[Python-checkins] GH-95704: Don't suppress errors from tasks when TG is cancelled (GH-95761)
miss-islington
webhook-mailer at python.org
Wed Aug 17 13:05:08 EDT 2022
https://github.com/python/cpython/commit/36c114ab11d478c9ede246035606c12fc080e6ff
commit: 36c114ab11d478c9ede246035606c12fc080e6ff
branch: 3.11
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: miss-islington <31488909+miss-islington at users.noreply.github.com>
date: 2022-08-17T10:04:59-07:00
summary:
GH-95704: Don't suppress errors from tasks when TG is cancelled (GH-95761)
When a task catches CancelledError and raises some other error,
the other error should not silently be suppressed.
Any scenario where a task crashes in cleanup upon cancellation
will now result in an ExceptionGroup wrapping the crash(es)
instead of propagating CancelledError and ignoring the side errors.
NOTE: This represents a change in behavior (hence the need to
change several tests). But it is only an edge case.
Co-authored-by: Thomas Grainger <tagrain at gmail.com>
(cherry picked from commit f51f54f39d384da63be622bcdc9cf4cfb43bad3d)
Co-authored-by: Guido van Rossum <guido at python.org>
files:
A Misc/NEWS.d/next/Library/2022-08-08-01-42-11.gh-issue-95704.MOPFfX.rst
M Lib/asyncio/taskgroups.py
M Lib/test/test_asyncio/test_taskgroups.py
diff --git a/Lib/asyncio/taskgroups.py b/Lib/asyncio/taskgroups.py
index 9be4838e3c7a..5d5e2a8a85dd 100644
--- a/Lib/asyncio/taskgroups.py
+++ b/Lib/asyncio/taskgroups.py
@@ -116,10 +116,9 @@ async def __aexit__(self, et, exc, tb):
if self._base_error is not None:
raise self._base_error
- if propagate_cancellation_error is not None:
- # The wrapping task was cancelled; since we're done with
- # closing all child tasks, just propagate the cancellation
- # request now.
+ # Propagate CancelledError if there is one, except if there
+ # are other errors -- those have priority.
+ if propagate_cancellation_error and not self._errors:
raise propagate_cancellation_error
if et is not None and et is not exceptions.CancelledError:
diff --git a/Lib/test/test_asyncio/test_taskgroups.py b/Lib/test/test_asyncio/test_taskgroups.py
index 74bae06af8e7..6a0231f2859a 100644
--- a/Lib/test/test_asyncio/test_taskgroups.py
+++ b/Lib/test/test_asyncio/test_taskgroups.py
@@ -230,29 +230,29 @@ async def runner():
self.assertEqual(NUM, 15)
- async def test_cancellation_in_body(self):
+ async def test_taskgroup_08(self):
async def foo():
- await asyncio.sleep(0.1)
- 1 / 0
+ try:
+ await asyncio.sleep(10)
+ finally:
+ 1 / 0
async def runner():
async with taskgroups.TaskGroup() as g:
for _ in range(5):
g.create_task(foo())
- try:
- await asyncio.sleep(10)
- except asyncio.CancelledError:
- raise
+ await asyncio.sleep(10)
r = asyncio.create_task(runner())
await asyncio.sleep(0.1)
self.assertFalse(r.done())
r.cancel()
- with self.assertRaises(asyncio.CancelledError) as cm:
+ with self.assertRaises(ExceptionGroup) as cm:
await r
+ self.assertEqual(get_error_types(cm.exception), {ZeroDivisionError})
async def test_taskgroup_09(self):
@@ -316,8 +316,10 @@ async def runner():
async def test_taskgroup_11(self):
async def foo():
- await asyncio.sleep(0.1)
- 1 / 0
+ try:
+ await asyncio.sleep(10)
+ finally:
+ 1 / 0
async def runner():
async with taskgroups.TaskGroup():
@@ -325,24 +327,26 @@ async def runner():
for _ in range(5):
g2.create_task(foo())
- try:
- await asyncio.sleep(10)
- except asyncio.CancelledError:
- raise
+ await asyncio.sleep(10)
r = asyncio.create_task(runner())
await asyncio.sleep(0.1)
self.assertFalse(r.done())
r.cancel()
- with self.assertRaises(asyncio.CancelledError):
+ with self.assertRaises(ExceptionGroup) as cm:
await r
+ self.assertEqual(get_error_types(cm.exception), {ExceptionGroup})
+ self.assertEqual(get_error_types(cm.exception.exceptions[0]), {ZeroDivisionError})
+
async def test_taskgroup_12(self):
async def foo():
- await asyncio.sleep(0.1)
- 1 / 0
+ try:
+ await asyncio.sleep(10)
+ finally:
+ 1 / 0
async def runner():
async with taskgroups.TaskGroup() as g1:
@@ -352,19 +356,19 @@ async def runner():
for _ in range(5):
g2.create_task(foo())
- try:
- await asyncio.sleep(10)
- except asyncio.CancelledError:
- raise
+ await asyncio.sleep(10)
r = asyncio.create_task(runner())
await asyncio.sleep(0.1)
self.assertFalse(r.done())
r.cancel()
- with self.assertRaises(asyncio.CancelledError):
+ with self.assertRaises(ExceptionGroup) as cm:
await r
+ self.assertEqual(get_error_types(cm.exception), {ExceptionGroup})
+ self.assertEqual(get_error_types(cm.exception.exceptions[0]), {ZeroDivisionError})
+
async def test_taskgroup_13(self):
async def crash_after(t):
@@ -424,8 +428,9 @@ async def runner():
self.assertFalse(r.done())
r.cancel()
- with self.assertRaises(asyncio.CancelledError):
+ with self.assertRaises(ExceptionGroup) as cm:
await r
+ self.assertEqual(get_error_types(cm.exception), {ZeroDivisionError})
async def test_taskgroup_16(self):
@@ -451,8 +456,9 @@ async def runner():
self.assertFalse(r.done())
r.cancel()
- with self.assertRaises(asyncio.CancelledError):
+ with self.assertRaises(ExceptionGroup) as cm:
await r
+ self.assertEqual(get_error_types(cm.exception), {ZeroDivisionError})
async def test_taskgroup_17(self):
NUM = 0
diff --git a/Misc/NEWS.d/next/Library/2022-08-08-01-42-11.gh-issue-95704.MOPFfX.rst b/Misc/NEWS.d/next/Library/2022-08-08-01-42-11.gh-issue-95704.MOPFfX.rst
new file mode 100644
index 000000000000..31f9fc6547d9
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-08-08-01-42-11.gh-issue-95704.MOPFfX.rst
@@ -0,0 +1,2 @@
+When a task catches :exc:`asyncio.CancelledError` and raises some other error,
+the other error should generally not silently be suppressed.
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