script: Make timers per-process (#34581)

Before all timers were managed by the Constellation process, meaning
that they had to trigger IPC calls to be scheduled and fired. Currently,
timers are only used in the `ScriptThread`, so it makes sense that they
are per-process.

This change restores the timer thread functionality that existed before
avoided entirely. Completion is done using a callback that is sent to
the timer thread similarly to how fetch is done. This allows reusing the
existing task queue without making any new channels.

Fixes #15219.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

19 files changed, 351 insertions, 325 deletions

diff --git a/components/constellation/constellation.rs b/components/constellation/constellation.rs
index 5282cbe26c9..b5efc709eb2 100644
--- a/components/constellation/constellation.rs
+++ b/components/constellation/constellation.rs
@@ -110,7 +110,7 @@ use canvas_traits::ConstellationCanvasMsg;
 use compositing_traits::{
     CompositorMsg, CompositorProxy, ConstellationMsg as FromCompositorMsg, SendableFrameTree,
 };
-use crossbeam_channel::{after, never, select, unbounded, Receiver, Sender};
+use crossbeam_channel::{select, unbounded, Receiver, Sender};
 use devtools_traits::{
     ChromeToDevtoolsControlMsg, DevtoolsControlMsg, DevtoolsPageInfo, NavigationState,
     ScriptToDevtoolsControlMsg,
@@ -143,7 +143,7 @@ use script_traits::{
     LogEntry, MediaSessionActionType, MessagePortMsg, MouseEventType, NavigationHistoryBehavior,
     PortMessageTask, SWManagerMsg, SWManagerSenders, ScriptMsg as FromScriptMsg,
     ScriptToConstellationChan, ServiceWorkerManagerFactory, ServiceWorkerMsg,
-    StructuredSerializedData, Theme, TimerSchedulerMsg, TraversalDirection, UpdatePipelineIdReason,
+    StructuredSerializedData, Theme, TraversalDirection, UpdatePipelineIdReason,
     WebDriverCommandMsg, WindowSizeData, WindowSizeType,
 };
 use serde::{Deserialize, Serialize};
@@ -172,7 +172,6 @@ use crate::serviceworker::ServiceWorkerUnprivilegedContent;
 use crate::session_history::{
     JointSessionHistory, NeedsToReload, SessionHistoryChange, SessionHistoryDiff,
 };
-use crate::timer_scheduler::TimerScheduler;
 use crate::webview::WebViewManager;
 
 type PendingApprovalNavigations = HashMap<PipelineId, (LoadData, NavigationHistoryBehavior)>;
@@ -381,15 +380,6 @@ pub struct Constellation<STF, SWF> {
     /// memory profiler thread.
     mem_profiler_chan: mem::ProfilerChan,
 
-    /// A channel for a pipeline to schedule timer events.
-    scheduler_ipc_sender: IpcSender<TimerSchedulerMsg>,
-
-    /// The receiver to which the IPC requests from scheduler_chan will be forwarded.
-    scheduler_receiver: Receiver<Result<TimerSchedulerMsg, IpcError>>,
-
-    /// The logic and data behing scheduling timer events.
-    timer_scheduler: TimerScheduler,
-
     /// A single WebRender document the constellation operates on.
     webrender_document: DocumentId,
 
@@ -660,13 +650,6 @@ where
                         namespace_ipc_receiver,
                     );
 
-                let (scheduler_ipc_sender, scheduler_ipc_receiver) =
-                    ipc::channel().expect("ipc channel failure");
-                let scheduler_receiver =
-                    route_ipc_receiver_to_new_crossbeam_receiver_preserving_errors(
-                        scheduler_ipc_receiver,
-                    );
-
                 let (background_hang_monitor_ipc_sender, background_hang_monitor_ipc_receiver) =
                     ipc::channel().expect("ipc channel failure");
                 let background_hang_monitor_receiver =
@@ -762,9 +745,6 @@ where
                     window_size: initial_window_size,
                     phantom: PhantomData,
                     webdriver: WebDriverData::new(),
-                    timer_scheduler: TimerScheduler::new(),
-                    scheduler_ipc_sender,
-                    scheduler_receiver,
                     document_states: HashMap::new(),
                     webrender_document: state.webrender_document,
                     #[cfg(feature = "webgpu")]
@@ -1015,7 +995,6 @@ where
                 .clone(),
             layout_to_constellation_chan: self.layout_sender.clone(),
             layout_factory: self.layout_factory.clone(),
-            scheduler_chan: self.scheduler_ipc_sender.clone(),
             compositor_proxy: self.compositor_proxy.clone(),
             devtools_sender: self.devtools_sender.clone(),
             bluetooth_thread: self.bluetooth_ipc_sender.clone(),
@@ -1187,16 +1166,7 @@ where
             Layout(FromLayoutMsg),
             NetworkListener((PipelineId, FetchResponseMsg)),
             FromSWManager(SWManagerMsg),
-            Timer(TimerSchedulerMsg),
         }
-
-        // A timeout corresponding to the earliest scheduled timer event, if any.
-        let scheduler_timeout = self
-            .timer_scheduler
-            .check_timers()
-            .map(after)
-            .unwrap_or(never());
-
         // Get one incoming request.
         // This is one of the few places where the compositor is
         // allowed to panic. If one of the receiver.recv() calls
@@ -1236,14 +1206,6 @@ where
                 recv(self.swmanager_receiver) -> msg => {
                     msg.expect("Unexpected SW channel panic in constellation").map(Request::FromSWManager)
                 }
-                recv(self.scheduler_receiver) -> msg => {
-                    msg.expect("Unexpected schedule channel panic in constellation").map(Request::Timer)
-                }
-                recv(scheduler_timeout) -> _ => {
-                    // Note: by returning, we go back to the top,
-                    // where check_timers will be called.
-                    return;
-                },
             }
         };
 
@@ -1272,9 +1234,6 @@ where
             Request::FromSWManager(message) => {
                 self.handle_request_from_swmanager(message);
             },
-            Request::Timer(message) => {
-                self.timer_scheduler.handle_timer_request(message);
-            },
         }
     }
 
diff --git a/components/constellation/lib.rs b/components/constellation/lib.rs
index f521b334f15..0f70773ccfc 100644
--- a/components/constellation/lib.rs
+++ b/components/constellation/lib.rs
@@ -16,7 +16,6 @@ mod pipeline;
 mod sandboxing;
 mod serviceworker;
 mod session_history;
-mod timer_scheduler;
 mod webview;
 
 pub use crate::constellation::{Constellation, InitialConstellationState};
diff --git a/components/constellation/pipeline.rs b/components/constellation/pipeline.rs
index 87966cfc3bf..0bd4a6cefe5 100644
--- a/components/constellation/pipeline.rs
+++ b/components/constellation/pipeline.rs
@@ -35,7 +35,7 @@ use script_layout_interface::{LayoutFactory, ScriptThreadFactory};
 use script_traits::{
     AnimationState, ConstellationControlMsg, DiscardBrowsingContext, DocumentActivity,
     InitialScriptState, LayoutMsg, LoadData, NewLayoutInfo, SWManagerMsg,
-    ScriptToConstellationChan, TimerSchedulerMsg, WindowSizeData,
+    ScriptToConstellationChan, WindowSizeData,
 };
 use serde::{Deserialize, Serialize};
 use servo_config::opts::{self, Opts};
@@ -139,9 +139,6 @@ pub struct InitialPipelineState {
     /// A fatory for creating layouts to be used by the ScriptThread.
     pub layout_factory: Arc<dyn LayoutFactory>,
 
-    /// A channel to schedule timer events.
-    pub scheduler_chan: IpcSender<TimerSchedulerMsg>,
-
     /// A channel to the compositor.
     pub compositor_proxy: CompositorProxy,
 
@@ -270,7 +267,6 @@ impl Pipeline {
                         .background_hang_monitor_to_constellation_chan
                         .clone(),
                     bhm_control_port: None,
-                    scheduler_chan: state.scheduler_chan,
                     devtools_ipc_sender: script_to_devtools_ipc_sender,
                     bluetooth_thread: state.bluetooth_thread,
                     swmanager_thread: state.swmanager_thread,
@@ -478,7 +474,6 @@ pub struct UnprivilegedPipelineContent {
     background_hang_monitor_to_constellation_chan: IpcSender<HangMonitorAlert>,
     bhm_control_port: Option<IpcReceiver<BackgroundHangMonitorControlMsg>>,
     layout_to_constellation_chan: IpcSender<LayoutMsg>,
-    scheduler_chan: IpcSender<TimerSchedulerMsg>,
     devtools_ipc_sender: Option<IpcSender<ScriptToDevtoolsControlMsg>>,
     bluetooth_thread: IpcSender<BluetoothRequest>,
     swmanager_thread: IpcSender<SWManagerMsg>,
@@ -528,7 +523,6 @@ impl UnprivilegedPipelineContent {
                 script_to_constellation_chan: self.script_to_constellation_chan.clone(),
                 background_hang_monitor_register: background_hang_monitor_register.clone(),
                 layout_to_constellation_chan: self.layout_to_constellation_chan.clone(),
-                scheduler_chan: self.scheduler_chan,
                 bluetooth_thread: self.bluetooth_thread,
                 resource_threads: self.resource_threads,
                 image_cache: image_cache.clone(),
diff --git a/components/constellation/timer_scheduler.rs b/components/constellation/timer_scheduler.rs
deleted file mode 100644
index 6481696fc73..00000000000
--- a/components/constellation/timer_scheduler.rs
+++ /dev/null
@@ -1,73 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * 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::cmp::{self, Ord};
-use std::collections::BinaryHeap;
-use std::time::{Duration, Instant};
-
-use script_traits::{TimerEvent, TimerEventRequest, TimerSchedulerMsg};
-
-pub struct TimerScheduler(BinaryHeap<ScheduledEvent>);
-
-struct ScheduledEvent {
-    request: TimerEventRequest,
-    for_time: Instant,
-}
-
-impl Ord for ScheduledEvent {
-    fn cmp(&self, other: &ScheduledEvent) -> cmp::Ordering {
-        self.for_time.cmp(&other.for_time).reverse()
-    }
-}
-
-impl PartialOrd for ScheduledEvent {
-    fn partial_cmp(&self, other: &ScheduledEvent) -> Option<cmp::Ordering> {
-        Some(self.cmp(other))
-    }
-}
-
-impl Eq for ScheduledEvent {}
-impl PartialEq for ScheduledEvent {
-    fn eq(&self, other: &ScheduledEvent) -> bool {
-        std::ptr::eq(self, other)
-    }
-}
-
-impl TimerScheduler {
-    pub fn new() -> Self {
-        TimerScheduler(BinaryHeap::<ScheduledEvent>::new())
-    }
-
-    /// Dispatch any events whose due time is past,
-    /// and return a timeout corresponding to the earliest scheduled event, if any.
-    pub fn check_timers(&mut self) -> Option<Duration> {
-        let now = Instant::now();
-        loop {
-            match self.0.peek() {
-                // Dispatch the event if its due time is past
-                Some(event) if event.for_time <= now => {
-                    let TimerEventRequest(ref sender, source, id, _) = event.request;
-                    let _ = sender.send(TimerEvent(source, id));
-                },
-                // Do not schedule a timeout.
-                None => return None,
-                // Schedule a timeout for the earliest event.
-                Some(event) => return Some(event.for_time - now),
-            }
-            // Remove the event from the priority queue
-            // (Note this only executes when the first event has been dispatched).
-            self.0.pop();
-        }
-    }
-
-    /// Handle an incoming timer request.
-    pub fn handle_timer_request(&mut self, request: TimerSchedulerMsg) {
-        let TimerEventRequest(_, _, _, delay) = request.0;
-        let event = ScheduledEvent {
-            request: request.0,
-            for_time: Instant::now() + delay,
-        };
-        self.0.push(event);
-    }
-}
diff --git a/components/malloc_size_of/lib.rs b/components/malloc_size_of/lib.rs
index c7c0e953c5a..297f93c3f69 100644
--- a/components/malloc_size_of/lib.rs
+++ b/components/malloc_size_of/lib.rs
@@ -46,6 +46,8 @@
 //!   Note: WebRender has a reduced fork of this crate, so that we can avoid
 //!   publishing this crate on crates.io.
 
+use std::cell::OnceCell;
+use std::collections::BinaryHeap;
 use std::hash::{BuildHasher, Hash};
 use std::ops::Range;
 
@@ -351,6 +353,12 @@ impl<T: MallocSizeOf> MallocSizeOf for thin_vec::ThinVec<T> {
     }
 }
 
+impl<T: MallocSizeOf> MallocSizeOf for BinaryHeap<T> {
+    fn size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
+        self.iter().map(|element| element.size_of(ops)).sum()
+    }
+}
+
 macro_rules! malloc_size_of_hash_set {
     ($ty:ty) => {
         impl<T, S> MallocShallowSizeOf for $ty
@@ -468,6 +476,14 @@ impl<T> MallocSizeOf for std::marker::PhantomData<T> {
     }
 }
 
+impl<T: MallocSizeOf> MallocSizeOf for OnceCell<T> {
+    fn size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
+        self.get()
+            .map(|interior| interior.size_of(ops))
+            .unwrap_or_default()
+    }
+}
+
 // See https://github.com/rust-lang/rust/issues/68318:
 // We don't want MallocSizeOf to be defined for Rc and Arc. If negative trait bounds are
 // ever allowed, this code should be uncommented.  Instead, there is a compile-fail test for
diff --git a/components/script/Cargo.toml b/components/script/Cargo.toml
index 98aec5908ec..c9db4b52034 100644
--- a/components/script/Cargo.toml
+++ b/components/script/Cargo.toml
@@ -118,6 +118,7 @@ swapper = "0.1"
 tempfile = "3"
 tendril = { version = "0.4.1", features = ["encoding_rs"] }
 time_03 = { workspace = true }
+timers = { path = "../timers" }
 tracing = { workspace = true, optional = true }
 unicode-bidi = { workspace = true }
 unicode-segmentation = { workspace = true }
diff --git a/components/script/dom/abstractworkerglobalscope.rs b/components/script/dom/abstractworkerglobalscope.rs
index 15277175075..869f8083d87 100644
--- a/components/script/dom/abstractworkerglobalscope.rs
+++ b/components/script/dom/abstractworkerglobalscope.rs
@@ -94,6 +94,7 @@ pub trait WorkerEventLoopMethods {
     fn from_control_msg(msg: Self::ControlMsg) -> Self::Event;
     fn from_worker_msg(msg: Self::WorkerMsg) -> Self::Event;
     fn from_devtools_msg(msg: DevtoolScriptControlMsg) -> Self::Event;
+    fn from_timer_msg() -> Self::Event;
     fn control_receiver(&self) -> &Receiver<Self::ControlMsg>;
 }
 
@@ -110,19 +111,25 @@ pub fn run_worker_event_loop<T, WorkerMsg, Event>(
         + DomObject,
 {
     let scope = worker_scope.upcast::<WorkerGlobalScope>();
-    let devtools_receiver = scope.devtools_receiver();
     let task_queue = worker_scope.task_queue();
+
+    let never = crossbeam_channel::never();
+    let devtools_receiver = scope.devtools_receiver().unwrap_or(&never);
+
     let event = select! {
         recv(worker_scope.control_receiver()) -> msg => T::from_control_msg(msg.unwrap()),
         recv(task_queue.select()) -> msg => {
             task_queue.take_tasks(msg.unwrap());
             T::from_worker_msg(task_queue.recv().unwrap())
         },
-        recv(devtools_receiver.unwrap_or(&crossbeam_channel::never())) -> msg =>
-            T::from_devtools_msg(msg.unwrap()),
+        recv(devtools_receiver) -> msg => T::from_devtools_msg(msg.unwrap()),
+        recv(scope.timer_scheduler().wait_channel()) -> _ => T::from_timer_msg(),
     };
-    let mut sequential = vec![];
-    sequential.push(event);
+
+    scope.timer_scheduler().dispatch_completed_timers();
+
+    let mut sequential = vec![event];
+
     // https://html.spec.whatwg.org/multipage/#worker-event-loop
     // Once the WorkerGlobalScope's closing flag is set to true,
     // the event loop's task queues must discard any further tasks
@@ -132,14 +139,14 @@ pub fn run_worker_event_loop<T, WorkerMsg, Event>(
         // Batch all events that are ready.
         // The task queue will throttle non-priority tasks if necessary.
         match task_queue.take_tasks_and_recv() {
-            Err(_) => match devtools_receiver.map(|port| port.try_recv()) {
-                None => {},
-                Some(Err(_)) => break,
-                Some(Ok(ev)) => sequential.push(T::from_devtools_msg(ev)),
+            Err(_) => match devtools_receiver.try_recv() {
+                Ok(message) => sequential.push(T::from_devtools_msg(message)),
+                Err(_) => break,
             },
             Ok(ev) => sequential.push(T::from_worker_msg(ev)),
         }
     }
+
     // Step 3
     for event in sequential {
         let _realm = enter_realm(worker_scope);
diff --git a/components/script/dom/dedicatedworkerglobalscope.rs b/components/script/dom/dedicatedworkerglobalscope.rs
index 01c55df4199..deb79f4684e 100644
--- a/components/script/dom/dedicatedworkerglobalscope.rs
+++ b/components/script/dom/dedicatedworkerglobalscope.rs
@@ -110,6 +110,7 @@ pub enum MixedMessage {
     Worker(DedicatedWorkerScriptMsg),
     Devtools(DevtoolScriptControlMsg),
     Control(DedicatedWorkerControlMsg),
+    Timer,
 }
 
 impl QueuedTaskConversion for DedicatedWorkerScriptMsg {
@@ -234,6 +235,10 @@ impl WorkerEventLoopMethods for DedicatedWorkerGlobalScope {
         MixedMessage::Devtools(msg)
     }
 
+    fn from_timer_msg() -> MixedMessage {
+        MixedMessage::Timer
+    }
+
     fn control_receiver(&self) -> &Receiver<DedicatedWorkerControlMsg> {
         &self.control_receiver
     }
@@ -564,6 +569,7 @@ impl DedicatedWorkerGlobalScope {
             MixedMessage::Control(DedicatedWorkerControlMsg::Exit) => {
                 return false;
             },
+            MixedMessage::Timer => {},
         }
         true
     }
diff --git a/components/script/dom/dissimilaroriginwindow.rs b/components/script/dom/dissimilaroriginwindow.rs
index 9337a3b7f34..6ec1956cc2b 100644
--- a/components/script/dom/dissimilaroriginwindow.rs
+++ b/components/script/dom/dissimilaroriginwindow.rs
@@ -55,7 +55,6 @@ impl DissimilarOriginWindow {
                 global_to_clone_from.mem_profiler_chan().clone(),
                 global_to_clone_from.time_profiler_chan().clone(),
                 global_to_clone_from.script_to_constellation_chan().clone(),
-                global_to_clone_from.scheduler_chan().clone(),
                 global_to_clone_from.resource_threads().clone(),
                 global_to_clone_from.origin().clone(),
                 global_to_clone_from.creation_url().clone(),
diff --git a/components/script/dom/globalscope.rs b/components/script/dom/globalscope.rs
index 722bda2d453..bdb8538ffd9 100644
--- a/components/script/dom/globalscope.rs
+++ b/components/script/dom/globalscope.rs
@@ -57,10 +57,10 @@ use script_traits::serializable::{BlobData, BlobImpl, FileBlob};
 use script_traits::transferable::MessagePortImpl;
 use script_traits::{
     BroadcastMsg, GamepadEvent, GamepadSupportedHapticEffects, GamepadUpdateType, MessagePortMsg,
-    PortMessageTask, ScriptMsg, ScriptToConstellationChan, TimerEvent, TimerEventId,
-    TimerSchedulerMsg, TimerSource,
+    PortMessageTask, ScriptMsg, ScriptToConstellationChan,
 };
 use servo_url::{ImmutableOrigin, MutableOrigin, ServoUrl};
+use timers::{BoxedTimerCallback, TimerEvent, TimerEventId, TimerEventRequest, TimerSource};
 use uuid::Uuid;
 #[cfg(feature = "webgpu")]
 use webgpu::{DeviceLostReason, WebGPUDevice};
@@ -134,7 +134,7 @@ use crate::script_module::{DynamicModuleList, ModuleScript, ModuleTree, ScriptFe
 use crate::script_runtime::{
     CanGc, CommonScriptMsg, JSContext as SafeJSContext, ScriptChan, ScriptPort, ThreadSafeJSContext,
 };
-use crate::script_thread::{MainThreadScriptChan, ScriptThread};
+use crate::script_thread::{with_script_thread, MainThreadScriptChan, ScriptThread};
 use crate::security_manager::CSPViolationReporter;
 use crate::task::TaskCanceller;
 use crate::task_source::dom_manipulation::DOMManipulationTaskSource;
@@ -258,10 +258,6 @@ pub struct GlobalScope {
     #[no_trace]
     script_to_constellation_chan: ScriptToConstellationChan,
 
-    #[ignore_malloc_size_of = "channels are hard"]
-    #[no_trace]
-    scheduler_chan: IpcSender<TimerSchedulerMsg>,
-
     /// <https://html.spec.whatwg.org/multipage/#in-error-reporting-mode>
     in_error_reporting_mode: Cell<bool>,
 
@@ -272,10 +268,7 @@ pub struct GlobalScope {
 
     /// The mechanism by which time-outs and intervals are scheduled.
     /// <https://html.spec.whatwg.org/multipage/#timers>
-    timers: OneshotTimers,
-
-    /// Have timers been initialized?
-    init_timers: Cell<bool>,
+    timers: OnceCell<OneshotTimers>,
 
     /// The origin of the globalscope
     #[no_trace]
@@ -401,7 +394,8 @@ struct BroadcastListener {
 }
 
 /// A wrapper between timer events coming in over IPC, and the event-loop.
-struct TimerListener {
+#[derive(Clone)]
+pub(crate) struct TimerListener {
     canceller: TaskCanceller,
     task_source: TimerTaskSource,
     context: Trusted<GlobalScope>,
@@ -542,7 +536,7 @@ impl BroadcastListener {
 }
 
 impl TimerListener {
-    /// Handle a timer-event coming-in over IPC,
+    /// Handle a timer-event coming from the [`timers::TimerScheduler`]
     /// by queuing the appropriate task on the relevant event-loop.
     fn handle(&self, event: TimerEvent) {
         let context = self.context.clone();
@@ -567,6 +561,10 @@ impl TimerListener {
             &self.canceller,
         );
     }
+
+    pub fn into_callback(self) -> BoxedTimerCallback {
+        Box::new(move |timer_event| self.handle(timer_event))
+    }
 }
 
 impl MessageListener {
@@ -783,7 +781,6 @@ impl GlobalScope {
         mem_profiler_chan: profile_mem::ProfilerChan,
         time_profiler_chan: profile_time::ProfilerChan,
         script_to_constellation_chan: ScriptToConstellationChan,
-        scheduler_chan: IpcSender<TimerSchedulerMsg>,
         resource_threads: ResourceThreads,
         origin: MutableOrigin,
         creation_url: Option<ServoUrl>,
@@ -811,11 +808,9 @@ impl GlobalScope {
             mem_profiler_chan,
             time_profiler_chan,
             script_to_constellation_chan,
-            scheduler_chan: scheduler_chan.clone(),
             in_error_reporting_mode: Default::default(),
             resource_threads,
-            timers: OneshotTimers::new(scheduler_chan),
-            init_timers: Default::default(),
+            timers: OnceCell::default(),
             origin,
             creation_url,
             permission_state_invocation_results: Default::default(),
@@ -861,34 +856,21 @@ impl GlobalScope {
         false
     }
 
-    /// Setup the IPC-to-event-loop glue for timers to schedule themselves.
-    fn setup_timers(&self) {
-        if self.init_timers.get() {
-            return;
-        }
-        self.init_timers.set(true);
-
-        let (timer_ipc_chan, timer_ipc_port) = ipc::channel().unwrap();
-        self.timers.setup_scheduling(timer_ipc_chan);
-
-        // Setup route from IPC to task-queue for the timer-task-source.
-        let context = Trusted::new(self);
-        let (task_source, canceller) = (
-            self.timer_task_source(),
-            self.task_canceller(TaskSourceName::Timer),
-        );
-        let timer_listener = TimerListener {
-            context,
-            task_source,
-            canceller,
-        };
-        ROUTER.add_typed_route(
-            timer_ipc_port,
-            Box::new(move |message| {
-                let event = message.unwrap();
-                timer_listener.handle(event);
-            }),
-        );
+    fn timers(&self) -> &OneshotTimers {
+        self.timers.get_or_init(|| {
+            let (task_source, canceller) = (
+                self.timer_task_source(),
+                self.task_canceller(TaskSourceName::Timer),
+            );
+            OneshotTimers::new(
+                self,
+                TimerListener {
+                    context: Trusted::new(self),
+                    task_source,
+                    canceller,
+                },
+            )
+        })
     }
 
     /// <https://w3c.github.io/ServiceWorker/#get-the-service-worker-registration-object>
@@ -2377,10 +2359,6 @@ impl GlobalScope {
         self.script_to_constellation_chan().send(msg).unwrap();
     }
 
-    pub fn scheduler_chan(&self) -> &IpcSender<TimerSchedulerMsg> {
-        &self.scheduler_chan
-    }
-
     /// Get the `PipelineId` for this global scope.
     pub fn pipeline_id(&self) -> PipelineId {
         self.pipeline_id
@@ -2409,6 +2387,16 @@ impl GlobalScope {
         unreachable!();
     }
 
+    /// Schedule a [`TimerEventRequest`] on this [`GlobalScope`]'s [`timers::TimerScheduler`].
+    /// Every Worker has its own scheduler, which handles events in the Worker event loop,
+    /// but `Window`s use a shared scheduler associated with their [`ScriptThread`].
+    pub(crate) fn schedule_timer(&self, request: TimerEventRequest) {
+        match self.downcast::<WorkerGlobalScope>() {
+            Some(worker_global) => worker_global.timer_scheduler().schedule_timer(request),
+            _ => with_script_thread(|script_thread| script_thread.schedule_timer(request)),
+        }
+    }
+
     /// <https://html.spec.whatwg.org/multipage/#concept-settings-object-policy-container>
     pub fn policy_container(&self) -> PolicyContainer {
         if let Some(window) = self.downcast::<Window>() {
@@ -2789,13 +2777,12 @@ impl GlobalScope {
         callback: OneshotTimerCallback,
         duration: Duration,
     ) -> OneshotTimerHandle {
-        self.setup_timers();
-        self.timers
+        self.timers()
             .schedule_callback(callback, duration, self.timer_source())
     }
 
     pub fn unschedule_callback(&self, handle: OneshotTimerHandle) {
-        self.timers.unschedule_callback(handle);
+        self.timers().unschedule_callback(handle);
     }
 
     /// <https://html.spec.whatwg.org/multipage/#timer-initialisation-steps>
@@ -2806,8 +2793,7 @@ impl GlobalScope {
         timeout: Duration,
         is_interval: IsInterval,
     ) -> i32 {
-        self.setup_timers();
-        self.timers.set_timeout_or_interval(
+        self.timers().set_timeout_or_interval(
             self,
             callback,
             arguments,
@@ -2818,7 +2804,7 @@ impl GlobalScope {
     }
 
     pub fn clear_timeout_or_interval(&self, handle: i32) {
-        self.timers.clear_timeout_or_interval(self, handle);
+        self.timers().clear_timeout_or_interval(self, handle);
     }
 
     pub fn queue_function_as_microtask(&self, callback: Rc<VoidFunction>) {
@@ -2925,23 +2911,23 @@ impl GlobalScope {
     }
 
     pub fn fire_timer(&self, handle: TimerEventId, can_gc: CanGc) {
-        self.timers.fire_timer(handle, self, can_gc);
+        self.timers().fire_timer(handle, self, can_gc);
     }
 
     pub fn resume(&self) {
-        self.timers.resume();
+        self.timers().resume();
     }
 
     pub fn suspend(&self) {
-        self.timers.suspend();
+        self.timers().suspend();
     }
 
     pub fn slow_down_timers(&self) {
-        self.timers.slow_down();
+        self.timers().slow_down();
     }
 
     pub fn speed_up_timers(&self) {
-        self.timers.speed_up();
+        self.timers().speed_up();
     }
 
     fn timer_source(&self) -> TimerSource {
diff --git a/components/script/dom/serviceworkerglobalscope.rs b/components/script/dom/serviceworkerglobalscope.rs
index df64ef6acce..b4ef6d9ade8 100644
--- a/components/script/dom/serviceworkerglobalscope.rs
+++ b/components/script/dom/serviceworkerglobalscope.rs
@@ -125,6 +125,7 @@ pub enum MixedMessage {
     ServiceWorker(ServiceWorkerScriptMsg),
     Devtools(DevtoolScriptControlMsg),
     Control(ServiceWorkerControlMsg),
+    Timer,
 }
 
 #[derive(Clone, JSTraceable)]
@@ -212,6 +213,10 @@ impl WorkerEventLoopMethods for ServiceWorkerGlobalScope {
         MixedMessage::Devtools(msg)
     }
 
+    fn from_timer_msg() -> MixedMessage {
+        MixedMessage::Timer
+    }
+
     fn control_receiver(&self) -> &Receiver<ServiceWorkerControlMsg> {
         &self.control_receiver
     }
@@ -433,6 +438,7 @@ impl ServiceWorkerGlobalScope {
             MixedMessage::Control(ServiceWorkerControlMsg::Exit) => {
                 return false;
             },
+            MixedMessage::Timer => {},
         }
         true
     }
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index c7678cce0ad..ac972fb80a8 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -57,8 +57,8 @@ use script_layout_interface::{
 use script_traits::webdriver_msg::{WebDriverJSError, WebDriverJSResult};
 use script_traits::{
     ConstellationControlMsg, DocumentState, LoadData, NavigationHistoryBehavior, ScriptMsg,
-    ScriptToConstellationChan, ScrollState, StructuredSerializedData, Theme, TimerSchedulerMsg,
-    WindowSizeData, WindowSizeType,
+    ScriptToConstellationChan, ScrollState, StructuredSerializedData, Theme, WindowSizeData,
+    WindowSizeType,
 };
 use selectors::attr::CaseSensitivity;
 use servo_arc::Arc as ServoArc;
@@ -2697,7 +2697,6 @@ impl Window {
         devtools_chan: Option<IpcSender<ScriptToDevtoolsControlMsg>>,
         constellation_chan: ScriptToConstellationChan,
         control_chan: IpcSender<ConstellationControlMsg>,
-        scheduler_chan: IpcSender<TimerSchedulerMsg>,
         pipelineid: PipelineId,
         parent_info: Option<PipelineId>,
         window_size: WindowSizeData,
@@ -2739,7 +2738,6 @@ impl Window {
                 mem_profiler_chan,
                 time_profiler_chan,
                 constellation_chan,
-                scheduler_chan,
                 resource_threads,
                 origin,
                 Some(creator_url),
diff --git a/components/script/dom/workerglobalscope.rs b/components/script/dom/workerglobalscope.rs
index d35ca2b98ee..7fd73750de7 100644
--- a/components/script/dom/workerglobalscope.rs
+++ b/components/script/dom/workerglobalscope.rs
@@ -2,6 +2,7 @@
  * 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::cell::{RefCell, RefMut};
 use std::default::Default;
 use std::rc::Rc;
 use std::sync::atomic::{AtomicBool, Ordering};
@@ -24,6 +25,7 @@ use net_traits::request::{
 use net_traits::IpcSend;
 use script_traits::WorkerGlobalScopeInit;
 use servo_url::{MutableOrigin, ServoUrl};
+use timers::TimerScheduler;
 use uuid::Uuid;
 
 use super::bindings::codegen::Bindings::MessagePortBinding::StructuredSerializeOptions;
@@ -80,7 +82,6 @@ pub fn prepare_workerscope_init(
         time_profiler_chan: global.time_profiler_chan().clone(),
         from_devtools_sender: devtools_sender,
         script_to_constellation_chan: global.script_to_constellation_chan().clone(),
-        scheduler_chan: global.scheduler_chan().clone(),
         worker_id: worker_id.unwrap_or_else(|| WorkerId(Uuid::new_v4())),
         pipeline_id: global.pipeline_id(),
         origin: global.origin().immutable().clone(),
@@ -129,6 +130,11 @@ pub struct WorkerGlobalScope {
     #[no_trace]
     navigation_start: CrossProcessInstant,
     performance: MutNullableDom<Performance>,
+
+    /// A [`TimerScheduler`] used to schedule timers for this [`ServiceWorkerGlobalScope`].
+    /// Timers are handled in the service worker event loop.
+    #[no_trace]
+    timer_scheduler: RefCell<TimerScheduler>,
 }
 
 impl WorkerGlobalScope {
@@ -158,7 +164,6 @@ impl WorkerGlobalScope {
                 init.mem_profiler_chan,
                 init.time_profiler_chan,
                 init.script_to_constellation_chan,
-                init.scheduler_chan,
                 init.resource_threads,
                 MutableOrigin::new(init.origin),
                 init.creation_url,
@@ -183,6 +188,7 @@ impl WorkerGlobalScope {
             _devtools_sender: init.from_devtools_sender,
             navigation_start: CrossProcessInstant::now(),
             performance: Default::default(),
+            timer_scheduler: RefCell::default(),
         }
     }
 
@@ -242,6 +248,11 @@ impl WorkerGlobalScope {
     pub fn policy_container(&self) -> Ref<PolicyContainer> {
         self.policy_container.borrow()
     }
+
+    /// Get a mutable reference to the [`TimerScheduler`] for this [`ServiceWorkerGlobalScope`].
+    pub(crate) fn timer_scheduler(&self) -> RefMut<TimerScheduler> {
+        self.timer_scheduler.borrow_mut()
+    }
 }
 
 impl WorkerGlobalScopeMethods<crate::DomTypeHolder> for WorkerGlobalScope {
diff --git a/components/script/dom/workletglobalscope.rs b/components/script/dom/workletglobalscope.rs
index 66f0720d931..3165ad77a9d 100644
--- a/components/script/dom/workletglobalscope.rs
+++ b/components/script/dom/workletglobalscope.rs
@@ -15,7 +15,7 @@ use js::rust::Runtime;
 use net_traits::image_cache::ImageCache;
 use net_traits::ResourceThreads;
 use profile_traits::{mem, time};
-use script_traits::{Painter, ScriptMsg, ScriptToConstellationChan, TimerSchedulerMsg};
+use script_traits::{Painter, ScriptMsg, ScriptToConstellationChan};
 use servo_atoms::Atom;
 use servo_url::{ImmutableOrigin, MutableOrigin, ServoUrl};
 
@@ -93,7 +93,6 @@ impl WorkletGlobalScope {
                 init.mem_profiler_chan.clone(),
                 init.time_profiler_chan.clone(),
                 script_to_constellation_chan,
-                init.scheduler_chan.clone(),
                 init.resource_threads.clone(),
                 MutableOrigin::new(ImmutableOrigin::new_opaque()),
                 None,
@@ -186,8 +185,6 @@ pub struct WorkletGlobalScopeInit {
     pub devtools_chan: Option<IpcSender<ScriptToDevtoolsControlMsg>>,
     /// Messages to send to constellation
     pub to_constellation_sender: IpcSender<(PipelineId, ScriptMsg)>,
-    /// Message to send to the scheduler
-    pub scheduler_chan: IpcSender<TimerSchedulerMsg>,
     /// The image cache
     pub image_cache: Arc<dyn ImageCache>,
     /// True if in headless mode
diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index 1ff221a29ab..7622a00d21f 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -85,14 +85,15 @@ use script_traits::{
     EventResult, InitialScriptState, JsEvalResult, LayoutMsg, LoadData, LoadOrigin,
     MediaSessionActionType, MouseButton, MouseEventType, NavigationHistoryBehavior, NewLayoutInfo,
     Painter, ProgressiveWebMetricType, ScriptMsg, ScriptToConstellationChan, ScrollState,
-    StructuredSerializedData, Theme, TimerSchedulerMsg, TouchEventType, TouchId,
-    UntrustedNodeAddress, UpdatePipelineIdReason, WheelDelta, WindowSizeData, WindowSizeType,
+    StructuredSerializedData, Theme, TouchEventType, TouchId, UntrustedNodeAddress,
+    UpdatePipelineIdReason, WheelDelta, WindowSizeData, WindowSizeType,
 };
 use servo_atoms::Atom;
 use servo_config::opts;
 use servo_url::{ImmutableOrigin, MutableOrigin, ServoUrl};
 use style::dom::OpaqueNode;
 use style::thread_state::{self, ThreadState};
+use timers::{TimerEventRequest, TimerScheduler};
 use url::Position;
 #[cfg(feature = "webgpu")]
 use webgpu::{WebGPUDevice, WebGPUMsg};
@@ -274,7 +275,6 @@ impl InProgressLoad {
 }
 
 #[derive(Debug)]
-#[allow(clippy::enum_variant_names)]
 enum MixedMessage {
     FromConstellation(ConstellationControlMsg),
     FromScript(MainThreadScriptMsg),
@@ -282,6 +282,7 @@ enum MixedMessage {
     FromImageCache((PipelineId, PendingImageResponse)),
     #[cfg(feature = "webgpu")]
     FromWebGPUServer(WebGPUMsg),
+    TimerFired,
 }
 
 /// Messages used to control the script event loop.
@@ -490,6 +491,11 @@ pub struct ScriptThread {
     /// events in the event queue.
     chan: MainThreadScriptChan,
 
+    /// A [`TimerScheduler`] used to schedule timers for this [`ScriptThread`]. Timers are handled
+    /// in the [`ScriptThread`] event loop.
+    #[no_trace]
+    timer_scheduler: RefCell<TimerScheduler>,
+
     dom_manipulation_task_sender: Box<dyn ScriptChan>,
 
     gamepad_task_sender: Box<dyn ScriptChan>,
@@ -574,9 +580,6 @@ pub struct ScriptThread {
     closed_pipelines: DomRefCell<HashSet<PipelineId>>,
 
     #[no_trace]
-    scheduler_chan: IpcSender<TimerSchedulerMsg>,
-
-    #[no_trace]
     content_process_shutdown_chan: Sender<()>,
 
     /// <https://html.spec.whatwg.org/multipage/#microtask-queue>
@@ -881,6 +884,11 @@ impl ScriptThread {
         })
     }
 
+    /// Schedule a [`TimerEventRequest`] on this [`ScriptThread`]'s [`TimerScheduler`].
+    pub(crate) fn schedule_timer(&self, request: TimerEventRequest) {
+        self.timer_scheduler.borrow_mut().schedule_timer(request);
+    }
+
     // https://html.spec.whatwg.org/multipage/#await-a-stable-state
     pub fn await_stable_state(task: Microtask) {
         with_script_thread(|script_thread| {
@@ -1052,7 +1060,6 @@ impl ScriptThread {
                         time_profiler_chan: script_thread.time_profiler_chan.clone(),
                         devtools_chan: script_thread.devtools_chan.clone(),
                         to_constellation_sender: script_thread.script_sender.clone(),
-                        scheduler_chan: script_thread.scheduler_chan.clone(),
                         image_cache: script_thread.image_cache.clone(),
                         is_headless: script_thread.headless,
                         user_agent: script_thread.user_agent.clone(),
@@ -1208,6 +1215,7 @@ impl ScriptThread {
             closing,
 
             chan: MainThreadScriptChan(chan.clone()),
+            timer_scheduler: Default::default(),
             dom_manipulation_task_sender: boxed_script_sender.clone(),
             gamepad_task_sender: boxed_script_sender.clone(),
             media_element_task_sender: chan.clone(),
@@ -1238,8 +1246,6 @@ impl ScriptThread {
             topmost_mouse_over_target: MutNullableDom::new(Default::default()),
             closed_pipelines: DomRefCell::new(HashSet::new()),
 
-            scheduler_chan: state.scheduler_chan,
-
             content_process_shutdown_chan: state.content_process_shutdown_chan,
 
             mutation_observer_microtask_queued: Default::default(),
@@ -1683,10 +1689,6 @@ impl ScriptThread {
 
     /// Handle incoming messages from other tasks and the task queue.
     fn handle_msgs(&self, can_gc: CanGc) -> bool {
-        #[cfg(feature = "webgpu")]
-        use self::MixedMessage::FromWebGPUServer;
-        use self::MixedMessage::{FromConstellation, FromDevtools, FromImageCache, FromScript};
-
         // Proritize rendering tasks and others, and gather all other events as `sequential`.
         let mut sequential = vec![];
 
@@ -1702,12 +1704,13 @@ impl ScriptThread {
                     .task_queue
                     .recv()
                     .expect("Spurious wake-up of the event-loop, task-queue has no tasks available");
-                FromScript(event)
+                MixedMessage::FromScript(event)
             },
-            recv(self.control_port) -> msg => FromConstellation(msg.unwrap()),
+            recv(self.control_port) -> msg => MixedMessage::FromConstellation(msg.unwrap()),
             recv(self.devtools_chan.as_ref().map(|_| &self.devtools_port).unwrap_or(&crossbeam_channel::never())) -> msg
-                => FromDevtools(msg.unwrap()),
-            recv(self.image_cache_port) -> msg => FromImageCache(msg.unwrap()),
+                => MixedMessage::FromDevtools(msg.unwrap()),
+            recv(self.image_cache_port) -> msg => MixedMessage::FromImageCache(msg.unwrap()),
+            recv(self.timer_scheduler.borrow().wait_channel()) -> _ => MixedMessage::TimerFired,
             recv({
                 #[cfg(feature = "webgpu")]
                 {
@@ -1720,7 +1723,7 @@ impl ScriptThread {
             }) -> msg => {
                 #[cfg(feature = "webgpu")]
                 {
-                    FromWebGPUServer(msg.unwrap())
+                    MixedMessage::FromWebGPUServer(msg.unwrap())
                 }
                 #[cfg(not(feature = "webgpu"))]
                 {
@@ -1733,6 +1736,11 @@ impl ScriptThread {
         loop {
             debug!("Handling event: {event:?}");
 
+            // Dispatch any completed timers, so that their tasks can be run below.
+            self.timer_scheduler
+                .borrow_mut()
+                .dispatch_completed_timers();
+
             let pipeline_id = self.message_to_pipeline(&event);
             let _realm = pipeline_id.map(|id| {
                 let global = self.documents.borrow().find_global(id);
@@ -1744,7 +1752,9 @@ impl ScriptThread {
                 // This has to be handled before the ResizeMsg below,
                 // otherwise the page may not have been added to the
                 // child list yet, causing the find() to fail.
-                FromConstellation(ConstellationControlMsg::AttachLayout(new_layout_info)) => {
+                MixedMessage::FromConstellation(ConstellationControlMsg::AttachLayout(
+                    new_layout_info,
+                )) => {
                     let pipeline_id = new_layout_info.new_pipeline_id;
                     self.profile_event(
                         ScriptThreadEventCategory::AttachLayout,
@@ -1780,14 +1790,19 @@ impl ScriptThread {
                         },
                     )
                 },
-                FromConstellation(ConstellationControlMsg::Resize(id, size, size_type)) => {
+                MixedMessage::FromConstellation(ConstellationControlMsg::Resize(
+                    id,
+                    size,
+                    size_type,
+                )) => {
                     self.handle_resize_message(id, size, size_type);
                 },
-                FromConstellation(ConstellationControlMsg::Viewport(id, rect)) => self
-                    .profile_event(ScriptThreadEventCategory::SetViewport, Some(id), || {
+                MixedMessage::FromConstellation(ConstellationControlMsg::Viewport(id, rect)) => {
+                    self.profile_event(ScriptThreadEventCategory::SetViewport, Some(id), || {
                         self.handle_viewport(id, rect);
-                    }),
-                FromConstellation(ConstellationControlMsg::TickAllAnimations(
+                    })
+                },
+                MixedMessage::FromConstellation(ConstellationControlMsg::TickAllAnimations(
                     pipeline_id,
                     tick_type,
                 )) => {
@@ -1801,10 +1816,10 @@ impl ScriptThread {
                         )
                     }
                 },
-                FromConstellation(ConstellationControlMsg::SendEvent(id, event)) => {
+                MixedMessage::FromConstellation(ConstellationControlMsg::SendEvent(id, event)) => {
                     self.handle_event(id, event)
                 },
-                FromScript(MainThreadScriptMsg::Common(CommonScriptMsg::Task(
+                MixedMessage::FromScript(MainThreadScriptMsg::Common(CommonScriptMsg::Task(
                     _,
                     _,
                     _,
@@ -1814,14 +1829,15 @@ impl ScriptThread {
                     // message handling, we run those steps only once at the end of each call of
                     // this function.
                 },
-                FromScript(MainThreadScriptMsg::Inactive) => {
+                MixedMessage::FromScript(MainThreadScriptMsg::Inactive) => {
                     // An event came-in from a document that is not fully-active, it has been stored by the task-queue.
                     // Continue without adding it to "sequential".
                 },
-                FromConstellation(ConstellationControlMsg::ExitFullScreen(id)) => self
-                    .profile_event(ScriptThreadEventCategory::ExitFullscreen, Some(id), || {
+                MixedMessage::FromConstellation(ConstellationControlMsg::ExitFullScreen(id)) => {
+                    self.profile_event(ScriptThreadEventCategory::ExitFullscreen, Some(id), || {
                         self.handle_exit_fullscreen(id, can_gc);
-                    }),
+                    })
+                },
                 _ => {
                     sequential.push(event);
                 },
@@ -1838,19 +1854,19 @@ impl ScriptThread {
                             Err(_) => match &*self.webgpu_port.borrow() {
                                 Some(p) => match p.try_recv() {
                                     Err(_) => break,
-                                    Ok(ev) => event = FromWebGPUServer(ev),
+                                    Ok(ev) => event = MixedMessage::FromWebGPUServer(ev),
                                 },
                                 None => break,
                             },
-                            Ok(ev) => event = FromImageCache(ev),
+                            Ok(ev) => event = MixedMessage::FromImageCache(ev),
                             #[cfg(not(feature = "webgpu"))]
                             Err(_) => break,
                         },
-                        Ok(ev) => event = FromDevtools(ev),
+                        Ok(ev) => event = MixedMessage::FromDevtools(ev),
                     },
-                    Ok(ev) => event = FromScript(ev),
+                    Ok(ev) => event = MixedMessage::FromScript(ev),
                 },
-                Ok(ev) => event = FromConstellation(ev),
+                Ok(ev) => event = MixedMessage::FromConstellation(ev),
             }
         }
 
@@ -1869,11 +1885,11 @@ impl ScriptThread {
             if self.closing.load(Ordering::SeqCst) {
                 // If we've received the closed signal from the BHM, only handle exit messages.
                 match msg {
-                    FromConstellation(ConstellationControlMsg::ExitScriptThread) => {
+                    MixedMessage::FromConstellation(ConstellationControlMsg::ExitScriptThread) => {
                         self.handle_exit_script_thread_msg(can_gc);
                         return false;
                     },
-                    FromConstellation(ConstellationControlMsg::ExitPipeline(
+                    MixedMessage::FromConstellation(ConstellationControlMsg::ExitPipeline(
                         pipeline_id,
                         discard_browsing_context,
                     )) => {
@@ -1890,20 +1906,25 @@ impl ScriptThread {
 
             let exiting = self.profile_event(category, pipeline_id, move || {
                 match msg {
-                    FromConstellation(ConstellationControlMsg::ExitScriptThread) => {
+                    MixedMessage::FromConstellation(ConstellationControlMsg::ExitScriptThread) => {
                         self.handle_exit_script_thread_msg(can_gc);
                         return true;
                     },
-                    FromConstellation(inner_msg) => {
+                    MixedMessage::FromConstellation(inner_msg) => {
                         self.handle_msg_from_constellation(inner_msg, can_gc)
                     },
-                    FromScript(inner_msg) => self.handle_msg_from_script(inner_msg),
-                    FromDevtools(inner_msg) => self.handle_msg_from_devtools(inner_msg, can_gc),
-                    FromImageCache(inner_msg) => self.handle_msg_from_image_cache(inner_msg),
+                    MixedMessage::FromScript(inner_msg) => self.handle_msg_from_script(inner_msg),
+                    MixedMessage::FromDevtools(inner_msg) => {
+                        self.handle_msg_from_devtools(inner_msg, can_gc)
+                    },
+                    MixedMessage::FromImageCache(inner_msg) => {
+                        self.handle_msg_from_image_cache(inner_msg)
+                    },
                     #[cfg(feature = "webgpu")]
-                    FromWebGPUServer(inner_msg) => {
+                    MixedMessage::FromWebGPUServer(inner_msg) => {
                         self.handle_msg_from_webgpu_server(inner_msg, can_gc)
                     },
+                    MixedMessage::TimerFired => {},
                 }
 
                 false
@@ -1955,6 +1976,7 @@ impl ScriptThread {
             },
             #[cfg(feature = "webgpu")]
             MixedMessage::FromWebGPUServer(_) => ScriptThreadEventCategory::WebGPUMsg,
+            MixedMessage::TimerFired => ScriptThreadEventCategory::TimerEvent,
         }
     }
 
@@ -2047,7 +2069,6 @@ impl ScriptThread {
                 SetScrollStates(id, ..) => Some(id),
                 SetEpochPaintTime(id, ..) => Some(id),
             },
-            MixedMessage::FromDevtools(_) => None,
             MixedMessage::FromScript(ref inner_msg) => match *inner_msg {
                 MainThreadScriptMsg::Common(CommonScriptMsg::Task(_, _, pipeline_id, _)) => {
                     pipeline_id
@@ -2059,6 +2080,7 @@ impl ScriptThread {
                 MainThreadScriptMsg::WakeUp => None,
             },
             MixedMessage::FromImageCache((pipeline_id, _)) => Some(pipeline_id),
+            MixedMessage::FromDevtools(_) | MixedMessage::TimerFired => None,
             #[cfg(feature = "webgpu")]
             MixedMessage::FromWebGPUServer(..) => None,
         }
@@ -3653,7 +3675,6 @@ impl ScriptThread {
             self.devtools_chan.clone(),
             script_to_constellation_chan,
             self.control_chan.clone(),
-            self.scheduler_chan.clone(),
             incomplete.pipeline_id,
             incomplete.parent_info,
             incomplete.window_size,
diff --git a/components/script/timers.rs b/components/script/timers.rs
index d3148f8f00d..75119ea1421 100644
--- a/components/script/timers.rs
+++ b/components/script/timers.rs
@@ -10,21 +10,21 @@ use std::rc::Rc;
 use std::time::{Duration, Instant};
 
 use deny_public_fields::DenyPublicFields;
-use ipc_channel::ipc::IpcSender;
 use js::jsapi::Heap;
 use js::jsval::{JSVal, UndefinedValue};
 use js::rust::HandleValue;
-use script_traits::{TimerEvent, TimerEventId, TimerEventRequest, TimerSchedulerMsg, TimerSource};
 use servo_config::pref;
+use timers::{TimerEventId, TimerEventRequest, TimerSource};
 
 use crate::dom::bindings::callback::ExceptionHandling::Report;
 use crate::dom::bindings::cell::DomRefCell;
 use crate::dom::bindings::codegen::Bindings::FunctionBinding::Function;
 use crate::dom::bindings::reflector::DomObject;
+use crate::dom::bindings::root::DomRoot;
 use crate::dom::bindings::str::DOMString;
 use crate::dom::document::FakeRequestAnimationFrameCallback;
 use crate::dom::eventsource::EventSourceTimeoutCallback;
-use crate::dom::globalscope::GlobalScope;
+use crate::dom::globalscope::{GlobalScope, TimerListener};
 use crate::dom::htmlmetaelement::RefreshRedirectDue;
 use crate::dom::testbinding::TestBindingCallback;
 use crate::dom::xmlhttprequest::XHRTimeoutCallback;
@@ -37,17 +37,11 @@ pub struct OneshotTimerHandle(i32);
 
 #[derive(DenyPublicFields, JSTraceable, MallocSizeOf)]
 pub struct OneshotTimers {
-    js_timers: JsTimers,
-    #[ignore_malloc_size_of = "Defined in std"]
-    #[no_trace]
-    /// The sender, to be cloned for each timer,
-    /// on which the timer scheduler in the constellation can send an event
-    /// when the timer is due.
-    timer_event_chan: DomRefCell<Option<IpcSender<TimerEvent>>>,
-    #[ignore_malloc_size_of = "Defined in std"]
+    global_scope: DomRoot<GlobalScope>,
+    #[ignore_malloc_size_of = "Missing malloc_size_of for task types"]
     #[no_trace]
-    /// The sender to the timer scheduler in the constellation.
-    scheduler_chan: IpcSender<TimerSchedulerMsg>,
+    timer_listener: TimerListener,
+    js_timers: JsTimers,
     next_timer_handle: Cell<OneshotTimerHandle>,
     timers: DomRefCell<Vec<OneshotTimer>>,
     suspended_since: Cell<Option<Instant>>,
@@ -124,11 +118,11 @@ impl PartialEq for OneshotTimer {
 }
 
 impl OneshotTimers {
-    pub fn new(scheduler_chan: IpcSender<TimerSchedulerMsg>) -> OneshotTimers {
+    pub fn new(global_scope: &GlobalScope, timer_listener: TimerListener) -> OneshotTimers {
         OneshotTimers {
+            global_scope: DomRoot::from_ref(global_scope),
+            timer_listener,
             js_timers: JsTimers::default(),
-            timer_event_chan: DomRefCell::new(None),
-            scheduler_chan,
             next_timer_handle: Cell::new(OneshotTimerHandle(1)),
             timers: DomRefCell::new(Vec::new()),
             suspended_since: Cell::new(None),
@@ -137,12 +131,6 @@ impl OneshotTimers {
         }
     }
 
-    pub fn setup_scheduling(&self, timer_event_chan: IpcSender<TimerEvent>) {
-        let mut chan = self.timer_event_chan.borrow_mut();
-        assert!(chan.is_none());
-        *chan = Some(timer_event_chan);
-    }
-
     pub fn schedule_callback(
         &self,
         callback: OneshotTimerCallback,
@@ -291,24 +279,19 @@ impl OneshotTimers {
         }
 
         let timers = self.timers.borrow();
+        let Some(timer) = timers.last() else {
+            return;
+        };
 
-        if let Some(timer) = timers.last() {
-            let expected_event_id = self.invalidate_expected_event_id();
-
-            let delay = timer.scheduled_for - Instant::now();
-            let request = TimerEventRequest(
-                self.timer_event_chan
-                    .borrow()
-                    .clone()
-                    .expect("Timer event chan not setup to schedule timers."),
-                timer.source,
-                expected_event_id,
-                delay,
-            );
-            self.scheduler_chan
-                .send(TimerSchedulerMsg(request))
-                .unwrap();
-        }
+        let expected_event_id = self.invalidate_expected_event_id();
+        let event_request = TimerEventRequest {
+            callback: self.timer_listener.clone().into_callback(),
+            source: timer.source,
+            id: expected_event_id,
+            duration: timer.scheduled_for - Instant::now(),
+        };
+
+        self.global_scope.schedule_timer(event_request);
     }
 
     fn invalidate_expected_event_id(&self) -> TimerEventId {
diff --git a/components/shared/script/lib.rs b/components/shared/script/lib.rs
index 8a248a873ae..783d1b4a670 100644
--- a/components/shared/script/lib.rs
+++ b/components/shared/script/lib.rs
@@ -18,7 +18,6 @@ use std::borrow::Cow;
 use std::collections::{HashMap, VecDeque};
 use std::fmt;
 use std::sync::Arc;
-use std::time::Duration;
 
 use background_hang_monitor_api::BackgroundHangMonitorRegister;
 use base::cross_process_instant::CrossProcessInstant;
@@ -598,38 +597,6 @@ impl From<&CompositorEvent> for CompositorEventVariant {
     }
 }
 
-/// Requests a TimerEvent-Message be sent after the given duration.
-#[derive(Debug, Deserialize, Serialize)]
-pub struct TimerEventRequest(
-    pub IpcSender<TimerEvent>,
-    pub TimerSource,
-    pub TimerEventId,
-    pub Duration,
-);
-
-/// The message used to send a request to the timer scheduler.
-#[derive(Debug, Deserialize, Serialize)]
-pub struct TimerSchedulerMsg(pub TimerEventRequest);
-
-/// Notifies the script thread to fire due timers.
-/// `TimerSource` must be `FromWindow` when dispatched to `ScriptThread` and
-/// must be `FromWorker` when dispatched to a `DedicatedGlobalWorkerScope`
-#[derive(Debug, Deserialize, Serialize)]
-pub struct TimerEvent(pub TimerSource, pub TimerEventId);
-
-/// Describes the thread that requested the TimerEvent.
-#[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, Serialize)]
-pub enum TimerSource {
-    /// The event was requested from a window (ScriptThread).
-    FromWindow(PipelineId),
-    /// The event was requested from a worker (DedicatedGlobalWorkerScope).
-    FromWorker,
-}
-
-/// The id to be used for a `TimerEvent` is defined by the corresponding `TimerEventRequest`.
-#[derive(Clone, Copy, Debug, Deserialize, Eq, MallocSizeOf, PartialEq, Serialize)]
-pub struct TimerEventId(pub u32);
-
 /// Data needed to construct a script thread.
 ///
 /// NB: *DO NOT* add any Senders or Receivers here! pcwalton will have to rewrite your code if you
@@ -658,8 +625,6 @@ pub struct InitialScriptState {
     pub background_hang_monitor_register: Box<dyn BackgroundHangMonitorRegister>,
     /// A sender layout to communicate to the constellation.
     pub layout_to_constellation_chan: IpcSender<LayoutMsg>,
-    /// A channel to schedule timer events.
-    pub scheduler_chan: IpcSender<TimerSchedulerMsg>,
     /// A channel to the resource manager thread.
     pub resource_threads: ResourceThreads,
     /// A channel to the bluetooth thread.
@@ -863,8 +828,6 @@ pub struct WorkerGlobalScopeInit {
     pub from_devtools_sender: Option<IpcSender<DevtoolScriptControlMsg>>,
     /// Messages to send to constellation
     pub script_to_constellation_chan: ScriptToConstellationChan,
-    /// Message to send to the scheduler
-    pub scheduler_chan: IpcSender<TimerSchedulerMsg>,
     /// The worker id
     pub worker_id: WorkerId,
     /// The pipeline id
diff --git a/components/timers/Cargo.toml b/components/timers/Cargo.toml
new file mode 100644
index 00000000000..122807cc038
--- /dev/null
+++ b/components/timers/Cargo.toml
@@ -0,0 +1,20 @@
+[package]
+name = "timers"
+version.workspace = true
+authors.workspace = true
+license.workspace = true
+edition.workspace = true
+publish.workspace = true
+rust-version.workspace = true
+
+[lib]
+name = "timers"
+path = "lib.rs"
+
+[dependencies]
+base = { workspace = true }
+crossbeam-channel = { workspace = true }
+log = { workspace = true }
+malloc_size_of = { workspace = true }
+malloc_size_of_derive = { workspace = true }
+serde = { workspace = true }
diff --git a/components/timers/lib.rs b/components/timers/lib.rs
new file mode 100644
index 00000000000..4527cc83265
--- /dev/null
+++ b/components/timers/lib.rs
@@ -0,0 +1,133 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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/. */
+
+//! A generic timer scheduler module that can be integrated into a crossbeam based event
+//! loop or used to launch a background timer thread.
+
+#![deny(unsafe_code)]
+
+use std::cmp::{self, Ord};
+use std::collections::BinaryHeap;
+use std::time::{Duration, Instant};
+
+use base::id::PipelineId;
+use crossbeam_channel::{after, never, Receiver};
+use malloc_size_of_derive::MallocSizeOf;
+use serde::{Deserialize, Serialize};
+
+/// Describes the source that requested the [`TimerEvent`].
+#[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, Serialize)]
+pub enum TimerSource {
+    /// The event was requested from a window (`ScriptThread`).
+    FromWindow(PipelineId),
+    /// The event was requested from a worker (`DedicatedGlobalWorkerScope`).
+    FromWorker,
+}
+
+/// The id to be used for a [`TimerEvent`] is defined by the corresponding [`TimerEventRequest`].
+#[derive(Clone, Copy, Debug, Deserialize, Eq, MallocSizeOf, PartialEq, Serialize)]
+pub struct TimerEventId(pub u32);
+
+/// A notification that a timer has fired. [`TimerSource`] must be `FromWindow` when
+/// dispatched to `ScriptThread` and must be `FromWorker` when dispatched to a
+/// `DedicatedGlobalWorkerScope`
+#[derive(Debug, Deserialize, Serialize)]
+pub struct TimerEvent(pub TimerSource, pub TimerEventId);
+
+/// A callback to pass to the [`TimerScheduler`] to be called when the timer is
+/// dispatched.
+pub type BoxedTimerCallback = Box<dyn Fn(TimerEvent) + Send + 'static>;
+
+/// Requests a TimerEvent-Message be sent after the given duration.
+#[derive(MallocSizeOf)]
+pub struct TimerEventRequest {
+    #[ignore_malloc_size_of = "Size of a boxed function"]
+    pub callback: BoxedTimerCallback,
+    pub source: TimerSource,
+    pub id: TimerEventId,
+    pub duration: Duration,
+}
+
+impl TimerEventRequest {
+    fn dispatch(self) {
+        (self.callback)(TimerEvent(self.source, self.id))
+    }
+}
+
+#[derive(MallocSizeOf)]
+struct ScheduledEvent {
+    request: TimerEventRequest,
+    for_time: Instant,
+}
+
+impl Ord for ScheduledEvent {
+    fn cmp(&self, other: &ScheduledEvent) -> cmp::Ordering {
+        self.for_time.cmp(&other.for_time).reverse()
+    }
+}
+
+impl PartialOrd for ScheduledEvent {
+    fn partial_cmp(&self, other: &ScheduledEvent) -> Option<cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Eq for ScheduledEvent {}
+impl PartialEq for ScheduledEvent {
+    fn eq(&self, other: &ScheduledEvent) -> bool {
+        std::ptr::eq(self, other)
+    }
+}
+
+/// A queue of [`TimerEventRequest`]s that are stored in order of next-to-fire.
+#[derive(Default, MallocSizeOf)]
+pub struct TimerScheduler {
+    /// A priority queue of future events, sorted by due time.
+    queue: BinaryHeap<ScheduledEvent>,
+}
+
+impl TimerScheduler {
+    /// Schedule a new timer for on this [`TimerScheduler`].
+    pub fn schedule_timer(&mut self, request: TimerEventRequest) {
+        let for_time = Instant::now() + request.duration;
+        self.queue.push(ScheduledEvent { request, for_time });
+    }
+
+    /// Get a [`Receiver<Instant>`] that receives a message after waiting for the next timer
+    /// to fire. If there are no timers, the channel will *never* send a message.
+    pub fn wait_channel(&self) -> Receiver<Instant> {
+        self.queue
+            .peek()
+            .map(|event| {
+                let now = Instant::now();
+                if event.for_time < now {
+                    after(Duration::ZERO)
+                } else {
+                    after(event.for_time - now)
+                }
+            })
+            .unwrap_or_else(never)
+    }
+
+    /// Dispatch any timer events from this [`TimerScheduler`]'s `queue` when `now` is
+    /// past the due time of the event.
+    pub fn dispatch_completed_timers(&mut self) {
+        let now = Instant::now();
+        loop {
+            match self.queue.peek() {
+                // Dispatch the event if its due time is past.
+                Some(event) if event.for_time <= now => {},
+                // Otherwise, we're done dispatching events.
+                _ => break,
+            }
+            // Remove the event from the priority queue (Note this only executes when the
+            // first event has been dispatched
+            self.queue
+                .pop()
+                .expect("Expected request")
+                .request
+                .dispatch();
+        }
+    }
+}