https://github.com/python/cpython/commit/d5dbbf4372cd3dbf3eead1cc70ddc4261c061fd9
commit: d5dbbf4372cd3dbf3eead1cc70ddc4261c061fd9
branch: main
author: Thomas Grainger <[email protected]>
committer: 1st1 <[email protected]>
date: 2024-10-14T08:19:56-07:00
summary:
gh-124958: fix asyncio.TaskGroup and _PyFuture refcycles (#124959)
files:
A Misc/NEWS.d/next/Library/2024-10-04-08-46-00.gh-issue-124958.rea9-x.rst
M Lib/asyncio/futures.py
M Lib/asyncio/taskgroups.py
M Lib/test/test_asyncio/test_futures.py
M Lib/test/test_asyncio/test_taskgroups.py
diff --git a/Lib/asyncio/futures.py b/Lib/asyncio/futures.py
index 5f6fa2348726cf..c95fce035cd548 100644
--- a/Lib/asyncio/futures.py
+++ b/Lib/asyncio/futures.py
@@ -190,8 +190,7 @@ def result(self):
the future is done and has an exception set, this exception is raised.
"""
if self._state == _CANCELLED:
- exc = self._make_cancelled_error()
- raise exc
+ raise self._make_cancelled_error()
if self._state != _FINISHED:
raise exceptions.InvalidStateError('Result is not ready.')
self.__log_traceback = False
@@ -208,8 +207,7 @@ def exception(self):
InvalidStateError.
"""
if self._state == _CANCELLED:
- exc = self._make_cancelled_error()
- raise exc
+ raise self._make_cancelled_error()
if self._state != _FINISHED:
raise exceptions.InvalidStateError('Exception is not set.')
self.__log_traceback = False
diff --git a/Lib/asyncio/taskgroups.py b/Lib/asyncio/taskgroups.py
index f2ee9648c43876..9fa772ca9d02cc 100644
--- a/Lib/asyncio/taskgroups.py
+++ b/Lib/asyncio/taskgroups.py
@@ -66,6 +66,20 @@ async def __aenter__(self):
return self
async def __aexit__(self, et, exc, tb):
+ tb = None
+ try:
+ return await self._aexit(et, exc)
+ finally:
+ # Exceptions are heavy objects that can have object
+ # cycles (bad for GC); let's not keep a reference to
+ # a bunch of them. It would be nicer to use a try/finally
+ # in __aexit__ directly but that introduced some diff noise
+ self._parent_task = None
+ self._errors = None
+ self._base_error = None
+ exc = None
+
+ async def _aexit(self, et, exc):
self._exiting = True
if (exc is not None and
@@ -122,7 +136,10 @@ async def __aexit__(self, et, exc, tb):
assert not self._tasks
if self._base_error is not None:
- raise self._base_error
+ try:
+ raise self._base_error
+ finally:
+ exc = None
if self._parent_cancel_requested:
# If this flag is set we *must* call uncancel().
@@ -133,8 +150,14 @@ async def __aexit__(self, et, exc, tb):
# Propagate CancelledError if there is one, except if there
# are other errors -- those have priority.
- if propagate_cancellation_error is not None and not self._errors:
- raise propagate_cancellation_error
+ try:
+ if propagate_cancellation_error is not None and not self._errors:
+ try:
+ raise propagate_cancellation_error
+ finally:
+ exc = None
+ finally:
+ propagate_cancellation_error = None
if et is not None and not issubclass(et, exceptions.CancelledError):
self._errors.append(exc)
@@ -146,14 +169,14 @@ async def __aexit__(self, et, exc, tb):
if self._parent_task.cancelling():
self._parent_task.uncancel()
self._parent_task.cancel()
- # Exceptions are heavy objects that can have object
- # cycles (bad for GC); let's not keep a reference to
- # a bunch of them.
try:
- me = BaseExceptionGroup('unhandled errors in a TaskGroup',
self._errors)
- raise me from None
+ raise BaseExceptionGroup(
+ 'unhandled errors in a TaskGroup',
+ self._errors,
+ ) from None
finally:
- self._errors = None
+ exc = None
+
def create_task(self, coro, *, name=None, context=None):
"""Create a new task in this group and return it.
diff --git a/Lib/test/test_asyncio/test_futures.py
b/Lib/test/test_asyncio/test_futures.py
index 458b70451a306a..c566b28adb2408 100644
--- a/Lib/test/test_asyncio/test_futures.py
+++ b/Lib/test/test_asyncio/test_futures.py
@@ -659,6 +659,28 @@ def __del__(self):
fut = self._new_future(loop=self.loop)
fut.set_result(Evil())
+ def test_future_cancelled_result_refcycles(self):
+ f = self._new_future(loop=self.loop)
+ f.cancel()
+ exc = None
+ try:
+ f.result()
+ except asyncio.CancelledError as e:
+ exc = e
+ self.assertIsNotNone(exc)
+ self.assertListEqual(gc.get_referrers(exc), [])
+
+ def test_future_cancelled_exception_refcycles(self):
+ f = self._new_future(loop=self.loop)
+ f.cancel()
+ exc = None
+ try:
+ f.exception()
+ except asyncio.CancelledError as e:
+ exc = e
+ self.assertIsNotNone(exc)
+ self.assertListEqual(gc.get_referrers(exc), [])
+
@unittest.skipUnless(hasattr(futures, '_CFuture'),
'requires the C _asyncio module')
diff --git a/Lib/test/test_asyncio/test_taskgroups.py
b/Lib/test/test_asyncio/test_taskgroups.py
index 4852536defc93d..138f59ebf57ef7 100644
--- a/Lib/test/test_asyncio/test_taskgroups.py
+++ b/Lib/test/test_asyncio/test_taskgroups.py
@@ -1,7 +1,7 @@
# Adapted with permission from the EdgeDB project;
# license: PSFL.
-
+import gc
import asyncio
import contextvars
import contextlib
@@ -11,7 +11,6 @@
from test.test_asyncio.utils import await_without_task
-
# To prevent a warning "test altered the execution environment"
def tearDownModule():
asyncio.set_event_loop_policy(None)
@@ -899,6 +898,95 @@ async def outer():
await outer()
+ async def test_exception_refcycles_direct(self):
+ """Test that TaskGroup doesn't keep a reference to the raised
ExceptionGroup"""
+ tg = asyncio.TaskGroup()
+ exc = None
+
+ class _Done(Exception):
+ pass
+
+ try:
+ async with tg:
+ raise _Done
+ except ExceptionGroup as e:
+ exc = e
+
+ self.assertIsNotNone(exc)
+ self.assertListEqual(gc.get_referrers(exc), [])
+
+
+ async def test_exception_refcycles_errors(self):
+ """Test that TaskGroup deletes self._errors, and __aexit__ args"""
+ tg = asyncio.TaskGroup()
+ exc = None
+
+ class _Done(Exception):
+ pass
+
+ try:
+ async with tg:
+ raise _Done
+ except* _Done as excs:
+ exc = excs.exceptions[0]
+
+ self.assertIsInstance(exc, _Done)
+ self.assertListEqual(gc.get_referrers(exc), [])
+
+
+ async def test_exception_refcycles_parent_task(self):
+ """Test that TaskGroup deletes self._parent_task"""
+ tg = asyncio.TaskGroup()
+ exc = None
+
+ class _Done(Exception):
+ pass
+
+ async def coro_fn():
+ async with tg:
+ raise _Done
+
+ try:
+ async with asyncio.TaskGroup() as tg2:
+ tg2.create_task(coro_fn())
+ except* _Done as excs:
+ exc = excs.exceptions[0].exceptions[0]
+
+ self.assertIsInstance(exc, _Done)
+ self.assertListEqual(gc.get_referrers(exc), [])
+
+ async def test_exception_refcycles_propagate_cancellation_error(self):
+ """Test that TaskGroup deletes propagate_cancellation_error"""
+ tg = asyncio.TaskGroup()
+ exc = None
+
+ try:
+ async with asyncio.timeout(-1):
+ async with tg:
+ await asyncio.sleep(0)
+ except TimeoutError as e:
+ exc = e.__cause__
+
+ self.assertIsInstance(exc, asyncio.CancelledError)
+ self.assertListEqual(gc.get_referrers(exc), [])
+
+ async def test_exception_refcycles_base_error(self):
+ """Test that TaskGroup deletes self._base_error"""
+ class MyKeyboardInterrupt(KeyboardInterrupt):
+ pass
+
+ tg = asyncio.TaskGroup()
+ exc = None
+
+ try:
+ async with tg:
+ raise MyKeyboardInterrupt
+ except MyKeyboardInterrupt as e:
+ exc = e
+
+ self.assertIsNotNone(exc)
+ self.assertListEqual(gc.get_referrers(exc), [])
+
if __name__ == "__main__":
unittest.main()
diff --git
a/Misc/NEWS.d/next/Library/2024-10-04-08-46-00.gh-issue-124958.rea9-x.rst
b/Misc/NEWS.d/next/Library/2024-10-04-08-46-00.gh-issue-124958.rea9-x.rst
new file mode 100644
index 00000000000000..534d5bb8c898da
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-10-04-08-46-00.gh-issue-124958.rea9-x.rst
@@ -0,0 +1 @@
+Fix refcycles in exceptions raised from :class:`asyncio.TaskGroup` and the
python implementation of :class:`asyncio.Future`
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