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Add support for timers on web platforms
This commit adds support for async-io on wasm32-unknown-unknown. Not all features of async-io can be ported to WASM; for instance: - Async<T> can't be ported over as WASM doesn't really have a reactor. WASI could eventually be supported here, but that is dependent on smol-rs/polling#102 - block_on() can't be ported over, as blocking isn't allowed on the web. The only thing left is Timer, which can be implemented using setTimeout and setInterval. So that's what's been done: when the WASM target family is enabled, Async<T> and block_on() will be disabled and Timer will switch to an implementation that uses web timeouts. This is not a breaking change, as this crate previously failed to compile on web platforms anyways. This functionality currently does not support Node.js. Signed-off-by: John Nunley <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,212 @@ | ||
| //! Timers for web targets. | ||
| //! | ||
| //! These use the `setTimeout` function on the web to handle timing. | ||
| use std::convert::TryInto; | ||
| use std::sync::atomic::{AtomicUsize, Ordering}; | ||
| use std::sync::Arc; | ||
| use std::task::{Context, Poll}; | ||
| use std::time::Duration; | ||
|
|
||
| use atomic_waker::AtomicWaker; | ||
| use wasm_bindgen::closure::Closure; | ||
| use wasm_bindgen::JsCast; | ||
|
|
||
| /// A timer for non-Web platforms. | ||
| /// | ||
| /// self registers a timeout in the global reactor, which in turn sets a timeout in the poll call. | ||
| #[derive(Debug)] | ||
| pub(super) struct Timer { | ||
| /// The waker to wake when the timer fires. | ||
| waker: Arc<State>, | ||
|
|
||
| /// The ongoing timeout or interval. | ||
| ongoing_timeout: TimerId, | ||
|
|
||
| /// Keep the closure alive so we don't drop it. | ||
| closure: Option<Closure<dyn FnMut()>>, | ||
| } | ||
|
|
||
| #[derive(Debug)] | ||
| struct State { | ||
| /// The number of times this timer has been woken. | ||
| woken: AtomicUsize, | ||
|
|
||
| /// The waker to wake when the timer fires. | ||
| waker: AtomicWaker, | ||
| } | ||
|
|
||
| #[derive(Debug)] | ||
| enum TimerId { | ||
| NoTimer, | ||
| Timeout(i32), | ||
| Interval(i32), | ||
| } | ||
|
|
||
| impl Timer { | ||
| /// Create a timer that will never fire. | ||
| #[inline] | ||
| pub(super) fn never() -> Self { | ||
| Self { | ||
| waker: Arc::new(State { | ||
| woken: AtomicUsize::new(0), | ||
| waker: AtomicWaker::new(), | ||
| }), | ||
| ongoing_timeout: TimerId::NoTimer, | ||
| closure: None, | ||
| } | ||
| } | ||
|
|
||
| /// Create a timer that will fire at the given instant. | ||
| #[inline] | ||
| pub(super) fn after(duration: Duration) -> Timer { | ||
| let mut this = Self::never(); | ||
| this.set_after(duration); | ||
| this | ||
| } | ||
|
|
||
| /// Create a timer that will fire at the given instant. | ||
| #[inline] | ||
| pub(super) fn interval(period: Duration) -> Timer { | ||
| let mut this = Self::never(); | ||
| this.set_interval(period); | ||
| this | ||
| } | ||
|
|
||
| /// Returns `true` if self timer will fire at some point. | ||
| #[inline] | ||
| pub(super) fn will_fire(&self) -> bool { | ||
| matches!( | ||
| self.ongoing_timeout, | ||
| TimerId::Timeout(_) | TimerId::Interval(_) | ||
| ) | ||
| } | ||
|
|
||
| /// Set the timer to fire after the given duration. | ||
| #[inline] | ||
| pub(super) fn set_after(&mut self, duration: Duration) { | ||
| // Set the timeout. | ||
| let id = { | ||
| let waker = self.waker.clone(); | ||
| let closure: Closure<dyn FnMut()> = Closure::wrap(Box::new(move || { | ||
| waker.wake(); | ||
| })); | ||
|
|
||
| let result = web_sys::window() | ||
| .unwrap() | ||
| .set_timeout_with_callback_and_timeout_and_arguments_0( | ||
| closure.as_ref().unchecked_ref(), | ||
| duration.as_millis().try_into().expect("timeout too long"), | ||
| ); | ||
|
|
||
| // Make sure we don't drop the closure before it's called. | ||
| self.closure = Some(closure); | ||
|
|
||
| match result { | ||
| Ok(id) => id, | ||
| Err(_) => { | ||
| panic!("failed to set timeout") | ||
| } | ||
| } | ||
| }; | ||
|
|
||
| // Set our ID. | ||
| self.ongoing_timeout = TimerId::Timeout(id); | ||
| } | ||
|
|
||
| /// Set the timer to emit events periodically. | ||
| #[inline] | ||
| pub(super) fn set_interval(&mut self, period: Duration) { | ||
| // Set the timeout. | ||
| let id = { | ||
| let waker = self.waker.clone(); | ||
| let closure: Closure<dyn FnMut()> = Closure::wrap(Box::new(move || { | ||
| waker.wake(); | ||
| })); | ||
|
|
||
| let result = web_sys::window() | ||
| .unwrap() | ||
| .set_interval_with_callback_and_timeout_and_arguments_0( | ||
| closure.as_ref().unchecked_ref(), | ||
| period.as_millis().try_into().expect("timeout too long"), | ||
| ); | ||
|
|
||
| // Make sure we don't drop the closure before it's called. | ||
| self.closure = Some(closure); | ||
|
|
||
| match result { | ||
| Ok(id) => id, | ||
| Err(_) => { | ||
| panic!("failed to set interval") | ||
| } | ||
| } | ||
| }; | ||
|
|
||
| // Set our ID. | ||
| self.ongoing_timeout = TimerId::Interval(id); | ||
| } | ||
|
|
||
| /// Poll for the next timer event. | ||
| #[inline] | ||
| pub(super) fn poll_next(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> { | ||
| let mut registered = false; | ||
| let mut woken = self.waker.woken.load(Ordering::Acquire); | ||
|
|
||
| loop { | ||
| if woken > 0 { | ||
| // Try to decrement the number of woken events. | ||
| if let Err(new_woken) = self.waker.woken.compare_exchange( | ||
| woken, | ||
| woken - 1, | ||
| Ordering::SeqCst, | ||
| Ordering::Acquire, | ||
| ) { | ||
| woken = new_woken; | ||
| continue; | ||
| } | ||
|
|
||
| // If we are using a one-shot timer, clear it. | ||
| if let TimerId::Timeout(_) = self.ongoing_timeout { | ||
| self.clear(); | ||
| } | ||
|
|
||
| return Poll::Ready(Some(())); | ||
| } | ||
|
|
||
| if !registered { | ||
| // Register the waker. | ||
| self.waker.waker.register(cx.waker()); | ||
| registered = true; | ||
| } else { | ||
| // We've already registered, so we can just return pending. | ||
| return Poll::Pending; | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// Clear the current timeout. | ||
| fn clear(&mut self) { | ||
| match self.ongoing_timeout { | ||
| TimerId::NoTimer => {} | ||
| TimerId::Timeout(id) => { | ||
| web_sys::window().unwrap().clear_timeout_with_handle(id); | ||
| } | ||
| TimerId::Interval(id) => { | ||
| web_sys::window().unwrap().clear_interval_with_handle(id); | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl State { | ||
| fn wake(&self) { | ||
| self.woken.fetch_add(1, Ordering::SeqCst); | ||
| self.waker.wake(); | ||
| } | ||
| } | ||
|
|
||
| impl Drop for Timer { | ||
| fn drop(&mut self) { | ||
| self.clear(); | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,3 +1,5 @@ | ||
| #![cfg(not(target_family = "wasm"))] | ||
|
|
||
| use async_io::block_on; | ||
| use std::{ | ||
| future::Future, | ||
|
|
||
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