current_async_library, None)
                if abandon_on_cancel or scope._parent_scope is None:
                    worker_scope = scope
                else:
                    worker_scope = scope._parent_scope

                worker.queue.put_nowait((context, func, args, future, worker_scope))
                return await future

    @classmethod
    def check_cancelled(cls) -> None:
        scope: CancelScope | None = threadlocals.current_cancel_scope
        while scope is not None:
            if scope.cancel_called:
                raise CancelledError(f"Cancelled via cancel scope {id(scope):x}")

            if scope.shield:
                return

            scope = scope._parent_scope

    @classmethod
    def run_async_from_thread(
        cls,
        func: Callable[[Unpack[PosArgsT]], Coroutine[Any, Any, T_co]],
        args: tuple[Unpack[PosArgsT]],
        token: object,
    ) -> T_co:
        async def task_wrapper() -> T_co:
            __tracebackhide__ = True
            if scope is not None:
                task = cast(asyncio.Task, current_task())
                _task_states[task] = TaskState(None, scope)
                scope._tasks.add(task)
            try:
                return await func(*args)
            except CancelledError as exc:
                raise concurrent.futures.CancelledError(str(exc)) from None
            finally:
                if scope is not None:
                    scope._tasks.discard(task)

        loop = cast(
            "AbstractEventLoop", token or threadlocals.current_token.native_token
        )
        if loop.is_closed():
            raise RunFinishedError

        context = copy_context()
        context.run(set_current_async_library, "asyncio")
        scope = getattr(threadlocals, "current_cancel_scope", None)
        f: concurrent.futures.Future[T_co] = context.run(
            asyncio.run_coroutine_threadsafe, task_wrapper(), loop=loop
        )
        return f.result()

    @classmethod
    def run_sync_from_thread(
        cls,
        func: Callable[[Unpack[PosArgsT]], T_Retval],
        args: tuple[Unpack[PosArgsT]],
        token: object,
    ) -> T_Retval:
        @wraps(func)
        def wrapper() -> None:
            try:
                set_current_async_library("asyncio")
                f.set_result(func(*args))
            except BaseException as exc:
                f.set_exception(exc)
                if not isinstance(exc, Exception):
                    raise

        loop = cast(
            "AbstractEventLoop", token or threadlocals.current_token.native_token
        )
        if loop.is_closed():
            raise RunFinishedError

        f: concurrent.futures.Future[T_Retval] = Future()
        loop.call_soon_threadsafe(wrapper)
        return f.result()

    @classmethod
    async def open_process(
        cls,
        command: StrOrBytesPath | Sequence[StrOrBytesPath],
        *,
        stdin: int | IO[Any] | None,
        stdout: int | IO[Any] | None,
        stderr: int | IO[Any] | None,
        **kwargs: Any,
    ) -> Process:
        await cls.checkpoint()
        if isinstance(command, PathLike):
            command = os.fspath(command)

        # Use loop.subprocess_shell()/subprocess_exec() rather than their
        # asyncio.create_subprocess_*() counterparts to get access to
        # transport/protocol.
        loop = asyncio.get_running_loop()
        if isinstance(command, (str, bytes)):
            transport, protocol = await loop.subprocess_shell(
                _ProcessStreamProtocol,
                command,
                stdin=stdin,
                stdout=stdout,
                stderr=stderr,
                **kwargs,
            )
        else:
            transport, protocol = await loop.subprocess_exec(
                _ProcessStreamProtocol,
                *command,
                stdin=stdin,
                stdout=stdout,
                stderr=stderr,
                **kwargs,
            )

        process = asyncio.subprocess.Process(transport, protocol, loop)
        stdin_stream = StreamWriterWrapper(process.stdin) if process.stdin else None
        stdout_stream = StreamReaderWrapper(process.stdout) if process.stdout else None
        stderr_stream = StreamReaderWrapper(process.stderr) if process.stderr else None
        return Process(
            process,
            stdin_stream,
            stdout_stream,
            stderr_stream,
            protocol.exited,
            transport,
        )

    @classmethod
    def setup_process_pool_exit_at_shutdown(cls, workers: set[abc.Process]) -> None:
        create_task(
            _shutdown_process_pool_on_exit(workers),
            name="AnyIO process pool shutdown task",
        )
        find_root_task().add_done_callback(
            partial(_forcibly_shutdown_process_pool_on_exit, workers)  # type:ignore[arg-type]
        )

    @classmethod
    async def connect_tcp(
        cls, host: str, port: int, local_address: IPSockAddrType | None = None
    ) -> abc.SocketStream:
        transport, protocol = cast(
            tuple[asyncio.Transport, StreamProtocol],
            await get_running_loop().create_connection(
                StreamProtocol, host, port, local_addr=local_address
            ),
        )
        transport.pause_reading()
        return SocketStream(transport, protocol)

    @classmethod
    async def connect_unix(cls, path: str | bytes) -> abc.UNIXSocketStream:
        await cls.checkpoint()
        loop = get_running_loop()
        raw_socket = socket.socket(socket.AF_UNIX)
        raw_socket.setblocking(False)
        while True:
            try:
                raw_socket.connect(path)
            except BlockingIOError:
                f: asyncio.Future = asyncio.Future()
                loop.add_writer(raw_socket, f.set_result, None)
                f.add_done_callback(lambda _: loop.remove_writer(raw_socket))
                await f
            except BaseException:
                raw_socket.close()
                raise
            else:
                return UNIXSocketStream(raw_socket)

    @classmethod
    def create_tcp_listener(cls, sock: socket.socket) -> SocketListener:
        return TCPSocketListener(sock)

    @classmethod
    def create_unix_listener(cls, sock: socket.socket) -> SocketListener:
        return UNIXSocketListener(sock)

    @classmethod
    async def create_udp_socket(
        cls,
        family: AddressFamily,
        local_address: IPSockAddrType | None,
        remote_address: IPSockAddrType | None,
        reuse_port: bool,
    ) -> UDPSocket | ConnectedUDPSocket:
        transport, protocol = await get_running_loop().create_datagram_endpoint(
            DatagramProtocol,
            local_addr=local_address,
            remote_addr=remote_address,
            family=family,
            reuse_port=reuse_port,
        )
        if protocol.exception:
            transport.close()
            raise protocol.exception

        if not remote_address:
            return UDPSocket(transport, protocol)
        else:
            return ConnectedUDPSocket(transport, protocol)

    @classmethod
    async def create_unix_datagram_socket(  # type: ignore[override]
        cls, raw_socket: socket.socket, remote_path: str | bytes | None
    ) -> abc.UNIXDatagramSocket | abc.ConnectedUNIXDatagramSocket:
        await cls.checkpoint()
        loop = get_running_loop()

        if remote_path:
            while True:
                try:
                    raw_socket.connect(remote_path)
                except BlockingIOError:
                    f: asyncio.Future = asyncio.Future()
                    loop.add_writer(raw_socket, f.set_result, None)
                    f.add_done_callback(lambda _: loop.remove_writer(raw_socket))
                    await f
                except BaseException:
                    raw_socket.close()
                    raise
                else:
                    return ConnectedUNIXDatagramSocket(raw_socket)
        else:
            return UNIXDatagramSocket(raw_socket)

    @classmethod
    async def getaddrinfo(
        cls,
        host: bytes | str | None,
        port: str | int | None,
        *,
        family: int | AddressFamily = 0,
        type: int | SocketKind = 0,
        proto: int = 0,
        flags: int = 0,
    ) -> Sequence[
        tuple[
            AddressFamily,
            SocketKind,
            int,
            str,
            tuple[str, int] | tuple[str, int, int, int] | tuple[int, bytes],
        ]
    ]:
        return await get_running_loop().getaddrinfo(
            host, port, family=family, type=type, proto=proto, flags=flags
        )

    @classmethod
    async def getnameinfo(
        cls, sockaddr: IPSockAddrType, flags: int = 0
    ) -> tuple[str, str]:
        return await get_running_loop().getnameinfo(sockaddr, flags)

    @classmethod
    async def wait_readable(cls, obj: FileDescriptorLike) -> None:
        try:
            read_events = _read_events.get()
        except LookupError:
            read_events = {}
            _read_events.set(read_events)

        fd = obj if isinstance(obj, int) else obj.fileno()
        if read_events.get(fd):
            raise BusyResourceError("reading from")

        loop = get_running_loop()
        fut: asyncio.Future[bool] = loop.create_future()

        def cb() -> None:
            try:
                del read_events[fd]
            except KeyError:
                pass
            else:
                remove_reader(fd)

            try:
                fut.set_result(True)
            except asyncio.InvalidStateError:
                pass

        try:
            loop.add_reader(fd, cb)
        except NotImplementedError:
            from anyio._core._asyncio_selector_thread import get_selector

            selector = get_selector()
            selector.add_reader(fd, cb)
            remove_reader = selector.remove_reader
        else:
            remove_reader = loop.remove_reader

        read_events[fd] = fut
        try:
            success = await fut
        finally:
            try:
                del read_events[fd]
            except KeyError:
                pass
            else:
                remove_reader(fd)

        if not success:
            raise ClosedResourceError

    @classmethod
    async def wait_writable(cls, obj: FileDescriptorLike) -> None:
        try:
            write_events = _write_events.get()
        except LookupError:
            write_events = {}
            _write_events.set(write_events)

        fd = obj if isinstance(obj, int) else obj.fileno()
        if write_events.get(fd):
            raise BusyResourceError("writing to")

        loop = get_running_loop()
        fut: asyncio.Future[bool] = loop.create_future()

        def cb() -> None:
            try:
                del write_events[fd]
            except KeyError:
                pass
            else:
                remove_writer(fd)

            try:
                fut.set_result(True)
            except asyncio.InvalidStateError:
                pass

        try:
            loop.add_writer(fd, cb)
        except NotImplementedError:
            from anyio._core._asyncio_selector_thread import get_selector

            selector = get_selector()
            selector.add_writer(fd, cb)
            remove_writer = selector.remove_writer
        else:
            remove_writer = loop.remove_writer

        write_events[fd] = fut
        try:
            success = await fut
        finally:
            try:
                del write_events[fd]
            except KeyError:
                pass
            else:
                remove_writer(fd)

        if not success:
            raise ClosedResourceError

    @classmethod
    def notify_closing(cls, obj: FileDescriptorLike) -> None:
        fd = obj if isinstance(obj, int) else obj.fileno()
        loop = get_running_loop()

        try:
            write_events = _write_events.get()
        except LookupError:
            pass
        else:
            try:
                fut = write_events.pop(fd)
            except KeyError:
                pass
            else:
                try:
                    fut.set_result(False)
                except asyncio.InvalidStateError:
                    pass

                try:
                    loop.remove_writer(fd)
                except NotImplementedError:
                    from anyio._core._asyncio_selector_thread import get_selector

                    get_selector().remove_writer(fd)

        try:
            read_events = _read_events.get()
        except LookupError:
            pass
        else:
            try:
                fut = read_events.pop(fd)
            except KeyError:
                pass
            else:
                try:
                    fut.set_result(False)
                except asyncio.InvalidStateError:
                    pass

                try:
                    loop.remove_reader(fd)
                except NotImplementedError:
                    from anyio._core._asyncio_selector_thread import get_selector

                    get_selector().remove_reader(fd)

    @classmethod
    async def wrap_listener_socket(cls, sock: socket.socket) -> SocketListener:
        if hasattr(socket, "AF_UNIX") and sock.family == socket.AF_UNIX:
            return UNIXSocketListener(sock)

        return TCPSocketListener(sock)

    @classmethod
    async def wrap_stream_socket(cls, sock: socket.socket) -> SocketStream:
        transport, protocol = await get_running_loop().create_connection(
            StreamProtocol, sock=sock
        )
        return SocketStream(transport, protocol)

    @classmethod
    async def wrap_unix_stream_socket(cls, sock: socket.socket) -> UNIXSocketStream:
        return UNIXSocketStream(sock)

    @classmethod
    async def wrap_udp_socket(cls, sock: socket.socket) -> UDPSocket:
        transport, protocol = await get_running_loop().create_datagram_endpoint(
            DatagramProtocol, sock=sock
        )
        return UDPSocket(transport, protocol)

    @classmethod
    async def wrap_connected_udp_socket(cls, sock: socket.socket) -> ConnectedUDPSocket:
        transport, protocol = await get_running_loop().create_datagram_endpoint(
            DatagramProtocol, sock=sock
        )
        return ConnectedUDPSocket(transport, protocol)

    @classmethod
    async def wrap_unix_datagram_socket(cls, sock: socket.socket) -> UNIXDatagramSocket:
        return UNIXDatagramSocket(sock)

    @classmethod
    async def wrap_connected_unix_datagram_socket(
        cls, sock: socket.socket
    ) -> ConnectedUNIXDatagramSocket:
        return ConnectedUNIXDatagramSocket(sock)

    @classmethod
    def current_default_thread_limiter(cls) -> CapacityLimiter:
        try:
            return _default_thread_limiter.get()
        except LookupError:
            limiter = CapacityLimiter(40)
            _default_thread_limiter.set(limiter)
            return limiter

    @classmethod
    def open_signal_receiver(
        cls, *signals: Signals
    ) -> AbstractContextManager[AsyncIterator[Signals]]:
        return _SignalReceiver(signals)

    @classmethod
    def get_current_task(cls) -> TaskInfo:
        return AsyncIOTaskInfo(current_task())  # type: ignore[arg-type]

    @classmethod
    def get_running_tasks(cls) -> Sequence[TaskInfo]:
        return [AsyncIOTaskInfo(task) for task in all_tasks() if not task.done()]

    @classmethod
    async def wait_all_tasks_blocked(cls) -> None:
        await cls.checkpoint()
        this_task = current_task()
        while True:
            for task in all_tasks():
                if task is this_task:
                    continue

                waiter = task._fut_waiter  # type: ignore[attr-defined]
                if waiter is None or waiter.done():
                    await sleep(0.1)
                    break
            else:
                return

    @classmethod
    def create_test_runner(cls, options: dict[str, Any]) -> TestRunner:
        return TestRunner(**options)


backend_class = AsyncIOBackend