test_taskgroups.py

from __future__ import annotations

import asyncio
import math
import sys
import time
from collections.abc import AsyncGenerator, Coroutine, Generator
from typing import Any, NoReturn, cast

import pytest
from exceptiongroup import catch

import anyio
from anyio import (
    TASK_STATUS_IGNORED,
    CancelScope,
    create_task_group,
    current_effective_deadline,
    current_time,
    fail_after,
    get_cancelled_exc_class,
    get_current_task,
    move_on_after,
    sleep,
    wait_all_tasks_blocked,
)
from anyio.abc import TaskGroup, TaskStatus
from anyio.lowlevel import checkpoint

if sys.version_info < (3, 11):
    from exceptiongroup import BaseExceptionGroup, ExceptionGroup

pytestmark = pytest.mark.anyio


async def async_error(text: str, delay: float = 0.1) -> NoReturn:
    try:
        if delay:
            await sleep(delay)
    finally:
        raise Exception(text)


async def test_already_closed() -> None:
    async with create_task_group() as tg:
        pass

    with pytest.raises(RuntimeError) as exc:
        tg.start_soon(async_error, "fail")

    exc.match("This task group is not active; no new tasks can be started")


async def test_success() -> None:
    async def async_add(value: str) -> None:
        results.add(value)

    results: set[str] = set()
    async with create_task_group() as tg:
        tg.start_soon(async_add, "a")
        tg.start_soon(async_add, "b")

    assert results == {"a", "b"}


@pytest.mark.parametrize(
    "module",
    [
        pytest.param(asyncio, id="asyncio"),
        pytest.param(pytest.importorskip("trio"), id="trio"),
    ],
)
def test_run_natively(module: Any) -> None:
    async def testfunc() -> None:
        async with create_task_group() as tg:
            tg.start_soon(sleep, 0)

    if module is asyncio:
        asyncio.run(testfunc())
    else:
        module.run(testfunc)


async def test_start_soon_while_running() -> None:
    async def task_func() -> None:
        tg.start_soon(sleep, 0)

    async with create_task_group() as tg:
        tg.start_soon(task_func)


async def test_start_soon_after_error() -> None:
    with pytest.raises(ExceptionGroup):
        async with create_task_group() as tg:
            a = 1 / 0  # noqa: F841

    with pytest.raises(RuntimeError) as exc:
        tg.start_soon(sleep, 0)

    exc.match("This task group is not active; no new tasks can be started")


async def test_start_no_value() -> None:
    async def taskfunc(*, task_status: TaskStatus) -> None:
        task_status.started()

    async with create_task_group() as tg:
        value = await tg.start(taskfunc)
        assert value is None


async def test_start_called_twice() -> None:
    async def taskfunc(*, task_status: TaskStatus) -> None:
        task_status.started()

        with pytest.raises(
            RuntimeError, match="called 'started' twice on the same task status"
        ):
            task_status.started()

    async with create_task_group() as tg:
        value = await tg.start(taskfunc)
        assert value is None


async def test_no_called_started_twice() -> None:
    async def taskfunc(*, task_status: TaskStatus) -> None:
        task_status.started()

    # anyio>4.3.0 should not raise "RuntimeError: called 'started' twice on the same task status"
    async with create_task_group() as tg:
        coro = tg.start(taskfunc)
        tg.cancel_scope.cancel()
        await coro


async def test_start_with_value() -> None:
    async def taskfunc(*, task_status: TaskStatus) -> None:
        task_status.started("foo")

    async with create_task_group() as tg:
        value = await tg.start(taskfunc)
        assert value == "foo"


async def test_start_crash_before_started_call() -> None:
    async def taskfunc(*, task_status: TaskStatus) -> NoReturn:
        raise Exception("foo")

    async with create_task_group() as tg:
        with pytest.raises(Exception) as exc:
            await tg.start(taskfunc)

    exc.match("foo")


async def test_start_crash_after_started_call() -> None:
    async def taskfunc(*, task_status: TaskStatus) -> NoReturn:
        task_status.started(2)
        raise Exception("foo")

    with pytest.raises(ExceptionGroup) as exc:
        async with create_task_group() as tg:
            value = await tg.start(taskfunc)

    assert len(exc.value.exceptions) == 1
    assert str(exc.value.exceptions[0]) == "foo"
    assert value == 2


async def test_start_no_started_call() -> None:
    async def taskfunc(*, task_status: TaskStatus) -> None:
        pass

    async with create_task_group() as tg:
        with pytest.raises(RuntimeError) as exc:
            await tg.start(taskfunc)

    exc.match("hild exited")


async def test_start_cancelled() -> None:
    started = finished = False

    async def taskfunc(*, task_status: TaskStatus) -> None:
        nonlocal started, finished
        started = True
        await sleep(2)
        finished = True

    async with create_task_group() as tg:
        tg.cancel_scope.cancel()
        await tg.start(taskfunc)

    assert started
    assert not finished


@pytest.mark.xfail(
    sys.version_info < (3, 9), reason="Requires a way to detect cancellation source"
)
@pytest.mark.parametrize("anyio_backend", ["asyncio"])
async def test_start_native_host_cancelled() -> None:
    started = finished = False

    async def taskfunc(*, task_status: TaskStatus) -> None:
        nonlocal started, finished
        started = True
        await sleep(2)
        finished = True

    async def start_another() -> None:
        async with create_task_group() as tg:
            await tg.start(taskfunc)

    task = asyncio.get_running_loop().create_task(start_another())
    await wait_all_tasks_blocked()
    task.cancel()
    with pytest.raises(asyncio.CancelledError):
        await task

    assert started
    assert not finished


@pytest.mark.parametrize("anyio_backend", ["asyncio"])
async def test_start_native_child_cancelled() -> None:
    task = None
    finished = False

    async def taskfunc(*, task_status: TaskStatus) -> None:
        nonlocal task, finished
        task = asyncio.current_task()
        await sleep(2)
        finished = True

    async def start_another() -> None:
        async with create_task_group() as tg2:
            await tg2.start(taskfunc)

    async with create_task_group() as tg:
        tg.start_soon(start_another)
        await wait_all_tasks_blocked()
        assert task is not None
        task.cancel()

    assert not finished


@pytest.mark.parametrize("anyio_backend", ["asyncio"])
async def test_propagate_native_cancellation_from_taskgroup() -> None:
    async def taskfunc() -> None:
        async with create_task_group() as tg:
            tg.start_soon(asyncio.sleep, 2)

    task = asyncio.create_task(taskfunc())
    await wait_all_tasks_blocked()
    task.cancel()
    with pytest.raises(asyncio.CancelledError):
        await task


async def test_start_exception_delivery(anyio_backend_name: str) -> None:
    def task_fn(*, task_status: TaskStatus = TASK_STATUS_IGNORED) -> None:
        task_status.started("hello")

    if anyio_backend_name == "trio":
        pattern = "appears to be synchronous"
    else:
        pattern = "is not a coroutine object"

    async with anyio.create_task_group() as tg:
        with pytest.raises(TypeError, match=pattern):
            await tg.start(task_fn)  # type: ignore[arg-type]


async def test_start_cancel_after_error() -> None:
    """Regression test for #517."""
    sleep_completed = False

    async def sleep_and_raise() -> None:
        await wait_all_tasks_blocked()
        raise RuntimeError("This should cancel the second start() call")

    async def sleep_only(task_status: TaskStatus[None]) -> None:
        nonlocal sleep_completed
        await sleep(1)
        sleep_completed = True
        task_status.started()

    with pytest.raises(ExceptionGroup) as exc:
        async with anyio.create_task_group() as outer_tg:
            async with anyio.create_task_group() as inner_tg:
                inner_tg.start_soon(sleep_and_raise)
                await outer_tg.start(sleep_only)

    assert isinstance(exc.value.exceptions[0], ExceptionGroup)
    assert isinstance(exc.value.exceptions[0].exceptions[0], RuntimeError)
    assert not sleep_completed


async def test_host_exception() -> None:
    result = None

    async def set_result(value: str) -> None:
        nonlocal result
        await sleep(3)
        result = value

    with pytest.raises(ExceptionGroup) as exc:
        async with create_task_group() as tg:
            tg.start_soon(set_result, "a")
            raise Exception("dummy error")

    assert len(exc.value.exceptions) == 1
    assert str(exc.value.exceptions[0]) == "dummy error"
    assert result is None


async def test_level_cancellation() -> None:
    marker = None

    async def dummy() -> None:
        nonlocal marker
        marker = 1
        # At this point the task has been cancelled so sleep() will raise an exception
        await sleep(0)
        # Execution should never get this far
        marker = 2

    async with create_task_group() as tg:
        tg.start_soon(dummy)
        assert marker is None
        tg.cancel_scope.cancel()

    assert marker == 1


async def test_failing_child_task_cancels_host() -> None:
    async def child() -> NoReturn:
        await wait_all_tasks_blocked()
        raise Exception("foo")

    sleep_completed = False
    with pytest.raises(ExceptionGroup) as exc:
        async with create_task_group() as tg:
            tg.start_soon(child)
            await sleep(0.5)
            sleep_completed = True

    assert len(exc.value.exceptions) == 1
    assert str(exc.value.exceptions[0]) == "foo"
    assert not sleep_completed


async def test_failing_host_task_cancels_children() -> None:
    sleep_completed = False

    async def child() -> None:
        nonlocal sleep_completed
        await sleep(1)
        sleep_completed = True

    with pytest.raises(ExceptionGroup) as exc:
        async with create_task_group() as tg:
            tg.start_soon(child)
            await wait_all_tasks_blocked()
            raise Exception("foo")

    assert len(exc.value.exceptions) == 1
    assert str(exc.value.exceptions[0]) == "foo"
    assert not sleep_completed


async def test_cancel_scope_in_another_task() -> None:
    local_scope = None
    result = False

    async def child() -> None:
        nonlocal result, local_scope
        with CancelScope() as local_scope:
            await sleep(2)
            result = True

    async with create_task_group() as tg:
        tg.start_soon(child)
        while local_scope is None:
            await sleep(0)

        local_scope.cancel()

    assert not result


async def test_cancel_propagation() -> None:
    async def g() -> NoReturn:
        async with create_task_group():
            await sleep(1)

        assert False

    async with create_task_group() as tg:
        tg.start_soon(g)
        await sleep(0)
        tg.cancel_scope.cancel()


async def test_cancel_twice() -> None:
    """Test that the same task can receive two cancellations."""

    async def cancel_group() -> None:
        await wait_all_tasks_blocked()
        tg.cancel_scope.cancel()

    for _ in range(2):
        async with create_task_group() as tg:
            tg.start_soon(cancel_group)
            await sleep(1)
            pytest.fail("Execution should not reach this point")


async def test_cancel_exiting_task_group() -> None:
    """
    Test that if a task group is waiting for subtasks to finish and it receives a
    cancellation, the subtasks are also cancelled and the waiting continues.

    """
    cancel_received = False

    async def waiter() -> None:
        nonlocal cancel_received
        try:
            await sleep(5)
        finally:
            cancel_received = True

    async def subgroup() -> None:
        async with create_task_group() as tg2:
            tg2.start_soon(waiter)

    async with create_task_group() as tg:
        tg.start_soon(subgroup)
        await wait_all_tasks_blocked()
        tg.cancel_scope.cancel()

    assert cancel_received


async def test_cancel_before_entering_scope() -> None:
    """
    Test that CancelScope.cancel() is honored even if called before entering the scope.

    """
    cancel_scope = anyio.CancelScope()
    cancel_scope.cancel()
    with cancel_scope:
        await anyio.sleep(1)  # Checkpoint to allow anyio to check for cancellation
        pytest.fail("execution should not reach this point")


@pytest.mark.xfail(
    sys.version_info < (3, 11), reason="Requires asyncio.Task.cancelling()"
)
@pytest.mark.parametrize("anyio_backend", ["asyncio"])
async def test_cancel_counter_nested_scopes() -> None:
    with CancelScope() as root_scope:
        with CancelScope():
            root_scope.cancel()
            await sleep(0.5)

    assert not cast(asyncio.Task, asyncio.current_task()).cancelling()


async def test_exception_group_children() -> None:
    with pytest.raises(BaseExceptionGroup) as exc:
        async with create_task_group() as tg:
            tg.start_soon(async_error, "task1")
            tg.start_soon(async_error, "task2", 0.15)

    assert len(exc.value.exceptions) == 2
    assert sorted(str(e) for e in exc.value.exceptions) == ["task1", "task2"]


async def test_exception_group_host() -> None:
    with pytest.raises(BaseExceptionGroup) as exc:
        async with create_task_group() as tg:
            tg.start_soon(async_error, "child", 2)
            await wait_all_tasks_blocked()
            raise Exception("host")

    assert len(exc.value.exceptions) == 2
    assert sorted(str(e) for e in exc.value.exceptions) == ["child", "host"]


async def test_escaping_cancelled_exception() -> None:
    async with create_task_group() as tg:
        tg.cancel_scope.cancel()
        await sleep(0)


async def test_cancel_scope_cleared() -> None:
    with move_on_after(0.1):
        await sleep(1)

    await sleep(0)


@pytest.mark.parametrize("delay", [0, 0.1], ids=["instant", "delayed"])
async def test_fail_after(delay: float) -> None:
    with pytest.raises(TimeoutError):
        with fail_after(delay) as scope:
            await sleep(1)

    assert scope.cancel_called
    assert scope.cancelled_caught


async def test_fail_after_no_timeout() -> None:
    with fail_after(None) as scope:
        assert scope.deadline == float("inf")
        await sleep(0.1)

    assert not scope.cancel_called
    assert not scope.cancelled_caught


async def test_fail_after_after_cancellation() -> None:
    event = anyio.Event()
    async with anyio.create_task_group() as tg:
        tg.cancel_scope.cancel()
        await event.wait()

    block_complete = False
    with pytest.raises(TimeoutError):
        with fail_after(0.1):
            await anyio.sleep(0.5)
            block_complete = True

    assert not block_complete


async def test_fail_after_cancelled_before_deadline() -> None:
    """
    Test that fail_after() won't raise TimeoutError if its scope is cancelled before the
    deadline.

    """
    with fail_after(1) as scope:
        scope.cancel()
        await checkpoint()


@pytest.mark.xfail(
    reason="There is currently no way to tell if cancellation happened due to timeout "
    "explicitly if the deadline has been exceeded"
)
async def test_fail_after_scope_cancelled_before_timeout() -> None:
    with fail_after(0.1) as scope:
        scope.cancel()
        time.sleep(0.11)  # noqa: ASYNC101
        await sleep(0)


@pytest.mark.parametrize("delay", [0, 0.1], ids=["instant", "delayed"])
async def test_move_on_after(delay: float) -> None:
    result = False
    with move_on_after(delay) as scope:
        await sleep(1)
        result = True

    assert not result
    assert scope.cancel_called
    assert scope.cancelled_caught


async def test_move_on_after_no_timeout() -> None:
    result = False
    with move_on_after(None) as scope:
        assert scope.deadline == float("inf")
        await sleep(0.1)
        result = True

    assert result
    assert not scope.cancel_called


async def test_nested_move_on_after() -> None:
    sleep_completed = inner_scope_completed = False
    with move_on_after(0.1) as outer_scope:
        assert current_effective_deadline() == outer_scope.deadline
        with move_on_after(1) as inner_scope:
            assert current_effective_deadline() == outer_scope.deadline
            await sleep(2)
            sleep_completed = True

        inner_scope_completed = True

    assert not sleep_completed
    assert not inner_scope_completed
    assert outer_scope.cancel_called
    assert outer_scope.cancelled_caught
    assert not inner_scope.cancel_called
    assert not inner_scope.cancelled_caught


async def test_shielding() -> None:
    async def cancel_when_ready() -> None:
        await wait_all_tasks_blocked()
        tg.cancel_scope.cancel()

    inner_sleep_completed = outer_sleep_completed = False
    async with create_task_group() as tg:
        tg.start_soon(cancel_when_ready)
        with move_on_after(10, shield=True) as inner_scope:
            assert inner_scope.shield
            await sleep(0.1)
            inner_sleep_completed = True

        await sleep(1)
        outer_sleep_completed = True

    assert inner_sleep_completed
    assert not outer_sleep_completed
    assert tg.cancel_scope.cancel_called
    assert not inner_scope.cancel_called


async def test_cancel_from_shielded_scope() -> None:
    async with create_task_group() as tg:
        with CancelScope(shield=True) as inner_scope:
            assert inner_scope.shield
            tg.cancel_scope.cancel()
            assert current_effective_deadline() == math.inf

        assert current_effective_deadline() == -math.inf

        with pytest.raises(get_cancelled_exc_class()):
            await sleep(0.01)

        with pytest.raises(get_cancelled_exc_class()):
            await sleep(0.01)


async def test_cancel_shielded_scope() -> None:
    with CancelScope(shield=True) as cancel_scope:
        assert cancel_scope.shield
        cancel_scope.cancel()
        assert current_effective_deadline() == -math.inf

        with pytest.raises(get_cancelled_exc_class()):
            await sleep(0)


async def test_cancelled_not_caught() -> None:
    with CancelScope() as scope:
        scope.cancel()

    assert scope.cancel_called
    assert not scope.cancelled_caught


@pytest.mark.parametrize("anyio_backend", ["asyncio"])
async def test_cancel_host_asyncgen() -> None:
    done = False

    async def host_task() -> None:
        nonlocal done
        async with create_task_group() as tg:
            with CancelScope(shield=True) as inner_scope:
                assert inner_scope.shield
                tg.cancel_scope.cancel()

            with pytest.raises(get_cancelled_exc_class()):
                await sleep(0)

            with pytest.raises(get_cancelled_exc_class()):
                await sleep(0)

            done = True

    async def host_agen_fn() -> AsyncGenerator[None, None]:
        await host_task()
        yield
        pytest.fail("host_agen_fn should only be __anext__ed once")

    host_agen = host_agen_fn()
    try:
        loop = asyncio.get_running_loop()
        await loop.create_task(host_agen.__anext__())  # type: ignore[arg-type]
    finally:
        await host_agen.aclose()

    assert done


async def test_shielding_immediate_scope_cancelled() -> None:
    async def cancel_when_ready() -> None:
        await wait_all_tasks_blocked()
        scope.cancel()

    sleep_completed = False
    async with create_task_group() as tg:
        with CancelScope(shield=True) as scope:
            tg.start_soon(cancel_when_ready)
            await sleep(0.5)
            sleep_completed = True

    assert not sleep_completed


async def test_shielding_mutate() -> None:
    completed = False

    async def task(task_status: TaskStatus) -> NoReturn:
        nonlocal completed
        with CancelScope() as scope:
            # Enable the shield a little after the scope starts to make this test
            # general, even though it has no bearing on the current implementation.
            await sleep(0.1)
            scope.shield = True
            task_status.started()
            await sleep(0.1)
            completed = True
            scope.shield = False
            await sleep(1)
            pytest.fail("Execution should not reach this point")

    async with create_task_group() as tg:
        await tg.start(task)
        tg.cancel_scope.cancel()

    assert completed


async def test_cancel_scope_in_child_task() -> None:
    child_scope = None

    async def child() -> None:
        nonlocal child_scope
        with CancelScope() as child_scope:
            await sleep(2)

    host_done = False
    async with create_task_group() as tg:
        tg.start_soon(child)
        await wait_all_tasks_blocked()
        assert child_scope is not None
        child_scope.cancel()
        await sleep(0.1)
        host_done = True

    assert host_done
    assert not tg.cancel_scope.cancel_called


async def test_exception_cancels_siblings() -> None:
    sleep_completed = False

    async def child(fail: bool) -> None:
        if fail:
            raise Exception("foo")
        else:
            nonlocal sleep_completed
            await sleep(1)
            sleep_completed = True

    with pytest.raises(ExceptionGroup) as exc:
        async with create_task_group() as tg:
            tg.start_soon(child, False)
            await wait_all_tasks_blocked()
            tg.start_soon(child, True)

    assert len(exc.value.exceptions) == 1
    assert str(exc.value.exceptions[0]) == "foo"
    assert not sleep_completed


async def test_cancel_cascade() -> None:
    async def do_something() -> NoReturn:
        async with create_task_group() as tg2:
            tg2.start_soon(sleep, 1)

        raise Exception("foo")

    async with create_task_group() as tg:
        tg.start_soon(do_something)
        await wait_all_tasks_blocked()
        tg.cancel_scope.cancel()


async def test_cancelled_parent() -> None:
    async def child() -> NoReturn:
        with CancelScope():
            await sleep(1)

        raise Exception("foo")

    async def parent(tg: TaskGroup) -> None:
        await wait_all_tasks_blocked()
        tg.start_soon(child)

    async with create_task_group() as tg:
        tg.start_soon(parent, tg)
        tg.cancel_scope.cancel()


async def test_shielded_deadline() -> None:
    with move_on_after(10):
        with CancelScope(shield=True):
            with move_on_after(1000):
                assert current_effective_deadline() - current_time() > 900


async def test_deadline_reached_on_start() -> None:
    with move_on_after(0):
        await sleep(0)
        pytest.fail("Execution should not reach this point")


async def test_deadline_moved() -> None:
    with fail_after(0.1) as scope:
        scope.deadline += 0.3
        await sleep(0.2)


async def test_timeout_error_with_multiple_cancellations() -> None:
    with pytest.raises(TimeoutError):
        with fail_after(0.1):
            async with create_task_group() as tg:
                tg.start_soon(sleep, 2)
                await sleep(2)


async def test_nested_fail_after() -> None:
    async def killer(scope: CancelScope) -> None:
        await wait_all_tasks_blocked()
        scope.cancel()

    async with create_task_group() as tg:
        with CancelScope() as scope:
            with CancelScope():
                tg.start_soon(killer, scope)
                with fail_after(1):
                    await sleep(2)
                    pytest.fail("Execution should not reach this point")

                pytest.fail("Execution should not reach this point either")

            pytest.fail("Execution should also not reach this point")

    assert scope.cancel_called


async def test_nested_shield() -> None:
    async def killer(scope: CancelScope) -> None:
        await wait_all_tasks_blocked()
        scope.cancel()

    with pytest.raises(ExceptionGroup) as exc:
        async with create_task_group() as tg:
            with CancelScope() as scope:
                with CancelScope(shield=True):
                    tg.start_soon(killer, scope)
                    with fail_after(0.2):
                        await sleep(2)

    assert len(exc.value.exceptions) == 1
    assert isinstance(exc.value.exceptions[0], TimeoutError)


async def test_triple_nested_shield_checkpoint_in_outer() -> None:
    """Regression test for #370."""

    got_past_checkpoint = False

    async def taskfunc() -> None:
        nonlocal got_past_checkpoint

        with CancelScope() as scope1:
            with CancelScope() as scope2:
                with CancelScope(shield=True):
                    scope1.cancel()
                    scope2.cancel()

            await checkpoint()
            got_past_checkpoint = True

    async with create_task_group() as tg:
        tg.start_soon(taskfunc)

    assert not got_past_checkpoint


async def test_triple_nested_shield_checkpoint_in_middle() -> None:
    got_past_checkpoint = False

    async def taskfunc() -> None:
        nonlocal got_past_checkpoint

        with CancelScope() as scope1:
            with CancelScope():
                with CancelScope(shield=True):
                    scope1.cancel()

                await checkpoint()
                got_past_checkpoint = True

    async with create_task_group() as tg:
        tg.start_soon(taskfunc)

    assert not got_past_checkpoint


def test_task_group_in_generator(
    anyio_backend_name: str, anyio_backend_options: dict[str, Any]
) -> None:
    async def task_group_generator() -> AsyncGenerator[None, None]:
        async with create_task_group():
            yield

    gen = task_group_generator()
    anyio.run(
        gen.__anext__,
        backend=anyio_backend_name,
        backend_options=anyio_backend_options,
    )
    pytest.raises(
        StopAsyncIteration,
        anyio.run,
        gen.__anext__,
        backend=anyio_backend_name,
        backend_options=anyio_backend_options,
    )


async def test_exception_group_filtering() -> None:
    """Test that CancelledErrors are filtered out of nested exception groups."""

    async def fail(name: str) -> NoReturn:
        try:
            await anyio.sleep(0.1)
        finally:
            raise Exception(f"{name} task failed")

    async def fn() -> None:
        async with anyio.create_task_group() as tg:
            tg.start_soon(fail, "parent")
            async with anyio.create_task_group() as tg2:
                tg2.start_soon(fail, "child")
                await anyio.sleep(1)

    with pytest.raises(BaseExceptionGroup) as exc:
        await fn()

    assert len(exc.value.exceptions) == 2
    assert str(exc.value.exceptions[0]) == "parent task failed"
    assert isinstance(exc.value.exceptions[1], ExceptionGroup)
    assert len(exc.value.exceptions[1].exceptions) == 1
    assert str(exc.value.exceptions[1].exceptions[0]) == "child task failed"


async def test_cancel_propagation_with_inner_spawn() -> None:
    async def g() -> NoReturn:
        async with anyio.create_task_group() as tg2:
            tg2.start_soon(anyio.sleep, 10)
            await anyio.sleep(1)

        assert False

    async with anyio.create_task_group() as tg:
        tg.start_soon(g)
        await wait_all_tasks_blocked()
        tg.cancel_scope.cancel()


async def test_escaping_cancelled_error_from_cancelled_task() -> None:
    """
    Regression test for issue #88. No CancelledError should escape the outer scope.

    """
    with CancelScope() as scope:
        with move_on_after(0.1):
            await sleep(1)

        scope.cancel()


@pytest.mark.skipif(
    sys.version_info >= (3, 11),
    reason="Generator based coroutines have been removed in Python 3.11",
)
@pytest.mark.filterwarnings(
    'ignore:"@coroutine" decorator is deprecated:DeprecationWarning'
)
def test_cancel_generator_based_task() -> None:
    async def native_coro_part() -> None:
        with CancelScope() as scope:
            asyncio.get_running_loop().call_soon(scope.cancel)
            await asyncio.sleep(1)
            pytest.fail("Execution should not have reached this line")

    @asyncio.coroutine  # type: ignore[attr-defined]
    def generator_part() -> Generator[object, BaseException, None]:
        yield from native_coro_part()  # type: ignore[misc]

    anyio.run(generator_part, backend="asyncio")


@pytest.mark.skipif(
    sys.version_info >= (3, 11),
    reason="Generator based coroutines have been removed in Python 3.11",
)
@pytest.mark.filterwarnings(
    'ignore:"@coroutine" decorator is deprecated:DeprecationWarning'
)
@pytest.mark.parametrize("anyio_backend", ["asyncio"])
async def test_schedule_old_style_coroutine_func() -> None:
    """
    Test that we give a sensible error when a user tries to spawn a task from a
    generator-style coroutine function.
    """

    @asyncio.coroutine  # type: ignore[attr-defined]
    def corofunc() -> Generator[Any, Any, None]:
        yield from asyncio.sleep(1)  # type: ignore[misc]

    async with create_task_group() as tg:
        funcname = (
            f"{__name__}.test_schedule_old_style_coroutine_func.<locals>.corofunc"
        )
        with pytest.raises(
            TypeError,
            match=f"Expected {funcname}\\(\\) to return a coroutine, but the return "
            f"value \\(<generator .+>\\) is not a coroutine object",
        ):
            tg.start_soon(corofunc)


@pytest.mark.parametrize("anyio_backend", ["asyncio"])
async def test_cancel_native_future_tasks() -> None:
    async def wait_native_future() -> None:
        loop = asyncio.get_running_loop()
        await loop.create_future()

    async with anyio.create_task_group() as tg:
        tg.start_soon(wait_native_future)
        tg.cancel_scope.cancel()


@pytest.mark.parametrize("anyio_backend", ["asyncio"])
async def test_cancel_native_future_tasks_cancel_scope() -> None:
    async def wait_native_future() -> None:
        with anyio.CancelScope():
            loop = asyncio.get_running_loop()
            await loop.create_future()

    async with anyio.create_task_group() as tg:
        tg.start_soon(wait_native_future)
        tg.cancel_scope.cancel()


@pytest.mark.parametrize("anyio_backend", ["asyncio"])
async def test_cancel_completed_task() -> None:
    loop = asyncio.get_running_loop()
    old_exception_handler = loop.get_exception_handler()
    exceptions = []

    def exception_handler(*args: object, **kwargs: object) -> None:
        exceptions.append((args, kwargs))

    loop.set_exception_handler(exception_handler)
    try:

        async def noop() -> None:
            pass

        async with anyio.create_task_group() as tg:
            tg.start_soon(noop)
            tg.cancel_scope.cancel()

        assert exceptions == []
    finally:
        loop.set_exception_handler(old_exception_handler)


async def test_task_in_sync_spawn_callback() -> None:
    outer_task_id = anyio.get_current_task().id
    inner_task_id = None

    def task_wrap() -> Coroutine[object, object, None]:
        assert anyio.get_current_task().id == outer_task_id

        async def corofn() -> None:
            nonlocal inner_task_id
            inner_task_id = anyio.get_current_task().id

        return corofn()

    async with create_task_group() as tg:
        tg.start_soon(task_wrap)

    assert inner_task_id is not None
    assert inner_task_id != outer_task_id


async def test_shielded_cancel_sleep_time() -> None:
    """
    Test that cancelling a shielded tasks spends more time sleeping than cancelling.

    """
    event = anyio.Event()
    hang_time = 0.2

    async def set_event() -> None:
        await sleep(hang_time)
        event.set()

    async def never_cancel_task() -> None:
        with CancelScope(shield=True):
            await sleep(0.2)
            await event.wait()

    async with create_task_group() as tg:
        tg.start_soon(set_event)

        async with create_task_group() as tg:
            tg.start_soon(never_cancel_task)
            tg.cancel_scope.cancel()
            process_time = time.process_time()

        assert (time.process_time() - process_time) < hang_time


async def test_cancelscope_wrong_exit_order() -> None:
    """
    Test that a RuntimeError is raised if the task tries to exit cancel scopes in the
    wrong order.

    """
    scope1 = CancelScope()
    scope2 = CancelScope()
    scope1.__enter__()
    scope2.__enter__()
    pytest.raises(RuntimeError, scope1.__exit__, None, None, None)


async def test_cancelscope_exit_before_enter() -> None:
    """
    Test that a RuntimeError is raised if one tries to exit a cancel scope before
    entering.

    """
    scope = CancelScope()
    pytest.raises(RuntimeError, scope.__exit__, None, None, None)


@pytest.mark.parametrize(
    "anyio_backend", ["asyncio"]
)  # trio does not check for this yet
async def test_cancelscope_exit_in_wrong_task() -> None:
    async def enter_scope(scope: CancelScope) -> None:
        scope.__enter__()

    async def exit_scope(scope: CancelScope) -> None:
        scope.__exit__(None, None, None)

    scope = CancelScope()
    async with create_task_group() as tg:
        tg.start_soon(enter_scope, scope)

    with pytest.raises(ExceptionGroup) as exc:
        async with create_task_group() as tg:
            tg.start_soon(exit_scope, scope)

    assert len(exc.value.exceptions) == 1
    assert str(exc.value.exceptions[0]) == (
        "Attempted to exit cancel scope in a different task than it was entered in"
    )


def test_unhandled_exception_group(caplog: pytest.LogCaptureFixture) -> None:
    def crash() -> NoReturn:
        raise KeyboardInterrupt

    async def nested() -> None:
        async with anyio.create_task_group() as tg:
            tg.start_soon(anyio.sleep, 5)
            await anyio.sleep(5)

    async def main() -> NoReturn:
        async with anyio.create_task_group() as tg:
            tg.start_soon(nested)
            await wait_all_tasks_blocked()
            asyncio.get_running_loop().call_soon(crash)
            await anyio.sleep(5)

        pytest.fail("Execution should never reach this point")

    with pytest.raises(KeyboardInterrupt):
        anyio.run(main, backend="asyncio")

    assert not caplog.messages


async def test_single_cancellation_exc() -> None:
    """
    Test that only a single cancellation exception bubbles out of the task group when
    case it was cancelled via an outer scope and no actual errors were raised.

    """
    with CancelScope() as outer:
        try:
            async with create_task_group() as tg:
                tg.start_soon(sleep, 5)
                await wait_all_tasks_blocked()
                outer.cancel()
                await sleep(5)
        except BaseException as exc:
            if isinstance(exc, get_cancelled_exc_class()):
                raise

            pytest.fail(f"Raised the wrong type of exception: {exc}")
        else:
            pytest.fail("Did not raise a cancellation exception")


async def test_start_soon_parent_id() -> None:
    root_task_id = get_current_task().id
    parent_id: int | None = None

    async def subtask() -> None:
        nonlocal parent_id
        parent_id = get_current_task().parent_id

    async def starter_task() -> None:
        tg.start_soon(subtask)

    async with anyio.create_task_group() as tg:
        tg.start_soon(starter_task)

    assert parent_id == root_task_id


async def test_start_parent_id() -> None:
    root_task_id = get_current_task().id
    starter_task_id: int | None = None
    initial_parent_id: int | None = None
    permanent_parent_id: int | None = None

    async def subtask(*, task_status: TaskStatus) -> None:
        nonlocal initial_parent_id, permanent_parent_id
        initial_parent_id = get_current_task().parent_id
        task_status.started()
        permanent_parent_id = get_current_task().parent_id

    async def starter_task() -> None:
        nonlocal starter_task_id
        starter_task_id = get_current_task().id
        await tg.start(subtask)

    async with anyio.create_task_group() as tg:
        tg.start_soon(starter_task)

    assert initial_parent_id != permanent_parent_id
    assert initial_parent_id == starter_task_id
    assert permanent_parent_id == root_task_id


@pytest.mark.skipif(
    sys.version_info < (3, 11),
    reason="Task uncancelling is only supported on Python 3.11",
)
@pytest.mark.parametrize("anyio_backend", ["asyncio"])
class TestUncancel:
    async def test_uncancel_after_native_cancel(self) -> None:
        task = cast(asyncio.Task, asyncio.current_task())
        with pytest.raises(asyncio.CancelledError), CancelScope():
            task.cancel()
            await anyio.sleep(0)

        assert task.cancelling() == 1
        task.uncancel()

    async def test_uncancel_after_scope_cancel(self) -> None:
        task = cast(asyncio.Task, asyncio.current_task())
        with CancelScope() as scope:
            scope.cancel()
            await anyio.sleep(0)

        assert task.cancelling() == 0

    async def test_uncancel_after_scope_and_native_cancel(self) -> None:
        task = cast(asyncio.Task, asyncio.current_task())
        with pytest.raises(asyncio.CancelledError), CancelScope() as scope:
            scope.cancel()
            task.cancel()
            await anyio.sleep(0)

        assert task.cancelling() == 1
        task.uncancel()

    async def test_cancel_message_replaced(self) -> None:
        task = asyncio.current_task()
        assert task
        try:
            task.cancel()
            await anyio.sleep(0)
        except asyncio.CancelledError:
            try:
                with CancelScope() as scope:
                    scope.cancel()
                    try:
                        await anyio.sleep(0)
                    except asyncio.CancelledError:
                        raise asyncio.CancelledError
            except asyncio.CancelledError:
                pytest.fail("Should have swallowed the CancelledError")


async def test_cancel_before_entering_task_group() -> None:
    with CancelScope() as scope:
        scope.cancel()
        try:
            async with create_task_group():
                pass
        except get_cancelled_exc_class():
            pytest.fail("This should not raise a cancellation exception")


async def test_reraise_cancelled_in_excgroup() -> None:
    def handler(excgrp: BaseExceptionGroup) -> None:
        raise

    with CancelScope() as scope:
        scope.cancel()
        with catch({get_cancelled_exc_class(): handler}):
            await anyio.sleep_forever()


async def test_cancel_child_task_when_host_is_shielded() -> None:
    # Regression test for #642
    # Tests that cancellation propagates to a child task even if the host task is within
    # a shielded cancel scope.
    cancelled = anyio.Event()

    async def wait_cancel() -> None:
        try:
            await anyio.sleep_forever()
        except anyio.get_cancelled_exc_class():
            cancelled.set()
            raise

    with CancelScope() as parent_scope:
        async with anyio.create_task_group() as task_group:
            task_group.start_soon(wait_cancel)
            await wait_all_tasks_blocked()

            with CancelScope(shield=True), fail_after(1):
                parent_scope.cancel()
                await cancelled.wait()


class TestTaskStatusTyping:
    """
    These tests do not do anything at run time, but since the test suite is also checked
    with a static type checker, it ensures that the `TaskStatus` typing works as
    intended.
    """

    async def typetest_None(*, task_status: TaskStatus[None]) -> None:
        task_status.started()
        task_status.started(None)

    async def typetest_None_Union(*, task_status: TaskStatus[int | None]) -> None:
        task_status.started()
        task_status.started(None)

    async def typetest_non_None(*, task_status: TaskStatus[int]) -> None:
        # We use `type: ignore` and `--warn-unused-ignores` to get type checking errors
        # if these ever stop failing.
        task_status.started()  # type: ignore[call-arg]
        task_status.started(None)  # type: ignore[arg-type]

    async def typetest_variance_good(*, task_status: TaskStatus[float]) -> None:
        task_status2: TaskStatus[int] = task_status
        task_status2.started(0)

    async def typetest_variance_bad(*, task_status: TaskStatus[int]) -> None:
        # We use `type: ignore` and `--warn-unused-ignores` to get type checking errors
        # if these ever stop failing.
        task_status2: TaskStatus[float] = task_status  # type: ignore[assignment]
        task_status2.started(0.0)

    async def typetest_optional_status(
        *,
        task_status: TaskStatus[int] = TASK_STATUS_IGNORED,
    ) -> None:
        task_status.started(1)