_asyncio.py

from __future__ import annotations

import array
import asyncio
import concurrent.futures
import math
import socket
import sys
import threading
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 AsyncIterator, Generator, Iterable
from concurrent.futures import Future
from contextlib import suppress
from contextvars import Context, copy_context
from dataclasses import dataclass
from functools import partial, wraps
from inspect import (
    CORO_RUNNING,
    CORO_SUSPENDED,
    getcoroutinestate,
    iscoroutine,
)
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 TracebackType
from typing import (
    IO,
    Any,
    AsyncGenerator,
    Awaitable,
    Callable,
    Collection,
    ContextManager,
    Coroutine,
    Mapping,
    Optional,
    Sequence,
    Tuple,
    TypeVar,
    cast,
)
from weakref import WeakKeyDictionary

import sniffio

from .. import CapacityLimiterStatistics, EventStatistics, TaskInfo, abc
from .._core._eventloop import claim_worker_thread, threadlocals
from .._core._exceptions import (
    BrokenResourceError,
    BusyResourceError,
    ClosedResourceError,
    EndOfStream,
    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 ResourceGuard
from .._core._tasks import CancelScope as BaseCancelScope
from ..abc import (
    AsyncBackend,
    IPSockAddrType,
    SocketListener,
    UDPPacketType,
    UNIXDatagramPacketType,
)
from ..lowlevel import RunVar
from ..streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream

if sys.version_info >= (3, 10):
    from typing import ParamSpec
else:
    from typing_extensions import ParamSpec

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

    from exceptiongroup import BaseExceptionGroup
    from typing_extensions import 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) -> Runner:
            self._lazy_init()
            return self

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

        def close(self) -> None:
            """Shutdown and close event loop."""
            if self._state is not _State.INITIALIZED:
                return
            try:
                loop = self._loop
                _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()
                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_contra = TypeVar("T_contra", contravariant=True)
PosArgsT = TypeVarTuple("PosArgsT")
P = ParamSpec("P")

_root_task: RunVar[asyncio.Task | 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():
            callbacks = [cb for cb, context in task._callbacks]
            for cb in callbacks:
                if (
                    cb is _run_until_complete_cb
                    or getattr(cb, "__module__", None) == "uvloop.loop"
                ):
                    _root_task.set(task)
                    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 get_callable_name(func: Callable) -> str:
    module = getattr(func, "__module__", None)
    qualname = getattr(func, "__qualname__", None)
    return ".".join([x for x in (module, qualname) if x])


#
# Event loop
#

_run_vars: WeakKeyDictionary[asyncio.AbstractEventLoop, Any] = WeakKeyDictionary()


def _task_started(task: asyncio.Task) -> bool:
    """Return ``True`` if the task has been started and has not finished."""
    try:
        return getcoroutinestate(task.get_coro()) in (CORO_RUNNING, CORO_SUSPENDED)
    except AttributeError:
        # task coro is async_genenerator_asend https://bugs.python.org/issue37771
        raise Exception(f"Cannot determine if task {task} has started or not") from None


#
# Timeouts and cancellation
#


class CancelScope(BaseCancelScope):
    def __new__(
        cls, *, deadline: float = math.inf, shield: bool = False
    ) -> CancelScope:
        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._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
        self._cancel_calls: int = 0
        self._cancelling: int | None = None

    def __enter__(self) -> CancelScope:
        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:
                self._parent_scope._child_scopes.add(self)
                self._parent_scope._tasks.remove(host_task)

        self._timeout()
        self._active = True
        if sys.version_info >= (3, 11):
            self._cancelling = self._host_task.cancelling()

        # 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 | None:
        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"
            )

        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 directly cancelled parent
        # scope if this one was shielded
        self._restart_cancellation_in_parent()

        if self._cancel_called and exc_val is not None:
            for exc in iterate_exceptions(exc_val):
                if isinstance(exc, CancelledError):
                    self._cancelled_caught = self._uncancel(exc)
                    if self._cancelled_caught:
                        break

            return self._cancelled_caught

        return None

    def _uncancel(self, cancelled_exc: CancelledError) -> bool:
        if sys.version_info < (3, 9) or self._host_task is None:
            self._cancel_calls = 0
            return True

        # Undo all cancellations done by this scope
        if self._cancelling is not None:
            while self._cancel_calls:
                self._cancel_calls -= 1
                if self._host_task.uncancel() <= self._cancelling:
                    return True

        self._cancel_calls = 0
        return f"Cancelled by cancel scope {id(self):x}" in cancelled_exc.args

    def _timeout(self) -> None:
        if self._deadline != math.inf:
            loop = get_running_loop()
            if loop.time() >= self._deadline:
                self.cancel()
            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:
            if task._must_cancel:  # type: ignore[attr-defined]
                continue

            # The task is eligible for cancellation if it has started
            should_retry = True
            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():
                    origin._cancel_calls += 1
                    if sys.version_info >= (3, 9):
                        task.cancel(f"Cancelled by cancel scope {id(origin):x}")
                    else:
                        task.cancel()

        # 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 _parent_cancelled(self) -> bool:
        # Check whether any parent has been cancelled
        cancel_scope = self._parent_scope
        while cancel_scope is not None and not cancel_scope._shield:
            if cancel_scope._cancel_called:
                return True
            else:
                cancel_scope = cancel_scope._parent_scope

        return False

    def cancel(self) -> None:
        if not self._cancel_called:
            if self._timeout_handle:
                self._timeout_handle.cancel()
                self._timeout_handle = None

            self._cancel_called = True
            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__ = "parent_id", "cancel_scope"

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


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


#
# Task groups
#


class _AsyncioTaskStatus(abc.TaskStatus):
    def __init__(self, future: asyncio.Future, parent_id: int):
        self._future = future
        self._parent_id = parent_id

    def started(self, value: T_contra | None = None) -> None:
        try:
            self._future.set_result(value)
        except asyncio.InvalidStateError:
            if not self._future.cancelled():
                raise RuntimeError(
                    "called 'started' twice on the same task status"
                ) from None

        task = cast(asyncio.Task, current_task())
        _task_states[task].parent_id = self._parent_id


def iterate_exceptions(
    exception: BaseException,
) -> Generator[BaseException, None, None]:
    if isinstance(exception, BaseExceptionGroup):
        for exc in exception.exceptions:
            yield from iterate_exceptions(exc)
    else:
        yield exception


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

    async def __aenter__(self) -> TaskGroup:
        self.cancel_scope.__enter__()
        self._active = True
        return self

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

        cancelled_exc_while_waiting_tasks: CancelledError | None = None
        while self._tasks:
            try:
                await asyncio.wait(self._tasks)
            except CancelledError as exc:
                # This task was cancelled natively; reraise the CancelledError later
                # unless this task was already interrupted by another exception
                self.cancel_scope.cancel()
                if cancelled_exc_while_waiting_tasks is None:
                    cancelled_exc_while_waiting_tasks = exc

        self._active = False
        if self._exceptions:
            raise BaseExceptionGroup(
                "unhandled errors in a TaskGroup", self._exceptions
            )

        # Raise the CancelledError received while waiting for child tasks to exit,
        # unless the context manager itself was previously exited with another
        # exception, or if any of the  child tasks raised an exception other than
        # CancelledError
        if cancelled_exc_while_waiting_tasks:
            if exc_val is None or ignore_exception:
                raise cancelled_exc_while_waiting_tasks

        return ignore_exception

    def _spawn(
        self,
        func: Callable[[Unpack[PosArgsT]], Awaitable[Any]],
        args: tuple[Unpack[PosArgsT]],
        name: object,
        task_status_future: asyncio.Future | None = None,
    ) -> asyncio.Task:
        def task_done(_task: asyncio.Task) -> None:
            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]

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

                exc = e

            if exc is not None:
                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._parent_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 not self._active:
            raise RuntimeError(
                "This task group is not active; no new tasks can be started."
            )

        kwargs = {}
        if task_status_future:
            parent_id = id(current_task())
            kwargs["task_status"] = _AsyncioTaskStatus(
                task_status_future, id(self.cancel_scope._host_task)
            )
        else:
            parent_id = id(self.cancel_scope._host_task)

        coro = func(*args, **kwargs)
        if not iscoroutine(coro):
            prefix = f"{func.__module__}." if hasattr(func, "__module__") else ""
            raise TypeError(
                f"Expected {prefix}{func.__qualname__}() to return a coroutine, but "
                f"the return value ({coro!r}) is not a coroutine object"
            )

        name = get_callable_name(func) if name is None else str(name)
        task = create_task(coro, name=name)
        task.add_done_callback(task_done)

        # Make the spawned task inherit the task group's cancel scope
        _task_states[task] = TaskState(
            parent_id=parent_id, cancel_scope=self.cancel_scope
        )
        self.cancel_scope._tasks.add(task)
        self._tasks.add(task)
        return task

    def start_soon(
        self,
        func: Callable[[Unpack[PosArgsT]], Awaitable[Any]],
        *args: Unpack[PosArgsT],
        name: object = None,
    ) -> None:
        self._spawn(func, args, name)

    async def start(
        self, func: Callable[..., Awaitable[Any]], *args: object, name: object = None
    ) -> Any:
        future: asyncio.Future = asyncio.Future()
        task = self._spawn(func, args, name, future)

        # 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:
            return await future
        except CancelledError:
            # Cancel the task and wait for it to exit before returning
            task.cancel()
            with CancelScope(shield=True), suppress(CancelledError):
                await task

            raise


#
# Threads
#

_Retval_Queue_Type = Tuple[Optional[T_Retval], Optional[BaseException]]


class WorkerThread(Thread):
    MAX_IDLE_TIME = 10  # seconds

    def __init__(
        self,
        root_task: asyncio.Task,
        workers: set[WorkerThread],
        idle_workers: deque[WorkerThread],
    ):
        super().__init__(name="AnyIO worker thread")
        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

                    if not self.loop.is_closed():
                        self.loop.call_soon_threadsafe(
                            self._report_result, future, result, exception
                        )

                self.queue.task_done()

    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")


class BlockingPortal(abc.BlockingPortal):
    def __new__(cls) -> BlockingPortal:
        return object.__new__(cls)

    def __init__(self) -> None:
        super().__init__()
        self._loop = get_running_loop()

    def _spawn_task_from_thread(
        self,
        func: Callable[[Unpack[PosArgsT]], Awaitable[T_Retval] | T_Retval],
        args: tuple[Unpack[PosArgsT]],
        kwargs: dict[str, Any],
        name: object,
        future: Future[T_Retval],
    ) -> None:
        AsyncIOBackend.run_sync_from_thread(
            partial(self._task_group.start_soon, name=name),
            (self._call_func, func, args, kwargs, future),
            self._loop,
        )


#
# Subprocesses
#


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

    async def receive(self, max_bytes: int = 65536) -> bytes:
        data = await self._stream.read(max_bytes)
        if data:
            return data
        else:
            raise EndOfStream

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


@dataclass(eq=False)
class StreamWriterWrapper(abc.ByteSendStream):
    _stream: asyncio.StreamWriter

    async def send(self, item: bytes) -> None:
        self._stream.write(item)
        await self._stream.drain()

    async def aclose(self) -> None:
        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

    async def aclose(self) -> None:
        with CancelScope(shield=True):
            if self._stdin:
                await self._stdin.aclose()
            if self._stdout:
                await self._stdout.aclose()
            if self._stderr:
                await self._stderr.aclose()

        try:
            await self.wait()
        except BaseException:
            self.kill()
            with CancelScope(shield=True):
                await self.wait()

            raise

    async def wait(self) -> int:
        return await self._process.wait()

    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
    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:
        if process.returncode is 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:
        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 = BrokenResourceError()
            self.exception.__cause__ = exc

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

    def data_received(self, data: bytes) -> None:
        self.read_queue.append(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
    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.write_event.set()

    def connection_lost(self, exc: Exception | None) -> None:
        self.read_event.set()
        self.write_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:
        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 self._protocol.exception from None
                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 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:
        if not self._transport.is_closing():
            self._closed = True
            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:
                self._receive_future.set_result(None)
            if self._send_future:
                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:
        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:
        if not self._transport.is_closing():
            self._closed = True
            self._transport.close()

    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:
        if not self._transport.is_closing():
            self._closed = True
            self._transport.close()

    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[Any, asyncio.Event]] = RunVar("read_events")
_write_events: RunVar[dict[Any, asyncio.Event]] = RunVar("write_events")


#
# Synchronization
#


class Event(BaseEvent):
    def __new__(cls) -> Event:
        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 CapacityLimiter(BaseCapacityLimiter):
    _total_tokens: float = 0

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

    def __init__(self, total_tokens: float):
        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 < 1:
            raise ValueError("total_tokens must be >= 1")

        waiters_to_notify = max(value - self._total_tokens, 0)
        self._total_tokens = value

        # Notify waiting tasks that they have acquired the limiter
        while self._wait_queue and waiters_to_notify:
            event = self._wait_queue.popitem(last=False)[1]
            event.set()
            waiters_to_notify -= 1

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

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

    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)
                raise

            self._borrowers.add(borrower)
        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

        # Notify the next task in line if this limiter has free capacity now
        if self._wait_queue and len(self._borrowers) < self._total_tokens:
            event = self._wait_queue.popitem(last=False)[1]
            event.set()

    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) -> _SignalReceiver:
        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,
    ) -> bool | None:
        for sig in self._handled_signals:
            self._loop.remove_signal_handler(sig)
        return None

    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
#


def _create_task_info(task: asyncio.Task) -> TaskInfo:
    task_state = _task_states.get(task)
    if task_state is None:
        parent_id = None
    else:
        parent_id = task_state.parent_id

    return TaskInfo(id(task), parent_id, task.get_name(), task.get_coro())


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:
            import uvloop

            loop_factory = uvloop.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) -> TestRunner:
        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 _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:
        with receive_stream, self._send_stream:
            async for coro, future in receive_stream:
                try:
                    retval = await coro
                except BaseException as exc:
                    if not future.cancelled():
                        future.set_exception(exc)
                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:
        try:
            self.get_loop().run_until_complete(
                self._call_in_runner_task(test_func, **kwargs)
            )
        except Exception as exc:
            self._exceptions.append(exc)

        self._raise_async_exceptions()


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):
            import uvloop

            loop_factory = uvloop.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:
        try:
            cancel_scope = _task_states[
                current_task()  # type: ignore[index]
            ].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) -> abc.Event:
        return Event()

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

    @classmethod
    async def run_sync_in_worker_thread(
        cls,
        func: Callable[[Unpack[PosArgsT]], T_Retval],
        args: tuple[Unpack[PosArgsT]],
        abandon_on_cancel: bool = False,
        limiter: abc.CapacityLimiter | 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 = asyncio.Future()
                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)
                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(sniffio.current_async_library_cvar.set, 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 by cancel scope {id(scope):x}")

            if scope.shield:
                return

            scope = scope._parent_scope

    @classmethod
    def run_async_from_thread(
        cls,
        func: Callable[[Unpack[PosArgsT]], Awaitable[T_Retval]],
        args: tuple[Unpack[PosArgsT]],
        token: object,
    ) -> T_Retval:
        async def task_wrapper(scope: CancelScope) -> T_Retval:
            __tracebackhide__ = True
            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:
                scope._tasks.discard(task)

        loop = cast(AbstractEventLoop, token)
        context = copy_context()
        context.run(sniffio.current_async_library_cvar.set, "asyncio")
        wrapper = task_wrapper(threadlocals.current_cancel_scope)
        f: concurrent.futures.Future[T_Retval] = context.run(
            asyncio.run_coroutine_threadsafe, wrapper, 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:
                sniffio.current_async_library_cvar.set("asyncio")
                f.set_result(func(*args))
            except BaseException as exc:
                f.set_exception(exc)
                if not isinstance(exc, Exception):
                    raise

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

    @classmethod
    def create_blocking_portal(cls) -> abc.BlockingPortal:
        return BlockingPortal()

    @classmethod
    async def open_process(
        cls,
        command: str | bytes | Sequence[str | bytes],
        *,
        shell: bool,
        stdin: int | IO[Any] | None,
        stdout: int | IO[Any] | None,
        stderr: int | IO[Any] | None,
        cwd: str | bytes | PathLike | None = None,
        env: Mapping[str, str] | None = None,
        start_new_session: bool = False,
    ) -> Process:
        await cls.checkpoint()
        if shell:
            process = await asyncio.create_subprocess_shell(
                cast("str | bytes", command),
                stdin=stdin,
                stdout=stdout,
                stderr=stderr,
                cwd=cwd,
                env=env,
                start_new_session=start_new_session,
            )
        else:
            process = await asyncio.create_subprocess_exec(
                *command,
                stdin=stdin,
                stdout=stdout,
                stderr=stderr,
                cwd=cwd,
                env=env,
                start_new_session=start_new_session,
            )

        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)

    @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)
        )

    @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,
    ) -> list[
        tuple[
            AddressFamily,
            SocketKind,
            int,
            str,
            tuple[str, int] | tuple[str, int, int, int],
        ]
    ]:
        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_socket_readable(cls, sock: socket.socket) -> None:
        await cls.checkpoint()
        try:
            read_events = _read_events.get()
        except LookupError:
            read_events = {}
            _read_events.set(read_events)

        if read_events.get(sock):
            raise BusyResourceError("reading from") from None

        loop = get_running_loop()
        event = read_events[sock] = asyncio.Event()
        loop.add_reader(sock, event.set)
        try:
            await event.wait()
        finally:
            if read_events.pop(sock, None) is not None:
                loop.remove_reader(sock)
                readable = True
            else:
                readable = False

        if not readable:
            raise ClosedResourceError

    @classmethod
    async def wait_socket_writable(cls, sock: socket.socket) -> None:
        await cls.checkpoint()
        try:
            write_events = _write_events.get()
        except LookupError:
            write_events = {}
            _write_events.set(write_events)

        if write_events.get(sock):
            raise BusyResourceError("writing to") from None

        loop = get_running_loop()
        event = write_events[sock] = asyncio.Event()
        loop.add_writer(sock.fileno(), event.set)
        try:
            await event.wait()
        finally:
            if write_events.pop(sock, None) is not None:
                loop.remove_writer(sock)
                writable = True
            else:
                writable = False

        if not writable:
            raise ClosedResourceError

    @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
    ) -> ContextManager[AsyncIterator[Signals]]:
        return _SignalReceiver(signals)

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

    @classmethod
    def get_running_tasks(cls) -> list[TaskInfo]:
        return [_create_task_info(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