perf(ipc): cache unchanged output event payloads

compositor/src/backends/direct.rs

@@ -246,7 +246,7 @@ impl DirectBackendState {
     }
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, PartialEq)]
 pub(crate) struct ConnectedOutputInfo {
     pub connector: String,
     pub connected: bool,
@@ -266,7 +266,7 @@ pub(crate) struct ConnectedOutputInfo {
     pub configured_position: Option<[i32; 2]>,
 }
 
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub(crate) struct ConnectedModeInfo {
     pub width: u16,
     pub height: u16,

compositor/src/ipc.rs

@@ -14,6 +14,7 @@ use ferese_core::LayoutMode;
 use ferese_ipc::{Request, Response, VERSION};
 
 pub(crate) mod activity_owner;
+pub(crate) mod outputs;
 mod transport;
 use ferese_layout::Direction;
 use serde_json::{Value, json};
@@ -1620,15 +1621,41 @@ impl Ferese {
 
     pub(crate) fn ipc_event_snapshot(&self) -> ferese_ipc::events::Snapshot {
         let locked = self.session_lock.active();
-        let mut outputs = self.outputs_json();
+        let outputs = if let Some(backend) = &self.direct_backend {
+            let state = outputs::State {
+                connected: &backend.connected_outputs,
+                focused: self.output_workspaces.focused_output(),
+                error: backend.output_configuration_error(),
+                confirmation_pending: backend.confirmation_pending(),
+                low_power: backend.low_power,
+            };
+            let presentations = backend.connected_outputs.iter().map(|info| {
+                let mapped = self.output_by_identity(&info.identity);
+                let id = self.persistent_output_id(&info.identity);
+                outputs::Presentation {
+                    id,
+                    geometry: mapped.and_then(|output| self.space.output_geometry(output)),
+                    workspace: id.and_then(|id| self.output_workspaces.active_workspace(id)),
+                    scale: mapped
+                        .map(|output| output.current_scale().fractional_scale())
+                        .unwrap_or(info.scale),
+                    transform: mapped
+                        .map(|output| transform_name(output.current_transform()))
+                        .unwrap_or_else(|| configured_transform_name(info.transform)),
+                }
+            });
+            self.ipc_events
+                .outputs
+                .borrow_mut()
+                .get_or_update(state, presentations, locked, || self.outputs_json())
+        } else {
+            // Nested outputs have no connector inventory or DRM mode lists.
+            let mut value = self.outputs_json();
             if locked {
-            for output in outputs.as_array_mut().into_iter().flatten() {
+                outputs::redact(&mut value);
-                if let Some(fields) = output.as_object_mut() {
-                    fields.remove("workspace");
-                    fields.remove("focused");
-                }
-            }
             }
+            Arc::new(value)
+        };
         let windows = if locked {
             Vec::new()
         } else {

compositor/src/ipc/outputs.rs

@@ -0,0 +1,318 @@
+use std::sync::Arc;
+
+use ferese_core::{OutputId, WorkspaceId};
+use serde_json::Value;
+use smithay::utils::{Logical, Rectangle};
+
+use crate::backends::direct::ConnectedOutputInfo;
+
+/// Connector data and policy borrowed for an exact, allocation-free comparison.
+pub(crate) struct State<'a> {
+    pub connected: &'a [ConnectedOutputInfo],
+    pub focused: Option<OutputId>,
+    pub error: Option<&'a str>,
+    pub confirmation_pending: bool,
+    pub low_power: bool,
+}
+
+#[derive(Clone, Copy, PartialEq)]
+pub(crate) struct Presentation {
+    pub id: Option<OutputId>,
+    pub geometry: Option<Rectangle<i32, Logical>>,
+    pub workspace: Option<WorkspaceId>,
+    pub scale: f64,
+    pub transform: &'static str,
+}
+
+struct Entry {
+    connected: Vec<ConnectedOutputInfo>,
+    focused: Option<OutputId>,
+    error: Option<String>,
+    confirmation_pending: bool,
+    low_power: bool,
+    presentations: Vec<Presentation>,
+    unlocked: Arc<Value>,
+    locked: Option<Arc<Value>>,
+}
+
+#[derive(Default)]
+pub(crate) struct Cache {
+    entry: Option<Entry>,
+}
+
+impl Cache {
+    pub(crate) fn clear(&mut self) {
+        self.entry = None;
+    }
+
+    pub(crate) fn get_or_update(
+        &mut self,
+        state: State<'_>,
+        presentations: impl Iterator<Item = Presentation> + Clone,
+        locked: bool,
+        build: impl FnOnce() -> Value,
+    ) -> Arc<Value> {
+        let unchanged = self.entry.as_ref().is_some_and(|entry| {
+            entry.connected == state.connected
+                && entry.focused == state.focused
+                && entry.error.as_deref() == state.error
+                && entry.confirmation_pending == state.confirmation_pending
+                && entry.low_power == state.low_power
+                && presentations
+                    .clone()
+                    .eq(entry.presentations.iter().copied())
+        });
+        if !unchanged {
+            self.entry = Some(Entry {
+                connected: state.connected.to_vec(),
+                focused: state.focused,
+                error: state.error.map(str::to_owned),
+                confirmation_pending: state.confirmation_pending,
+                low_power: state.low_power,
+                presentations: presentations.collect(),
+                unlocked: Arc::new(build()),
+                locked: None,
+            });
+        }
+        let entry = self.entry.as_mut().expect("output snapshot was populated");
+        if locked {
+            entry
+                .locked
+                .get_or_insert_with(|| {
+                    let mut value = entry.unlocked.as_ref().clone();
+                    redact(&mut value);
+                    Arc::new(value)
+                })
+                .clone()
+        } else {
+            entry.unlocked.clone()
+        }
+    }
+}
+
+pub(super) fn redact(value: &mut Value) {
+    for output in value.as_array_mut().into_iter().flatten() {
+        if let Some(fields) = output.as_object_mut() {
+            fields.remove("workspace");
+            fields.remove("focused");
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::backends::direct::ConnectedModeInfo;
+    use crate::config::OutputTransform;
+    use serde_json::json;
+
+    fn connector() -> ConnectedOutputInfo {
+        let mode = ConnectedModeInfo {
+            width: 3840,
+            height: 2160,
+            refresh_millihertz: 60_000,
+            preferred: true,
+        };
+        ConnectedOutputInfo {
+            connector: "HDMI-A-1".into(),
+            connected: true,
+            identity: "test-monitor".into(),
+            internal: false,
+            requested_enabled: true,
+            mirror_source: None,
+            enabled: true,
+            profile: Some("desktop".into()),
+            requested_profile: None,
+            auto_refresh: true,
+            physical_size: Some((600, 340)),
+            current_mode: Some(mode),
+            available_modes: vec![mode],
+            scale: 1.75,
+            transform: OutputTransform::Normal,
+            configured_position: Some([0, 0]),
+        }
+    }
+
+    fn state(connected: &[ConnectedOutputInfo]) -> State<'_> {
+        State {
+            connected,
+            focused: Some(OutputId(1)),
+            error: None,
+            confirmation_pending: false,
+            low_power: false,
+        }
+    }
+
+    fn presentation() -> Presentation {
+        Presentation {
+            id: Some(OutputId(1)),
+            geometry: Some(Rectangle::new((0, 0).into(), (2195, 1235).into())),
+            workspace: Some(WorkspaceId(3)),
+            scale: 1.75,
+            transform: "normal",
+        }
+    }
+
+    fn value() -> Value {
+        json!([{"id": 1, "workspace": 3, "focused": true, "scale": 1.75}])
+    }
+
+    #[test]
+    fn unchanged_outputs_reuse_storage_without_serializing_and_release_when_cleared() {
+        let connected = [connector()];
+        let mut cache = Cache::default();
+        let first = cache.get_or_update(
+            state(&connected),
+            [presentation()].into_iter(),
+            false,
+            value,
+        );
+        for _ in 0..1000 {
+            let next = cache.get_or_update(
+                state(&connected),
+                [presentation()].into_iter(),
+                false,
+                || panic!("unchanged outputs must not rebuild JSON"),
+            );
+            assert!(Arc::ptr_eq(&first, &next));
+        }
+        cache.clear();
+        let next = cache.get_or_update(
+            state(&connected),
+            [presentation()].into_iter(),
+            false,
+            value,
+        );
+        assert!(!Arc::ptr_eq(&first, &next));
+        assert_eq!(first, next);
+    }
+
+    #[test]
+    fn lock_redaction_is_cached_without_mutating_public_or_older_snapshots() {
+        let connected = [connector()];
+        let mut cache = Cache::default();
+        let public = cache.get_or_update(
+            state(&connected),
+            [presentation()].into_iter(),
+            false,
+            value,
+        );
+        let locked = cache.get_or_update(
+            state(&connected),
+            [presentation()].into_iter(),
+            true,
+            || panic!("lock redaction must reuse connector data"),
+        );
+        assert_eq!(*locked, json!([{"id": 1, "scale": 1.75}]));
+        assert_eq!(*public, value());
+        let again = cache.get_or_update(
+            state(&connected),
+            [presentation()].into_iter(),
+            true,
+            || panic!("repeated locked snapshots must not rebuild"),
+        );
+        assert!(Arc::ptr_eq(&locked, &again));
+        let unlocked = cache.get_or_update(
+            state(&connected),
+            [presentation()].into_iter(),
+            false,
+            || panic!("unlock must reuse public data"),
+        );
+        assert!(Arc::ptr_eq(&public, &unlocked));
+        let changed = cache.get_or_update(state(&[]), [].into_iter(), true, || json!([]));
+        assert_eq!(*changed, json!([]));
+        assert_eq!(*locked, json!([{"id": 1, "scale": 1.75}]));
+    }
+
+    #[test]
+    fn connector_inventory_and_every_reported_property_invalidate_the_snapshot() {
+        let changes: &[fn(&mut ConnectedOutputInfo)] = &[
+            |info| info.connector.push('2'),
+            |info| info.connected = false,
+            |info| info.identity.push('2'),
+            |info| info.internal = true,
+            |info| info.requested_enabled = false,
+            |info| info.mirror_source = Some("DP-1".into()),
+            |info| info.enabled = false,
+            |info| info.profile = None,
+            |info| info.requested_profile = Some("mobile".into()),
+            |info| info.auto_refresh = false,
+            |info| info.physical_size = None,
+            |info| info.current_mode = None,
+            |info| info.available_modes[0].width = 1920,
+            |info| info.available_modes[0].height = 1080,
+            |info| info.available_modes[0].refresh_millihertz = 120_000,
+            |info| info.available_modes[0].preferred = false,
+            |info| info.available_modes.clear(),
+            |info| info.scale = 1.5,
+            |info| info.transform = OutputTransform::Rotate90,
+            |info| info.configured_position = None,
+        ];
+        for (index, change) in changes.iter().enumerate() {
+            let mut cache = Cache::default();
+            let mut connected = [connector()];
+            let first = cache.get_or_update(
+                state(&connected),
+                [presentation()].into_iter(),
+                false,
+                value,
+            );
+            change(&mut connected[0]);
+            let next = cache.get_or_update(
+                state(&connected),
+                [presentation()].into_iter(),
+                false,
+                || json!({"changed": index}),
+            );
+            assert_eq!(*next, json!({"changed": index}));
+            assert!(!Arc::ptr_eq(&first, &next));
+        }
+        let mut cache = Cache::default();
+        let first = cache.get_or_update(
+            state(&[connector()]),
+            [presentation()].into_iter(),
+            false,
+            value,
+        );
+        let next = cache.get_or_update(state(&[]), [].into_iter(), false, || json!([]));
+        assert_eq!(*next, json!([]));
+        assert_eq!(*first, value());
+    }
+
+    #[test]
+    fn focus_workspace_geometry_and_output_policy_changes_refresh_the_snapshot() {
+        let connected = [connector()];
+        for index in 0..10 {
+            let mut cache = Cache::default();
+            let first = cache.get_or_update(
+                state(&connected),
+                [presentation()].into_iter(),
+                false,
+                value,
+            );
+            let mut state = state(&connected);
+            let mut presentation = presentation();
+            match index {
+                0 => state.focused = None,
+                1 => state.error = Some("output rejected"),
+                2 => state.confirmation_pending = true,
+                3 => state.low_power = true,
+                4 => presentation.id = None,
+                5 => presentation.geometry = None,
+                6 => presentation.geometry.as_mut().unwrap().loc.x += 100,
+                7 => presentation.workspace = Some(WorkspaceId(4)),
+                8 => presentation.scale = 1.25,
+                9 => presentation.transform = "rotate_90",
+                _ => unreachable!(),
+            }
+            let next = cache.get_or_update(
+                state,
+                [presentation].into_iter(),
+                false,
+                || json!({"changed": index}),
+            );
+            assert_eq!(*next, json!({"changed": index}));
+            assert!(!Arc::ptr_eq(&first, &next));
+        }
+    }
+}

compositor/src/ipc_events.rs

@@ -1,3 +1,4 @@
+use std::cell::RefCell;
 use std::collections::HashMap;
 use std::sync::Arc;
 use std::sync::mpsc::SyncSender;
@@ -18,6 +19,7 @@ pub(crate) struct Subscribers {
     previous: Option<Snapshot>,
     generation: u64,
     pub(crate) config_revision: u64,
+    pub(crate) outputs: RefCell<crate::ipc::outputs::Cache>,
 }
 
 impl Subscribers {
@@ -43,6 +45,7 @@ impl Subscribers {
         self.subscribers.remove(&owner);
         if self.subscribers.is_empty() {
             self.previous = None;
+            self.outputs.get_mut().clear();
         }
     }
 
@@ -121,6 +124,9 @@ impl Subscribers {
             delivered
         });
         self.previous = self.active().then_some(snapshot);
+        if !self.active() {
+            self.outputs.get_mut().clear();
+        }
     }
 }
 
@@ -246,7 +252,7 @@ mod tests {
 
     fn snapshot() -> Snapshot {
         Snapshot {
-            outputs: json!([]),
+            outputs: json!([]).into(),
             workspaces: json!([]),
             windows: Vec::new(),
             focus: json!(null),
@@ -272,7 +278,7 @@ mod tests {
         ));
         hub.publish(state.clone());
         assert!(matches!(receive.try_recv(), Err(TryRecvError::Empty)));
-        state.outputs = json!([{"id": 2}]);
+        state.outputs = json!([{"id": 2}]).into();
         state.workspaces = json!([{"output": 2}]);
         state.focus = json!({"output": 2});
         hub.publish(state);
@@ -356,7 +362,7 @@ mod tests {
         let mut state = snapshot();
         hub.publish(state.clone());
         receive.try_recv().unwrap();
-        state.outputs = json!([{"id": 1}]);
+        state.outputs = json!([{"id": 1}]).into();
         state.workspaces = json!([{"output": 1}]);
         state.windows = vec![ferese_ipc::events::Window {
             id: 7,

crates/ferese-ipc/src/events.rs

@@ -33,7 +33,7 @@ pub struct Window {
 /// A coherent logical desktop view. Desktop objects are redacted while locked.
 #[derive(Clone, Debug, Deserialize, Serialize, PartialEq)]
 pub struct Snapshot {
-    pub outputs: Value,
+    pub outputs: Arc<Value>,
     pub workspaces: Value,
     pub windows: Vec<Window>,
     pub focus: Value,
@@ -80,9 +80,9 @@ impl Snapshot {
     #[must_use]
     pub fn changes_since(&self, previous: &Self) -> Vec<Change> {
         let mut changes = Vec::new();
-        if self.outputs != previous.outputs {
+        if !Arc::ptr_eq(&self.outputs, &previous.outputs) && self.outputs != previous.outputs {
             changes.push(Change::OutputsChanged {
-                outputs: self.outputs.clone(),
+                outputs: self.outputs.as_ref().clone(),
             });
         }
         if self.workspaces != previous.workspaces {
@@ -123,6 +123,36 @@ impl Snapshot {
 mod tests {
     use super::*;
 
+    #[test]
+    fn shared_outputs_preserve_wire_fields_and_detect_value_changes() {
+        let outputs = serde_json::json!([{
+            "id": 1, "connector": "HDMI-A-1", "scale": 1.75,
+            "available_modes": [{"width": 3840, "height": 2160, "preferred": true}],
+            "configuration_error": null
+        }]);
+        let wire = serde_json::json!({
+            "outputs": outputs, "workspaces": [], "windows": [], "focus": null,
+            "config": {"revision": 0, "error": null}, "theme": null,
+            "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.outputs, &next.outputs));
+        assert!(next.changes_since(&snapshot).is_empty());
+        next.outputs = Arc::new(outputs.clone());
+        assert!(next.changes_since(&snapshot).is_empty());
+        next.outputs = serde_json::json!([]).into();
+        let changes = next.changes_since(&snapshot);
+        assert_eq!(
+            serde_json::to_value(&changes).unwrap(),
+            serde_json::json!([
+                {"type": "outputs_changed", "outputs": []}
+            ])
+        );
+        assert_eq!(*snapshot.outputs, outputs);
+    }
+
     #[test]
     fn typed_windows_preserve_snapshot_and_replacement_wire_fields() {
         let windows = serde_json::json!([{

portal/src/permissions.rs

@@ -527,7 +527,7 @@ mod tests {
                 last: true,
                 change: Change::Snapshot {
                     desktop: Box::new(ferese_ipc::events::Snapshot {
-                        outputs: serde_json::json!([]),
+                        outputs: serde_json::json!([]).into(),
                         workspaces: serde_json::json!([]),
                         windows: vec![window(1, "one.desktop", true, 1)],
                         focus: serde_json::json!({"window":1}),