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Commit93a5746

Browse files
gschaffnergraingertagronholm
authored
Fixedasyncio.Task.cancelling issues (#790)
* Shrink TaskState to save a little memory* Fix uncancel() being called too early* Refactor to avoid duplicate computation* Test TaskInfo.has_pending_cancellation in cleanup code* Fix TaskInfo.has_pending_cancellation in cleanup code on asyncio* Test that uncancel() isn't called too earlyCo-authored-by: Thomas Grainger <tagrain@gmail.com>Co-authored-by: Alex Grönholm <alex.gronholm@nextday.fi>
1 parent39cf394 commit93a5746

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3 files changed

+117
-60
lines changed

3 files changed

+117
-60
lines changed

‎docs/versionhistory.rst

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -18,6 +18,12 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
1818
- Fixed the return type annotations of ``readinto()`` and ``readinto1()`` methods in the
1919
``anyio.AsyncFile`` class
2020
(`#825<https://github.com/agronholm/anyio/issues/825>`_)
21+
- Fixed ``TaskInfo.has_pending_cancellation()`` on asyncio returning false positives in
22+
cleanup code on Python >= 3.11
23+
(`#832<https://github.com/agronholm/anyio/issues/832>`_; PR by @gschaffner)
24+
- Fixed cancelled cancel scopes on asyncio calling ``asyncio.Task.uncancel`` when
25+
propagating a ``CancelledError`` on exit to a cancelled parent scope
26+
(`#790<https://github.com/agronholm/anyio/pull/790>`_; PR by @gschaffner)
2127

2228
**4.6.2**
2329

‎src/anyio/_backends/_asyncio.py

Lines changed: 59 additions & 60 deletions
Original file line numberDiff line numberDiff line change
@@ -372,11 +372,22 @@ def _task_started(task: asyncio.Task) -> bool:
372372

373373

374374
defis_anyio_cancellation(exc:CancelledError)->bool:
375-
return (
376-
bool(exc.args)
377-
andisinstance(exc.args[0],str)
378-
andexc.args[0].startswith("Cancelled by cancel scope ")
379-
)
375+
# Sometimes third party frameworks catch a CancelledError and raise a new one, so as
376+
# a workaround we have to look at the previous ones in __context__ too for a
377+
# matching cancel message
378+
whileTrue:
379+
if (
380+
exc.args
381+
andisinstance(exc.args[0],str)
382+
andexc.args[0].startswith("Cancelled by cancel scope ")
383+
):
384+
returnTrue
385+
386+
ifisinstance(exc.__context__,CancelledError):
387+
exc=exc.__context__
388+
continue
389+
390+
returnFalse
380391

381392

382393
classCancelScope(BaseCancelScope):
@@ -397,8 +408,10 @@ def __init__(self, deadline: float = math.inf, shield: bool = False):
397408
self._cancel_handle:asyncio.Handle|None=None
398409
self._tasks:set[asyncio.Task]=set()
399410
self._host_task:asyncio.Task|None=None
400-
self._cancel_calls:int=0
401-
self._cancelling:int|None=None
411+
ifsys.version_info>= (3,11):
412+
self._pending_uncancellations:int|None=0
413+
else:
414+
self._pending_uncancellations=None
402415

403416
def__enter__(self)->CancelScope:
404417
ifself._active:
@@ -424,8 +437,6 @@ def __enter__(self) -> CancelScope:
424437

425438
self._timeout()
426439
self._active=True
427-
ifsys.version_info>= (3,11):
428-
self._cancelling=self._host_task.cancelling()
429440

430441
# Start cancelling the host task if the scope was cancelled before entering
431442
ifself._cancel_called:
@@ -470,30 +481,41 @@ def __exit__(
470481

471482
host_task_state.cancel_scope=self._parent_scope
472483

473-
# Undo all cancellations done by this scope
474-
ifself._cancellingisnotNone:
475-
whileself._cancel_calls:
476-
self._cancel_calls-=1
477-
ifself._host_task.uncancel()<=self._cancelling:
478-
break
484+
# Restart the cancellation effort in the closest visible, cancelled parent
485+
# scope if necessary
486+
self._restart_cancellation_in_parent()
479487

480488
# We only swallow the exception iff it was an AnyIO CancelledError, either
481489
# directly as exc_val or inside an exception group and there are no cancelled
482490
# parent cancel scopes visible to us here
483-
not_swallowed_exceptions=0
484-
swallow_exception=False
485-
ifexc_valisnotNone:
486-
forexciniterate_exceptions(exc_val):
487-
ifself._cancel_calledandisinstance(exc,CancelledError):
488-
ifnot (swallow_exception:=self._uncancel(exc)):
489-
not_swallowed_exceptions+=1
490-
else:
491-
not_swallowed_exceptions+=1
491+
ifself._cancel_calledandnotself._parent_cancellation_is_visible_to_us:
492+
# For each level-cancel() call made on the host task, call uncancel()
493+
whileself._pending_uncancellations:
494+
self._host_task.uncancel()
495+
self._pending_uncancellations-=1
496+
497+
# Update cancelled_caught and check for exceptions we must not swallow
498+
cannot_swallow_exc_val=False
499+
ifexc_valisnotNone:
500+
forexciniterate_exceptions(exc_val):
501+
ifisinstance(exc,CancelledError)andis_anyio_cancellation(
502+
exc
503+
):
504+
self._cancelled_caught=True
505+
else:
506+
cannot_swallow_exc_val=True
492507

493-
# Restart the cancellation effort in the closest visible, cancelled parent
494-
# scope if necessary
495-
self._restart_cancellation_in_parent()
496-
returnswallow_exceptionandnotnot_swallowed_exceptions
508+
returnself._cancelled_caughtandnotcannot_swallow_exc_val
509+
else:
510+
ifself._pending_uncancellations:
511+
assertself._parent_scopeisnotNone
512+
assertself._parent_scope._pending_uncancellationsisnotNone
513+
self._parent_scope._pending_uncancellations+= (
514+
self._pending_uncancellations
515+
)
516+
self._pending_uncancellations=0
517+
518+
returnFalse
497519
finally:
498520
self._host_task=None
499521
delexc_val
@@ -520,31 +542,6 @@ def _parent_cancellation_is_visible_to_us(self) -> bool:
520542
andself._parent_scope._effectively_cancelled
521543
)
522544

523-
def_uncancel(self,cancelled_exc:CancelledError)->bool:
524-
ifself._host_taskisNone:
525-
self._cancel_calls=0
526-
returnTrue
527-
528-
whileTrue:
529-
ifis_anyio_cancellation(cancelled_exc):
530-
# Only swallow the cancellation exception if it's an AnyIO cancel
531-
# exception and there are no other cancel scopes down the line pending
532-
# cancellation
533-
self._cancelled_caught= (
534-
self._effectively_cancelled
535-
andnotself._parent_cancellation_is_visible_to_us
536-
)
537-
returnself._cancelled_caught
538-
539-
# Sometimes third party frameworks catch a CancelledError and raise a new
540-
# one, so as a workaround we have to look at the previous ones in
541-
# __context__ too for a matching cancel message
542-
ifisinstance(cancelled_exc.__context__,CancelledError):
543-
cancelled_exc=cancelled_exc.__context__
544-
continue
545-
546-
returnFalse
547-
548545
def_timeout(self)->None:
549546
ifself._deadline!=math.inf:
550547
loop=get_running_loop()
@@ -576,8 +573,11 @@ def _deliver_cancellation(self, origin: CancelScope) -> bool:
576573
waiter=task._fut_waiter# type: ignore[attr-defined]
577574
ifnotisinstance(waiter,asyncio.Future)ornotwaiter.done():
578575
task.cancel(f"Cancelled by cancel scope{id(origin):x}")
579-
iftaskisorigin._host_task:
580-
origin._cancel_calls+=1
576+
if (
577+
taskisorigin._host_task
578+
andorigin._pending_uncancellationsisnotNone
579+
):
580+
origin._pending_uncancellations+=1
581581

582582
# Deliver cancellation to child scopes that aren't shielded or running their own
583583
# cancellation callbacks
@@ -2154,12 +2154,11 @@ def has_pending_cancellation(self) -> bool:
21542154
# If the task isn't around anymore, it won't have a pending cancellation
21552155
returnFalse
21562156

2157-
ifsys.version_info>= (3,11):
2158-
iftask.cancelling():
2159-
returnTrue
2157+
iftask._must_cancel:# type: ignore[attr-defined]
2158+
returnTrue
21602159
elif (
2161-
isinstance(task._fut_waiter,asyncio.Future)
2162-
andtask._fut_waiter.cancelled()
2160+
isinstance(task._fut_waiter,asyncio.Future)# type: ignore[attr-defined]
2161+
andtask._fut_waiter.cancelled()# type: ignore[attr-defined]
21632162
):
21642163
returnTrue
21652164

‎tests/test_taskgroups.py

Lines changed: 52 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -673,6 +673,38 @@ async def test_cancel_shielded_scope() -> None:
673673
awaitcheckpoint()
674674

675675

676+
asyncdeftest_shielded_cleanup_after_cancel()->None:
677+
"""Regression test for #832."""
678+
withCancelScope()asouter_scope:
679+
outer_scope.cancel()
680+
try:
681+
awaitcheckpoint()
682+
finally:
683+
assertcurrent_effective_deadline()==-math.inf
684+
assertget_current_task().has_pending_cancellation()
685+
686+
withCancelScope(shield=True):# noqa: ASYNC100
687+
assertcurrent_effective_deadline()==math.inf
688+
assertnotget_current_task().has_pending_cancellation()
689+
690+
assertcurrent_effective_deadline()==-math.inf
691+
assertget_current_task().has_pending_cancellation()
692+
693+
694+
@pytest.mark.parametrize("anyio_backend", ["asyncio"])
695+
asyncdeftest_cleanup_after_native_cancel()->None:
696+
"""Regression test for #832."""
697+
# See also https://github.com/python/cpython/pull/102815.
698+
task=asyncio.current_task()
699+
asserttask
700+
task.cancel()
701+
withpytest.raises(asyncio.CancelledError):
702+
try:
703+
awaitcheckpoint()
704+
finally:
705+
assertnotget_current_task().has_pending_cancellation()
706+
707+
676708
asyncdeftest_cancelled_not_caught()->None:
677709
withCancelScope()asscope:# noqa: ASYNC100
678710
scope.cancel()
@@ -1488,6 +1520,26 @@ async def taskfunc() -> None:
14881520
assertstr(exc_info.value.exceptions[0])=="dummy error"
14891521
assertnotcast(asyncio.Task,asyncio.current_task()).cancelling()
14901522

1523+
asyncdeftest_uncancel_cancelled_scope_based_checkpoint(self)->None:
1524+
"""See also test_cancelled_scope_based_checkpoint."""
1525+
task=asyncio.current_task()
1526+
asserttask
1527+
1528+
withCancelScope()asouter_scope:
1529+
outer_scope.cancel()
1530+
1531+
try:
1532+
# The following three lines are a way to implement a checkpoint
1533+
# function. See also https://github.com/python-trio/trio/issues/860.
1534+
withCancelScope()asinner_scope:
1535+
inner_scope.cancel()
1536+
awaitsleep_forever()
1537+
finally:
1538+
assertisinstance(sys.exc_info()[1],asyncio.CancelledError)
1539+
asserttask.cancelling()
1540+
1541+
assertnottask.cancelling()
1542+
14911543

14921544
asyncdeftest_cancel_before_entering_task_group()->None:
14931545
withCancelScope()asscope:

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