Add a test for waker-updating behaviour

crates/tests/winrt/Cargo.toml

@@ -23,6 +23,7 @@ features = [
     "Foundation_Numerics",
     "Storage_Streams",
     "System",
+    "System_Threading",
     "UI_Composition",
     "Win32_System_Com",
     "Win32_System_WinRT",

crates/tests/winrt/tests/async.rs

@@ -1,7 +1,13 @@
+use std::future::IntoFuture;
+
+use futures::{executor::LocalPool, future, task::SpawnExt};
+use windows::{
+    Storage::Streams::*,
+    System::Threading::{ThreadPool, WorkItemHandler},
+};
+
 #[test]
 fn async_get() -> windows::core::Result<()> {
-    use windows::Storage::Streams::*;
-
     let stream = &InMemoryRandomAccessStream::new()?;
 
     let writer = DataWriter::CreateDataWriter(stream)?;
@@ -25,8 +31,6 @@ fn async_get() -> windows::core::Result<()> {
 }
 
 async fn async_await() -> windows::core::Result<()> {
-    use windows::Storage::Streams::*;
-
     let stream = &InMemoryRandomAccessStream::new()?;
 
     let writer = DataWriter::CreateDataWriter(stream)?;
@@ -53,3 +57,43 @@ async fn async_await() -> windows::core::Result<()> {
 fn test_async_await() -> windows::core::Result<()> {
     futures::executor::block_on(async_await())
 }
+
+#[test]
+fn test_async_updates_waker() -> windows::core::Result<()> {
+    let mut pool = LocalPool::new();
+
+    let (tx, rx) = std::sync::mpsc::channel::<()>();
+
+    let winrt_future = ThreadPool::RunAsync(&WorkItemHandler::new(move |_| {
+        rx.recv().unwrap();
+        Ok(())
+    }))?
+    .into_future();
+
+    let task = pool
+        .spawner()
+        .spawn_with_handle(async move {
+            // Poll the future once on a LocalPool task
+            match future::select(winrt_future, future::ready(())).await {
+                future::Either::Left(_) => panic!("threadpool action can't finish yet"),
+                future::Either::Right(((), future)) => future,
+            }
+        })
+        .unwrap();
+    let winrt_future = pool.run_until(task);
+
+    pool.spawner()
+        .spawn(async move {
+            // Now run the future to completion on a *different* LocalPool task.
+            // This will hang unless winrt_future properly updates its saved waker to the new task.
+            let (result, ()) = future::join(winrt_future, async {
+                tx.send(()).unwrap();
+            })
+            .await;
+            result.unwrap();
+        })
+        .unwrap();
+    pool.run();
+
+    Ok(())
+}