gh-160414: pass a notification on when Condition.wait() times out

Lib/test/lock_tests.py

@@ -772,6 +772,44 @@ def test_nan_timeout(self):
             self.assertRaises(ValueError, cond.wait_for, lambda: False, nan)
             self.assertEqual(len(cond._waiters), 0)
 
+    def test_notify_after_timeout(self):
+        # gh-160414: check that notify() still wakes a waiter when the one
+        # it picks has just timed out.
+        cond = self.condtype()
+        waiting = threading.Event()
+        notified = threading.Event()
+        results = []
+        acquire_restore = cond._acquire_restore
+        def hold_t1(state):
+            if threading.current_thread() is t1:
+                waiting.set()
+                notified.wait(support.SHORT_TIMEOUT)
+            acquire_restore(state)
+        cond._acquire_restore = hold_t1
+        def short():
+            with cond:
+                results.append(("short", cond.wait(0.01)))
+        def long():
+            waiting.wait()
+            with cond:
+                results.append(("long", cond.wait(support.SHORT_TIMEOUT)))
+        t1 = threading.Thread(target=short)
+        t2 = threading.Thread(target=long)
+        t1.start()
+        t2.start()
+        try:
+            waiting.wait()
+            for _ in support.sleeping_retry(support.SHORT_TIMEOUT):
+                with cond:
+                    if len(cond._waiters) == 2:
+                        cond.notify()
+                        break
+        finally:
+            notified.set()
+            t1.join()
+            t2.join()
+        self.assertEqual(sorted(results), [("long", True), ("short", False)])
+
     def test_waitfor(self):
         cond = self.condtype()
         state = 0

Lib/threading.py

@@ -368,14 +368,18 @@ def wait(self, timeout=None):
                 else:
                     # A NaN timeout is rejected by acquire().
                     gotit = waiter.acquire(True, timeout)
-            return gotit
         finally:
             self._acquire_restore(saved_state)
             if not gotit:
-                try:
-                    self._waiters.remove(waiter)
-                except ValueError:
-                    pass
+                if waiter.acquire(False):
+                    # gh-160414: notified after the timeout; pass it on.
+                    self.notify()
+                else:
+                    try:
+                        self._waiters.remove(waiter)
+                    except ValueError:
+                        pass
+        return gotit
 
     def wait_for(self, predicate, timeout=None):
         """Wait until a condition evaluates to True.

Misc/NEWS.d/next/Library/2026-10-23-09-46-09.gh-issue-160414.Vq8sLm.rst

@@ -0,0 +1,2 @@
+Fix :meth:`threading.Condition.notify` waking no thread when the waiter it
+picks has just timed out; the notification now goes to the next waiter.