rt: improve robustness of wake_in_drop_after_panic test (#6238)

tokio/tests/rt_basic.rs

@@ -181,25 +181,35 @@ fn drop_tasks_in_context() {
 #[cfg_attr(target_os = "wasi", ignore = "Wasi does not support panic recovery")]
 #[should_panic(expected = "boom")]
 fn wake_in_drop_after_panic() {
-    let (tx, rx) = oneshot::channel::<()>();
-
     struct WakeOnDrop(Option<oneshot::Sender<()>>);
 
     impl Drop for WakeOnDrop {
         fn drop(&mut self) {
-            self.0.take().unwrap().send(()).unwrap();
+            let _ = self.0.take().unwrap().send(());
         }
     }
 
     let rt = rt();
 
+    let (tx1, rx1) = oneshot::channel::<()>();
+    let (tx2, rx2) = oneshot::channel::<()>();
+
+    // Spawn two tasks. We don't know the order in which they are dropped, so we
+    // make both tasks identical. When the first task is dropped, we wake up the
+    // second task. This ensures that we trigger a wakeup on a live task while
+    // handling the "boom" panic, no matter the order in which the tasks are
+    // dropped.
     rt.spawn(async move {
-        let _wake_on_drop = WakeOnDrop(Some(tx));
-        // wait forever
-        futures::future::pending::<()>().await;
+        let _wake_on_drop = WakeOnDrop(Some(tx2));
+        let _ = rx1.await;
+        unreachable!()
     });
 
-    let _join = rt.spawn(async move { rx.await });
+    rt.spawn(async move {
+        let _wake_on_drop = WakeOnDrop(Some(tx1));
+        let _ = rx2.await;
+        unreachable!()
+    });
 
     rt.block_on(async {
         tokio::task::yield_now().await;