gh-92530: Fix an issue that occurred after interrupting threading.Condition.notify (GH-92534)

If Condition.notify() was interrupted just after it released the waiter lock,
but before removing it from the queue, the following calls of notify() failed
with RuntimeError: cannot release un-acquired lock.

1 files changed, 14 insertions, 7 deletions

diff --git a/Lib/threading.py b/Lib/threading.py
index 40edcde1153..a3df587f106 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -368,14 +368,21 @@ class Condition:
         """
         if not self._is_owned():
             raise RuntimeError("cannot notify on un-acquired lock")
-        all_waiters = self._waiters
-        waiters_to_notify = _deque(_islice(all_waiters, n))
-        if not waiters_to_notify:
-            return
-        for waiter in waiters_to_notify:
-            waiter.release()
+        waiters = self._waiters
+        while waiters and n > 0:
+            waiter = waiters[0]
+            try:
+                waiter.release()
+            except RuntimeError:
+                # gh-92530: The previous call of notify() released the lock,
+                # but was interrupted before removing it from the queue.
+                # It can happen if a signal handler raises an exception,
+                # like CTRL+C which raises KeyboardInterrupt.
+                pass
+            else:
+                n -= 1
             try:
-                all_waiters.remove(waiter)
+                waiters.remove(waiter)
             except ValueError:
                 pass