Introduce TaskOnce

Having both TaskBox and TaskOnce allows us to remove the superfluous inner boxing
from CancellableTask<T>.

26 files changed, 144 insertions, 124 deletions

diff --git a/components/script/dom/bindings/refcounted.rs b/components/script/dom/bindings/refcounted.rs
index 1f1f9c52722..45d7d721307 100644
--- a/components/script/dom/bindings/refcounted.rs
+++ b/components/script/dom/bindings/refcounted.rs
@@ -40,7 +40,7 @@ use std::marker::PhantomData;
 use std::os;
 use std::rc::Rc;
 use std::sync::{Arc, Weak};
-use task::TaskBox;
+use task::TaskOnce;
 
 
 #[allow(missing_docs)]  // FIXME
@@ -122,7 +122,7 @@ impl TrustedPromise {
 
     /// A task which will reject the promise.
     #[allow(unrooted_must_root)]
-    pub fn reject_task(self, error: Error) -> impl TaskBox {
+    pub fn reject_task(self, error: Error) -> impl TaskOnce {
         let this = self;
         task!(reject_promise: move || {
             debug!("Rejecting promise.");
@@ -135,7 +135,7 @@ impl TrustedPromise {
 
     /// A task which will resolve the promise.
     #[allow(unrooted_must_root)]
-    pub fn resolve_task<T>(self, value: T) -> impl TaskBox
+    pub fn resolve_task<T>(self, value: T) -> impl TaskOnce
     where
         T: ToJSValConvertible + Send,
     {
diff --git a/components/script/dom/bluetooth.rs b/components/script/dom/bluetooth.rs
index 27a588a1a63..526ebe576fc 100644
--- a/components/script/dom/bluetooth.rs
+++ b/components/script/dom/bluetooth.rs
@@ -40,7 +40,7 @@ use std::collections::HashMap;
 use std::rc::Rc;
 use std::str::FromStr;
 use std::sync::{Arc, Mutex};
-use task::TaskBox;
+use task::TaskOnce;
 
 const KEY_CONVERSION_ERROR: &'static str = "This `manufacturerData` key can not be parsed as unsigned short:";
 const FILTER_EMPTY_ERROR: &'static str = "'filters' member, if present, must be nonempty to find any devices.";
@@ -229,18 +229,17 @@ pub fn response_async<T: AsyncBluetoothListener + DomObject + 'static>(
             action: BluetoothResponseResult,
         }
 
-        impl<T> TaskBox for ListenerTask<T>
+        impl<T> TaskOnce for ListenerTask<T>
         where
             T: AsyncBluetoothListener + DomObject,
         {
-            fn run_box(self: Box<Self>) {
-                let this = *self;
-                let mut context = this.context.lock().unwrap();
-                context.response(this.action);
+            fn run_once(self) {
+                let mut context = self.context.lock().unwrap();
+                context.response(self.action);
             }
         }
 
-        let task = box ListenerTask {
+        let task = ListenerTask {
             context: context.clone(),
             action: message.to().unwrap(),
         };
diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index 0d180ca9934..e3bb46bf5c0 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -1716,7 +1716,7 @@ impl Document {
         debug!("Document loads are complete.");
         let document = Trusted::new(self);
         self.window.dom_manipulation_task_source().queue(
-            box task!(fire_load_event: move || {
+            task!(fire_load_event: move || {
                 let document = document.root();
                 let window = document.window();
                 if !window.is_alive() {
diff --git a/components/script/dom/element.rs b/components/script/dom/element.rs
index b96d2bf56aa..195884bebab 100644
--- a/components/script/dom/element.rs
+++ b/components/script/dom/element.rs
@@ -119,7 +119,7 @@ use style::thread_state;
 use style::values::{CSSFloat, Either};
 use style::values::{specified, computed};
 use stylesheet_loader::StylesheetOwner;
-use task::TaskBox;
+use task::TaskOnce;
 
 // TODO: Update focus state when the top-level browsing context gains or loses system focus,
 // and when the element enters or leaves a browsing context container.
@@ -3047,9 +3047,9 @@ impl ElementPerformFullscreenEnter {
     }
 }
 
-impl TaskBox for ElementPerformFullscreenEnter {
+impl TaskOnce for ElementPerformFullscreenEnter {
     #[allow(unrooted_must_root)]
-    fn run_box(self: Box<Self>) {
+    fn run_once(self) {
         let element = self.element.root();
         let document = document_from_node(element.r());
 
@@ -3100,9 +3100,9 @@ impl ElementPerformFullscreenExit {
     }
 }
 
-impl TaskBox for ElementPerformFullscreenExit {
+impl TaskOnce for ElementPerformFullscreenExit {
     #[allow(unrooted_must_root)]
-    fn run_box(self: Box<Self>) {
+    fn run_once(self) {
         let element = self.element.root();
         let document = document_from_node(element.r());
         // TODO Step 9.1-5
diff --git a/components/script/dom/event.rs b/components/script/dom/event.rs
index 5121768cd51..c9ef22bc6c1 100644
--- a/components/script/dom/event.rs
+++ b/components/script/dom/event.rs
@@ -23,7 +23,7 @@ use dom_struct::dom_struct;
 use servo_atoms::Atom;
 use std::cell::Cell;
 use std::default::Default;
-use task::TaskBox;
+use task::TaskOnce;
 use time;
 
 #[dom_struct]
@@ -388,8 +388,8 @@ pub struct EventTask {
     pub cancelable: EventCancelable,
 }
 
-impl TaskBox for EventTask {
-    fn run_box(self: Box<Self>) {
+impl TaskOnce for EventTask {
+    fn run_once(self) {
         let target = self.target.root();
         let bubbles = self.bubbles;
         let cancelable = self.cancelable;
@@ -403,8 +403,8 @@ pub struct SimpleEventTask {
     pub name: Atom,
 }
 
-impl TaskBox for SimpleEventTask {
-    fn run_box(self: Box<Self>) {
+impl TaskOnce for SimpleEventTask {
+    fn run_once(self) {
         let target = self.target.root();
         target.fire_event(self.name);
     }
diff --git a/components/script/dom/eventsource.rs b/components/script/dom/eventsource.rs
index bf4c1c78c95..07f5c3b4500 100644
--- a/components/script/dom/eventsource.rs
+++ b/components/script/dom/eventsource.rs
@@ -100,7 +100,7 @@ impl EventSourceContext {
         let event_source = self.event_source.clone();
         // FIXME(nox): Why are errors silenced here?
         let _ = global.networking_task_source().queue(
-            box task!(announce_the_event_source_connection: move || {
+            task!(announce_the_event_source_connection: move || {
                 let event_source = event_source.root();
                 if event_source.ready_state.get() != ReadyState::Closed {
                     event_source.ready_state.set(ReadyState::Open);
@@ -121,7 +121,7 @@ impl EventSourceContext {
         let event_source = self.event_source.clone();
         // FIXME(nox): Why are errors silenced here?
         let _ = global.networking_task_source().queue(
-            box task!(fail_the_event_source_connection: move || {
+            task!(fail_the_event_source_connection: move || {
                 let event_source = event_source.root();
                 if event_source.ready_state.get() != ReadyState::Closed {
                     event_source.ready_state.set(ReadyState::Closed);
@@ -145,7 +145,7 @@ impl EventSourceContext {
         let global = event_source.global();
         // FIXME(nox): Why are errors silenced here?
         let _ = global.networking_task_source().queue(
-            box task!(reestablish_the_event_source_onnection: move || {
+            task!(reestablish_the_event_source_onnection: move || {
                 let event_source = trusted_event_source.root();
 
                 // Step 1.1.
@@ -242,7 +242,7 @@ impl EventSourceContext {
         let event = Trusted::new(&*event);
         // FIXME(nox): Why are errors silenced here?
         let _ = global.networking_task_source().queue(
-            box task!(dispatch_the_event_source_event: move || {
+            task!(dispatch_the_event_source_event: move || {
                 let event_source = event_source.root();
                 if event_source.ready_state.get() != ReadyState::Closed {
                     event.root().upcast::<Event>().fire(&event_source.upcast());
diff --git a/components/script/dom/filereader.rs b/components/script/dom/filereader.rs
index b2f5b1ca36f..3ee3c146b75 100644
--- a/components/script/dom/filereader.rs
+++ b/components/script/dom/filereader.rs
@@ -416,11 +416,11 @@ fn perform_annotated_read_operation(
 ) {
     // Step 4
     let task = FileReadingTask::ProcessRead(filereader.clone(), gen_id);
-    task_source.queue_with_canceller(box task, &canceller).unwrap();
+    task_source.queue_with_canceller(task, &canceller).unwrap();
 
     let task = FileReadingTask::ProcessReadData(filereader.clone(), gen_id);
-    task_source.queue_with_canceller(box task, &canceller).unwrap();
+    task_source.queue_with_canceller(task, &canceller).unwrap();
 
     let task = FileReadingTask::ProcessReadEOF(filereader, gen_id, data, blob_contents);
-    task_source.queue_with_canceller(box task, &canceller).unwrap();
+    task_source.queue_with_canceller(task, &canceller).unwrap();
 }
diff --git a/components/script/dom/htmldetailselement.rs b/components/script/dom/htmldetailselement.rs
index 59090f80f48..72952da8310 100644
--- a/components/script/dom/htmldetailselement.rs
+++ b/components/script/dom/htmldetailselement.rs
@@ -70,7 +70,7 @@ impl VirtualMethods for HTMLDetailsElement {
             let this = Trusted::new(self);
             // FIXME(nox): Why are errors silenced here?
             let _ = window.dom_manipulation_task_source().queue(
-                box task!(details_notification_task_steps: move || {
+                task!(details_notification_task_steps: move || {
                     let this = this.root();
                     if counter == this.toggle_counter.get() {
                         this.upcast::<EventTarget>().fire_event(atom!("toggle"));
diff --git a/components/script/dom/htmlformelement.rs b/components/script/dom/htmlformelement.rs
index 81b9cdb44a1..f396bc51715 100755
--- a/components/script/dom/htmlformelement.rs
+++ b/components/script/dom/htmlformelement.rs
@@ -440,7 +440,7 @@ impl HTMLFormElement {
         let pipeline_id = window.upcast::<GlobalScope>().pipeline_id();
         let script_chan = window.main_thread_script_chan().clone();
         let this = Trusted::new(self);
-        let task = box task!(navigate_to_form_planned_navigation: move || {
+        let task = task!(navigate_to_form_planned_navigation: move || {
             if generation_id != this.root().generation_id.get() {
                 return;
             }
diff --git a/components/script/dom/htmliframeelement.rs b/components/script/dom/htmliframeelement.rs
index 81a0f8417a7..7f0b82fa239 100644
--- a/components/script/dom/htmliframeelement.rs
+++ b/components/script/dom/htmliframeelement.rs
@@ -236,7 +236,7 @@ impl HTMLIFrameElement {
             let pipeline_id = self.pipeline_id().unwrap();
             // FIXME(nox): Why are errors silenced here?
             let _ = window.dom_manipulation_task_source().queue(
-                box task!(iframe_load_event_steps: move || {
+                task!(iframe_load_event_steps: move || {
                     this.root().iframe_load_event_steps(pipeline_id);
                 }),
                 window.upcast(),
diff --git a/components/script/dom/htmlimageelement.rs b/components/script/dom/htmlimageelement.rs
index 30ef64da97e..49db07a3242 100644
--- a/components/script/dom/htmlimageelement.rs
+++ b/components/script/dom/htmlimageelement.rs
@@ -174,7 +174,7 @@ impl HTMLImageElement {
                 let image = message.to().unwrap();
                 // FIXME(nox): Why are errors silenced here?
                 let _ = task_source.queue_with_canceller(
-                    box task!(process_image_response: move || {
+                    task!(process_image_response: move || {
                         let element = element.root();
                         // Ignore any image response for a previous request that has been discarded.
                         if generation == element.generation.get() {
@@ -425,7 +425,7 @@ impl HTMLImageElement {
                 // Step 9.
                 // FIXME(nox): Why are errors silenced here?
                 let _ = task_source.queue(
-                    box task!(image_null_source_error: move || {
+                    task!(image_null_source_error: move || {
                         let this = this.root();
                         {
                             let mut current_request =
@@ -451,7 +451,7 @@ impl HTMLImageElement {
         let target = Trusted::new(self.upcast::<EventTarget>());
         // FIXME(nox): Why are errors silenced here?
         let _ = task_source.queue(
-            box task!(fire_progress_event: move || {
+            task!(fire_progress_event: move || {
                 let target = target.root();
 
                 let event = ProgressEvent::new(
@@ -480,7 +480,7 @@ impl HTMLImageElement {
                 let src = String::from(src);
                 // FIXME(nox): Why are errors silenced here?
                 let _ = task_source.queue(
-                    box task!(image_selected_source_error: move || {
+                    task!(image_selected_source_error: move || {
                         let this = this.root();
                         {
                             let mut current_request =
@@ -549,7 +549,7 @@ impl HTMLImageElement {
                     let this = Trusted::new(self);
                     let src = String::from(src);
                     let _ = window.dom_manipulation_task_source().queue(
-                        box task!(image_load_event: move || {
+                        task!(image_load_event: move || {
                             let this = this.root();
                             {
                                 let mut current_request =
diff --git a/components/script/dom/htmlmediaelement.rs b/components/script/dom/htmlmediaelement.rs
index 594c0ea221e..3700a64364e 100644
--- a/components/script/dom/htmlmediaelement.rs
+++ b/components/script/dom/htmlmediaelement.rs
@@ -154,7 +154,7 @@ impl HTMLMediaElement {
             let target = Trusted::new(self.upcast::<EventTarget>());
             // FIXME(nox): Why are errors silenced here?
             let _ = window.dom_manipulation_task_source().queue(
-                box task!(internal_pause_steps: move || {
+                task!(internal_pause_steps: move || {
                     let target = target.root();
 
                     // Step 2.3.1.
@@ -186,7 +186,7 @@ impl HTMLMediaElement {
         let window = window_from_node(self);
         // FIXME(nox): Why are errors silenced here?
         let _ = window.dom_manipulation_task_source().queue(
-            box task!(notify_about_playing: move || {
+            task!(notify_about_playing: move || {
                 let target = target.root();
 
                 // Step 2.1.
@@ -495,7 +495,7 @@ impl HTMLMediaElement {
         let window = window_from_node(self);
         // FIXME(nox): Why are errors silenced here?
         let _ = window.dom_manipulation_task_source().queue(
-            box task!(dedicated_media_source_failure_steps: move || {
+            task!(dedicated_media_source_failure_steps: move || {
                 let this = this.root();
 
                 // Step 1.
diff --git a/components/script/dom/serviceworker.rs b/components/script/dom/serviceworker.rs
index 9a4d85caa69..51c75309050 100644
--- a/components/script/dom/serviceworker.rs
+++ b/components/script/dom/serviceworker.rs
@@ -19,7 +19,7 @@ use js::jsapi::{HandleValue, JSContext};
 use script_traits::{ScriptMsg, DOMMessage};
 use servo_url::ServoUrl;
 use std::cell::Cell;
-use task::TaskBox;
+use task::TaskOnce;
 
 pub type TrustedServiceWorkerAddress = Trusted<ServiceWorker>;
 
@@ -104,10 +104,9 @@ impl ServiceWorkerMethods for ServiceWorker {
     event_handler!(statechange, GetOnstatechange, SetOnstatechange);
 }
 
-impl TaskBox for SimpleWorkerErrorHandler<ServiceWorker> {
+impl TaskOnce for SimpleWorkerErrorHandler<ServiceWorker> {
     #[allow(unrooted_must_root)]
-    fn run_box(self: Box<Self>) {
-        let this = *self;
-        ServiceWorker::dispatch_simple_error(this.addr);
+    fn run_once(self) {
+        ServiceWorker::dispatch_simple_error(self.addr);
     }
 }
diff --git a/components/script/dom/storage.rs b/components/script/dom/storage.rs
index 3dbada1b334..e7b948e46d6 100644
--- a/components/script/dom/storage.rs
+++ b/components/script/dom/storage.rs
@@ -167,7 +167,7 @@ impl Storage {
         let global = self.global();
         let this = Trusted::new(self);
         global.as_window().dom_manipulation_task_source().queue(
-            box task!(send_storage_notification: move || {
+            task!(send_storage_notification: move || {
                 let this = this.root();
                 let global = this.global();
                 let event = StorageEvent::new(
diff --git a/components/script/dom/websocket.rs b/components/script/dom/websocket.rs
index bb48cec942e..3d482bb4fa5 100644
--- a/components/script/dom/websocket.rs
+++ b/components/script/dom/websocket.rs
@@ -37,7 +37,7 @@ use std::borrow::ToOwned;
 use std::cell::Cell;
 use std::ptr;
 use std::thread;
-use task::{TaskBox, TaskCanceller};
+use task::{TaskOnce, TaskCanceller};
 use task_source::TaskSource;
 use task_source::networking::NetworkingTaskSource;
 
@@ -74,7 +74,7 @@ pub fn close_the_websocket_connection(
     code: Option<u16>,
     reason: String,
 ) {
-    let close_task = box CloseTask {
+    let close_task = CloseTask {
         address: address,
         failed: false,
         code: code,
@@ -88,7 +88,7 @@ pub fn fail_the_websocket_connection(
     task_source: &NetworkingTaskSource,
     canceller: &TaskCanceller,
 ) {
-    let close_task = box CloseTask {
+    let close_task = CloseTask {
         address: address,
         failed: true,
         code: Some(close_code::ABNORMAL),
@@ -206,14 +206,14 @@ impl WebSocket {
             while let Ok(event) = dom_event_receiver.recv() {
                 match event {
                     WebSocketNetworkEvent::ConnectionEstablished { protocol_in_use } => {
-                        let open_thread = box ConnectionEstablishedTask {
+                        let open_thread = ConnectionEstablishedTask {
                             address: address.clone(),
                             protocol_in_use,
                         };
                         task_source.queue_with_canceller(open_thread, &canceller).unwrap();
                     },
                     WebSocketNetworkEvent::MessageReceived(message) => {
-                        let message_thread = box MessageReceivedTask {
+                        let message_thread = MessageReceivedTask {
                             address: address.clone(),
                             message: message,
                         };
@@ -397,9 +397,9 @@ struct ConnectionEstablishedTask {
     protocol_in_use: Option<String>,
 }
 
-impl TaskBox for ConnectionEstablishedTask {
+impl TaskOnce for ConnectionEstablishedTask {
     /// https://html.spec.whatwg.org/multipage/#feedback-from-the-protocol:concept-websocket-established
-    fn run_box(self: Box<Self>) {
+    fn run_once(self) {
         let ws = self.address.root();
 
         // Step 1.
@@ -422,13 +422,13 @@ struct BufferedAmountTask {
     address: Trusted<WebSocket>,
 }
 
-impl TaskBox for BufferedAmountTask {
+impl TaskOnce for BufferedAmountTask {
     // See https://html.spec.whatwg.org/multipage/#dom-websocket-bufferedamount
     //
     // To be compliant with standards, we need to reset bufferedAmount only when the event loop
     // reaches step 1.  In our implementation, the bytes will already have been sent on a background
     // thread.
-    fn run_box(self: Box<Self>) {
+    fn run_once(self) {
         let ws = self.address.root();
 
         ws.buffered_amount.set(0);
@@ -443,8 +443,8 @@ struct CloseTask {
     reason: Option<String>,
 }
 
-impl TaskBox for CloseTask {
-    fn run_box(self: Box<Self>) {
+impl TaskOnce for CloseTask {
+    fn run_once(self) {
         let ws = self.address.root();
 
         if ws.ready_state.get() == WebSocketRequestState::Closed {
@@ -483,9 +483,9 @@ struct MessageReceivedTask {
     message: MessageData,
 }
 
-impl TaskBox for MessageReceivedTask {
+impl TaskOnce for MessageReceivedTask {
     #[allow(unsafe_code)]
-    fn run_box(self: Box<Self>) {
+    fn run_once(self) {
         let ws = self.address.root();
         debug!("MessageReceivedTask::handler({:p}): readyState={:?}", &*ws,
                ws.ready_state.get());
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index c4a22c70757..1cb38d0a7ca 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -1977,7 +1977,7 @@ impl Window {
         serialize_with_transfer_result: StructuredCloneData,
     ) {
         let this = Trusted::new(self);
-        let task = box task!(post_serialised_message: move || {
+        let task = task!(post_serialised_message: move || {
             let this = this.root();
 
             // Step 7.1.
@@ -2012,7 +2012,7 @@ impl Window {
         // TODO(#12718): Use the "posted message task source".
         let _ = self.script_chan.send(CommonScriptMsg::Task(
             ScriptThreadEventCategory::DomEvent,
-            self.task_canceller().wrap_task(task),
+            box self.task_canceller().wrap_task(task),
         ));
     }
 }
diff --git a/components/script/dom/worker.rs b/components/script/dom/worker.rs
index cf62e46e456..7d9a3875f1b 100644
--- a/components/script/dom/worker.rs
+++ b/components/script/dom/worker.rs
@@ -28,7 +28,7 @@ use std::cell::Cell;
 use std::sync::{Arc, Mutex};
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::mpsc::{Sender, channel};
-use task::TaskBox;
+use task::TaskOnce;
 
 pub type TrustedWorkerAddress = Trusted<Worker>;
 
@@ -175,10 +175,9 @@ impl WorkerMethods for Worker {
     event_handler!(error, GetOnerror, SetOnerror);
 }
 
-impl TaskBox for SimpleWorkerErrorHandler<Worker> {
+impl TaskOnce for SimpleWorkerErrorHandler<Worker> {
     #[allow(unrooted_must_root)]
-    fn run_box(self: Box<Self>) {
-        let this = *self;
-        Worker::dispatch_simple_error(this.addr);
+    fn run_once(self) {
+        Worker::dispatch_simple_error(self.addr);
     }
 }
diff --git a/components/script/network_listener.rs b/components/script/network_listener.rs
index 10bce087064..1e86f61dffe 100644
--- a/components/script/network_listener.rs
+++ b/components/script/network_listener.rs
@@ -4,7 +4,7 @@
 
 use net_traits::{Action, FetchResponseListener, FetchResponseMsg};
 use std::sync::{Arc, Mutex};
-use task::{TaskBox, TaskCanceller};
+use task::{TaskCanceller, TaskOnce};
 use task_source::TaskSource;
 use task_source::networking::NetworkingTaskSource;
 
@@ -18,7 +18,7 @@ pub struct NetworkListener<Listener: PreInvoke + Send + 'static> {
 
 impl<Listener: PreInvoke + Send + 'static> NetworkListener<Listener> {
     pub fn notify<A: Action<Listener> + Send + 'static>(&self, action: A) {
-        let task = box ListenerTask {
+        let task = ListenerTask {
             context: self.context.clone(),
             action: action,
         };
@@ -55,16 +55,15 @@ struct ListenerTask<A: Action<Listener> + Send + 'static, Listener: PreInvoke +
     action: A,
 }
 
-impl<A, Listener> TaskBox for ListenerTask<A, Listener>
+impl<A, Listener> TaskOnce for ListenerTask<A, Listener>
 where
     A: Action<Listener> + Send + 'static,
     Listener: PreInvoke + Send,
 {
-    fn run_box(self: Box<Self>) {
-        let this = *self;
-        let mut context = this.context.lock().unwrap();
+    fn run_once(self) {
+        let mut context = self.context.lock().unwrap();
         if context.should_invoke() {
-            this.action.process(&mut *context);
+            self.action.process(&mut *context);
         }
     }
 }
diff --git a/components/script/serviceworkerjob.rs b/components/script/serviceworkerjob.rs
index cae17fc65b1..07d6c13ecfb 100644
--- a/components/script/serviceworkerjob.rs
+++ b/components/script/serviceworkerjob.rs
@@ -275,7 +275,7 @@ fn queue_settle_promise_for_job(job: &Job, settle: SettleType, task_source: &DOM
     let promise = TrustedPromise::new(job.promise.clone());
     // FIXME(nox): Why are errors silenced here?
     let _ = task_source.queue(
-        box task!(settle_promise_for_job: move || {
+        task!(settle_promise_for_job: move || {
             let promise = promise.root();
             settle_job_promise(&promise.global(), &promise, settle)
         }),
diff --git a/components/script/task.rs b/components/script/task.rs
index 83ed7737190..e90fc21c55c 100644
--- a/components/script/task.rs
+++ b/components/script/task.rs
@@ -13,7 +13,7 @@ macro_rules! task {
     ($name:ident: move || $body:tt) => {{
         #[allow(non_camel_case_types)]
         struct $name<F>(F);
-        impl<F> ::task::TaskBox for $name<F>
+        impl<F> ::task::TaskOnce for $name<F>
         where
             F: ::std::ops::FnOnce() + Send,
         {
@@ -21,7 +21,7 @@ macro_rules! task {
                 stringify!($name)
             }
 
-            fn run_box(self: Box<Self>) {
+            fn run_once(self) {
                 (self.0)();
             }
         }
@@ -30,14 +30,35 @@ macro_rules! task {
 }
 
 /// A task that can be run. The name method is for profiling purposes.
-///
-/// All tasks must be boxed to be run.
-pub trait TaskBox: Send {
+pub trait TaskOnce: Send {
     #[allow(unsafe_code)]
-    fn name(&self) -> &'static str { unsafe { intrinsics::type_name::<Self>() } }
+    fn name(&self) -> &'static str {
+        unsafe { intrinsics::type_name::<Self>() }
+    }
+
+    fn run_once(self);
+}
+
+/// A boxed version of `TaskOnce`.
+pub trait TaskBox: Send {
+    fn name(&self) -> &'static str;
+
     fn run_box(self: Box<Self>);
 }
 
+impl<T> TaskBox for T
+where
+    T: TaskOnce,
+{
+    fn name(&self) -> &'static str {
+        TaskOnce::name(self)
+    }
+
+    fn run_box(self: Box<Self>) {
+        self.run_once()
+    }
+}
+
 impl fmt::Debug for TaskBox {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         fmt.debug_tuple(self.name()).field(&format_args!("...")).finish()
@@ -52,11 +73,11 @@ pub struct TaskCanceller {
 impl TaskCanceller {
     /// Returns a wrapped `task` that will be cancelled if the `TaskCanceller`
     /// says so.
-    pub fn wrap_task<T>(&self, task: Box<T>) -> Box<TaskBox>
+    pub fn wrap_task<T>(&self, task: T) -> impl TaskOnce
     where
-        T: TaskBox + 'static,
+        T: TaskOnce,
     {
-        box CancellableTask {
+        CancellableTask {
             cancelled: self.cancelled.clone(),
             inner: task,
         }
@@ -64,14 +85,14 @@ impl TaskCanceller {
 }
 
 /// A task that can be cancelled by toggling a shared flag.
-pub struct CancellableTask<T: TaskBox> {
+pub struct CancellableTask<T: TaskOnce> {
     cancelled: Option<Arc<AtomicBool>>,
-    inner: Box<T>,
+    inner: T,
 }
 
 impl<T> CancellableTask<T>
 where
-    T: TaskBox,
+    T: TaskOnce,
 {
     fn is_cancelled(&self) -> bool {
         self.cancelled.as_ref().map_or(false, |cancelled| {
@@ -80,17 +101,17 @@ where
     }
 }
 
-impl<T> TaskBox for CancellableTask<T>
+impl<T> TaskOnce for CancellableTask<T>
 where
-    T: TaskBox,
+    T: TaskOnce,
 {
     fn name(&self) -> &'static str {
         self.inner.name()
     }
 
-    fn run_box(self: Box<Self>) {
+    fn run_once(self) {
         if !self.is_cancelled() {
-            self.inner.run_box()
+            self.inner.run_once()
         }
     }
 }
diff --git a/components/script/task_source/dom_manipulation.rs b/components/script/task_source/dom_manipulation.rs
index f5f38e68044..30dd3df8851 100644
--- a/components/script/task_source/dom_manipulation.rs
+++ b/components/script/task_source/dom_manipulation.rs
@@ -13,7 +13,7 @@ use servo_atoms::Atom;
 use std::fmt;
 use std::result::Result;
 use std::sync::mpsc::Sender;
-use task::{TaskBox, TaskCanceller};
+use task::{TaskCanceller, TaskOnce};
 use task_source::TaskSource;
 
 #[derive(Clone, JSTraceable)]
@@ -28,15 +28,15 @@ impl fmt::Debug for DOMManipulationTaskSource {
 impl TaskSource for DOMManipulationTaskSource {
     fn queue_with_canceller<T>(
         &self,
-        msg: Box<T>,
+        task: T,
         canceller: &TaskCanceller,
     ) -> Result<(), ()>
     where
-        T: TaskBox + 'static,
+        T: TaskOnce + 'static,
     {
         let msg = MainThreadScriptMsg::Common(CommonScriptMsg::Task(
             ScriptThreadEventCategory::ScriptEvent,
-            canceller.wrap_task(msg),
+            box canceller.wrap_task(task),
         ));
         self.0.send(msg).map_err(|_| ())
     }
@@ -50,7 +50,7 @@ impl DOMManipulationTaskSource {
                        cancelable: EventCancelable,
                        window: &Window) {
         let target = Trusted::new(target);
-        let task = box EventTask {
+        let task = EventTask {
             target: target,
             name: name,
             bubbles: bubbles,
@@ -61,6 +61,6 @@ impl DOMManipulationTaskSource {
 
     pub fn queue_simple_event(&self, target: &EventTarget, name: Atom, window: &Window) {
         let target = Trusted::new(target);
-        let _ = self.queue(box SimpleEventTask { target, name }, window.upcast());
+        let _ = self.queue(SimpleEventTask { target, name }, window.upcast());
     }
 }
diff --git a/components/script/task_source/file_reading.rs b/components/script/task_source/file_reading.rs
index 2ed44165b92..fc9af75794c 100644
--- a/components/script/task_source/file_reading.rs
+++ b/components/script/task_source/file_reading.rs
@@ -6,7 +6,7 @@ use dom::domexception::DOMErrorName;
 use dom::filereader::{FileReader, TrustedFileReader, GenerationId, ReadMetaData};
 use script_runtime::{CommonScriptMsg, ScriptThreadEventCategory, ScriptChan};
 use std::sync::Arc;
-use task::{TaskBox, TaskCanceller};
+use task::{TaskCanceller, TaskOnce};
 use task_source::TaskSource;
 
 #[derive(JSTraceable)]
@@ -21,21 +21,21 @@ impl Clone for FileReadingTaskSource {
 impl TaskSource for FileReadingTaskSource {
     fn queue_with_canceller<T>(
         &self,
-        msg: Box<T>,
+        task: T,
         canceller: &TaskCanceller,
     ) -> Result<(), ()>
     where
-        T: TaskBox + 'static,
+        T: TaskOnce + 'static,
     {
         self.0.send(CommonScriptMsg::Task(
             ScriptThreadEventCategory::FileRead,
-            canceller.wrap_task(msg),
+            box canceller.wrap_task(task),
         ))
     }
 }
 
-impl TaskBox for FileReadingTask {
-    fn run_box(self: Box<Self>) {
+impl TaskOnce for FileReadingTask {
+    fn run_once(self) {
         self.handle_task();
     }
 }
diff --git a/components/script/task_source/mod.rs b/components/script/task_source/mod.rs
index e361ccf2d99..4818ba2c80c 100644
--- a/components/script/task_source/mod.rs
+++ b/components/script/task_source/mod.rs
@@ -11,21 +11,21 @@ pub mod user_interaction;
 
 use dom::globalscope::GlobalScope;
 use std::result::Result;
-use task::{TaskBox, TaskCanceller};
+use task::{TaskCanceller, TaskOnce};
 
 pub trait TaskSource {
     fn queue_with_canceller<T>(
         &self,
-        msg: Box<T>,
+        task: T,
         canceller: &TaskCanceller,
     ) -> Result<(), ()>
     where
-        T: TaskBox + 'static;
+        T: TaskOnce + 'static;
 
-    fn queue<T>(&self, msg: Box<T>, global: &GlobalScope) -> Result<(), ()>
+    fn queue<T>(&self, task: T, global: &GlobalScope) -> Result<(), ()>
     where
-        T: TaskBox + 'static,
+        T: TaskOnce + 'static,
     {
-        self.queue_with_canceller(msg, &global.task_canceller())
+        self.queue_with_canceller(task, &global.task_canceller())
     }
 }
diff --git a/components/script/task_source/networking.rs b/components/script/task_source/networking.rs
index 80acc324f52..8b167c5d905 100644
--- a/components/script/task_source/networking.rs
+++ b/components/script/task_source/networking.rs
@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use script_runtime::{CommonScriptMsg, ScriptChan, ScriptThreadEventCategory};
-use task::{TaskBox, TaskCanceller};
+use task::{TaskCanceller, TaskOnce};
 use task_source::TaskSource;
 
 #[derive(JSTraceable)]
@@ -18,15 +18,15 @@ impl Clone for NetworkingTaskSource {
 impl TaskSource for NetworkingTaskSource {
     fn queue_with_canceller<T>(
         &self,
-        msg: Box<T>,
+        task: T,
         canceller: &TaskCanceller,
     ) -> Result<(), ()>
     where
-        T: TaskBox + 'static,
+        T: TaskOnce + 'static,
     {
         self.0.send(CommonScriptMsg::Task(
             ScriptThreadEventCategory::NetworkEvent,
-            canceller.wrap_task(msg),
+            box canceller.wrap_task(task),
         ))
     }
 }
@@ -34,10 +34,13 @@ impl TaskSource for NetworkingTaskSource {
 impl NetworkingTaskSource {
     /// This queues a task that will not be cancelled when its associated
     /// global scope gets destroyed.
-    pub fn queue_unconditionally<T>(&self, msg: Box<T>) -> Result<(), ()>
+    pub fn queue_unconditionally<T>(&self, task: T) -> Result<(), ()>
     where
-        T: TaskBox + 'static,
+        T: TaskOnce + 'static,
     {
-        self.0.send(CommonScriptMsg::Task(ScriptThreadEventCategory::NetworkEvent, msg))
+        self.0.send(CommonScriptMsg::Task(
+            ScriptThreadEventCategory::NetworkEvent,
+            box task,
+        ))
     }
 }
diff --git a/components/script/task_source/performance_timeline.rs b/components/script/task_source/performance_timeline.rs
index 3c77c1527fd..1a3ffeb7fc7 100644
--- a/components/script/task_source/performance_timeline.rs
+++ b/components/script/task_source/performance_timeline.rs
@@ -11,7 +11,7 @@ use dom::globalscope::GlobalScope;
 use script_runtime::{CommonScriptMsg, ScriptChan, ScriptThreadEventCategory};
 use std::fmt;
 use std::result::Result;
-use task::{TaskBox, TaskCanceller};
+use task::{TaskCanceller, TaskOnce};
 use task_source::TaskSource;
 
 #[derive(JSTraceable)]
@@ -32,15 +32,15 @@ impl fmt::Debug for PerformanceTimelineTaskSource {
 impl TaskSource for PerformanceTimelineTaskSource {
     fn queue_with_canceller<T>(
         &self,
-        msg: Box<T>,
+        task: T,
         canceller: &TaskCanceller,
     ) -> Result<(), ()>
     where
-        T: TaskBox + 'static,
+        T: TaskOnce + 'static,
     {
         let msg = CommonScriptMsg::Task(
             ScriptThreadEventCategory::PerformanceTimelineTask,
-            canceller.wrap_task(msg)
+            box canceller.wrap_task(task)
         );
         self.0.send(msg).map_err(|_| ())
     }
@@ -51,7 +51,7 @@ impl PerformanceTimelineTaskSource {
         let owner = Trusted::new(&*global.performance());
         // FIXME(nox): Why are errors silenced here?
         let _ = self.queue(
-            box task!(notify_performance_observers: move || {
+            task!(notify_performance_observers: move || {
                 owner.root().notify_observers();
             }),
             global,
diff --git a/components/script/task_source/user_interaction.rs b/components/script/task_source/user_interaction.rs
index 0ca5687fe46..9891f474529 100644
--- a/components/script/task_source/user_interaction.rs
+++ b/components/script/task_source/user_interaction.rs
@@ -13,7 +13,7 @@ use servo_atoms::Atom;
 use std::fmt;
 use std::result::Result;
 use std::sync::mpsc::Sender;
-use task::{TaskBox, TaskCanceller};
+use task::{TaskCanceller, TaskOnce};
 use task_source::TaskSource;
 
 #[derive(Clone, JSTraceable)]
@@ -28,15 +28,15 @@ impl fmt::Debug for UserInteractionTaskSource {
 impl TaskSource for UserInteractionTaskSource {
     fn queue_with_canceller<T>(
         &self,
-        msg: Box<T>,
+        task: T,
         canceller: &TaskCanceller,
     ) -> Result<(), ()>
     where
-        T: TaskBox + 'static,
+        T: TaskOnce + 'static,
     {
         let msg = MainThreadScriptMsg::Common(CommonScriptMsg::Task(
             ScriptThreadEventCategory::InputEvent,
-            canceller.wrap_task(msg),
+            box canceller.wrap_task(task),
         ));
         self.0.send(msg).map_err(|_| ())
     }
@@ -50,7 +50,7 @@ impl UserInteractionTaskSource {
                        cancelable: EventCancelable,
                        window: &Window) {
         let target = Trusted::new(target);
-        let task = box EventTask { target, name, bubbles, cancelable };
+        let task = EventTask { target, name, bubbles, cancelable };
         let _ = self.queue(task, window.upcast());
     }
 }