Merge pull request #744 from Smithay/fix/destructor_deadlock

backend/rs: server: Fix potential deadlock on object destruction

wayland-backend/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### Bugfixes
+
+- backend/rs: server: Fixed potential deadlock on object destruction
+
 ## 0.3.5 -- 2024-07-03
 
 #### Additions

wayland-backend/src/rs/server_impl/common_poll.rs

@@ -296,6 +296,11 @@ impl<D> InnerBackend<D> {
                             panic!("An object data was returned from a callback not creating any object");
                         }
                     }
+                    // dropping the object calls destructors from which users could call into wayland-backend again.
+                    // so lets release and relock the state again, to avoid a deadlock
+                    std::mem::drop(state);
+                    std::mem::drop(object);
+                    state = self.state.lock().unwrap();
                 }
                 DispatchAction::Bind { object, client, global, handler } => {
                     // temporarily unlock the state Mutex while this request is dispatched

wayland-backend/src/server_api.rs

@@ -580,8 +580,12 @@ impl<D> Backend<D> {
     }
 }
 
+// Workaround: Some versions of rustc throw a `struct is never constructed`-warning here,
+// if the `server_system`-feature is enabled, even though the `rs`-module makes use if it.
+#[allow(dead_code)]
 pub(crate) struct DumbObjectData;
 
+#[allow(dead_code)]
 impl<D> ObjectData<D> for DumbObjectData {
     #[cfg_attr(coverage, coverage(off))]
     fn request(

wayland-client/src/event_queue.rs

@@ -703,20 +703,6 @@ impl<I: Proxy, U: std::fmt::Debug, State> std::fmt::Debug for QueueProxyData<I,
     }
 }
 
-struct TemporaryData;
-
-impl ObjectData for TemporaryData {
-    fn event(
-        self: Arc<Self>,
-        _: &Backend,
-        _: Message<ObjectId, OwnedFd>,
-    ) -> Option<Arc<dyn ObjectData>> {
-        unreachable!()
-    }
-
-    fn destroyed(&self, _: ObjectId) {}
-}
-
 /*
  * Dispatch delegation helpers
  */