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gh-109538: Catch closed loop runtime error and issue warning #111983

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Nov 15, 2023
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8 changes: 5 additions & 3 deletions Lib/asyncio/streams.py
Original file line number Diff line number Diff line change
Expand Up @@ -406,9 +406,11 @@ async def start_tls(self, sslcontext, *,

def __del__(self, warnings=warnings):
if not self._transport.is_closing():
self.close()
warnings.warn(f"unclosed {self!r}", ResourceWarning)

if self._loop.is_closed():
warnings.warn("loop is closed", ResourceWarning)
else:
self.close()
warnings.warn(f"unclosed {self!r}", ResourceWarning)

class StreamReader:

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41 changes: 39 additions & 2 deletions Lib/test/test_asyncio/test_streams.py
Original file line number Diff line number Diff line change
Expand Up @@ -1082,10 +1082,11 @@ async def inner(httpd):
self.assertEqual(data, b'HTTP/1.0 200 OK\r\n')
data = await rd.read()
self.assertTrue(data.endswith(b'\r\n\r\nTest message'))
with self.assertWarns(ResourceWarning):
with self.assertWarns(ResourceWarning) as cm:
del wr
gc.collect()

self.assertEqual(len(cm.warnings), 1)
self.assertTrue(str(cm.warnings[0].message).startswith("unclosed <StreamWriter"))

messages = []
self.loop.set_exception_handler(lambda loop, ctx: messages.append(ctx))
Expand All @@ -1095,6 +1096,42 @@ async def inner(httpd):

self.assertEqual(messages, [])

def test_loop_is_closed_resource_warnings(self):
async def inner(httpd):
rd, wr = await asyncio.open_connection(*httpd.address)

wr.write(b'GET / HTTP/1.0\r\n\r\n')
data = await rd.readline()
self.assertEqual(data, b'HTTP/1.0 200 OK\r\n')
data = await rd.read()
self.assertTrue(data.endswith(b'\r\n\r\nTest message'))

# Make "loop is closed" occur first before "del wr" for this test.
self.loop.stop()
wr.close()
while not self.loop.is_closed():
await asyncio.sleep(0.0)

with self.assertWarns(ResourceWarning) as cm:
del wr
gc.collect()
self.assertEqual(len(cm.warnings), 1)
self.assertEqual("loop is closed", str(cm.warnings[0].message))

messages = []
self.loop.set_exception_handler(lambda loop, ctx: messages.append(ctx))

with test_utils.run_test_server() as httpd:
try:
self.loop.run_until_complete(inner(httpd))
# This exception is caused by `self.loop.stop()` as expected.
except RuntimeError:
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If this exception is expected then why not use self.assertRaises etc?

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except allows/tolerates an exception, assert requires one and will fail if it does not happen because of other improvements.

pass
Comment on lines +1128 to +1129
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Add a comment at least showing why we expectRuntimeError here.

finally:
gc.collect()

self.assertEqual(messages, [])

def test_unhandled_exceptions(self) -> None:
port = socket_helper.find_unused_port()

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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Issue warning message instead of having :class:`RuntimeError` be displayed when event loop has already been closed at :meth:`StreamWriter.__del__`.