don't let that reference hang

src/application.rs

@@ -36,15 +36,16 @@ mod imp {
                     self.mpv.set_property("gapless-audio", true).unwrap();
                     // TODO: observe properties
 
-                    glib::spawn_future_local(glib::clone!(
-                        #[weak(rename_to = app)]
-                        self,
-                        async move {
-                            loop {
-                                app.mpv.tick().await;
+                    let self_weak = self.obj().downgrade();
+                    glib::spawn_future_local(async move {
+                        while let Some(app) = self_weak.upgrade() {
+                            // this song and dance is required so the strong reference to app
+                            // isn't uselessly preserved during the await
+                            let future = app.imp().mpv.tick();
+                            drop(app);
+                            future.await;
                         }
-                        }
-                    ));
+                    });
 
                     glib::spawn_future_local(async move {
                         let conn = zbus::connection::Builder::session()

src/mpv.rs

@@ -45,12 +45,14 @@ impl fmt::Debug for Error {
 impl std::error::Error for Error {}
 
 use event_listener::{Event, IntoNotification};
+use std::cell::RefCell;
 use std::pin::Pin;
 use std::ptr::NonNull;
 
 pub struct Handle {
     inner: NonNull<ffi::mpv_handle>,
     wakeup: Pin<Box<Event>>, // the wakeup callback holds a pointer to this
+    wait_event_cell: RefCell<()>,
 }
 
 // The client API is generally fully thread-safe, unless otherwise noted.
@@ -89,7 +91,11 @@ impl Handle {
         Error::from_return_code(unsafe { ffi::mpv_initialize(inner.as_ptr()) })
             .expect("could not initialize mpv handle");
 
-        Self { inner, wakeup }
+        Self {
+            inner,
+            wakeup,
+            wait_event_cell: RefCell::new(()),
+        }
     }
 
     pub fn set_property(&self, name: &str, value: impl FormatValue) -> Result<(), Error> {
@@ -104,7 +110,9 @@ impl Handle {
 
     fn drain_event_queue(&self) {
         loop {
+            let borrowed = self.wait_event_cell.borrow_mut();
             let event = unsafe { &*ffi::mpv_wait_event(self.inner.as_ptr(), 0.0) };
+
             match event.event_id {
                 ffi::mpv_event_id_MPV_EVENT_NONE => break,
 
@@ -112,14 +120,15 @@ impl Handle {
 
                 _ => todo!("event {}", event.event_id),
             }
+            drop(borrowed); // make sure the borrow is held until here
         }
     }
 
-    pub async fn tick(&self) {
+    pub fn tick(&self) -> impl std::future::Future<Output = ()> {
         // take listener before we drain the event queue, so we don't miss any notifications
         let listener = self.wakeup.listen();
         self.drain_event_queue();
-        listener.await;
+        listener
     }
 }