Skip to content

[3.14] gh-155888: Fix asyncio writelines() hanging on an empty last chunk #155913

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
deadlovelll wants to merge 1 commit into
base: 3.14
Choose a base branch
from
+20 −1
Open

[3.14] gh-155888: Fix asyncio writelines() hanging on an empty last chunk #155913

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
6 changes: 5 additions & 1 deletion Lib/asyncio/selector_events.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1183,7 +1183,11 @@ def writelines(self, list_of_data):
self._conn_lost += 1
return

self._buffer.extend([memoryview(data) for data in list_of_data])
# gh-155888: an empty chunk can never be drained, so never buffer it
self._buffer.extend(
[memoryview(data) for data in list_of_data if data])
if not self._buffer:
return
self._write_ready()
# If the entire buffer couldn't be written, register a write handler
if self._buffer:
Expand Down
13 changes: 13 additions & 0 deletions Lib/test/test_asyncio/test_events.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -560,6 +560,19 @@ def writer(data):
r.close()
self.assertEqual(read, data)

def test_writelines_empty_chunk(self):
# gh-155888: an empty chunk can never be drained, so never buffer it
rsock, wsock = socket.socketpair()
self.addCleanup(rsock.close)

async def main():
reader, writer = await asyncio.open_connection(sock=wsock)
writer.writelines([b'data', b''])
writer.close()
await asyncio.wait_for(writer.wait_closed(), support.SHORT_TIMEOUT)

self.loop.run_until_complete(main())

@unittest.skipUnless(hasattr(signal, 'SIGKILL'), 'No SIGKILL')
def test_add_signal_handler(self):
caught = 0
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-08-16-11-38-17.gh-issue-155888.pO-nAp.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix :meth:`asyncio.WriteTransport.writelines` hanging the transport when the
last data chunk is empty.
Loading