time: wake DelayQueue when cleared (#8320)

tokio-util/src/time/delay_queue.rs

@@ -1031,10 +1031,18 @@ impl<T> DelayQueue<T> {
     /// # }
     /// ```
     pub fn clear(&mut self) {
+        let had_entries = !self.slab.is_empty();
+
         self.slab.clear();
         self.expired = Stack::default();
         self.wheel = Wheel::new();
         self.delay = None;
+
+        if had_entries {
+            if let Some(waker) = self.waker.take() {
+                waker.wake();
+            }
+        }
     }
 
     /// Returns the number of elements the queue can hold without reallocating.

tokio-util/tests/time_delay_queue.rs

@@ -915,6 +915,20 @@ async fn wake_after_remove_last() {
     assert!(assert_ready!(poll!(queue)).is_none());
 }
 
+#[tokio::test(start_paused = true)]
+async fn wake_after_clear() {
+    let mut queue = task::spawn(DelayQueue::new());
+    queue.insert("foo", ms(1000));
+
+    assert_pending!(poll!(queue));
+    assert!(!queue.is_woken());
+
+    queue.clear();
+
+    assert!(queue.is_woken());
+    assert!(assert_ready!(poll!(queue)).is_none());
+}
+
 fn ms(n: u64) -> Duration {
     Duration::from_millis(n)
 }