perf(ipc): reuse theme snapshots and typed window records

Cargo.toml

@@ -61,7 +61,7 @@ smithay = { git = "https://github.com/Smithay/smithay", rev = "8a270232f1bfc416c
 ] }
 tracing = "0.1.41"
 tracing-subscriber = { version = "0.3.20", features = ["env-filter"] }
-serde = { version = "1.0.228", features = ["derive"] }
+serde = { version = "1.0.228", features = ["derive", "rc"] }
 serde_json = "1.0.145"
 tempfile = "3.23.0"
 xcursor = "0.3.11"

compositor/src/ipc.rs

@@ -1630,24 +1630,31 @@ impl Ferese {
             }
         }
         let windows = if locked {
-            json!([])
+            Vec::new()
         } else {
-            Value::Array(self.windows.ordered_ids().filter_map(|id| {
-                let record = self.windows.record(id)?;
-                let workspace = self.workspaces.workspace_for_window(id)?;
-                Some(json!({
-                    "id": id.0, "app_id": record.app_id, "title": record.title,
-                    "focused": self.focused_window == Some(id), "workspace": workspace.0,
-                    "floating": matches!(self.workspaces.placement(id), Some(ferese_core::WindowPlacement::Floating { .. })),
-                    "fullscreen": self.workspaces.workspace(workspace).is_some_and(|workspace| workspace.fullscreen == Some(id)),
-                }))
-            }).collect())
+            self.windows
+                .ordered_ids()
+                .filter_map(|id| {
+                    let record = self.windows.record(id)?;
+                    let workspace = self.workspaces.workspace_for_window(id)?;
+                    Some(ferese_ipc::events::Window {
+                        id: id.0,
+                        app_id: record.app_id.clone(),
+                        title: record.title.clone(),
+                        focused: self.focused_window == Some(id),
+                        workspace: workspace.0,
+                        floating: matches!(
+                            self.workspaces.placement(id),
+                            Some(ferese_core::WindowPlacement::Floating { .. })
+                        ),
+                        fullscreen: self
+                            .workspaces
+                            .workspace(workspace)
+                            .is_some_and(|workspace| workspace.fullscreen == Some(id)),
+                    })
+                })
+                .collect()
         };
-        let live = &self.theme_engine.live;
-        let theme = json!({
-            "mode": live.mode, "theme": live.theme, "families": live.families,
-            "warnings": live.warnings, "error": live.error, "fallback_note": live.fallback_note,
-        });
         ferese_ipc::events::Snapshot {
             outputs,
             workspaces: if locked {
@@ -1669,7 +1676,7 @@ impl Ferese {
                 revision: self.ipc_events.config_revision,
                 error: self.theme_engine.live.error.clone(),
             },
-            theme,
+            theme: self.theme_engine.event_value(),
             lock: self.session_lock.event_state(),
         }
     }
@@ -2512,7 +2519,15 @@ mod tests {
                 generation: 1,
                 last: true,
                 change: ferese_ipc::events::Change::WindowsChanged {
-                    windows: json!([{"title": "x".repeat(900_000)}]),
+                    windows: vec![ferese_ipc::events::Window {
+                        id: 1,
+                        app_id: "org.example.Test".into(),
+                        title: "x".repeat(900_000),
+                        focused: false,
+                        workspace: 1,
+                        floating: false,
+                        fullscreen: false,
+                    }],
                 },
             }))
             .unwrap();

compositor/src/ipc_events.rs

@@ -63,6 +63,9 @@ impl Subscribers {
                 .values()
                 .any(|subscriber| subscriber.initial)
         {
+            // Keep the latest shared payload even when a theme publication
+            // produced equal logical values, so later comparisons stay cheap.
+            self.previous = self.active().then_some(snapshot);
             return;
         }
         self.generation = self.generation.wrapping_add(1);
@@ -144,14 +147,111 @@ mod tests {
     use serde_json::json;
     use std::sync::mpsc::{TryRecvError, sync_channel};
 
+    #[test]
+    #[ignore = "manual release benchmark for IPC snapshot construction"]
+    fn profile_unchanged_event_snapshots() {
+        let name = "ipc_events::tests::profile_unchanged_event_snapshots";
+        if !crate::startup_tests::private_runtime(name) {
+            return;
+        }
+        let mut events = smithay::reexports::calloop::EventLoop::try_new().unwrap();
+        let state = crate::startup_tests::state(&mut events);
+        for _ in 0..100 {
+            std::hint::black_box(state.ipc_event_snapshot());
+        }
+        for run in 1..=3 {
+            let started = std::time::Instant::now();
+            for _ in 0..2000 {
+                std::hint::black_box(state.ipc_event_snapshot());
+            }
+            eprintln!(
+                "event_snapshot_benchmark run={run} iterations=2000 elapsed_us={}",
+                started.elapsed().as_micros()
+            );
+        }
+    }
+
+    #[test]
+    #[ignore = "manual release benchmark for populated IPC publication"]
+    fn profile_populated_event_publication() {
+        use crate::state::DesktopOutput;
+        use smithay::output::{Mode, Output, PhysicalProperties, Scale, Subpixel};
+        use smithay::utils::Transform;
+
+        if !crate::startup_tests::private_runtime(
+            "ipc_events::tests::profile_populated_event_publication",
+        ) {
+            return;
+        }
+        let mut events = smithay::reexports::calloop::EventLoop::try_new().unwrap();
+        let mut state = crate::startup_tests::state(&mut events);
+        let output = DesktopOutput {
+            output: Output::new(
+                "benchmark".into(),
+                PhysicalProperties {
+                    serial_number: String::new(),
+                    size: (0, 0).into(),
+                    subpixel: Subpixel::Unknown,
+                    make: "test".into(),
+                    model: "test".into(),
+                },
+            ),
+            identity: "benchmark".into(),
+            mode: Mode {
+                size: (1920, 1080).into(),
+                refresh: 60_000,
+            },
+            transform: Transform::Normal,
+            scale: Scale::Fractional(1.0),
+            position: (0, 0).into(),
+        };
+        state.begin_desktop_transition();
+        let changes = state.publish_desktop(vec![output]).unwrap();
+        state.finish_desktop_transition(changes);
+        let mut clients = Vec::new();
+        for window_count in [0, 1, 20, 100] {
+            while clients.len() < window_count {
+                let (window, client) =
+                    crate::state::test_window(&mut state, &mut events, 0xff204060);
+                let id = state.windows.ids()[&window];
+                let record = state.windows.record_mut(id).unwrap();
+                record.app_id = "org.example.Editor".into();
+                record.title = format!("Document {} — publication benchmark", id.0);
+                clients.push(client);
+            }
+            let (sender, receive) = sync_channel(QUEUE_CAPACITY);
+            state.ipc_events.subscribe(1, sender).unwrap();
+            state.publish_ipc_events();
+            assert!(matches!(
+                receive.try_recv().unwrap().change,
+                Change::Snapshot { .. }
+            ));
+            for _ in 0..100 {
+                state.publish_ipc_events();
+            }
+            for run in 1..=3 {
+                let started = std::time::Instant::now();
+                for _ in 0..2000 {
+                    state.publish_ipc_events();
+                }
+                eprintln!(
+                    "event_publication_benchmark windows={window_count} run={run} iterations=2000 elapsed_us={}",
+                    started.elapsed().as_micros()
+                );
+            }
+            assert!(matches!(receive.try_recv(), Err(TryRecvError::Empty)));
+            state.ipc_events.remove(1);
+        }
+    }
+
     fn snapshot() -> Snapshot {
         Snapshot {
             outputs: json!([]),
             workspaces: json!([]),
-            windows: json!([]),
+            windows: Vec::new(),
             focus: json!(null),
             config: ConfigState::default(),
-            theme: json!({}),
+            theme: json!({}).into(),
             lock: LockState {
                 phase: "unlocked".into(),
                 sleeping: false,
@@ -186,6 +286,24 @@ mod tests {
         assert!(!events[0].last && !events[1].last && events[2].last);
     }
 
+    #[test]
+    fn equal_theme_publications_retain_shared_storage_without_emitting_events() {
+        let mut hub = Subscribers::default();
+        let (sender, receive) = sync_channel(QUEUE_CAPACITY);
+        hub.subscribe(1, sender).unwrap();
+        let first = snapshot();
+        hub.publish(first.clone());
+        receive.try_recv().unwrap();
+        let generation = hub.generation;
+        let mut next = first;
+        next.theme = Arc::new(next.theme.as_ref().clone());
+        let payload = next.theme.clone();
+        hub.publish(next);
+        assert!(matches!(receive.try_recv(), Err(TryRecvError::Empty)));
+        assert_eq!(hub.generation, generation);
+        assert!(Arc::ptr_eq(&hub.previous.as_ref().unwrap().theme, &payload));
+    }
+
     #[test]
     fn full_and_disconnected_subscribers_do_not_block_healthy_readers() {
         let mut hub = Subscribers::default();
@@ -240,10 +358,18 @@ mod tests {
         receive.try_recv().unwrap();
         state.outputs = json!([{"id": 1}]);
         state.workspaces = json!([{"output": 1}]);
-        state.windows = json!([{"id": 7, "title": "Terminal"}]);
+        state.windows = vec![ferese_ipc::events::Window {
+            id: 7,
+            app_id: "org.example.Terminal".into(),
+            title: "Terminal".into(),
+            focused: false,
+            workspace: 1,
+            floating: false,
+            fullscreen: false,
+        }];
         state.focus = json!({"window": 7});
         state.config.revision = 1;
-        state.theme = json!({"mode": "light"});
+        state.theme = json!({"mode": "light"}).into();
         state.lock.phase = "locked".into();
         hub.publish(state);
         let events = receive.try_iter().collect::<Vec<_>>();

compositor/src/theme.rs

@@ -1,3 +1,4 @@
+use std::cell::OnceCell;
 use std::collections::{HashMap, HashSet};
 use std::io;
 use std::os::fd::{AsRawFd, FromRawFd, OwnedFd};
@@ -138,6 +139,7 @@ impl Default for LiveTheme {
 pub(crate) struct Engine {
     pub(crate) live: LiveTheme,
     pub(crate) revision: u64,
+    event_value: OnceCell<Arc<Value>>,
     waiters: HashMap<u64, (u64, mpsc::SyncSender<Response>)>,
     watcher: Option<RecommendedWatcher>,
     watched_directories: HashSet<PathBuf>,
@@ -207,7 +209,24 @@ impl Engine {
         serde_json::to_value(snapshot).expect("serializable theme snapshot")
     }
 
+    /// Share the logical event payload until the next theme publication.
+    pub(crate) fn event_value(&self) -> Arc<Value> {
+        self.event_value
+            .get_or_init(|| {
+                Arc::new(json!({
+                    "mode": self.live.mode,
+                    "theme": self.live.theme,
+                    "families": self.live.families,
+                    "warnings": self.live.warnings,
+                    "error": self.live.error,
+                    "fallback_note": self.live.fallback_note,
+                }))
+            })
+            .clone()
+    }
+
     fn publish(&mut self) {
+        self.event_value.take();
         self.revision = self.revision.wrapping_add(1);
         let value = self.value();
         for (_, (id, response)) in self.waiters.drain() {
@@ -216,6 +235,7 @@ impl Engine {
     }
 
     pub(crate) fn startup_failed(&mut self, path: Option<&Path>, error: String) {
+        self.event_value.take();
         let path = path
             .map(|path| path.display().to_string())
             .unwrap_or_else(|| "configuration".into());
@@ -793,6 +813,42 @@ mod tests {
         assert_eq!(engine.revision, 3);
     }
 
+    #[test]
+    fn event_values_reuse_storage_and_follow_theme_and_error_publication() {
+        let mut engine = Engine::default();
+        let original = engine.event_value();
+        let mut expected = engine.value();
+        for key in ["version", "revision", "presented"] {
+            expected.as_object_mut().unwrap().remove(key);
+        }
+        assert_eq!(original.as_ref(), &expected);
+        assert!(Arc::ptr_eq(&original, &engine.event_value()));
+
+        engine.live.mode = Mode::Light;
+        engine.publish();
+        let light = engine.event_value();
+        assert!(!Arc::ptr_eq(&original, &light));
+        assert_eq!(light["mode"], "light");
+        assert_eq!(
+            original["mode"], "dark",
+            "queued snapshots remain immutable"
+        );
+
+        engine.reject("invalid theme".into());
+        let rejected = engine.event_value();
+        assert_eq!(rejected["error"], "invalid theme");
+        assert!(light["error"].is_null());
+        engine.startup_failed(None, "invalid startup configuration".into());
+        let startup = engine.event_value();
+        assert!(
+            startup["error"]
+                .as_str()
+                .unwrap()
+                .contains("invalid startup configuration")
+        );
+        assert!(Arc::ptr_eq(&startup, &engine.event_value()));
+    }
+
     #[test]
     fn publication_projects_live_values_and_preserves_revision_semantics() {
         let mut engine = Engine::default();

crates/ferese-ipc/src/events.rs

@@ -1,3 +1,5 @@
+use std::sync::Arc;
+
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
 
@@ -16,15 +18,27 @@ pub struct LockState {
     pub sleeping: bool,
 }
 
+/// Window metadata included in desktop event snapshots.
+#[derive(Clone, Debug, Deserialize, Serialize, PartialEq, Eq)]
+pub struct Window {
+    pub id: u64,
+    pub app_id: String,
+    pub title: String,
+    pub focused: bool,
+    pub workspace: u64,
+    pub floating: bool,
+    pub fullscreen: bool,
+}
+
 /// A coherent logical desktop view. Desktop objects are redacted while locked.
 #[derive(Clone, Debug, Deserialize, Serialize, PartialEq)]
 pub struct Snapshot {
     pub outputs: Value,
     pub workspaces: Value,
-    pub windows: Value,
+    pub windows: Vec<Window>,
     pub focus: Value,
     pub config: ConfigState,
-    pub theme: Value,
+    pub theme: Arc<Value>,
     pub lock: LockState,
 }
 
@@ -35,7 +49,7 @@ pub enum Change {
     Snapshot { desktop: Box<Snapshot> },
     OutputsChanged { outputs: Value },
     WorkspacesChanged { workspaces: Value },
-    WindowsChanged { windows: Value },
+    WindowsChanged { windows: Vec<Window> },
     FocusChanged { focus: Value },
     ConfigChanged { config: ConfigState },
     ThemeChanged { theme: Value },
@@ -91,9 +105,9 @@ impl Snapshot {
                 config: self.config.clone(),
             });
         }
-        if self.theme != previous.theme {
+        if !Arc::ptr_eq(&self.theme, &previous.theme) && self.theme != previous.theme {
             changes.push(Change::ThemeChanged {
-                theme: self.theme.clone(),
+                theme: self.theme.as_ref().clone(),
             });
         }
         if self.lock != previous.lock {
@@ -108,6 +122,75 @@ impl Snapshot {
 #[cfg(test)]
 mod tests {
     use super::*;
+
+    #[test]
+    fn typed_windows_preserve_snapshot_and_replacement_wire_fields() {
+        let windows = serde_json::json!([{
+            "id": u64::MAX,
+            "app_id": "org.example.Editor.desktop",
+            "title": "Chapter \"one\"\n第二课",
+            "focused": true,
+            "workspace": u64::MAX - 1,
+            "floating": true,
+            "fullscreen": false
+        }]);
+        let snapshot = serde_json::json!({
+            "outputs": [], "workspaces": [], "windows": windows,
+            "focus": {"window": u64::MAX},
+            "config": {"revision": 0, "error": null},
+            "theme": null, "lock": {"phase": "unlocked", "sleeping": false}
+        });
+        for change in [
+            serde_json::json!({"type": "snapshot", "desktop": snapshot}),
+            serde_json::json!({"type": "windows_changed", "windows": windows}),
+        ] {
+            let decoded: Change = serde_json::from_value(change.clone()).unwrap();
+            assert_eq!(serde_json::to_value(&decoded).unwrap(), change);
+            let decoded_windows = match decoded {
+                Change::Snapshot { desktop } => desktop.windows,
+                Change::WindowsChanged { windows } => windows,
+                _ => unreachable!(),
+            };
+            assert_eq!(
+                decoded_windows,
+                vec![Window {
+                    id: u64::MAX,
+                    app_id: "org.example.Editor.desktop".into(),
+                    title: "Chapter \"one\"\n第二课".into(),
+                    focused: true,
+                    workspace: u64::MAX - 1,
+                    floating: true,
+                    fullscreen: false,
+                }]
+            );
+        }
+    }
+
+    #[test]
+    fn shared_themes_preserve_the_wire_format_and_compare_by_value_after_replacement() {
+        let wire = serde_json::json!({
+            "outputs": [], "workspaces": [], "windows": [], "focus": null,
+            "config": {"revision": 0, "error": null},
+            "theme": {"mode": "dark"},
+            "lock": {"phase": "unlocked", "sleeping": false}
+        });
+        let snapshot: Snapshot = serde_json::from_value(wire.clone()).unwrap();
+        assert_eq!(serde_json::to_value(&snapshot).unwrap(), wire);
+        let mut next = snapshot.clone();
+        assert!(Arc::ptr_eq(&snapshot.theme, &next.theme));
+        assert!(next.changes_since(&snapshot).is_empty());
+        next.theme = Arc::new(next.theme.as_ref().clone());
+        assert!(!Arc::ptr_eq(&snapshot.theme, &next.theme));
+        assert!(next.changes_since(&snapshot).is_empty());
+        next.theme = serde_json::json!({"mode": "light"}).into();
+        assert_eq!(
+            next.changes_since(&snapshot),
+            [Change::ThemeChanged {
+                theme: serde_json::json!({"mode": "light"})
+            }]
+        );
+    }
+
     #[test]
     fn events_round_trip_with_an_independent_schema_version() {
         let event = Event {

shell/ferese-shell/src/control.rs

@@ -520,7 +520,7 @@ impl Dispatch<FereseShellV1, ()> for ControlState {
             {
                 let _ = state
                     .sender
-                    .send(ControlUpdate::Snapshot(state.pending.clone()));
+                    .send(ControlUpdate::Snapshot(std::mem::take(&mut state.pending)));
             }
             ferese_shell_v1::Event::LogoutRequested {
                 serial,
@@ -656,6 +656,107 @@ mod tests {
         }
     }
 
+    #[test]
+    #[ignore = "manual release benchmark for shell snapshot handoff"]
+    fn profile_snapshot_handoff() {
+        let (control, mut state, queue, _peer) = control_fixture();
+        for window_count in [1, 20, 100] {
+            let template = ShellSnapshot {
+                windows: (0..window_count)
+                    .map(|id| WindowSnapshot {
+                        id,
+                        workspace: 1,
+                        geometry: Some([0., 0., 800., 600.]),
+                        app_id: "org.example.Editor".into(),
+                        title: format!("Document {id} — Ferese workspace"),
+                        focused: id == 0,
+                        urgent: false,
+                        fullscreen: false,
+                        maximized: false,
+                        floating: false,
+                    })
+                    .collect(),
+                ..ShellSnapshot::default()
+            };
+            for run in 1..=3 {
+                // Decoding is outside the timed handoff, as it is unchanged.
+                let snapshots: Vec<_> = (0..2000).map(|_| template.clone()).collect();
+                let started = std::time::Instant::now();
+                for snapshot in snapshots {
+                    state.pending = snapshot;
+                    state.serial = Some(1);
+                    dispatch_event(
+                        &control,
+                        &mut state,
+                        &queue,
+                        ferese_shell_v1::Event::SnapshotEnd { serial: 1 },
+                    );
+                    std::hint::black_box(control.poll().snapshot.unwrap());
+                }
+                // Include destruction of the last pending snapshot in both builds.
+                state.pending = ShellSnapshot::default();
+                eprintln!(
+                    "snapshot_handoff_benchmark windows={window_count} run={run} iterations=2000 elapsed_us={}",
+                    started.elapsed().as_micros()
+                );
+            }
+        }
+    }
+
+    #[test]
+    fn completed_snapshots_transfer_their_storage_and_remain_independent() {
+        let (control, mut state, queue, _peer) = control_fixture();
+        dispatch_event(
+            &control,
+            &mut state,
+            &queue,
+            ferese_shell_v1::Event::SnapshotBegin { serial: 1 },
+        );
+        dispatch_event(&control, &mut state, &queue, window_event(10, 0));
+        let windows = state.pending.windows.as_ptr();
+        let app_id = state.pending.windows[0].app_id.as_ptr();
+        let title = state.pending.windows[0].title.as_ptr();
+        assert!(control.poll().snapshot.is_none());
+        dispatch_event(
+            &control,
+            &mut state,
+            &queue,
+            ferese_shell_v1::Event::SnapshotEnd { serial: 1 },
+        );
+        let first = control.poll().snapshot.unwrap();
+        assert_eq!(first.windows.as_ptr(), windows);
+        assert_eq!(first.windows[0].app_id.as_ptr(), app_id);
+        assert_eq!(first.windows[0].title.as_ptr(), title);
+        for (begin, end, id) in [(2, 99, 20), (3, 3, 30)] {
+            dispatch_event(
+                &control,
+                &mut state,
+                &queue,
+                ferese_shell_v1::Event::SnapshotBegin { serial: begin },
+            );
+            dispatch_event(&control, &mut state, &queue, window_event(id, 0));
+            assert!(control.poll().snapshot.is_none());
+            dispatch_event(
+                &control,
+                &mut state,
+                &queue,
+                ferese_shell_v1::Event::SnapshotEnd { serial: end },
+            );
+            let next = control.poll().snapshot;
+            if begin == end {
+                let next = next.unwrap();
+                assert_eq!(next.windows.len(), 1);
+                assert_eq!(next.windows[0].id, id);
+            } else {
+                assert!(next.is_none(), "mismatched serials must not publish");
+            }
+        }
+        assert_eq!(first.windows.len(), 1);
+        assert_eq!(first.windows[0].id, 10);
+        assert_eq!(first.windows[0].app_id, "dev.ferese.Test");
+        assert_eq!(first.windows[0].title, "Same title");
+    }
+
     #[test]
     fn window_id_words_round_trip_without_truncation() {
         for (id, hi, lo) in [