From 16ec20f8e0c098d8d114085fddfc567f1b56a8dc Mon Sep 17 00:00:00 2001
From: Kadir Can Ozden <101993364+bysiber@users.noreply.github.com>
Date: Fri, 20 Feb 2026 09:27:11 +0300
Subject: [PATCH] Fix CapacityLimiter._pending_borrowers leak on non-Cancelled
 exceptions

acquire_on_behalf_of only catches trio.Cancelled when cleaning up
_pending_borrowers.  If park() raises any other exception (e.g.
KeyboardInterrupt delivered via the abort mechanism), the task's
entry remains in _pending_borrowers permanently.  This is a slow
memory leak and can also cause _wake_waiters to encounter stale
entries.

Broaden the handler to BaseException and use pop with a default
to be safe against double-removal.
---
 src/trio/_sync.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/trio/_sync.py b/src/trio/_sync.py
index dbdee0798..d8c16f6d9 100644
--- a/src/trio/_sync.py
+++ b/src/trio/_sync.py
@@ -377,8 +377,8 @@ async def acquire_on_behalf_of(self, borrower: Task | object) -> None:
             self._pending_borrowers[task] = borrower
             try:
                 await self._lot.park()
-            except trio.Cancelled:
-                self._pending_borrowers.pop(task)
+            except BaseException:
+                self._pending_borrowers.pop(task, None)
                 raise
         else:
             await trio.lowlevel.cancel_shielded_checkpoint()