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gh-146507: Make _SelectorTransport.get_write_buffer_size() O(1) #146518

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Merged
kumaraditya303 merged 5 commits into from
Mar 27, 2026
+16 −3
Merged

gh-146507: Make _SelectorTransport.get_write_buffer_size() O(1) #146518

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e4b2b38
gh-146507: Make _SelectorTransport.get_write_buffer_size() O(1)
moktamd Mar 27, 2026
6a79a27
Add NEWS entry for gh-146507
moktamd Mar 27, 2026
ce68375
Simplify writelines buffer_size tracking per review
moktamd Mar 27, 2026
7eeccba
Iterate list_of_data once in writelines per review
moktamd Mar 27, 2026
bfed0bd
Append directly to self._buffer in writelines per review
moktamd Mar 27, 2026
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gh-146507: Make _SelectorTransport.get_write_buffer_size() O(1) 
Maintain a running _buffer_size counter instead of recalculating
with sum(map(len, _buffer)) on every call. This matches the O(1)
pattern already used by _SelectorDatagramTransport and
_ProactorBaseWritePipeTransport in the same codebase.
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@moktamd
moktamd committed Mar 27, 2026
commit e4b2b383714d49e6023ba141a5a3f7a5e87304d4
16 changes: 13 additions & 3 deletions Lib/asyncio/selector_events.py
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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
Expand All @@ -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():
Expand Down Expand Up @@ -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):
Expand All @@ -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)
Expand All @@ -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()
Expand All @@ -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)
Expand Down Expand Up @@ -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])
views = [memoryview(data) for data in list_of_data]
self._buffer.extend(views)
self._buffer_size += sum(len(v) for v in views)
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self._write_ready()
# If the entire buffer couldn't be written, register a write handler
if self._buffer:
Expand Down
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