Use setTimeout() trick instead of Window.requestIdleCallback()

CHANGELOG.md

@@ -9,6 +9,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 # Unreleased
 
 - Fix window size sometimes being invalid when resizing on macOS.
+- On Web, `ControlFlow::Poll` and `ControlFlow::WaitUntil` are now using the Prioritized Task Scheduling API. `setTimeout()` with a trick to circumvent throttling to 4ms is used as a fallback.
 
 # 0.29.1-beta
 

Cargo.toml

@@ -164,6 +164,8 @@ redox_syscall = "0.3"
 package = "web-sys"
 version = "0.3.64"
 features = [
+    'AbortController',
+    'AbortSignal',
     'console',
     'CssStyleDeclaration',
     'Document',
@@ -179,6 +181,8 @@ features = [
     'IntersectionObserverEntry',
     'KeyboardEvent',
     'MediaQueryList',
+    'MessageChannel',
+    'MessagePort',
     'Node',
     'PageTransitionEvent',
     'PointerEvent',

src/platform_impl/web/event_loop/runner.rs

@@ -627,9 +627,11 @@ impl<T: 'static> Shared<T> {
             ControlFlow::Poll => {
                 let cloned = self.clone();
                 State::Poll {
-                    request: backend::IdleCallback::new(self.window().clone(), move || {
-                        cloned.poll()
-                    }),
+                    request: backend::Schedule::new(
+                        self.window().clone(),
+                        move || cloned.poll(),
+                        None,
+                    ),
                 }
             }
             ControlFlow::Wait => State::Wait {
@@ -649,10 +651,10 @@ impl<T: 'static> Shared<T> {
                 State::WaitUntil {
                     start,
                     end,
-                    timeout: backend::Timeout::new(
+                    timeout: backend::Schedule::new(
                         self.window().clone(),
                         move || cloned.resume_time_reached(start, end),
-                        delay,
+                        Some(delay),
                     ),
                 }
             }

src/platform_impl/web/event_loop/state.rs

@@ -7,15 +7,15 @@ use web_time::Instant;
 pub enum State {
     Init,
     WaitUntil {
-        timeout: backend::Timeout,
+        timeout: backend::Schedule,
         start: Instant,
         end: Instant,
     },
     Wait {
         start: Instant,
     },
     Poll {
-        request: backend::IdleCallback,
+        request: backend::Schedule,
     },
     Exit,
 }

src/platform_impl/web/web_sys/mod.rs

@@ -7,13 +7,13 @@ mod intersection_handle;
 mod media_query_handle;
 mod pointer;
 mod resize_scaling;
-mod timeout;
+mod schedule;
 
 pub use self::canvas::Canvas;
 pub use self::event::ButtonsState;
 pub use self::event_handle::EventListenerHandle;
 pub use self::resize_scaling::ResizeScaleHandle;
-pub use self::timeout::{IdleCallback, Timeout};
+pub use self::schedule::Schedule;
 
 use crate::dpi::{LogicalPosition, LogicalSize};
 use wasm_bindgen::closure::Closure;

src/platform_impl/web/web_sys/schedule.rs

@@ -0,0 +1,182 @@
+use js_sys::{Function, Object, Promise, Reflect};
+use once_cell::unsync::{Lazy, OnceCell};
+use std::time::Duration;
+use wasm_bindgen::closure::Closure;
+use wasm_bindgen::prelude::wasm_bindgen;
+use wasm_bindgen::{JsCast, JsValue};
+use web_sys::{AbortController, AbortSignal, MessageChannel, MessagePort};
+
+#[derive(Debug)]
+pub struct Schedule(Inner);
+
+#[derive(Debug)]
+enum Inner {
+    Scheduler {
+        controller: AbortController,
+        _closure: Closure<dyn FnMut()>,
+    },
+    Timeout {
+        window: web_sys::Window,
+        handle: i32,
+        port: MessagePort,
+        _message_closure: Closure<dyn FnMut()>,
+        _timeout_closure: Closure<dyn FnMut()>,
+    },
+}
+
+impl Schedule {
+    pub fn new<F>(window: web_sys::Window, f: F, duration: Option<Duration>) -> Schedule
+    where
+        F: 'static + FnMut(),
+    {
+        if has_scheduler_support(&window) {
+            Self::new_scheduler(window, f, duration)
+        } else {
+            Self::new_timeout(window, f, duration)
+        }
+    }
+
+    fn new_scheduler<F>(window: web_sys::Window, f: F, duration: Option<Duration>) -> Schedule
+    where
+        F: 'static + FnMut(),
+    {
+        let window: WindowSupportExt = window.unchecked_into();
+        let scheduler = window.scheduler();
+
+        let closure = Closure::new(f);
+        let mut options = SchedulerPostTaskOptions::new();
+        let controller = AbortController::new().expect("Failed to create `AbortController`");
+        options.signal(&controller.signal());
+
+        if let Some(duration) = duration {
+            options.delay(duration.as_millis() as f64);
+        }
+
+        thread_local! {
+            static REJECT_HANDLER: Lazy<Closure<dyn FnMut(JsValue)>> = Lazy::new(|| Closure::new(|_| ()));
+        }
+        REJECT_HANDLER.with(|handler| {
+            let _ = scheduler
+                .post_task_with_options(closure.as_ref().unchecked_ref(), &options)
+                .catch(handler);
+        });
+
+        Schedule(Inner::Scheduler {
+            controller,
+            _closure: closure,
+        })
+    }
+
+    fn new_timeout<F>(window: web_sys::Window, f: F, duration: Option<Duration>) -> Schedule
+    where
+        F: 'static + FnMut(),
+    {
+        let channel = MessageChannel::new().unwrap();
+        let message_closure = Closure::new(f);
+        let port_1 = channel.port1();
+        port_1
+            .add_event_listener_with_callback("message", message_closure.as_ref().unchecked_ref())
+            .expect("Failed to set message handler");
+        port_1.start();
+
+        let port_2 = channel.port2();
+        let timeout_closure = Closure::new(move || {
+            port_2
+                .post_message(&JsValue::UNDEFINED)
+                .expect("Failed to send message")
+        });
+        let handle = if let Some(duration) = duration {
+            window.set_timeout_with_callback_and_timeout_and_arguments_0(
+                timeout_closure.as_ref().unchecked_ref(),
+                duration.as_millis() as i32,
+            )
+        } else {
+            window.set_timeout_with_callback(timeout_closure.as_ref().unchecked_ref())
+        }
+        .expect("Failed to set timeout");
+
+        Schedule(Inner::Timeout {
+            window,
+            handle,
+            port: port_1,
+            _message_closure: message_closure,
+            _timeout_closure: timeout_closure,
+        })
+    }
+}
+
+impl Drop for Schedule {
+    fn drop(&mut self) {
+        match &self.0 {
+            Inner::Scheduler { controller, .. } => controller.abort(),
+            Inner::Timeout {
+                window,
+                handle,
+                port,
+                ..
+            } => {
+                window.clear_timeout_with_handle(*handle);
+                port.close();
+            }
+        }
+    }
+}
+
+fn has_scheduler_support(window: &web_sys::Window) -> bool {
+    thread_local! {
+        static SCHEDULER_SUPPORT: OnceCell<bool> = OnceCell::new();
+    }
+
+    SCHEDULER_SUPPORT.with(|support| {
+        *support.get_or_init(|| {
+            #[wasm_bindgen]
+            extern "C" {
+                type SchedulerSupport;
+
+                #[wasm_bindgen(method, getter, js_name = scheduler)]
+                fn has_scheduler(this: &SchedulerSupport) -> JsValue;
+            }
+
+            let support: &SchedulerSupport = window.unchecked_ref();
+
+            !support.has_scheduler().is_undefined()
+        })
+    })
+}
+
+#[wasm_bindgen]
+extern "C" {
+    type WindowSupportExt;
+
+    #[wasm_bindgen(method, getter)]
+    fn scheduler(this: &WindowSupportExt) -> Scheduler;
+
+    type Scheduler;
+
+    #[wasm_bindgen(method, js_name = postTask)]
+    fn post_task_with_options(
+        this: &Scheduler,
+        callback: &Function,
+        options: &SchedulerPostTaskOptions,
+    ) -> Promise;
+
+    type SchedulerPostTaskOptions;
+}
+
+impl SchedulerPostTaskOptions {
+    fn new() -> Self {
+        Object::new().unchecked_into()
+    }
+
+    fn delay(&mut self, val: f64) -> &mut Self {
+        let r = Reflect::set(self, &JsValue::from("delay"), &val.into());
+        debug_assert!(r.is_ok(), "Failed to set `delay` property");
+        self
+    }
+
+    fn signal(&mut self, val: &AbortSignal) -> &mut Self {
+        let r = Reflect::set(self, &JsValue::from("signal"), &val.into());
+        debug_assert!(r.is_ok(), "Failed to set `signal` property");
+        self
+    }
+}