Remove more IPC messages between script and layout (#32377)

Instead of bouncing messages from the compositor to script and then to
layout, just have script call methods on Layout. Additionally, we do not
need to send any followup messages to script for these messages. Instead
just execute code after calling the method on Layout.

components/compositing/compositor.rs

@@ -30,9 +30,8 @@ use pixels::{CorsStatus, Image, PixelFormat};
 use profile_traits::time::{self as profile_time, profile, ProfilerCategory};
 use script_traits::CompositorEvent::{MouseButtonEvent, MouseMoveEvent, TouchEvent, WheelEvent};
 use script_traits::{
-    AnimationState, AnimationTickType, ConstellationControlMsg, LayoutControlMsg, MouseButton,
+    AnimationState, AnimationTickType, ConstellationControlMsg, MouseButton, MouseEventType,
-    MouseEventType, ScrollState, TouchEventType, TouchId, WheelDelta, WindowSizeData,
+    ScrollState, TouchEventType, TouchId, WheelDelta, WindowSizeData, WindowSizeType,
-    WindowSizeType,
 };
 use servo_geometry::{DeviceIndependentPixel, FramebufferUintLength};
 use style_traits::{CSSPixel, DevicePixel, PinchZoomFactor};
@@ -1940,10 +1939,7 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
         });
 
         if let Some(pipeline) = details.pipeline.as_ref() {
-            let message = ConstellationControlMsg::ForLayoutFromConstellation(
+            let message = ConstellationControlMsg::SetScrollStates(*pipeline_id, scroll_states);
-                LayoutControlMsg::SetScrollStates(scroll_states),
-                *pipeline_id,
-            );
             let _ = pipeline.script_chan.send(message);
         }
     }
@@ -2154,11 +2150,14 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
                     to_remove.push(*id);
                     if let Some(pipeline) = self.pipeline(*id) {
                         // and inform layout with the measured paint time.
-                        let message = LayoutControlMsg::PaintMetric(epoch, paint_time);
+                        if let Err(e) =
-                        let message =
+                            pipeline
-                            ConstellationControlMsg::ForLayoutFromConstellation(message, *id);
+                                .script_chan
-                        if let Err(e) = pipeline.script_chan.send(message) {
+                                .send(ConstellationControlMsg::SetEpochPaintTime(
-                            warn!("Sending PaintMetric message to layout failed ({:?}).", e);
+                                    *id, epoch, paint_time,
+                                ))
+                        {
+                            warn!("Sending RequestLayoutPaintMetric message to layout failed ({e:?}).");
                         }
                     }
                 }

components/layout_thread/lib.rs

@@ -10,7 +10,6 @@
 
 use std::borrow::ToOwned;
 use std::cell::{Cell, RefCell};
-use std::collections::HashMap;
 use std::ops::{Deref, DerefMut};
 use std::process;
 use std::sync::{Arc, Mutex};
@@ -63,13 +62,12 @@ use profile_traits::time::{
 use script::layout_dom::{ServoLayoutDocument, ServoLayoutElement, ServoLayoutNode};
 use script_layout_interface::wrapper_traits::LayoutNode;
 use script_layout_interface::{
-    node_id_from_scroll_id, Layout, LayoutConfig, LayoutFactory, NodesFromPointQueryType,
+    Layout, LayoutConfig, LayoutFactory, NodesFromPointQueryType, OffsetParentResponse, Reflow,
-    OffsetParentResponse, Reflow, ReflowComplete, ReflowGoal, ScriptReflow, TrustedNodeAddress,
+    ReflowComplete, ReflowGoal, ScriptReflow, TrustedNodeAddress,
 };
 use script_traits::{
-    ConstellationControlMsg, DrawAPaintImageResult, IFrameSizeMsg, LayoutControlMsg,
+    ConstellationControlMsg, DrawAPaintImageResult, IFrameSizeMsg, LayoutMsg as ConstellationMsg,
-    LayoutMsg as ConstellationMsg, PaintWorkletError, Painter, ScrollState, UntrustedNodeAddress,
+    PaintWorkletError, Painter, ScrollState, UntrustedNodeAddress, WindowSizeData, WindowSizeType,
-    WindowSizeData, WindowSizeType,
 };
 use servo_arc::Arc as ServoArc;
 use servo_atoms::Atom;
@@ -245,20 +243,6 @@ impl Drop for ScriptReflowResult {
 }
 
 impl Layout for LayoutThread {
-    fn handle_constellation_message(
-        &mut self,
-        constellation_message: script_traits::LayoutControlMsg,
-    ) {
-        match constellation_message {
-            LayoutControlMsg::SetScrollStates(new_scroll_states) => {
-                self.set_scroll_states(new_scroll_states);
-            },
-            LayoutControlMsg::PaintMetric(epoch, paint_time) => {
-                self.paint_time_metrics.maybe_set_metric(epoch, paint_time);
-            },
-        }
-    }
-
     fn device(&self) -> &Device {
         self.stylist.device()
     }
@@ -550,6 +534,17 @@ impl Layout for LayoutThread {
             || self.handle_reflow(&mut result),
         );
     }
+
+    fn set_scroll_states(&mut self, scroll_states: &[ScrollState]) {
+        *self.scroll_offsets.borrow_mut() = scroll_states
+            .iter()
+            .map(|scroll_state| (scroll_state.scroll_id, scroll_state.scroll_offset))
+            .collect();
+    }
+
+    fn set_epoch_paint_time(&mut self, epoch: Epoch, paint_time: u64) {
+        self.paint_time_metrics.maybe_set_metric(epoch, paint_time);
+    }
 }
 impl LayoutThread {
     fn root_flow_for_query(&self) -> Option<FlowRef> {
@@ -1181,28 +1176,6 @@ impl LayoutThread {
         );
     }
 
-    fn set_scroll_states(&mut self, new_scroll_states: Vec<ScrollState>) {
-        let mut script_scroll_states = vec![];
-        let mut layout_scroll_states = HashMap::new();
-        for new_state in &new_scroll_states {
-            let offset = new_state.scroll_offset;
-            layout_scroll_states.insert(new_state.scroll_id, offset);
-
-            if new_state.scroll_id.is_root() {
-                script_scroll_states.push((UntrustedNodeAddress::from_id(0), offset))
-            } else if let Some(node_id) = node_id_from_scroll_id(new_state.scroll_id.0 as usize) {
-                script_scroll_states.push((UntrustedNodeAddress::from_id(node_id), offset))
-            }
-        }
-        let _ = self
-            .script_chan
-            .send(ConstellationControlMsg::SetScrollState(
-                self.id,
-                script_scroll_states,
-            ));
-        *self.scroll_offsets.borrow_mut() = layout_scroll_states
-    }
-
     /// Cancel animations for any nodes which have been removed from flow tree.
     /// TODO(mrobinson): We should look into a way of doing this during flow tree construction.
     /// This also doesn't yet handles nodes that have been reparented.

components/layout_thread_2020/lib.rs

@@ -50,13 +50,12 @@ use profile_traits::time::{
 };
 use script::layout_dom::{ServoLayoutDocument, ServoLayoutElement, ServoLayoutNode};
 use script_layout_interface::{
-    node_id_from_scroll_id, Layout, LayoutConfig, LayoutFactory, NodesFromPointQueryType,
+    Layout, LayoutConfig, LayoutFactory, NodesFromPointQueryType, OffsetParentResponse,
-    OffsetParentResponse, ReflowComplete, ReflowGoal, ScriptReflow, TrustedNodeAddress,
+    ReflowComplete, ReflowGoal, ScriptReflow, TrustedNodeAddress,
 };
 use script_traits::{
-    ConstellationControlMsg, DrawAPaintImageResult, IFrameSizeMsg, LayoutControlMsg,
+    ConstellationControlMsg, DrawAPaintImageResult, IFrameSizeMsg, LayoutMsg as ConstellationMsg,
-    LayoutMsg as ConstellationMsg, PaintWorkletError, Painter, ScrollState, UntrustedNodeAddress,
+    PaintWorkletError, Painter, ScrollState, UntrustedNodeAddress, WindowSizeData, WindowSizeType,
-    WindowSizeData, WindowSizeType,
 };
 use servo_arc::Arc as ServoArc;
 use servo_atoms::Atom;
@@ -221,20 +220,6 @@ impl Drop for ScriptReflowResult {
 }
 
 impl Layout for LayoutThread {
-    fn handle_constellation_message(
-        &mut self,
-        constellation_message: script_traits::LayoutControlMsg,
-    ) {
-        match constellation_message {
-            LayoutControlMsg::SetScrollStates(new_scroll_states) => {
-                self.set_scroll_states(new_scroll_states);
-            },
-            LayoutControlMsg::PaintMetric(epoch, paint_time) => {
-                self.paint_time_metrics.maybe_set_metric(epoch, paint_time);
-            },
-        }
-    }
-
     fn device(&self) -> &Device {
         self.stylist.device()
     }
@@ -469,6 +454,17 @@ impl Layout for LayoutThread {
         _painter: Box<dyn Painter>,
     ) {
     }
+
+    fn set_scroll_states(&mut self, scroll_states: &[ScrollState]) {
+        *self.scroll_offsets.borrow_mut() = scroll_states
+            .iter()
+            .map(|scroll_state| (scroll_state.scroll_id, scroll_state.scroll_offset))
+            .collect();
+    }
+
+    fn set_epoch_paint_time(&mut self, epoch: Epoch, paint_time: u64) {
+        self.paint_time_metrics.maybe_set_metric(epoch, paint_time);
+    }
 }
 
 impl LayoutThread {
@@ -831,28 +827,6 @@ impl LayoutThread {
         );
     }
 
-    fn set_scroll_states(&mut self, new_scroll_states: Vec<ScrollState>) {
-        let mut script_scroll_states = vec![];
-        let mut layout_scroll_states = HashMap::new();
-        for new_state in &new_scroll_states {
-            let offset = new_state.scroll_offset;
-            layout_scroll_states.insert(new_state.scroll_id, offset);
-
-            if new_state.scroll_id.is_root() {
-                script_scroll_states.push((UntrustedNodeAddress::from_id(0), offset))
-            } else if let Some(node_id) = node_id_from_scroll_id(new_state.scroll_id.0 as usize) {
-                script_scroll_states.push((UntrustedNodeAddress::from_id(node_id), offset))
-            }
-        }
-        let _ = self
-            .script_chan
-            .send(ConstellationControlMsg::SetScrollState(
-                self.id,
-                script_scroll_states,
-            ));
-        self.scroll_offsets = RefCell::new(layout_scroll_states);
-    }
-
     fn perform_post_style_recalc_layout_passes(
         &self,
         fragment_tree: Arc<FragmentTree>,

components/script/script_thread.rs

@@ -26,8 +26,8 @@ use std::rc::Rc;
 use std::result::Result;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
+use std::thread;
 use std::time::{Duration, Instant, SystemTime, UNIX_EPOCH};
-use std::{ptr, thread};
 
 use background_hang_monitor_api::{
     BackgroundHangMonitor, BackgroundHangMonitorExitSignal, HangAnnotation, MonitoredComponentId,
@@ -36,6 +36,7 @@ use background_hang_monitor_api::{
 use base::id::{
     BrowsingContextId, HistoryStateId, PipelineId, PipelineNamespace, TopLevelBrowsingContextId,
 };
+use base::Epoch;
 use bluetooth_traits::BluetoothRequest;
 use canvas_traits::webgl::WebGLPipeline;
 use chrono::{DateTime, Local};
@@ -46,7 +47,6 @@ use devtools_traits::{
 };
 use embedder_traits::EmbedderMsg;
 use euclid::default::{Point2D, Rect};
-use euclid::Vector2D;
 use gfx::font_cache_thread::FontCacheThread;
 use headers::{HeaderMapExt, LastModified, ReferrerPolicy as ReferrerPolicyHeader};
 use html5ever::{local_name, namespace_url, ns};
@@ -73,13 +73,15 @@ use parking_lot::Mutex;
 use percent_encoding::percent_decode;
 use profile_traits::mem::{self as profile_mem, OpaqueSender, ReportsChan};
 use profile_traits::time::{self as profile_time, profile, ProfilerCategory};
-use script_layout_interface::{LayoutConfig, LayoutFactory, ReflowGoal, ScriptThreadFactory};
+use script_layout_interface::{
+    node_id_from_scroll_id, LayoutConfig, LayoutFactory, ReflowGoal, ScriptThreadFactory,
+};
 use script_traits::webdriver_msg::WebDriverScriptCommand;
 use script_traits::{
     CompositorEvent, ConstellationControlMsg, DiscardBrowsingContext, DocumentActivity,
-    EventResult, HistoryEntryReplacement, InitialScriptState, JsEvalResult, LayoutControlMsg,
+    EventResult, HistoryEntryReplacement, InitialScriptState, JsEvalResult, LayoutMsg, LoadData,
-    LayoutMsg, LoadData, LoadOrigin, MediaSessionActionType, MouseButton, MouseEventType,
+    LoadOrigin, MediaSessionActionType, MouseButton, MouseEventType, NewLayoutInfo, Painter,
-    NewLayoutInfo, Painter, ProgressiveWebMetricType, ScriptMsg, ScriptToConstellationChan,
+    ProgressiveWebMetricType, ScriptMsg, ScriptToConstellationChan, ScrollState,
     StructuredSerializedData, TimerSchedulerMsg, TouchEventType, TouchId, UntrustedNodeAddress,
     UpdatePipelineIdReason, WheelDelta, WindowSizeData, WindowSizeType,
 };
@@ -91,7 +93,6 @@ use style::thread_state::{self, ThreadState};
 use time::precise_time_ns;
 use url::Position;
 use webgpu::WebGPUMsg;
-use webrender_api::units::LayoutPixel;
 use webrender_api::DocumentId;
 use webrender_traits::WebRenderScriptApi;
 
@@ -1836,11 +1837,6 @@ impl ScriptThread {
                     .profile_event(ScriptThreadEventCategory::SetViewport, Some(id), || {
                         self.handle_viewport(id, rect);
                     }),
-                FromConstellation(ConstellationControlMsg::SetScrollState(id, scroll_state)) => {
-                    self.profile_event(ScriptThreadEventCategory::SetScrollState, Some(id), || {
-                        self.handle_set_scroll_state(id, &scroll_state);
-                    })
-                },
                 FromConstellation(ConstellationControlMsg::TickAllAnimations(
                     pipeline_id,
                     tick_type,
@@ -2097,7 +2093,6 @@ impl ScriptThread {
                 ExitScriptThread => None,
                 SendEvent(id, ..) => Some(id),
                 Viewport(id, ..) => Some(id),
-                SetScrollState(id, ..) => Some(id),
                 GetTitle(id) => Some(id),
                 SetDocumentActivity(id, ..) => Some(id),
                 SetThrottled(id, ..) => Some(id),
@@ -2123,7 +2118,8 @@ impl ScriptThread {
                 ExitFullScreen(id, ..) => Some(id),
                 MediaSessionAction(..) => None,
                 SetWebGPUPort(..) => None,
-                ForLayoutFromConstellation(_, id) => Some(id),
+                SetScrollStates(id, ..) => Some(id),
+                SetEpochPaintTime(id, ..) => Some(id),
             },
             MixedMessage::FromDevtools(_) => None,
             MixedMessage::FromScript(ref inner_msg) => match *inner_msg {
@@ -2348,7 +2344,6 @@ impl ScriptThread {
             },
             msg @ ConstellationControlMsg::AttachLayout(..) |
             msg @ ConstellationControlMsg::Viewport(..) |
-            msg @ ConstellationControlMsg::SetScrollState(..) |
             msg @ ConstellationControlMsg::Resize(..) |
             msg @ ConstellationControlMsg::ExitFullScreen(..) |
             msg @ ConstellationControlMsg::SendEvent(..) |
@@ -2356,22 +2351,53 @@ impl ScriptThread {
             msg @ ConstellationControlMsg::ExitScriptThread => {
                 panic!("should have handled {:?} already", msg)
             },
-            ConstellationControlMsg::ForLayoutFromConstellation(msg, pipeline_id) => {
+            ConstellationControlMsg::SetScrollStates(pipeline_id, scroll_states) => {
-                self.handle_layout_message_from_constellation(msg, pipeline_id)
+                self.handle_set_scroll_states_msg(pipeline_id, scroll_states)
+            },
+            ConstellationControlMsg::SetEpochPaintTime(pipeline_id, epoch, time) => {
+                self.handle_set_epoch_paint_time(pipeline_id, epoch, time)
             },
         }
     }
 
-    fn handle_layout_message_from_constellation(
+    fn handle_set_scroll_states_msg(
         &self,
-        msg: LayoutControlMsg,
         pipeline_id: PipelineId,
+        scroll_states: Vec<ScrollState>,
     ) {
         let Some(window) = self.documents.borrow().find_window(pipeline_id) else {
-            warn!("Received layout message pipeline {pipeline_id} closed: {msg:?}.");
+            warn!("Received scroll states for closed pipeline {pipeline_id}");
             return;
         };
-        window.layout_mut().handle_constellation_message(msg);
+
+        self.profile_event(
+            ScriptThreadEventCategory::SetScrollState,
+            Some(pipeline_id),
+            || {
+                window.layout_mut().set_scroll_states(&scroll_states);
+
+                let mut scroll_offsets = HashMap::new();
+                for scroll_state in scroll_states.into_iter() {
+                    let scroll_offset = scroll_state.scroll_offset;
+                    if scroll_state.scroll_id.is_root() {
+                        window.update_viewport_for_scroll(-scroll_offset.x, -scroll_offset.y);
+                    } else if let Some(node_id) =
+                        node_id_from_scroll_id(scroll_state.scroll_id.0 as usize)
+                    {
+                        scroll_offsets.insert(OpaqueNode(node_id), -scroll_offset);
+                    }
+                }
+                window.set_scroll_offsets(scroll_offsets)
+            },
+        )
+    }
+
+    fn handle_set_epoch_paint_time(&self, pipeline_id: PipelineId, epoch: Epoch, time: u64) {
+        let Some(window) = self.documents.borrow().find_window(pipeline_id) else {
+            warn!("Received set epoch paint time message for closed pipeline {pipeline_id}.");
+            return;
+        };
+        window.layout_mut().set_epoch_paint_time(epoch, time);
     }
 
     fn handle_msg_from_webgpu_server(&self, msg: WebGPUMsg) {
@@ -2763,32 +2789,6 @@ impl ScriptThread {
         warn!("Page rect message sent to nonexistent pipeline");
     }
 
-    fn handle_set_scroll_state(
-        &self,
-        id: PipelineId,
-        scroll_states: &[(UntrustedNodeAddress, Vector2D<f32, LayoutPixel>)],
-    ) {
-        let window = match self.documents.borrow().find_window(id) {
-            Some(window) => window,
-            None => {
-                return warn!(
-                    "Set scroll state message sent to nonexistent pipeline: {:?}",
-                    id
-                );
-            },
-        };
-
-        let mut scroll_offsets = HashMap::new();
-        for &(node_address, ref scroll_offset) in scroll_states {
-            if node_address == UntrustedNodeAddress(ptr::null()) {
-                window.update_viewport_for_scroll(-scroll_offset.x, -scroll_offset.y);
-            } else {
-                scroll_offsets.insert(OpaqueNode(node_address.0 as usize), -*scroll_offset);
-            }
-        }
-        window.set_scroll_offsets(scroll_offsets)
-    }
-
     fn handle_new_layout(&self, new_layout_info: NewLayoutInfo, origin: MutableOrigin) {
         let NewLayoutInfo {
             parent_info,

components/shared/script/lib.rs

@@ -110,15 +110,6 @@ impl UntrustedNodeAddress {
     }
 }
 
-/// Messages sent to layout from the constellation and/or compositor.
-#[derive(Debug, Deserialize, Serialize)]
-pub enum LayoutControlMsg {
-    /// Tells layout about the new scrolling offsets of each scrollable stacking context.
-    SetScrollStates(Vec<ScrollState>),
-    /// Send the paint time for a specific epoch to layout.
-    PaintMetric(Epoch, u64),
-}
-
 /// The origin where a given load was initiated.
 /// Useful for origin checks, for example before evaluation a JS URL.
 #[derive(Clone, Debug, Deserialize, Serialize)]
@@ -302,11 +293,6 @@ pub enum ConstellationControlMsg {
     SendEvent(PipelineId, CompositorEvent),
     /// Notifies script of the viewport.
     Viewport(PipelineId, Rect<f32, UnknownUnit>),
-    /// Notifies script of a new set of scroll offsets.
-    SetScrollState(
-        PipelineId,
-        Vec<(UntrustedNodeAddress, Vector2D<f32, LayoutPixel>)>,
-    ),
     /// Requests that the script thread immediately send the constellation the title of a pipeline.
     GetTitle(PipelineId),
     /// Notifies script thread of a change to one of its document's activity
@@ -391,8 +377,11 @@ pub enum ConstellationControlMsg {
     MediaSessionAction(PipelineId, MediaSessionActionType),
     /// Notifies script thread that WebGPU server has started
     SetWebGPUPort(IpcReceiver<WebGPUMsg>),
-    /// A mesage for a layout from the constellation.
+    /// The compositor scrolled and is updating the scroll states of the nodes in the given
-    ForLayoutFromConstellation(LayoutControlMsg, PipelineId),
+    /// pipeline via the Constellation.
+    SetScrollStates(PipelineId, Vec<ScrollState>),
+    /// Send the paint time for a specific epoch.
+    SetEpochPaintTime(PipelineId, Epoch, u64),
 }
 
 impl fmt::Debug for ConstellationControlMsg {
@@ -409,7 +398,6 @@ impl fmt::Debug for ConstellationControlMsg {
             ExitScriptThread => "ExitScriptThread",
             SendEvent(..) => "SendEvent",
             Viewport(..) => "Viewport",
-            SetScrollState(..) => "SetScrollState",
             GetTitle(..) => "GetTitle",
             SetDocumentActivity(..) => "SetDocumentActivity",
             SetThrottled(..) => "SetThrottled",
@@ -431,7 +419,8 @@ impl fmt::Debug for ConstellationControlMsg {
             ExitFullScreen(..) => "ExitFullScreen",
             MediaSessionAction(..) => "MediaSessionAction",
             SetWebGPUPort(..) => "SetWebGPUPort",
-            ForLayoutFromConstellation(..) => "ForLayoutFromConstellation",
+            SetScrollStates(..) => "SetScrollStates",
+            SetEpochPaintTime(..) => "SetEpochPaintTime",
         };
         write!(formatter, "ConstellationControlMsg::{}", variant)
     }

components/shared/script_layout/lib.rs

@@ -33,8 +33,8 @@ use net_traits::ResourceThreads;
 use profile_traits::mem::Report;
 use profile_traits::time;
 use script_traits::{
-    ConstellationControlMsg, InitialScriptState, LayoutControlMsg, LayoutMsg, LoadData, Painter,
+    ConstellationControlMsg, InitialScriptState, LayoutMsg, LoadData, Painter, ScrollState,
-    ScrollState, UntrustedNodeAddress, WindowSizeData,
+    UntrustedNodeAddress, WindowSizeData,
 };
 use serde::{Deserialize, Serialize};
 use servo_arc::Arc as ServoArc;
@@ -178,9 +178,6 @@ pub trait LayoutFactory: Send + Sync {
 }
 
 pub trait Layout {
-    /// Handle a single message from the Constellation.
-    fn handle_constellation_message(&mut self, msg: LayoutControlMsg);
-
     /// Get a reference to this Layout's Stylo `Device` used to handle media queries and
     /// resolve font metrics.
     fn device(&self) -> &Device;
@@ -228,6 +225,12 @@ pub trait Layout {
         painter: Box<dyn Painter>,
     );
 
+    /// Set the scroll states of this layout after a compositor scroll.
+    fn set_scroll_states(&mut self, scroll_states: &[ScrollState]);
+
+    /// Set the paint time for a specific epoch.
+    fn set_epoch_paint_time(&mut self, epoch: Epoch, paint_time: u64);
+
     fn query_content_box(&self, node: OpaqueNode) -> Option<Rect<Au>>;
     fn query_content_boxes(&self, node: OpaqueNode) -> Vec<Rect<Au>>;
     fn query_client_rect(&self, node: OpaqueNode) -> Rect<i32>;