constellation: Use FnvHashMap for hashmaps that use ids as keys (#39106)

FNV is faster for hashing less than 16 bytes of data and the
cryptographic properties of the default HashMap are not needed for the
various ids.

Testing: This does not change functionality.

Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>

Cargo.lock

@@ -1500,6 +1500,7 @@ dependencies = [
  "dpi",
  "embedder_traits",
  "euclid",
+ "fnv",
  "gleam",
  "glow",
  "image",
@@ -1563,6 +1564,7 @@ dependencies = [
  "devtools_traits",
  "embedder_traits",
  "euclid",
+ "fnv",
  "fonts",
  "gaol",
  "ipc-channel",
@@ -1601,6 +1603,7 @@ dependencies = [
  "devtools_traits",
  "embedder_traits",
  "euclid",
+ "fnv",
  "fonts_traits",
  "http 1.3.1",
  "hyper_serde",
@@ -7459,6 +7462,7 @@ dependencies = [
  "devtools_traits",
  "embedder_traits",
  "euclid",
+ "fnv",
  "ipc-channel",
  "keyboard-types",
  "log",

components/compositing/compositor.rs

@@ -28,6 +28,7 @@ use crossbeam_channel::Sender;
 use dpi::PhysicalSize;
 use embedder_traits::{CompositorHitTestResult, InputEvent, ShutdownState, ViewportDetails};
 use euclid::{Point2D, Rect, Scale, Size2D, Transform3D};
+use fnv::FnvHashMap;
 use ipc_channel::ipc::{self, IpcSharedMemory};
 use log::{debug, info, trace, warn};
 use pixels::{CorsStatus, ImageFrame, ImageMetadata, PixelFormat, RasterImage};
@@ -1183,7 +1184,7 @@ impl IOCompositor {
                 // complete (i.e. has *all* layers painted to the requested epoch).
                 // This gets sent to the constellation for comparison with the current
                 // frame tree.
-                let mut pipeline_epochs = HashMap::new();
+                let mut pipeline_epochs = FnvHashMap::default();
                 for id in self
                     .webview_renderers
                     .iter()

components/constellation/Cargo.toml

@@ -38,6 +38,7 @@ devtools_traits = { workspace = true }
 embedder_traits = { workspace = true }
 euclid = { workspace = true }
 fonts = { path = "../fonts" }
+fnv = { workspace = true }
 ipc-channel = { workspace = true }
 keyboard-types = { workspace = true }
 layout_api = { workspace = true }

components/constellation/broadcastchannel.rs

@@ -6,6 +6,7 @@ use std::collections::HashMap;
 
 use base::id::BroadcastChannelRouterId;
 use constellation_traits::BroadcastChannelMsg;
+use fnv::FnvHashMap;
 use ipc_channel::ipc::IpcSender;
 use log::warn;
 use servo_url::ImmutableOrigin;
@@ -13,7 +14,7 @@ use servo_url::ImmutableOrigin;
 #[derive(Default)]
 pub(crate) struct BroadcastChannels {
     /// A map of broadcast routers to their IPC sender.
-    routers: HashMap<BroadcastChannelRouterId, IpcSender<BroadcastChannelMsg>>,
+    routers: FnvHashMap<BroadcastChannelRouterId, IpcSender<BroadcastChannelMsg>>,
 
     /// A map of origin to a map of channel name to a list of relevant routers.
     channels: HashMap<ImmutableOrigin, HashMap<String, Vec<BroadcastChannelRouterId>>>,

components/constellation/browsingcontext.rs

@@ -2,10 +2,9 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-use std::collections::{HashMap, HashSet};
-
 use base::id::{BrowsingContextGroupId, BrowsingContextId, PipelineId, WebViewId};
 use embedder_traits::ViewportDetails;
+use fnv::{FnvHashMap, FnvHashSet};
 use log::warn;
 
 use crate::pipeline::Pipeline;
@@ -71,7 +70,7 @@ pub struct BrowsingContext {
 
     /// All the pipelines that have been presented or will be presented in
     /// this browsing context.
-    pub pipelines: HashSet<PipelineId>,
+    pub pipelines: FnvHashSet<PipelineId>,
 }
 
 impl BrowsingContext {
@@ -89,7 +88,7 @@ impl BrowsingContext {
         inherited_secure_context: Option<bool>,
         throttled: bool,
     ) -> BrowsingContext {
-        let mut pipelines = HashSet::new();
+        let mut pipelines = FnvHashSet::default();
         pipelines.insert(pipeline_id);
         BrowsingContext {
             bc_group_id,
@@ -123,12 +122,12 @@ pub struct FullyActiveBrowsingContextsIterator<'a> {
     pub stack: Vec<BrowsingContextId>,
 
     /// The set of all browsing contexts.
-    pub browsing_contexts: &'a HashMap<BrowsingContextId, BrowsingContext>,
+    pub browsing_contexts: &'a FnvHashMap<BrowsingContextId, BrowsingContext>,
 
     /// The set of all pipelines.  We use this to find the active
     /// children of a frame, which are the iframes in the currently
     /// active document.
-    pub pipelines: &'a HashMap<PipelineId, Pipeline>,
+    pub pipelines: &'a FnvHashMap<PipelineId, Pipeline>,
 }
 
 impl<'a> Iterator for FullyActiveBrowsingContextsIterator<'a> {
@@ -170,12 +169,12 @@ pub struct AllBrowsingContextsIterator<'a> {
     pub stack: Vec<BrowsingContextId>,
 
     /// The set of all browsing contexts.
-    pub browsing_contexts: &'a HashMap<BrowsingContextId, BrowsingContext>,
+    pub browsing_contexts: &'a FnvHashMap<BrowsingContextId, BrowsingContext>,
 
     /// The set of all pipelines.  We use this to find the
     /// children of a browsing context, which are the iframes in all documents
     /// in the session history.
-    pub pipelines: &'a HashMap<PipelineId, Pipeline>,
+    pub pipelines: &'a FnvHashMap<PipelineId, Pipeline>,
 }
 
 impl<'a> Iterator for AllBrowsingContextsIterator<'a> {

components/constellation/constellation.rs

@@ -139,6 +139,7 @@ use embedder_traits::{
 };
 use euclid::Size2D;
 use euclid::default::Size2D as UntypedSize2D;
+use fnv::{FnvHashMap, FnvHashSet};
 use fonts::SystemFontServiceProxy;
 use ipc_channel::Error as IpcError;
 use ipc_channel::ipc::{self, IpcReceiver, IpcSender};
@@ -240,7 +241,7 @@ struct WebrenderWGPU {
 #[derive(Clone, Default)]
 struct BrowsingContextGroup {
     /// A browsing context group holds a set of top-level browsing contexts.
-    top_level_browsing_context_set: HashSet<WebViewId>,
+    top_level_browsing_context_set: FnvHashSet<WebViewId>,
 
     /// The set of all event loops in this BrowsingContextGroup.
     /// We store the event loops in a map
@@ -384,25 +385,25 @@ pub struct Constellation<STF, SWF> {
     webrender_wgpu: WebrenderWGPU,
 
     /// A map of message-port Id to info.
-    message_ports: HashMap<MessagePortId, MessagePortInfo>,
+    message_ports: FnvHashMap<MessagePortId, MessagePortInfo>,
 
     /// A map of router-id to ipc-sender, to route messages to ports.
-    message_port_routers: HashMap<MessagePortRouterId, IpcSender<MessagePortMsg>>,
+    message_port_routers: FnvHashMap<MessagePortRouterId, IpcSender<MessagePortMsg>>,
 
     /// Bookkeeping for BroadcastChannel functionnality.
     broadcast_channels: BroadcastChannels,
 
     /// The set of all the pipelines in the browser.  (See the `pipeline` module
     /// for more details.)
-    pipelines: HashMap<PipelineId, Pipeline>,
+    pipelines: FnvHashMap<PipelineId, Pipeline>,
 
     /// The set of all the browsing contexts in the browser.
-    browsing_contexts: HashMap<BrowsingContextId, BrowsingContext>,
+    browsing_contexts: FnvHashMap<BrowsingContextId, BrowsingContext>,
 
     /// A user agent holds a a set of browsing context groups.
     ///
     /// <https://html.spec.whatwg.org/multipage/#browsing-context-group-set>
-    browsing_context_group_set: HashMap<BrowsingContextGroupId, BrowsingContextGroup>,
+    browsing_context_group_set: FnvHashMap<BrowsingContextGroupId, BrowsingContextGroup>,
 
     /// The Id counter for BrowsingContextGroup.
     browsing_context_group_next_id: u32,
@@ -425,7 +426,7 @@ pub struct Constellation<STF, SWF> {
     webdriver_input_command_reponse_sender: Option<IpcSender<WebDriverCommandResponse>>,
 
     /// Document states for loaded pipelines (used only when writing screenshots).
-    document_states: HashMap<PipelineId, DocumentState>,
+    document_states: FnvHashMap<PipelineId, DocumentState>,
 
     /// Are we shutting down?
     shutting_down: bool,
@@ -481,7 +482,7 @@ pub struct Constellation<STF, SWF> {
     async_runtime: Box<dyn AsyncRuntime>,
 
     /// When in single-process mode, join handles for script-threads.
-    script_join_handles: HashMap<WebViewId, JoinHandle<()>>,
+    script_join_handles: FnvHashMap<WebViewId, JoinHandle<()>>,
 
     /// A list of URLs that can access privileged internal APIs.
     privileged_urls: Vec<ServoUrl>,
@@ -696,11 +697,11 @@ where
                     swmanager_ipc_sender,
                     browsing_context_group_set: Default::default(),
                     browsing_context_group_next_id: Default::default(),
-                    message_ports: HashMap::new(),
+                    message_ports: Default::default(),
-                    message_port_routers: HashMap::new(),
+                    message_port_routers: Default::default(),
                     broadcast_channels: Default::default(),
-                    pipelines: HashMap::new(),
+                    pipelines: Default::default(),
-                    browsing_contexts: HashMap::new(),
+                    browsing_contexts: Default::default(),
                     pending_changes: vec![],
                     // We initialize the namespace at 2, since we reserved
                     // namespace 0 for the embedder, and 0 for the constellation
@@ -710,7 +711,7 @@ where
                     phantom: PhantomData,
                     webdriver_load_status_sender: None,
                     webdriver_input_command_reponse_sender: None,
-                    document_states: HashMap::new(),
+                    document_states: Default::default(),
                     #[cfg(feature = "webgpu")]
                     webrender_wgpu,
                     shutting_down: false,
@@ -725,7 +726,7 @@ where
                     webgl_threads: state.webgl_threads,
                     webxr_registry: state.webxr_registry,
                     canvas: OnceCell::new(),
-                    pending_approval_navigations: HashMap::new(),
+                    pending_approval_navigations: Default::default(),
                     pressed_mouse_buttons: 0,
                     active_keyboard_modifiers: Modifiers::empty(),
                     hard_fail,
@@ -2119,7 +2120,7 @@ where
 
     fn handle_message_port_transfer_failed(
         &mut self,
-        ports: HashMap<MessagePortId, PortTransferInfo>,
+        ports: FnvHashMap<MessagePortId, PortTransferInfo>,
     ) {
         for (port_id, mut transfer_info) in ports.into_iter() {
             let entry = match self.message_ports.remove(&port_id) {
@@ -2201,7 +2202,7 @@ where
         router_id: MessagePortRouterId,
         ports: Vec<MessagePortId>,
     ) {
-        let mut response = HashMap::new();
+        let mut response = FnvHashMap::default();
         for port_id in ports.into_iter() {
             let entry = match self.message_ports.remove(&port_id) {
                 None => {
@@ -3784,9 +3785,11 @@ where
         webview_id: WebViewId,
         direction: TraversalDirection,
     ) {
-        let mut browsing_context_changes = HashMap::<BrowsingContextId, NeedsToReload>::new();
+        let mut browsing_context_changes =
-        let mut pipeline_changes = HashMap::<PipelineId, (Option<HistoryStateId>, ServoUrl)>::new();
+            FnvHashMap::<BrowsingContextId, NeedsToReload>::default();
-        let mut url_to_load = HashMap::<PipelineId, ServoUrl>::new();
+        let mut pipeline_changes =
+            FnvHashMap::<PipelineId, (Option<HistoryStateId>, ServoUrl)>::default();
+        let mut url_to_load = FnvHashMap::<PipelineId, ServoUrl>::default();
         {
             let session_history = self.get_joint_session_history(webview_id);
             match direction {
@@ -4792,7 +4795,7 @@ where
                     };
 
                     let mut pipelines_to_close = vec![];
-                    let mut states_to_close = HashMap::new();
+                    let mut states_to_close = FnvHashMap::default();
 
                     let diffs_to_close = self
                         .get_joint_session_history(change.webview_id)
@@ -5049,7 +5052,7 @@ where
     #[servo_tracing::instrument(skip_all)]
     fn handle_is_ready_to_save_image(
         &mut self,
-        pipeline_states: HashMap<PipelineId, Epoch>,
+        pipeline_states: FnvHashMap<PipelineId, Epoch>,
     ) -> ReadyToSave {
         // Note that this function can panic, due to ipc-channel creation
         // failure. Avoiding this panic would require a mechanism for dealing
@@ -5593,7 +5596,7 @@ where
     fn handle_set_scroll_states(
         &self,
         pipeline_id: PipelineId,
-        scroll_states: HashMap<ExternalScrollId, LayoutVector2D>,
+        scroll_states: FnvHashMap<ExternalScrollId, LayoutVector2D>,
     ) {
         let Some(pipeline) = self.pipelines.get(&pipeline_id) else {
             warn!("Discarding scroll offset update for unknown pipeline");

components/constellation/constellation_webview.rs

@@ -2,11 +2,10 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-use std::collections::HashMap;
-
 use base::id::{BrowsingContextId, PipelineId};
 use embedder_traits::{InputEvent, MouseLeftViewportEvent, Theme};
 use euclid::Point2D;
+use fnv::FnvHashMap;
 use log::warn;
 use script_traits::{ConstellationInputEvent, ScriptThreadMessage};
 use style_traits::CSSPixel;
@@ -64,7 +63,7 @@ impl ConstellationWebView {
     fn target_pipeline_id_for_input_event(
         &self,
         event: &ConstellationInputEvent,
-        browsing_contexts: &HashMap<BrowsingContextId, BrowsingContext>,
+        browsing_contexts: &FnvHashMap<BrowsingContextId, BrowsingContext>,
     ) -> Option<PipelineId> {
         if let Some(hit_test_result) = &event.hit_test_result {
             return Some(hit_test_result.pipeline_id);
@@ -85,8 +84,8 @@ impl ConstellationWebView {
     pub(crate) fn forward_input_event(
         &mut self,
         event: ConstellationInputEvent,
-        pipelines: &HashMap<PipelineId, Pipeline>,
+        pipelines: &FnvHashMap<PipelineId, Pipeline>,
-        browsing_contexts: &HashMap<BrowsingContextId, BrowsingContext>,
+        browsing_contexts: &FnvHashMap<BrowsingContextId, BrowsingContext>,
     ) {
         let Some(pipeline_id) = self.target_pipeline_id_for_input_event(&event, browsing_contexts)
         else {

components/constellation/webview_manager.rs

@@ -5,12 +5,13 @@
 use std::collections::HashMap;
 
 use base::id::WebViewId;
+use fnv::FnvHashMap;
 
 #[derive(Debug)]
 pub struct WebViewManager<WebView> {
     /// Our top-level browsing contexts. In the WebRender scene, their pipelines are the children of
     /// a single root pipeline that also applies any pinch zoom transformation.
-    webviews: HashMap<WebViewId, WebView>,
+    webviews: FnvHashMap<WebViewId, WebView>,
 
     /// The order in which they were focused, latest last.
     focus_order: Vec<WebViewId>,

components/layout/layout_impl.rs

@@ -5,7 +5,6 @@
 #![allow(unsafe_code)]
 
 use std::cell::{Cell, RefCell};
-use std::collections::HashMap;
 use std::fmt::Debug;
 use std::process;
 use std::rc::Rc;
@@ -503,7 +502,7 @@ impl Layout for LayoutThread {
 
     fn set_scroll_offsets_from_renderer(
         &mut self,
-        scroll_states: &HashMap<ExternalScrollId, LayoutVector2D>,
+        scroll_states: &FnvHashMap<ExternalScrollId, LayoutVector2D>,
     ) {
         let mut stacking_context_tree = self.stacking_context_tree.borrow_mut();
         let Some(stacking_context_tree) = stacking_context_tree.as_mut() else {

components/script/dom/globalscope.rs

@@ -27,6 +27,7 @@ use crossbeam_channel::Sender;
 use devtools_traits::{PageError, ScriptToDevtoolsControlMsg};
 use dom_struct::dom_struct;
 use embedder_traits::{EmbedderMsg, JavaScriptEvaluationError, ScriptToEmbedderChan};
+use fnv::FnvHashMap;
 use fonts::FontContext;
 use ipc_channel::ipc::{self, IpcSender};
 use ipc_channel::router::ROUTER;
@@ -561,7 +562,7 @@ impl MessageListener {
                         };
 
                         let mut succeeded = vec![];
-                        let mut failed = HashMap::new();
+                        let mut failed = FnvHashMap::default();
 
                         for (id, info) in ports.into_iter() {
                             if global.is_managing_port(&id) {

components/script/script_thread.rs

@@ -55,6 +55,7 @@ use embedder_traits::{
 };
 use euclid::Point2D;
 use euclid::default::Rect;
+use fnv::FnvHashMap;
 use fonts::{FontContext, SystemFontServiceProxy};
 use headers::{HeaderMapExt, LastModified, ReferrerPolicy as ReferrerPolicyHeader};
 use http::header::REFRESH;
@@ -1943,7 +1944,7 @@ impl ScriptThread {
     fn handle_set_scroll_states(
         &self,
         pipeline_id: PipelineId,
-        scroll_states: HashMap<ExternalScrollId, LayoutVector2D>,
+        scroll_states: FnvHashMap<ExternalScrollId, LayoutVector2D>,
     ) {
         let Some(window) = self.documents.borrow().find_window(pipeline_id) else {
             warn!("Received scroll states for closed pipeline {pipeline_id}");

components/shared/compositing/Cargo.toml

@@ -22,6 +22,7 @@ crossbeam-channel = { workspace = true }
 dpi = { version = "0.1" }
 embedder_traits = { workspace = true }
 euclid = { workspace = true }
+fnv = { workspace = true }
 gleam = { workspace = true }
 glow = { workspace = true }
 image = { workspace = true }

components/shared/compositing/display_list.rs

@@ -12,6 +12,7 @@ use base::print_tree::PrintTree;
 use bitflags::bitflags;
 use embedder_traits::ViewportDetails;
 use euclid::SideOffsets2D;
+use fnv::FnvHashMap;
 use malloc_size_of_derive::MallocSizeOf;
 use serde::{Deserialize, Serialize};
 use servo_geometry::FastLayoutTransform;
@@ -558,7 +559,10 @@ impl ScrollTree {
 
     /// Given a set of all scroll offsets coming from the Servo renderer, update all of the offsets
     /// for nodes that actually exist in this tree.
-    pub fn set_all_scroll_offsets(&mut self, offsets: &HashMap<ExternalScrollId, LayoutVector2D>) {
+    pub fn set_all_scroll_offsets(
+        &mut self,
+        offsets: &FnvHashMap<ExternalScrollId, LayoutVector2D>,
+    ) {
         for node in self.nodes.iter_mut() {
             if let SpatialTreeNodeInfo::Scroll(ref mut scroll_info) = node.info {
                 if let Some(offset) = offsets.get(&scroll_info.external_id) {
@@ -583,7 +587,7 @@ impl ScrollTree {
 
     /// Collect all of the scroll offsets of the scrolling nodes of this tree into a
     /// [`HashMap`] which can be applied to another tree.
-    pub fn scroll_offsets(&self) -> HashMap<ExternalScrollId, LayoutVector2D> {
+    pub fn scroll_offsets(&self) -> FnvHashMap<ExternalScrollId, LayoutVector2D> {
         HashMap::from_iter(self.nodes.iter().filter_map(|node| match node.info {
             SpatialTreeNodeInfo::Scroll(ref scroll_info) => {
                 Some((scroll_info.external_id, scroll_info.offset))

components/shared/constellation/Cargo.toml

@@ -23,6 +23,7 @@ devtools_traits = { workspace = true }
 embedder_traits = { workspace = true }
 euclid = { workspace = true }
 fonts_traits = { workspace = true }
+fnv = { workspace = true }
 http = { workspace = true }
 hyper_serde = { workspace = true }
 ipc-channel = { workspace = true }

components/shared/constellation/from_script_message.rs

@@ -4,7 +4,6 @@
 
 //! Messages send from the ScriptThread to the Constellation.
 
-use std::collections::HashMap;
 use std::fmt;
 
 use base::Epoch;
@@ -22,6 +21,7 @@ use embedder_traits::{
     ViewportDetails, WebDriverMessageId,
 };
 use euclid::default::Size2D as UntypedSize2D;
+use fnv::FnvHashMap;
 use fonts_traits::SystemFontServiceProxySender;
 use http::{HeaderMap, Method};
 use ipc_channel::ipc::IpcSender;
@@ -492,7 +492,7 @@ pub enum ScriptToConstellationMessage {
         /* The ids of ports transferred successfully */
         Vec<MessagePortId>,
         /* The ids, and buffers, of ports whose transfer failed */
-        HashMap<MessagePortId, PortTransferInfo>,
+        FnvHashMap<MessagePortId, PortTransferInfo>,
     ),
     /// A new message-port was created or transferred, with corresponding control-sender.
     NewMessagePort(MessagePortRouterId, MessagePortId),

components/shared/constellation/lib.rs

@@ -11,7 +11,7 @@
 mod from_script_message;
 mod structured_data;
 
-use std::collections::{HashMap, VecDeque};
+use std::collections::VecDeque;
 use std::fmt;
 use std::time::Duration;
 
@@ -22,6 +22,7 @@ use embedder_traits::{
     CompositorHitTestResult, FocusId, InputEvent, JavaScriptEvaluationId, MediaSessionActionType,
     Theme, TraversalId, ViewportDetails, WebDriverCommandMsg, WebDriverCommandResponse,
 };
+use fnv::FnvHashMap;
 pub use from_script_message::*;
 use ipc_channel::ipc::IpcSender;
 use malloc_size_of_derive::MallocSizeOf;
@@ -41,7 +42,7 @@ pub enum EmbedderToConstellationMessage {
     /// Exit the constellation.
     Exit,
     /// Query the constellation to see if the current compositor output is stable
-    IsReadyToSaveImage(HashMap<PipelineId, Epoch>),
+    IsReadyToSaveImage(FnvHashMap<PipelineId, Epoch>),
     /// Whether to allow script to navigate.
     AllowNavigationResponse(PipelineId, bool),
     /// Request to load a page.
@@ -94,7 +95,7 @@ pub enum EmbedderToConstellationMessage {
     SetWebViewThrottled(WebViewId, bool),
     /// The Servo renderer scrolled and is updating the scroll states of the nodes in the
     /// given pipeline via the constellation.
-    SetScrollStates(PipelineId, HashMap<ExternalScrollId, LayoutVector2D>),
+    SetScrollStates(PipelineId, FnvHashMap<ExternalScrollId, LayoutVector2D>),
     /// Notify the constellation that a particular paint metric event has happened for the given pipeline.
     PaintMetric(PipelineId, PaintMetricEvent),
     /// Evaluate a JavaScript string in the context of a `WebView`. When execution is complete or an
@@ -180,7 +181,7 @@ pub struct PortTransferInfo {
 #[allow(clippy::large_enum_variant)]
 pub enum MessagePortMsg {
     /// Complete the transfer for a batch of ports.
-    CompleteTransfer(HashMap<MessagePortId, PortTransferInfo>),
+    CompleteTransfer(FnvHashMap<MessagePortId, PortTransferInfo>),
     /// Complete the transfer of a single port,
     /// whose transfer was pending because it had been requested
     /// while a previous failed transfer was being rolled-back.

components/shared/layout/lib.rs

@@ -12,7 +12,6 @@ mod layout_damage;
 pub mod wrapper_traits;
 
 use std::any::Any;
-use std::collections::HashMap;
 use std::sync::Arc;
 use std::sync::atomic::{AtomicIsize, AtomicU64, Ordering};
 use std::thread::JoinHandle;
@@ -281,7 +280,7 @@ pub trait Layout {
     /// Set the scroll states of this layout after a compositor scroll.
     fn set_scroll_offsets_from_renderer(
         &mut self,
-        scroll_states: &HashMap<ExternalScrollId, LayoutVector2D>,
+        scroll_states: &FnvHashMap<ExternalScrollId, LayoutVector2D>,
     );
 
     /// Get the scroll offset of the given scroll node with id of [`ExternalScrollId`] or `None` if it does

components/shared/script/Cargo.toml

@@ -26,6 +26,7 @@ crossbeam-channel = { workspace = true }
 devtools_traits = { workspace = true }
 embedder_traits = { workspace = true }
 euclid = { workspace = true }
+fnv = { workspace = true }
 ipc-channel = { workspace = true }
 keyboard-types = { workspace = true }
 malloc_size_of = { workspace = true }

components/shared/script/lib.rs

@@ -9,7 +9,6 @@
 #![deny(missing_docs)]
 #![deny(unsafe_code)]
 
-use std::collections::HashMap;
 use std::fmt;
 use std::sync::Arc;
 
@@ -33,6 +32,7 @@ use embedder_traits::{
     MediaSessionActionType, ScriptToEmbedderChan, Theme, ViewportDetails, WebDriverScriptCommand,
 };
 use euclid::{Rect, Scale, Size2D, UnknownUnit};
+use fnv::FnvHashMap;
 use ipc_channel::ipc::{IpcReceiver, IpcSender};
 use keyboard_types::Modifiers;
 use malloc_size_of_derive::MallocSizeOf;
@@ -253,7 +253,7 @@ pub enum ScriptThreadMessage {
     SetWebGPUPort(IpcReceiver<WebGPUMsg>),
     /// The compositor scrolled and is updating the scroll states of the nodes in the given
     /// pipeline via the Constellation.
-    SetScrollStates(PipelineId, HashMap<ExternalScrollId, LayoutVector2D>),
+    SetScrollStates(PipelineId, FnvHashMap<ExternalScrollId, LayoutVector2D>),
     /// Evaluate the given JavaScript and return a result via a corresponding message
     /// to the Constellation.
     EvaluateJavaScript(PipelineId, JavaScriptEvaluationId, String),