https://github.com/python/cpython/commit/83dbe6ae9f47f51948184f612d8443bd7ac79ff2
commit: 83dbe6ae9f47f51948184f612d8443bd7ac79ff2
branch: main
author: Timofei Ivankov <[email protected]>
committer: kumaraditya303 <[email protected]>
date: 2026-09-06T16:03:49+05:30
summary:
gh-156512: Fix asyncio calling connection_lost() twice from resume_writing()
(#156657)
files:
A Misc/NEWS.d/next/Library/2026-08-30-13-25-53.gh-issue-156512.tVTOIV.rst
M Lib/asyncio/selector_events.py
M Lib/test/test_asyncio/test_selector_events.py
diff --git a/Lib/asyncio/selector_events.py b/Lib/asyncio/selector_events.py
index 16d5c1b6f0a3e1..a682063d9d3d6e 100644
--- a/Lib/asyncio/selector_events.py
+++ b/Lib/asyncio/selector_events.py
@@ -1127,7 +1127,9 @@ def _write_sendmsg(self):
self._loop._remove_writer(self._sock_fd)
if self._empty_waiter is not None:
self._empty_waiter.set_result(None)
- if self._closing:
+ # gh-156512: don't let _call_connection_lost be called twice
+ if self._closing and not self._conn_lost:
+ self._conn_lost += 1
self._call_connection_lost(None)
elif self._eof:
self._sock.shutdown(socket.SHUT_WR)
@@ -1173,7 +1175,9 @@ def _write_send(self):
self._loop._remove_writer(self._sock_fd)
if self._empty_waiter is not None:
self._empty_waiter.set_result(None)
- if self._closing:
+ # gh-156512: don't let _call_connection_lost be called twice
+ if self._closing and not self._conn_lost:
+ self._conn_lost += 1
self._call_connection_lost(None)
elif self._eof:
self._sock.shutdown(socket.SHUT_WR)
diff --git a/Lib/test/test_asyncio/test_selector_events.py
b/Lib/test/test_asyncio/test_selector_events.py
index a323084d262ebf..74322105a7c757 100644
--- a/Lib/test/test_asyncio/test_selector_events.py
+++ b/Lib/test/test_asyncio/test_selector_events.py
@@ -1195,6 +1195,49 @@ def _resume_writing():
self.assertEqual(transport.get_write_buffer_size(), 0)
self.assertTrue(self.protocol.connection_lost.called)
+ def test_write_ready_resume_writing_closes(self):
+ # gh-156512: closing from resume_writing() must not lose the
connection twice
+ self.sock.send.return_value = 2
+
+ def _resume_writing():
+ transport.close()
+
+ self.protocol.resume_writing.side_effect = _resume_writing
+ self.loop.call_exception_handler = mock.Mock()
+
+ transport = self.socket_transport()
+ transport.set_write_buffer_limits(high=1, low=0)
+ transport.write(b'data')
+
+ self.loop.writers[7]._run()
+ test_utils.run_briefly(self.loop)
+
+ self.assertEqual(self.protocol.connection_lost.call_count, 1)
+ self.loop.call_exception_handler.assert_not_called()
+
+ @unittest.skipUnless(selector_events._HAS_SENDMSG, 'no sendmsg')
+ def test_write_sendmsg_resume_writing_closes(self):
+ # gh-156512: same as above, for the sendmsg write path
+ self.sock.send.return_value = 2
+ self.sock.sendmsg.return_value = 2
+
+ def _resume_writing():
+ transport.close()
+
+ self.protocol.resume_writing.side_effect = _resume_writing
+ self.loop.call_exception_handler = mock.Mock()
+
+ transport = self.socket_transport(sendmsg=True)
+ transport.set_write_buffer_limits(high=1, low=0)
+ transport.write(b'data')
+
+ self.loop.writers[7]._run()
+ test_utils.run_briefly(self.loop)
+
+ self.assertEqual(self.protocol.connection_lost.call_count, 1)
+ self.loop.call_exception_handler.assert_not_called()
+
+
class SelectorSocketTransportBufferedProtocolTests(test_utils.TestCase):
def setUp(self):
diff --git
a/Misc/NEWS.d/next/Library/2026-08-30-13-25-53.gh-issue-156512.tVTOIV.rst
b/Misc/NEWS.d/next/Library/2026-08-30-13-25-53.gh-issue-156512.tVTOIV.rst
new file mode 100644
index 00000000000000..16d6b7bdeae985
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-08-30-13-25-53.gh-issue-156512.tVTOIV.rst
@@ -0,0 +1,2 @@
+Fix :mod:`asyncio` losing a connection twice when ``resume_writing()``
+closes the transport.
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