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[Bug]: async generator aclose() does not suspend on an await in a finally block

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55/100
Issue-Typ
Bug
Klarheit
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Tech-Stack
python
Bereich
backend

Rechercherichtung

Start with GraalPy’s async-generator implementation and the CPython test_asyncgen cases named in the report, especially test_async_gen_asyncio_aclose_07, which reproduces the failure. Compare how aclose() handles a yielded value during an await in a finally block with the expected CPython behavior. Done means the yielded value reaches the caller of send(), the generator resumes only on the next send, and the listed tests pass.

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Beschreibung

bug
Describe the bug

When aclose() throws GeneratorExit into an async generator, an await in the generator's finally block does not suspend. GraalPy discards the value that the awaited object yields and resumes the generator at once. The full cleanup then runs inside one send() call on the aclose() awaitable.

CPython passes the yielded value out to the caller of send(), so the event loop sees it. On GraalPy the value never reaches the event loop. With asyncio, any await on a future in a finally block during aclose() fails with RuntimeError: await wasn't used with future.

Operating system

Linux

CPU architecture

x86_64

GraalPy version

GraalPy 3.13.14 (GraalVM CE Native 25.3.4.1), also GraalPy 3.13.14 (GraalVM CE Native 25.4.4.1.1)

JDK version

No response

Context configuration

Minimal reproducer without asyncio:

class Suspend:
    def __await__(self):
        print("  Suspend: about to yield")
        yield "suspended"
        print("  Suspend: resumed")

async def agen():
    try:
        yield 1
    finally:
        print("  finally: before await")
        await Suspend()
        print("  finally: after await")

g = agen()
try:
    g.__anext__().send(None)
except StopIteration as s:
    print("first", s.value)

c = g.aclose()
for i in range(3):
    try:
        print("send %d ->" % i, repr(c.send(None)))
    except StopIteration:
        print("send %d -> StopIteration" % i)
        break

Output on GraalPy:

first 1
  finally: before await
  Suspend: about to yield
  Suspend: resumed
  finally: after await
send 0 -> StopIteration

Reproducer with asyncio:

import asyncio

async def agen():
    try:
        yield 1
    finally:
        await asyncio.sleep(0.01)
        print("cleanup done")

async def main():
    g = agen()
    await g.__anext__()
    await g.aclose()

asyncio.run(main())

On GraalPy this raises RuntimeError: await wasn't used with future (see the stack trace below).

Steps to reproduce

Minimal reproducer without asyncio:

class Suspend:
    def __await__(self):
        print("  Suspend: about to yield")
        yield "suspended"
        print("  Suspend: resumed")

async def agen():
    try:
        yield 1
    finally:
        print("  finally: before await")
        await Suspend()
        print("  finally: after await")

g = agen()
try:
    g.__anext__().send(None)
except StopIteration as s:
    print("first", s.value)

c = g.aclose()
for i in range(3):
    try:
        print("send %d ->" % i, repr(c.send(None)))
    except StopIteration:
        print("send %d -> StopIteration" % i)
        break

Output on GraalPy:

first 1
  finally: before await
  Suspend: about to yield
  Suspend: resumed
  finally: after await
send 0 -> StopIteration

Reproducer with asyncio:

import asyncio

async def agen():
    try:
        yield 1
    finally:
        await asyncio.sleep(0.01)
        print("cleanup done")

async def main():
    g = agen()
    await g.__anext__()
    await g.aclose()

asyncio.run(main())

On GraalPy this raises RuntimeError: await wasn't used with future (see the stack trace below).

Expected behavior

Same as CPython 3.13. The first send() on the aclose() awaitable returns the value that the await yields. The generator resumes only on the next send():

first 1
  finally: before await
  Suspend: about to yield
send 0 -> 'suspended'
  Suspend: resumed
  finally: after await
send 1 -> StopIteration

The asyncio reproducer prints cleanup done and exits with no error.

Stack trace
Traceback (most recent call last):
  File "repro_asyncio.py", line 5, in agen
    yield 1
GeneratorExit

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "repro_asyncio.py", line 15, in <module>
    asyncio.run(main())
  File "<graalpy>/lib/python3.13/asyncio/runners.py", line 196, in run
    return runner.run(main)
  File "<graalpy>/lib/python3.13/asyncio/runners.py", line 119, in run
    return self._loop.run_until_complete(task)
  File "<graalpy>/lib/python3.13/asyncio/base_events.py", line 725, in run_until_complete
    return future.result()
  File "<graalpy>/lib/python3.13/asyncio/futures.py", line 199, in result
    raise self._exception.with_traceback(self._exception_tb)
  File "<graalpy>/lib/python3.13/asyncio/tasks.py", line 304, in __step_run_and_handle_result
    result = coro.send(None)
  File "repro_asyncio.py", line 13, in main
    await g.aclose()
  File "repro_asyncio.py", line 7, in agen
    await asyncio.sleep(0.01)
  File "<graalpy>/lib/python3.13/asyncio/tasks.py", line 721, in sleep
    return await future
  File "<graalpy>/lib/python3.13/asyncio/futures.py", line 288, in __await__
    raise RuntimeError("await wasn't used with future")
RuntimeError: await wasn't used with future
Additional context

The CPython tests in test_asyncgen that await in finally during aclose() are not in GraalPy's passing list (graalpython/com.oracle.graal.python.test/src/tests/unittest_tags/test_asyncgen.txt): test_async_gen_asyncio_aclose_07, aclose_08, gc_aclose_09 and aclose_12. aclose_07 fails with the same RuntimeError when run on its own.

Found with a Cython test that now excludes this case on GraalPy: https://github.com/cython/cython/pull/8028

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