EVOLUTION-MANAGER

Edit File: test_async_generator.py

import pytest

import types
import sys
import collections.abc
from functools import wraps
import gc

from .conftest import mock_sleep
from .. import (
    async_generator,
    yield_,
    yield_from_,
    isasyncgen,
    isasyncgenfunction,
    get_asyncgen_hooks,
    set_asyncgen_hooks,
)

# like list(it) but works on async iterators
async def collect(ait):
    items = []
    async for value in ait:
        items.append(value)
    return items

################################################################
#
# Basic test
#
################################################################

@async_generator
async def async_range(count):
    for i in range(count):
        print("Calling yield_({})".format(i))
        await yield_(i)

@async_generator
async def double(ait):
    async for value in ait:
        await yield_(value * 2)
        await mock_sleep()

class HasAsyncGenMethod:
    def __init__(self, factor):
        self._factor = factor

@async_generator
    async def async_multiplied(self, ait):
        async for value in ait:
            await yield_(value * self._factor)

async def test_async_generator():
    assert await collect(async_range(10)) == list(range(10))
    assert (await collect(double(async_range(5))) == [0, 2, 4, 6, 8])

tripler = HasAsyncGenMethod(3)
    assert (
        await
        collect(tripler.async_multiplied(async_range(5))) == [0, 3, 6, 9, 12]
    )

@async_generator
async def agen_yield_no_arg():
    await yield_()

async def test_yield_no_arg():
    assert await collect(agen_yield_no_arg()) == [None]

################################################################
#
# async_generators return value
#
################################################################

@async_generator
async def async_gen_with_non_None_return():
    await yield_(1)
    await yield_(2)
    return "hi"

async def test_bad_return_value():
    gen = async_gen_with_non_None_return()
    async for item in gen:  # pragma: no branch
        assert item == 1
        break
    async for item in gen:  # pragma: no branch
        assert item == 2
        break
    try:
        await gen.__anext__()
    except StopAsyncIteration as e:
        assert e.args[0] == "hi"

################################################################
#
# Exhausitve tests of the different ways to re-enter a coroutine.
#
# It used to be that re-entering via send/__next__ would work, but throw()
# immediately followed by an await yield_(...)  wouldn't work, and the
# YieldWrapper object would propagate back out to the coroutine runner.
#
# Before I fixed this, the 'assert value is None' check below would fail
# (because of the YieldWrapper leaking out), and if you removed that
# assertion, then the code would appear to run successfully but the final list
# would just be [1, 3] instead of [1, 2, 3].
#
################################################################

class MyTestError(Exception):
    pass

# This unconditionally raises a MyTestError exception, so from the outside
# it's equivalent to a simple 'raise MyTestError`. But, for this test to check
# the thing we want it to check, the point is that the exception must be
# thrown in from the coroutine runner -- this simulates something like an
# 'await sock.recv(...) -> TimeoutError'.
@types.coroutine
def hit_me():
    yield "hit me"

@types.coroutine
def number_me():
    assert (yield "number me") == 1

@types.coroutine
def next_me():
    assert (yield "next me") is None

@async_generator
async def yield_after_different_entries():
    await yield_(1)
    try:
        await hit_me()
    except MyTestError:
        await yield_(2)
    await number_me()
    await yield_(3)
    await next_me()
    await yield_(4)

def hostile_coroutine_runner(coro):
    coro_iter = coro.__await__()
    value = None
    while True:
        try:
            if value == "hit me":
                value = coro_iter.throw(MyTestError())
            elif value == "number me":
                value = coro_iter.send(1)
            else:
                assert value in (None, "next me")
                value = coro_iter.__next__()
        except StopIteration as exc:
            return exc.value

def test_yield_different_entries():
    coro = collect(yield_after_different_entries())
    yielded = hostile_coroutine_runner(coro)
    assert yielded == [1, 2, 3, 4]

async def test_reentrance_forbidden():
    @async_generator
    async def recurse():
        async for obj in agen:  # pragma: no branch
            await yield_(obj)  # pragma: no cover

agen = recurse()
    with pytest.raises(ValueError):
        async for _ in agen:  # pragma: no branch
            pass  # pragma: no cover

async def test_reentrance_forbidden_simultaneous_asends():
    @async_generator
    async def f():
        await mock_sleep()

ag = f()
    sender1 = ag.asend(None)
    sender2 = ag.asend(None)
    assert sender1.send(None) == "mock_sleep"
    with pytest.raises(ValueError):
        sender2.send(None)
    with pytest.raises(StopAsyncIteration):
        sender1.send(None)
    await ag.aclose()

# https://bugs.python.org/issue32526
async def test_reentrance_forbidden_while_suspended_in_coroutine_runner():
    @async_generator
    async def f():
        await mock_sleep()
        await yield_("final yield")

ag = f()
    asend_coro = ag.asend(None)
    fut = asend_coro.send(None)
    assert fut == "mock_sleep"
    # Now the async generator's frame is not executing, but a call to asend()
    # *is* executing. Make sure that in this case, ag_running is True, and we
    # can't start up another call to asend().
    assert ag.ag_running
    with pytest.raises(ValueError):
        await ag.asend(None)
    # Clean up
    with pytest.raises(StopIteration):
        asend_coro.send(None)
    with pytest.raises(StopAsyncIteration):
        ag.asend(None).send(None)

################################################################
#
# asend
#
################################################################

@async_generator
async def asend_me():
    assert (await yield_(1)) == 2
    assert (await yield_(3)) == 4

async def test_asend():
    aiter = asend_me()
    assert (await aiter.__anext__()) == 1
    assert (await aiter.asend(2)) == 3
    with pytest.raises(StopAsyncIteration):
        await aiter.asend(4)

################################################################
#
# athrow
#
################################################################

@async_generator
async def athrow_me():
    with pytest.raises(KeyError):
        await yield_(1)
    with pytest.raises(ValueError):
        await yield_(2)
    await yield_(3)

async def test_athrow():
    aiter = athrow_me()
    assert (await aiter.__anext__()) == 1
    assert (await aiter.athrow(KeyError("oops"))) == 2
    assert (await aiter.athrow(ValueError("oops"))) == 3
    with pytest.raises(OSError):
        await aiter.athrow(OSError("oops"))

################################################################
#
# aclose
#
################################################################

@async_generator
async def close_me_aiter(track):
    try:
        await yield_(1)
    except GeneratorExit:
        track[0] = "closed"
        raise
    else:  # pragma: no cover
        track[0] = "wtf"

async def test_aclose():
    track = [None]
    aiter = close_me_aiter(track)
    async for obj in aiter:  # pragma: no branch
        assert obj == 1
        break
    assert track[0] is None
    await aiter.aclose()
    assert track[0] == "closed"

async def test_aclose_on_unstarted_generator():
    aiter = close_me_aiter([None])
    await aiter.aclose()
    async for obj in aiter:
        assert False  # pragma: no cover

async def test_aclose_on_finished_generator():
    aiter = async_range(3)
    async for obj in aiter:
        pass  # pragma: no cover
    await aiter.aclose()

@async_generator
async def sync_yield_during_aclose():
    try:
        await yield_(1)
    finally:
        await mock_sleep()

@async_generator
async def async_yield_during_aclose():
    try:
        await yield_(1)
    finally:
        await yield_(2)

async def test_aclose_yielding():
    aiter = sync_yield_during_aclose()
    assert (await aiter.__anext__()) == 1
    # Doesn't raise:
    await aiter.aclose()

aiter = async_yield_during_aclose()
    assert (await aiter.__anext__()) == 1
    with pytest.raises(RuntimeError):
        await aiter.aclose()

################################################################
#
# yield from
#
################################################################

@async_generator
async def async_range_twice(count):
    await yield_from_(async_range(count))
    await yield_(None)
    await yield_from_(async_range(count))

if sys.version_info >= (3, 6):
    exec(
        """
async def native_async_range(count):
    for i in range(count):
        yield i

# XX uncomment if/when we re-enable the ctypes hacks:
# async def native_async_range_twice(count):
#     # make sure yield_from_ works inside a native async generator
#     await yield_from_(async_range(count))
#     yield None
#     # make sure we can yield_from_ a native async generator
#     await yield_from_(native_async_range(count))
    """
    )

async def test_async_yield_from_():
    assert await collect(async_range_twice(3)) == [
        0,
        1,
        2,
        None,
        0,
        1,
        2,
    ]

if sys.version_info >= (3, 6):
        # Make sure we can yield_from_ a native generator
        @async_generator
        async def yield_from_native():
            await yield_from_(native_async_range(3))

assert await collect(yield_from_native()) == [0, 1, 2]

# XX uncomment if/when we re-enable the ctypes hacks:
    # if sys.version_info >= (3, 6):
    #     assert await collect(native_async_range_twice(3)) == [
    #         0, 1, 2, None, 0, 1, 2,
    #     ]

@async_generator
async def doubles_sends(value):
    while True:
        value = await yield_(2 * value)

@async_generator
async def wraps_doubles_sends(value):
    await yield_from_(doubles_sends(value))

async def test_async_yield_from_asend():
    gen = wraps_doubles_sends(10)
    await gen.__anext__() == 20
    assert (await gen.asend(2)) == 4
    assert (await gen.asend(5)) == 10
    assert (await gen.asend(0)) == 0
    await gen.aclose()

async def test_async_yield_from_athrow():
    gen = async_range_twice(2)
    assert (await gen.__anext__()) == 0
    with pytest.raises(ValueError):
        await gen.athrow(ValueError)

@async_generator
async def returns_1():
    await yield_(0)
    return 1

@async_generator
async def yields_from_returns_1():
    await yield_(await yield_from_(returns_1()))

async def test_async_yield_from_return_value():
    assert await collect(yields_from_returns_1()) == [0, 1]

# Special cases to get coverage
async def test_yield_from_empty():
    @async_generator
    async def empty():
        return "done"

@async_generator
    async def yield_from_empty():
        assert (await yield_from_(empty())) == "done"

assert await collect(yield_from_empty()) == []

async def test_yield_from_non_generator():
    class Countdown:
        def __init__(self, count):
            self.count = count
            self.closed = False

if sys.version_info < (3, 5, 2):

async def __aiter__(self):
                return self
        else:

def __aiter__(self):
                return self

async def __anext__(self):
            self.count -= 1
            if self.count < 0:
                raise StopAsyncIteration("boom")
            return self.count

async def aclose(self):
            self.closed = True

@async_generator
    async def yield_from_countdown(count, happenings):
        try:
            c = Countdown(count)
            assert (await yield_from_(c)) == "boom"
        except BaseException as e:
            if c.closed:
                happenings.append("countdown closed")
            happenings.append("raise")
            return e

h = []
    assert await collect(yield_from_countdown(3, h)) == [2, 1, 0]
    assert h == []

# Throwing into a yield_from_(object with no athrow) just raises the
    # exception in the generator.
    h = []
    agen = yield_from_countdown(3, h)
    assert await agen.__anext__() == 2
    exc = ValueError("x")
    try:
        await agen.athrow(exc)
    except StopAsyncIteration as e:
        assert e.args[0] is exc
    assert h == ["raise"]

# Calling aclose on the generator calls aclose on the iterator
    h = []
    agen = yield_from_countdown(3, h)
    assert await agen.__anext__() == 2
    await agen.aclose()
    assert h == ["countdown closed", "raise"]

# Throwing GeneratorExit into the generator calls *aclose* on the iterator
    # (!)
    h = []
    agen = yield_from_countdown(3, h)
    assert await agen.__anext__() == 2
    exc = GeneratorExit()
    with pytest.raises(StopAsyncIteration):
        await agen.athrow(exc)
    assert h == ["countdown closed", "raise"]

async def test_yield_from_non_generator_with_no_aclose():
    class Countdown:
        def __init__(self, count):
            self.count = count
            self.closed = False

if sys.version_info < (3, 5, 2):

async def __aiter__(self):
                return self
        else:

def __aiter__(self):
                return self

async def __anext__(self):
            self.count -= 1
            if self.count < 0:
                raise StopAsyncIteration("boom")
            return self.count

@async_generator
    async def yield_from_countdown(count):
        return await yield_from_(Countdown(count))

assert await collect(yield_from_countdown(3)) == [2, 1, 0]

agen = yield_from_countdown(3)
    assert await agen.__anext__() == 2
    assert await agen.__anext__() == 1
    # It's OK that Countdown has no aclose
    await agen.aclose()

async def test_yield_from_with_old_style_aiter():
    # old-style 'async def __aiter__' should still work even on newer pythons
    class Countdown:
        def __init__(self, count):
            self.count = count
            self.closed = False

# This is wrong, that's the point
        async def __aiter__(self):
            return self

async def __anext__(self):
            self.count -= 1
            if self.count < 0:
                raise StopAsyncIteration("boom")
            return self.count

@async_generator
    async def yield_from_countdown(count):
        return await yield_from_(Countdown(count))

assert await collect(yield_from_countdown(3)) == [2, 1, 0]

async def test_yield_from_athrow_raises_StopAsyncIteration():
    @async_generator
    async def catch():
        try:
            while True:
                await yield_("hi")
        except Exception as exc:
            return ("bye", exc)

@async_generator
    async def yield_from_catch():
        return await yield_from_(catch())

agen = yield_from_catch()
    assert await agen.__anext__() == "hi"
    assert await agen.__anext__() == "hi"
    thrown = ValueError("oops")
    try:
        print(await agen.athrow(thrown))
    except StopAsyncIteration as caught:
        assert caught.args == (("bye", thrown),)
    else:
        raise AssertionError  # pragma: no cover

################################################################
# __del__
################################################################

async def test___del__(capfd):
    completions = 0

@async_generator
    async def awaits_when_unwinding():
        await yield_(0)
        try:
            await yield_(1)
        finally:
            await mock_sleep()
        try:
            await yield_(2)
        finally:
            nonlocal completions
            completions += 1

gen = awaits_when_unwinding()
    # Hasn't started yet, so no problem
    gen.__del__()

gen = awaits_when_unwinding()
    assert await collect(gen) == [0, 1, 2]
    # Exhausted, so no problem
    gen.__del__()

for stop_after_turn in (1, 2, 3):
        gen = awaits_when_unwinding()
        for turn in range(stop_after_turn):
            assert await gen.__anext__() == turn
        await gen.aclose()
        # Closed, so no problem
        gen.__del__()

for stop_after_turn in (1, 2, 3):
        gen = awaits_when_unwinding()
        for turn in range(stop_after_turn):
            assert await gen.__anext__() == turn

if stop_after_turn == 2:
            # Stopped in the middle of a try/finally that awaits in the finally,
            # so __del__ can't cleanup.
            with pytest.raises(RuntimeError) as info:
                gen.__del__()
            assert "awaited during finalization; install a finalization hook" in str(
                info.value
            )
        else:
            # Can clean up without awaiting, so __del__ is fine
            gen.__del__()

assert completions == 3

@async_generator
    async def yields_when_unwinding():
        try:
            await yield_(1)
        finally:
            await yield_(2)

gen = yields_when_unwinding()
    assert await gen.__anext__() == 1
    with pytest.raises(RuntimeError) as info:
        gen.__del__()

################################################################
# introspection
################################################################

def test_isasyncgen():
    assert not isasyncgen(async_range)
    assert isasyncgen(async_range(10))

if sys.version_info >= (3, 6):
        assert not isasyncgen(native_async_range)
        assert isasyncgen(native_async_range(10))

def test_isasyncgenfunction():
    assert isasyncgenfunction(async_range)
    assert not isasyncgenfunction(list)
    assert not isasyncgenfunction(async_range(10))

if sys.version_info >= (3, 6):
        assert isasyncgenfunction(native_async_range)
        assert not isasyncgenfunction(native_async_range(10))

# Very subtle bug: functools.wraps copies across the entire contents of the
# wrapped function's __dict__. We used to use a simple _is_async_gen=True
# attribute to mark async generators. But if we do that, then simple wrappers
# like async_range_wrapper *do* return True for isasyncgenfunction. But that's
# not how inspect.isasyncgenfunction works, and it also caused problems for
# sphinxcontrib-trio, because given a function like:
#
# @acontextmanager
# @async_generator
# async def async_cm():
#    ...
#
# then we end up with async_cm introspecting as both an async context manager
# and an async generator, and it doesn't know who to believe. With the
# correct, inspect.isasyncgenfunction-compliant behavior, we have async_cm
# introspecting as an async context manager, and async_cm.__wrapped__
# introspecting as an async generator.
def test_isasyncgenfunction_is_not_inherited_by_wrappers():
    @wraps(async_range)
    def async_range_wrapper(*args, **kwargs):  # pragma: no cover
        return async_range(*args, **kwargs)

assert not isasyncgenfunction(async_range_wrapper)
    assert isasyncgenfunction(async_range_wrapper.__wrapped__)

def test_collections_abc_AsyncGenerator():
    if hasattr(collections.abc, "AsyncGenerator"):
        assert isinstance(async_range(10), collections.abc.AsyncGenerator)

async def test_ag_attributes():
    @async_generator
    async def f():
        x = 1
        await yield_()

agen = f()
    assert agen.ag_code.co_name == "f"
    async for _ in agen:  # pragma: no branch
        assert agen.ag_frame.f_locals["x"] == 1
        break

################################################################
# Finicky tests to check that the overly clever ctype stuff has plausible
# refcounting

from .. import _impl

@pytest.mark.skipif(not hasattr(sys, "getrefcount"), reason="CPython only")
def test_refcnt():
    x = object()
    print(sys.getrefcount(x))
    print(sys.getrefcount(x))
    print(sys.getrefcount(x))
    print(sys.getrefcount(x))
    base_count = sys.getrefcount(x)
    l = [_impl._wrap(x) for _ in range(100)]
    print(sys.getrefcount(x))
    print(sys.getrefcount(x))
    print(sys.getrefcount(x))
    assert sys.getrefcount(x) >= base_count + 100
    l2 = [_impl._unwrap(box) for box in l]
    assert sys.getrefcount(x) >= base_count + 200
    print(sys.getrefcount(x))
    print(sys.getrefcount(x))
    print(sys.getrefcount(x))
    print(sys.getrefcount(x))
    del l
    print(sys.getrefcount(x))
    print(sys.getrefcount(x))
    print(sys.getrefcount(x))
    del l2
    print(sys.getrefcount(x))
    print(sys.getrefcount(x))
    print(sys.getrefcount(x))
    assert sys.getrefcount(x) == base_count
    print(sys.getrefcount(x))

################################################################
#
# Edge cases
#
################################################################

# PEP 479: StopIteration or StopAsyncIteration exiting from inside an async
# generator should produce a RuntimeError with the __cause__ set to the
# original exception. Note that contextlib.asynccontextmanager depends on this
# behavior.
@async_generator
async def lets_exception_out():
    await yield_()

async def test_throw_StopIteration_or_StopAsyncIteration():
    for cls in [StopIteration, StopAsyncIteration]:
        agen = lets_exception_out()
        await agen.asend(None)
        exc = cls()
        with pytest.raises(RuntimeError) as excinfo:
            await agen.athrow(exc)
        assert excinfo.type is RuntimeError
        assert excinfo.value.__cause__ is exc

# No "coroutine was never awaited" warnings for async generators that are not
# iterated
async def test_no_spurious_unawaited_coroutine_warning(recwarn):
    agen = async_range(10)
    del agen

# Run collection a few times to make sure any
    # loops/resurrection/etc. stuff gets fully handled (necessary on pypy)
    for _ in range(4):
        gc.collect()

# I've seen DeprecationWarnings here triggered by pytest-asyncio, so let's
    # filter for RuntimeWarning. But if there are no warnings at all, then
    # that's OK too, so tell coverage not to worry about it.
    for msg in recwarn:  # pragma: no cover
        print(msg)
        assert not issubclass(msg.category, RuntimeWarning)

################################################################
#
# GC hooks
#
################################################################

@pytest.fixture
def local_asyncgen_hooks():
    old_hooks = get_asyncgen_hooks()
    yield
    set_asyncgen_hooks(*old_hooks)

def test_gc_hooks_interface(local_asyncgen_hooks):
    def one(agen):  # pragma: no cover
        pass

def two(agen):  # pragma: no cover
        pass

set_asyncgen_hooks(None, None)
    assert get_asyncgen_hooks() == (None, None)
    set_asyncgen_hooks(finalizer=two)
    assert get_asyncgen_hooks() == (None, two)
    set_asyncgen_hooks(firstiter=one)
    assert get_asyncgen_hooks() == (one, two)
    set_asyncgen_hooks(finalizer=None, firstiter=two)
    assert get_asyncgen_hooks() == (two, None)
    set_asyncgen_hooks(None, one)
    assert get_asyncgen_hooks() == (None, one)
    tup = (one, two)
    set_asyncgen_hooks(*tup)
    assert get_asyncgen_hooks() == tup

with pytest.raises(TypeError):
        set_asyncgen_hooks(firstiter=42)

with pytest.raises(TypeError):
        set_asyncgen_hooks(finalizer=False)

def in_thread(results):
        results.append(get_asyncgen_hooks())
        set_asyncgen_hooks(two, one)
        results.append(get_asyncgen_hooks())

from threading import Thread
    results = []
    thread = Thread(target=in_thread, args=(results,))
    thread.start()
    thread.join()
    assert results == [(None, None), (two, one)]
    assert get_asyncgen_hooks() == (one, two)

async def test_gc_hooks_behavior(local_asyncgen_hooks):
    events = []
    to_finalize = []

def firstiter(agen):
        events.append("firstiter {}".format(agen.ag_frame.f_locals["ident"]))

def finalizer(agen):
        events.append("finalizer {}".format(agen.ag_frame.f_locals["ident"]))
        to_finalize.append(agen)

@async_generator
    async def agen(ident):
        events.append("yield 1 {}".format(ident))
        await yield_(1)
        try:
            events.append("yield 2 {}".format(ident))
            await yield_(2)
            events.append("after yield 2 {}".format(ident))
        finally:
            events.append("mock_sleep {}".format(ident))
            await mock_sleep()
        try:
            events.append("yield 3 {}".format(ident))
            await yield_(3)
        finally:
            events.append("unwind 3 {}".format(ident))
        # this one is included to make sure we _don't_ execute it
        events.append("done {}".format(ident))  # pragma: no cover

async def anext_verbosely(iter, ident):
        events.append("before asend {}".format(ident))
        sender = iter.asend(None)
        events.append("before send {}".format(ident))
        await sender
        events.append("after asend {}".format(ident))

# Ensure that firstiter is called immediately on asend(),
    # before the first turn of the coroutine that asend() returns,
    # to match the behavior of native generators.
    # Ensure that the firstiter that gets used is the one in effect
    # at the time of that first call, rather than at the time of iteration.
    iterA = agen("A")
    iterB = agen("B")
    await anext_verbosely(iterA, "A")
    set_asyncgen_hooks(firstiter, finalizer)
    await anext_verbosely(iterB, "B")
    iterC = agen("C")
    await anext_verbosely(iterC, "C")

assert events == [
        "before asend A", "before send A", "yield 1 A", "after asend A",
        "before asend B", "firstiter B", "before send B", "yield 1 B",
        "after asend B", "before asend C", "firstiter C", "before send C",
        "yield 1 C", "after asend C"
    ]
    del events[:]

# Ensure that firstiter is only called once, even if we create
    # two asend() coroutines before iterating either of them.
    iterX = agen("X")
    sender1 = iterX.asend(None)
    sender2 = iterX.asend(None)
    events.append("before close")
    sender1.close()
    sender2.close()
    await iterX.aclose()
    assert events == ["firstiter X", "before close"]
    del events[:]

from weakref import ref
    refA, refB, refC = map(ref, (iterA, iterB, iterC))

# iterA uses the finalizer that was in effect when it started, i.e. no finalizer
    await iterA.__anext__()
    await iterA.__anext__()
    del iterA
    # Do multiple GC passes since we're deliberately shielding the
    # coroutine objects from the first pass due to PyPy issue 2786.
    for _ in range(4):
        gc.collect()
    assert refA() is None
    assert events == [
        "yield 2 A", "after yield 2 A", "mock_sleep A", "yield 3 A",
        "unwind 3 A"
    ]
    assert not to_finalize
    del events[:]

# iterB and iterC do use our finalizer
    await iterC.__anext__()
    await iterB.__anext__()
    await iterC.__anext__()
    idB, idC = id(iterB), id(iterC)
    del iterB
    for _ in range(4):
        gc.collect()
    del iterC
    for _ in range(4):
        gc.collect()
    assert events == [
        "yield 2 C", "yield 2 B", "after yield 2 C", "mock_sleep C",
        "yield 3 C", "finalizer B", "finalizer C"
    ]
    del events[:]

# finalizer invokes aclose() is not called again once the revived reference drops
    assert list(map(id, to_finalize)) == [idB, idC]
    events.append("before aclose B")
    await to_finalize[0].aclose()
    events.append("before aclose C")
    await to_finalize[1].aclose()
    events.append("after aclose both")
    del to_finalize[:]
    for _ in range(4):
        gc.collect()
    assert refB() is None and refC() is None

assert events == [
        "before aclose B", "mock_sleep B", "before aclose C", "unwind 3 C",
        "after aclose both"
    ]