https://github.com/python/cpython/commit/1417737810e2250ca5cd80574c82e8aa2542560a
commit: 1417737810e2250ca5cd80574c82e8aa2542560a
branch: main
author: moktamd <[email protected]>
committer: kumaraditya303 <[email protected]>
date: 2026-03-27T21:43:15+05:30
summary:
gh-146507: cache the buffer size for
`SelectorTransport.get_write_buffer_size()` (#146518)
files:
A Misc/NEWS.d/next/Library/2026-03-27-12-00-00.gh-issue-146507.1D95A7.rst
M Lib/asyncio/selector_events.py
diff --git a/Lib/asyncio/selector_events.py b/Lib/asyncio/selector_events.py
index 9685e7fc05d241..961dbfb4b96303 100644
--- a/Lib/asyncio/selector_events.py
+++ b/Lib/asyncio/selector_events.py
@@ -793,6 +793,7 @@ def __init__(self, loop, sock, protocol, extra=None,
server=None, context=None):
self._server = server
self._buffer = collections.deque()
+ self._buffer_size = 0
self._conn_lost = 0 # Set when call to connection_lost scheduled.
self._closing = False # Set when close() called.
self._paused = False # Set when pause_reading() called
@@ -897,6 +898,7 @@ def _force_close(self, exc):
return
if self._buffer:
self._buffer.clear()
+ self._buffer_size = 0
self._loop._remove_writer(self._sock_fd)
if not self._closing:
self._closing = True
@@ -919,7 +921,7 @@ def _call_connection_lost(self, exc):
self._server = None
def get_write_buffer_size(self):
- return sum(map(len, self._buffer))
+ return self._buffer_size
def _add_reader(self, fd, callback, *args):
if not self.is_reading():
@@ -1090,6 +1092,7 @@ def write(self, data):
# Add it to the buffer.
self._buffer.append(data)
+ self._buffer_size += len(data)
self._maybe_pause_protocol()
def _get_sendmsg_buffer(self):
@@ -1109,6 +1112,7 @@ def _write_sendmsg(self):
except BaseException as exc:
self._loop._remove_writer(self._sock_fd)
self._buffer.clear()
+ self._buffer_size = 0
self._fatal_error(exc, 'Fatal write error on socket transport')
if self._empty_waiter is not None:
self._empty_waiter.set_exception(exc)
@@ -1124,6 +1128,7 @@ def _write_sendmsg(self):
self._sock.shutdown(socket.SHUT_WR)
def _adjust_leftover_buffer(self, nbytes: int) -> None:
+ self._buffer_size -= nbytes
buffer = self._buffer
while nbytes:
b = buffer.popleft()
@@ -1144,13 +1149,16 @@ def _write_send(self):
if n != len(buffer):
# Not all data was written
self._buffer.appendleft(buffer[n:])
+ self._buffer_size -= n
except (BlockingIOError, InterruptedError):
- pass
+ self._buffer.appendleft(buffer)
+ return
except (SystemExit, KeyboardInterrupt):
raise
except BaseException as exc:
self._loop._remove_writer(self._sock_fd)
self._buffer.clear()
+ self._buffer_size = 0
self._fatal_error(exc, 'Fatal write error on socket transport')
if self._empty_waiter is not None:
self._empty_waiter.set_exception(exc)
@@ -1186,7 +1194,9 @@ def writelines(self, list_of_data):
self._conn_lost += 1
return
- self._buffer.extend([memoryview(data) for data in list_of_data])
+ for data in list_of_data:
+ self._buffer.append(memoryview(data))
+ self._buffer_size += len(data)
self._write_ready()
# If the entire buffer couldn't be written, register a write handler
if self._buffer:
diff --git
a/Misc/NEWS.d/next/Library/2026-03-27-12-00-00.gh-issue-146507.1D95A7.rst
b/Misc/NEWS.d/next/Library/2026-03-27-12-00-00.gh-issue-146507.1D95A7.rst
new file mode 100644
index 00000000000000..f0aae2068fc9e6
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-03-27-12-00-00.gh-issue-146507.1D95A7.rst
@@ -0,0 +1,3 @@
+Make :meth:`asyncio.SelectorEventLoop` stream transport's
+:meth:`~asyncio.WriteTransport.get_write_buffer_size` O(1) by maintaining a
+running byte counter instead of iterating the buffer on every call.
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