asyncgui/src/asyncgui.py

__all__ = (
    # core (exceptions)
    'ExceptionGroup', 'BaseExceptionGroup', 'InvalidStateError', 'Cancelled',

    # core
    'Aw_or_Task', 'start', 'Task', 'TaskState', 'disable_cancellation', 'open_cancel_scope',
    'dummy_task', 'current_task', '_current_task', 'sleep_forever', '_sleep_forever',

    # structured concurrency
    'wait_all', 'wait_any', 'and_', 'or_', 'wait_all_cm', 'wait_any_cm', 'move_on_when',
    'run_as_main', 'run_as_daemon',
    'open_nursery', 'Nursery',

    # synchronization
    'Event', 'Box', 'ExclusiveEvent', 'ExclusiveBox',

    # deprecated
    'run_as_primary', 'run_as_secondary', 'AsyncEvent', 'AsyncBox',
)
import types
import typing as T
from inspect import getcoroutinestate, CORO_CREATED, CORO_SUSPENDED, isawaitable
import sys
import itertools
from functools import cached_property, partial
import enum
from contextlib import asynccontextmanager

# -----------------------------------------------------------------------------
# Core
# -----------------------------------------------------------------------------

if sys.version_info < (3, 11):
    from exceptiongroup import BaseExceptionGroup, ExceptionGroup
else:
    BaseExceptionGroup = BaseExceptionGroup  #: :meta private:
    ExceptionGroup = ExceptionGroup  #: :meta private:

potential_bug_msg = \
    r"You might found a bug in the library. Please make a minimal code that reproduces it, " \
    r"and open an issue at the GitHub repository, then post the code there. (https://github.com/asyncgui/asyncgui)."


class InvalidStateError(Exception):
    """Operation is not allowed in the current state."""


class _Cancelled(BaseException):
    @cached_property
    def level(self) -> int:
        return self.args[0]


Cancelled = (_Cancelled, GeneratorExit, )
'''
Exception class that represents cancellation.
See :ref:`dealing-with-cancellation`.

.. warning::

    Actually, this is not an exception class but a tuple of exception classes for now.
    But that's an implementation detail, and it might become an actual class in the future;
    therefore, your code must be compatible in both cases.

:meta hide-value:
'''


class TaskState(enum.Enum):
    '''
    Enum class that represents the Task state.
    '''

    CREATED = enum.auto()
    '''
    Waiting to start execution.

    :meta hide-value:
    '''

    STARTED = enum.auto()
    '''
    Currently running or suspended.

    :meta hide-value:
    '''

    CANCELLED = enum.auto()
    '''
    The execution has been cancelled. The cause of the cancellation is either an explicit or implicit call to
    :meth:`Task.cancel` or an unhandled exception.

    :meta hide-value:
    '''

    FINISHED = enum.auto()
    '''
    The execution has been completed.

    :meta hide-value:
    '''


_next_Task_uid = itertools.count().__next__


class Task:
    __slots__ = (
        '_uid', '_root_coro', '_state', '_result', '_on_end',
        '_exc_caught', '_suppresses_exc',
        '_cancel_disabled', '_cancel_depth', '_cancel_level',
    )

    def __init__(self, aw: T.Awaitable, /):
        if not isawaitable(aw):
            raise ValueError(str(aw) + " is not awaitable.")
        self._uid = _next_Task_uid()
        self._cancel_disabled = 0
        self._root_coro = self._wrapper(aw)
        self._state = TaskState.CREATED
        self._on_end = None
        self._cancel_depth = 0
        self._cancel_level = None
        self._exc_caught = None
        self._suppresses_exc = False

    def __str__(self):
        return f'Task(state={self._state.name}, uid={self._uid})'

    @property
    def uid(self) -> int:
        '''
        An unique integer assigned to the task.
        '''
        return self._uid

    @property
    def root_coro(self) -> T.Coroutine:
        '''
        The starting point of the coroutine chain for the task.
        '''
        return self._root_coro

    @property
    def state(self) -> TaskState:
        '''
        The current state of the task.
        '''
        return self._state

    @property
    def finished(self) -> bool:
        '''Whether the task has been completed.'''
        return self._state is TaskState.FINISHED

    @property
    def cancelled(self) -> bool:
        '''Whether the task has been cancelled.'''
        return self._state is TaskState.CANCELLED

    @property
    def result(self) -> T.Any:
        '''Result of the task. If the task is not finished, :exc:`InvalidStateError` will be raised. '''
        state = self._state
        if state is TaskState.FINISHED:
            return self._result
        elif state is TaskState.CANCELLED:
            raise InvalidStateError(f"{self} was cancelled")
        else:
            raise InvalidStateError(f"Result of {self} is not ready")

    async def _wrapper(self, aw, /):
        try:
            self._state = TaskState.STARTED
            self._result = await aw
        except _Cancelled as e:
            self._state = TaskState.CANCELLED
            assert e.level == 0, potential_bug_msg
            assert self._cancel_level == 0, potential_bug_msg
        except Exception as e:
            self._state = TaskState.CANCELLED
            self._exc_caught = e
            if not self._suppresses_exc:
                raise
        except:  # noqa: E722
            self._state = TaskState.CANCELLED
            raise
        else:
            self._state = TaskState.FINISHED
        finally:
            assert self._cancel_depth == 0, potential_bug_msg
            if (on_end := self._on_end) is not None:
                on_end(self)

    def cancel(self, _level=0, /):
        '''Cancel the task as soon as possible.'''
        if self._cancel_level is None:
            self._cancel_level = _level
            state = getcoroutinestate(self._root_coro)
            if state is CORO_SUSPENDED:
                if not self._cancel_disabled:
                    self._actual_cancel()
            elif state is CORO_CREATED:
                self._root_coro.close()
                self._state = TaskState.CANCELLED
        else:
            self._cancel_level = min(self._cancel_level, _level)

    def _actual_cancel(self):
        try:
            self._root_coro.throw(_Cancelled(self._cancel_level))(self)
        except StopIteration:
            pass
        else:
            self._cancel_if_needed()

    close = cancel
    '''An alias for :meth:`cancel`.'''

    @property
    def _cancel_requested(self) -> bool:
        return self._cancel_level is not None

    @property
    def _is_cancellable(self) -> bool:
        '''Whether the task can be cancelled immediately.'''
        return (not self._cancel_disabled) and getcoroutinestate(self._root_coro) is CORO_SUSPENDED

    def _cancel_if_needed(self, getcoroutinestate=getcoroutinestate, CORO_SUSPENDED=CORO_SUSPENDED):
        if (self._cancel_level is None) or self._cancel_disabled or \
                (getcoroutinestate(self._root_coro) is not CORO_SUSPENDED):
            pass
        else:
            self._actual_cancel()

    def _step(self, *args, **kwargs):
        coro = self._root_coro
        if getcoroutinestate(coro) is not CORO_SUSPENDED:
            return
        try:
            coro.send((args, kwargs, ))(self)
        except StopIteration:
            pass
        else:
            self._cancel_if_needed()

    def _throw_exc(self, exc):
        '''停止中のTaskへ例外を投げる。Taskが停止中ではない場合は :exc:`InvalidStateError` が起こる。'''
        coro = self._root_coro
        if getcoroutinestate(coro) is not CORO_SUSPENDED:
            raise InvalidStateError("Throwing an exception to an unstarted/running/closed task is not allowed.")
        try:
            coro.throw(exc)(self)
        except StopIteration:
            pass
        else:
            self._cancel_if_needed()


Aw_or_Task = T.Union[T.Awaitable, Task]


def start(aw: Aw_or_Task, /) -> Task:
    '''*Immediately* start a Task/Awaitable.

    If the argument is a :class:`Task`, itself will be returned. If it's an :class:`typing.Awaitable`,
    it will be wrapped in a Task, and that Task will be returned.

    .. code-block::

        async def async_func():
            ...

        task = start(async_func())
    '''
    if isawaitable(aw):
        task = Task(aw)
    elif isinstance(aw, Task):
        task = aw
        if task._state is not TaskState.CREATED:
            raise ValueError(f"{task} has already started")
    else:
        raise ValueError("Argument must be either a Task or an awaitable.")

    try:
        task._root_coro.send(None)(task)
    except StopIteration:
        pass
    else:
        task._cancel_if_needed()

    return task


class CancelScope:
    '''
    (internal)
    An equivalence of :class:`trio.CancelScope`.
    You should not directly instantiate this, use :func:`open_cancel_scope`.
    '''
    __slots__ = ('_task', '_level', 'cancelled_caught', 'cancel_called', )

    def __init__(self, task: Task, /):
        self._task = task
        self.cancelled_caught = False  #: Whether the scope caught a corresponding :class:`Cancelled` instance.
        self.cancel_called = False  #: Whether the :meth:`cancel` has been called.

    def __enter__(self) -> 'CancelScope':
        t = self._task
        t._cancel_depth = self._level = t._cancel_depth + 1
        return self

    def __exit__(self, exc_type, exc, __):
        # LOAD_FAST
        task = self._task
        level = task._cancel_level
        scope_level = self._level

        self._task = None
        task._cancel_depth -= 1
        if level is not None:
            if level == scope_level:
                task._cancel_level = None
            else:
                assert level < scope_level, potential_bug_msg
        if exc_type is not _Cancelled:
            return
        level = exc.level
        if level == scope_level:
            self.cancelled_caught = True
            return True
        else:
            assert level < scope_level, potential_bug_msg

    @property
    def closed(self) -> bool:
        '''
        Whether this scope has been closed.
        The cause of the closure of the scope can be either an exception occurred or the scope exited gracefully,
        '''
        return self._task is None

    def cancel(self):
        '''Cancel the execution inside this scope as soon as possible. '''
        if self.cancel_called:
            return
        self.cancel_called = True
        if not self.closed:
            self._task.cancel(self._level)


class open_cancel_scope:
    '''
    Same as :class:`trio.CancelScope` except this one returns an async context manager.

    .. code-block::

        async with open_cancel_scope() as scope:
            ...
    '''
    __slots__ = ('_scope', )

    async def __aenter__(self) -> T.Awaitable[CancelScope]:
        self._scope = CancelScope(await current_task())
        return self._scope.__enter__()

    async def __aexit__(self, *args):
        return self._scope.__exit__(*args)


def _current_task(task):
    return task._step(task)


@types.coroutine
def current_task(_f=_current_task) -> T.Awaitable[Task]:
    '''Returns the Task instance corresponding to the caller.

    .. code-block::

        task = await current_task()
    '''
    return (yield _f)[0][0]


class disable_cancellation:
    '''
    Return an async context manager that protects its code-block from cancellation.

    .. code-block::

        async with disable_cancellation():
            await something  # <- never gets cancelled
    '''

    __slots__ = ('_task', )

    async def __aenter__(self):
        self._task = task = await current_task()
        task._cancel_disabled += 1

    async def __aexit__(self, *__):
        self._task._cancel_disabled -= 1


def _sleep_forever(task):
    pass


@types.coroutine
def sleep_forever(_f=_sleep_forever) -> T.Awaitable:
    '''
    .. code-block::

        await sleep_forever()
    '''
    yield _f


dummy_task = Task(sleep_forever())
'''
An already closed task.
This can be utilized to prevent the need for the common null validation mentioned below.

*Before:*

.. code-block::
    :emphasize-lines: 3, 6,7

    class MyClass:
        def __init__(self):
            self._task = None

        def restart(self):
            if self._task is not None:
                self._task.cancel()
            self._task = asyncgui.start(self.main())

        async def main(self):
            ...

*After:*

.. code-block::
    :emphasize-lines: 3, 6

    class MyClass:
        def __init__(self):
            self._task = asyncgui.dummy_task

        def restart(self):
            self._task.cancel()
            self._task = asyncgui.start(self.main())

        async def main(self):
            ...
'''
dummy_task.cancel()

# -----------------------------------------------------------------------------
# Synchronization
# -----------------------------------------------------------------------------


class ExclusiveEvent:
    '''
    Similar to :class:`Event`, but this version does not allow multiple tasks to :meth:`wait` simultaneously.
    As a result, it operates faster.
    '''
    __slots__ = ('_callback', )

    def __init__(self):
        self._callback = None

    def fire(self, *args, **kwargs):
        if (f := self._callback) is not None:
            f(*args, **kwargs)

    @types.coroutine
    def wait(self) -> T.Awaitable[tuple]:
        if self._callback is not None:
            raise InvalidStateError("There's already a task waiting for the event to fire.")
        try:
            return (yield self._attach_task)
        finally:
            self._callback = None

    def _attach_task(self, task):
        self._callback = task._step


class ExclusiveBox:
    '''
    Similar to :class:`Box`, but this version does not allow multiple tasks to :meth:`get` simultaneously.

    .. deprecated:: 0.7.1
        Use :class:`Box` instead.
    '''
    __slots__ = ('_item', '_callback', )

    def __init__(self):
        self._item = None
        self._callback = None

    @property
    def is_empty(self) -> bool:
        '''Whether the box is empty.'''
        return self._item is None

    def put(self, *args, **kwargs):
        '''Put an item into the box if it's empty.'''
        if self._item is None:
            self.put_or_update(*args, **kwargs)

    def update(self, *args, **kwargs):
        '''Replace the item in the box if there is one already.'''
        if self._item is not None:
            self.put_or_update(*args, **kwargs)

    def put_or_update(self, *args, **kwargs):
        self._item = (args, kwargs, )
        if (callback := self._callback) is not None:
            callback(*args, **kwargs)

    @types.coroutine
    def get(self) -> T.Awaitable[tuple]:
        '''Get the item from the box if there is one. Otherwise, wait until it's put.'''
        if self._callback is not None:
            raise InvalidStateError("There's already a task waiting for an item to be put in the box.")
        if self._item is None:
            try:
                return (yield self._attach_task)
            finally:
                self._callback = None
        else:
            return self._item

    def clear(self):
        '''Remove the item from the box if there is one.'''
        self._item = None

    _attach_task = ExclusiveEvent._attach_task


class Event:
    '''
    .. code-block::

        async def async_fn(e):
            args, kwargs = await e.wait()
            assert args == (2, )
            assert kwargs == {'crow': 'raven', }

            args, kwargs = await e.wait()
            assert args == (3, )
            assert kwargs == {'toad': 'frog', }

        e = Event()
        e.fire(1, crocodile='alligator')
        task = start(async_fn(e))
        e.fire(2, crow='raven')
        e.fire(3, toad='frog')
        assert task.finished

    .. warning::

        This differs significantly from :class:`asyncio.Event`, as this one does not have a "set" state.
        When a Task calls its :meth:`wait` method, it will always be blocked until :meth:`fire` is called after that.
        Use :class:`Box` if you want something closer to :class:`asyncio.Event`.

    .. versionchanged:: 0.7.0

        This is now completely different from the previous version's.
    '''

    __slots__ = ('_waiting_tasks', )

    def __init__(self):
        self._waiting_tasks = []

    def fire(self, *args, **kwargs):
        tasks = self._waiting_tasks
        self._waiting_tasks = []
        for t in tasks:
            if t is not None:
                t._step(*args, **kwargs)

    @types.coroutine
    def wait(self) -> T.Awaitable[tuple]:
        '''
        Waits for the event to be fired.
        '''
        try:
            tasks = self._waiting_tasks
            idx = len(tasks)
            return (yield tasks.append)
        finally:
            tasks[idx] = None


class Box:
    '''
    .. code-block::

        async def async_fn(box):
            args, kwargs = await box.get()
            assert args == (1, )
            assert kwargs == {'crow': 'raven', }

        box = Box()
        box.put(1, crow='raven')

        # This task will immediately end because the 'box' already has an item.
        task = start(async_fn(box))
        assert task.finished

        box.clear()
        # Now the box is empty, so this task will wait until an item is added.
        task = start(async_fn(box))
        assert not task.finished

        # Put an item into the box, which will cause the task to end.
        box.put(1, crow='raven')
        assert task.finished
    '''
    __slots__ = ('_item', '_waiting_tasks', )

    def __init__(self):
        self._item = None
        self._waiting_tasks = []

    @property
    def is_empty(self) -> bool:
        return self._item is None

    def put(self, *args, **kwargs):
        '''Put an item into the box if it's empty.'''
        if self._item is None:
            self.put_or_update(*args, **kwargs)

    def update(self, *args, **kwargs):
        '''Replace the item in the box if there is one already.'''
        if self._item is not None:
            self.put_or_update(*args, **kwargs)

    def put_or_update(self, *args, **kwargs):
        self._item = (args, kwargs, )
        tasks = self._waiting_tasks
        self._waiting_tasks = []
        for t in tasks:
            if t is not None:
                t._step(*args, **kwargs)

    def clear(self):
        '''Remove the item from the box if there is one.'''
        self._item = None

    @types.coroutine
    def get(self) -> T.Awaitable[tuple]:
        '''Get the item from the box if there is one. Otherwise, wait until it's put.'''
        if self._item is not None:
            return self._item
        tasks = self._waiting_tasks
        idx = len(tasks)
        try:
            return (yield tasks.append)
        finally:
            tasks[idx] = None


# -----------------------------------------------------------------------------
# Structured concurrency
# -----------------------------------------------------------------------------


class TaskCounter:
    '''
    (internal)
    数値が零になった事を通知する仕組みを持つカウンター。
    親taskが自分の子task達の終了を待つのに用いる。
    '''

    __slots__ = ('_parent', '_n_children', )

    def __init__(self, initial=0, /):
        self._n_children = initial
        self._parent = None

    def increase(self):
        self._n_children += 1

    def decrease(self, potential_bug_msg=potential_bug_msg):
        n = self._n_children - 1
        assert n >= 0, potential_bug_msg
        self._n_children = n
        if (parent := self._parent) is not None and (not n):
            parent._step()

    @types.coroutine
    def to_be_zero(self, _current_task=_current_task, _sleep_forever=_sleep_forever):
        if not self._n_children:
            return
        self._parent = (yield _current_task)[0][0]
        try:
            yield _sleep_forever
        finally:
            self._parent = None

    def __bool__(self):
        return not not self._n_children  # 'not not' is not a typo


async def _wait_xxx(debug_msg, on_child_end, *aws: T.Iterable[Aw_or_Task]) -> T.Awaitable[T.Sequence[Task]]:
    children = tuple(v if isinstance(v, Task) else Task(v) for v in aws)
    if not children:
        return children
    counter = TaskCounter(len(children))
    parent = await current_task()

    try:
        with CancelScope(parent) as scope:
            on_child_end = partial(on_child_end, scope, counter)
            for c in children:
                c._suppresses_exc = True
                c._on_end = on_child_end
                start(c)
            await counter.to_be_zero()
    finally:
        if counter:
            for c in children:
                c.cancel()
            if counter:
                try:
                    parent._cancel_disabled += 1
                    await counter.to_be_zero()
                finally:
                    parent._cancel_disabled -= 1
        exceptions = tuple(e for c in children if (e := c._exc_caught) is not None)
        if exceptions:
            raise ExceptionGroup(debug_msg, exceptions)
        if (parent._cancel_level is not None) and (not parent._cancel_disabled):
            await sleep_forever()
            assert False, potential_bug_msg
    return children


def _on_child_end__ver_all(scope, counter, child):
    counter.decrease()
    if child._exc_caught is not None:
        scope.cancel()


def _on_child_end__ver_any(scope, counter, child):
    counter.decrease()
    if child._exc_caught is not None or child.finished:
        scope.cancel()


_wait_xxx_type = T.Callable[..., T.Awaitable[T.Sequence[Task]]]
wait_all: _wait_xxx_type = partial(_wait_xxx, "wait_all()", _on_child_end__ver_all)
'''
Run multiple tasks concurrently, and wait for **all** of them to **end**. When any of them raises an exception, the
others will be cancelled, and the exception will be propagated to the caller, like :class:`trio.Nursery`.

.. code-block::

    tasks = await wait_all(async_fn1(), async_fn2(), async_fn3())
    if tasks[0].finished:
        print("The return value of async_fn1() :", tasks[0].result)
'''
wait_any: _wait_xxx_type = partial(_wait_xxx, "wait_any()", _on_child_end__ver_any)
'''
Run multiple tasks concurrently, and wait for **any** of them to **finish**. As soon as that happens, the others will be
cancelled. When any of them raises an exception, the others will be cancelled, and the exception will be propagated to
the caller, like :class:`trio.Nursery`.

.. code-block::

    tasks = await wait_any(async_fn1(), async_fn2(), async_fn3())
    if tasks[0].finished:
        print("The return value of async_fn1() :", tasks[0].result)
'''


@asynccontextmanager
async def _wait_xxx_cm(debug_msg, on_child_end, wait_bg, aw: Aw_or_Task):
    counter = TaskCounter(1)
    fg_task = await current_task()
    bg_task = aw if isinstance(aw, Task) else Task(aw)
    exc = None

    try:
        with CancelScope(fg_task) as scope:
            bg_task._on_end = partial(on_child_end, scope, counter)
            bg_task._suppresses_exc = True
            yield start(bg_task)
            if wait_bg:
                await counter.to_be_zero()
    except Exception as e:
        exc = e
    finally:
        bg_task.cancel()
        if counter:
            try:
                fg_task._cancel_disabled += 1
                await counter.to_be_zero()
            finally:
                fg_task._cancel_disabled -= 1
        excs = tuple(
            e for e in (exc, bg_task._exc_caught, )
            if e is not None
        )
        if excs:
            raise ExceptionGroup(debug_msg, excs)
        if (fg_task._cancel_level is not None) and (not fg_task._cancel_disabled):
            await sleep_forever()
            assert False, potential_bug_msg


_wait_xxx_cm_type = T.Callable[[Aw_or_Task], T.AsyncContextManager[Task]]
wait_all_cm: _wait_xxx_cm_type = partial(_wait_xxx_cm, "wait_all_cm()", _on_child_end__ver_all, True)
'''
The context manager form of :func:`wait_all`.

.. code-block::

    async with wait_all_cm(async_fn()) as bg_task:
        ...
'''
wait_any_cm: _wait_xxx_cm_type = partial(_wait_xxx_cm, "wait_any_cm()", _on_child_end__ver_any, False)
'''
The context manager form of :func:`wait_any`, an equivalence of :func:`trio_util.move_on_when`.

.. code-block::

    async with wait_any_cm(async_fn()) as bg_task:
        ...
'''
run_as_main: _wait_xxx_cm_type = partial(_wait_xxx_cm, "run_as_main()", _on_child_end__ver_any, True)
'''
.. code-block::

    async with run_as_main(async_fn()) as task:
        ...

.. note::

    You need to use its older name, ``run_as_primary``, if you are using ``asyncgui`` 0.6.2 or older.
'''
run_as_daemon: _wait_xxx_cm_type = partial(_wait_xxx_cm, "run_as_daemon()", _on_child_end__ver_all, False)
'''
.. code-block::

    async with run_as_daemon(async_fn()) as bg_task:
        ...
'''


class Nursery:
    '''
    Similar to :class:`trio.Nursery`.
    You should not directly instantiate this, use :func:`open_nursery`.
    '''

    __slots__ = ('_closed', '_children', '_scope', '_counters', '_callbacks', '_gc_in_every', '_n_until_gc', )

    def __init__(self, scope, counter, daemon_counter, gc_in_every):
        self._gc_in_every = self._n_until_gc = gc_in_every
        self._closed = False
        self._children = []
        self._scope = scope
        self._counters = (daemon_counter, counter, )
        self._callbacks = (
            partial(_on_child_end__ver_all, scope, daemon_counter),
            partial(_on_child_end__ver_all, scope, counter),
        )

    def start(self, aw: Aw_or_Task, /, *, daemon=False) -> Task:
        '''
        *Immediately* start a Task/Awaitable under the supervision of the nursery.

        If the argument is a :class:`Task`, itself will be returned. If it's an :class:`typing.Awaitable`,
        it will be wrapped in a Task, and that Task will be returned.

        The ``daemon`` parameter acts like the one in the :mod:`threading` module.
        When only daemon tasks are left, they get cancelled, and the nursery closes.
        '''
        if self._closed:
            raise InvalidStateError("Nursery has been already closed")
        if not self._n_until_gc:
            self._collect_garbage()
            self._n_until_gc = self._gc_in_every
        self._n_until_gc -= 1
        child = aw if isinstance(aw, Task) else Task(aw)
        child._suppresses_exc = True
        child._on_end = self._callbacks[not daemon]
        self._counters[not daemon].increase()
        self._children.append(child)
        return start(child)

    def _collect_garbage(self, STARTED=TaskState.STARTED):
        self._children = [
            c for c in self._children
            if c.state is STARTED or c._exc_caught is not None
        ]

    def close(self):
        '''Cancel all the child tasks in the nursery as soon as possible. '''
        self._closed = True
        self._scope.cancel()

    @property
    def closed(self) -> bool:
        return self._closed


@asynccontextmanager
async def open_nursery(*, _gc_in_every=1000) -> T.AsyncContextManager[Nursery]:
    '''
    Similar to :func:`trio.open_nursery`.

    .. code-block::

        async with open_nursery() as nursery:
            nursery.start(async_fn1())
            nursery.start(async_fn2(), daemon=True)
    '''
    exc = None
    parent = await current_task()
    counter = TaskCounter()
    daemon_counter = TaskCounter()

    try:
        with CancelScope(parent) as scope:
            nursery = Nursery(scope, counter, daemon_counter, _gc_in_every)
            yield nursery
            await counter.to_be_zero()
    except Exception as e:
        exc = e
    finally:
        nursery._closed = True
        children = nursery._children
        for c in children:
            c.cancel()
        try:
            parent._cancel_disabled += 1
            await daemon_counter.to_be_zero()
            await counter.to_be_zero()
        finally:
            parent._cancel_disabled -= 1
        excs = tuple(
            e for e in itertools.chain((exc, ), (c._exc_caught for c in children))
            if e is not None
        )
        if excs:
            raise ExceptionGroup("Nursery", excs)
        if (parent._cancel_level is not None) and (not parent._cancel_disabled):
            await sleep_forever()
            assert False, potential_bug_msg


# -----------------------------------------------------------------------------
# Aliases
# -----------------------------------------------------------------------------
run_as_primary = run_as_main
run_as_secondary = run_as_daemon
AsyncEvent = ExclusiveEvent
AsyncBox = ExclusiveBox

and_ = wait_all  #: An alias for :func:`wait_all`.
or_ = wait_any  #: An alias for :func:`wait_any`.
move_on_when = wait_any_cm  #: An alias for :func:`wait_any_cm`.