mirror of
https://github.com/fluencelabs/wasm-bindgen
synced 2025-06-24 02:01:35 +00:00
Clean up atomics/futures + polyfill
* Remove now-unneeded `State` enum * Remove timeout argument from polyfill since we don't need it * Call `Atomics.waitAsync` if it's available instead of using our polyfill * Remove some extraneous dead code from the polyfill * Add a `val: i32` argument to the polyfill * Simplify the flow of futures with `Package` since `waitAsync` handles all the heavy lifting for us. * Remove `Arc<Package>` and just use `Package` * Remove `RefCell` from inside of `Package` now that it is no longer needed.
This commit is contained in:
Alex Crichton
@ -1,4 +1,4 @@
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use std::cell::{Cell, RefCell};
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use std::cell::RefCell;
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use std::fmt;
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use std::rc::Rc;
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use std::sync::atomic::{AtomicI32, Ordering};
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@ -8,8 +8,9 @@ use futures::executor::{self, Notify, Spawn};
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use futures::future;
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use futures::prelude::*;
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use futures::sync::oneshot;
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use js_sys::{Function, Promise};
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use js_sys::Function;
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use wasm_bindgen::prelude::*;
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use wasm_bindgen::JsCast;
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/// A Rust `Future` backed by a JavaScript `Promise`.
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///
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@ -23,14 +24,28 @@ pub struct JsFuture {
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rx: oneshot::Receiver<Result<JsValue, JsValue>>,
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}
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// Duplicate a bit here because `then` takes a `JsValue` instead of a `Closure`.
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#[wasm_bindgen]
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extern "C" {
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type Promise;
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#[wasm_bindgen(method)]
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fn then(this: &Promise, cb: &JsValue) -> Promise;
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type Atomics;
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#[wasm_bindgen(static_method_of = Atomics, js_name = waitAsync)]
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fn wait_async(buf: &JsValue, index: i32, value: i32) -> js_sys::Promise;
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#[wasm_bindgen(static_method_of = Atomics, js_name = waitAsync, getter)]
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fn get_wait_async() -> JsValue;
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}
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impl fmt::Debug for JsFuture {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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write!(f, "JsFuture {{ ... }}")
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}
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}
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impl From<Promise> for JsFuture {
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fn from(js: Promise) -> JsFuture {
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impl From<js_sys::Promise> for JsFuture {
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fn from(js: js_sys::Promise) -> JsFuture {
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// Use the `then` method to schedule two callbacks, one for the
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// resolved value and one for the rejected value. We're currently
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// assuming that JS engines will unconditionally invoke precisely one of
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@ -112,205 +127,132 @@ impl Future for JsFuture {
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/// If the `future` provided panics then the returned `Promise` **will not
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/// resolve**. Instead it will be a leaked promise. This is an unfortunate
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/// limitation of wasm currently that's hoped to be fixed one day!
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pub fn future_to_promise<F>(future: F) -> Promise
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where
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F: Future<Item = JsValue, Error = JsValue> + 'static,
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pub fn future_to_promise<F>(future: F) -> js_sys::Promise
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where
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F: Future<Item = JsValue, Error = JsValue> + 'static,
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{
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_future_to_promise(Box::new(future))
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}
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// Implementation of actually transforming a future into a JavaScript `Promise`.
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//
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// The only primitive we have to work with here is `Promise::new`, which gives
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// us two callbacks that we can use to either reject or resolve the promise.
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// It's our job to ensure that one of those callbacks is called at the
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// appropriate time.
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// The main primitives used here are `Promise::new` to actually create a JS
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// promise to return as well as `Atomics.waitAsync` to create a promise that we
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// can asynchronously wait on. The general idea here is that we'll create a
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// promise to return and schedule work to happen in `Atomics.waitAsync`
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// callbacks.
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//
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// Now we know that JavaScript (in general) can't block and is largely
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// notification/callback driven. That means that our future must either have
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// synchronous computational work to do, or it's "scheduled a notification" to
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// happen. These notifications are likely callbacks to get executed when things
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// finish (like a different promise or something like `setTimeout`). The general
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// idea here is thus to do as much synchronous work as we can and then otherwise
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// translate notifications of a future's task into "let's poll the future!"
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//
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// This isn't necessarily the greatest future executor in the world, but it
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// should get the job done for now hopefully.
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fn _future_to_promise(future: Box<dyn Future<Item = JsValue, Error = JsValue>>) -> Promise {
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// After we've created a promise we start polling a future, and whenever it's
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// not ready we'll execute `Atomics.waitAsync`. When that resolves we'll keep
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// polling the future, and this happens until the future is done. Finally
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// when it's all finished we call either resolver or reject depending on the
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// result of the future.
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fn _future_to_promise(future: Box<dyn Future<Item = JsValue, Error = JsValue>>) -> js_sys::Promise {
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let mut future = Some(executor::spawn(future));
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return Promise::new(&mut |resolve, reject| {
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Package::poll(&Arc::new(Package {
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spawn: RefCell::new(future.take().unwrap()),
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return js_sys::Promise::new(&mut |resolve, reject| {
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Package {
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spawn: future.take().unwrap(),
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resolve,
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reject,
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notified: Cell::new(State::Notified),
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waker: Arc::new(Waker::default()),
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}));
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waker: Arc::new(Waker {
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value: AtomicI32::new(1), // 1 == "notified, ready to poll"
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}),
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}
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.poll();
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});
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struct Package {
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// Our "spawned future". This'll have everything we need to poll the
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// future and continue to move it forward.
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spawn: RefCell<Spawn<Box<dyn Future<Item = JsValue, Error = JsValue>>>>,
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// The current state of this future, expressed in an enum below. This
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// indicates whether we're currently polling the future, received a
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// notification and need to keep polling, or if we're waiting for a
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// notification to come in (and no one is polling).
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notified: Cell<State>,
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spawn: Spawn<Box<dyn Future<Item = JsValue, Error = JsValue>>>,
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// Our two callbacks connected to the `Promise` that we returned to
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// JavaScript. We'll be invoking one of these at the end.
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resolve: Function,
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reject: Function,
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// Struct to wake a future
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// Shared state used to communicate waking up this future, this is the
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// `Send + Sync` piece needed by the async task system.
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waker: Arc<Waker>,
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}
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// The possible states our `Package` (future) can be in, tracked internally
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// and used to guide what happens when polling a future.
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enum State {
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// This future is currently and actively being polled. Attempting to
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// access the future will result in a runtime panic and is considered a
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// bug.
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Polling,
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// This future has been notified, while it was being polled. This marker
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// is used in the `Notify` implementation below, and indicates that a
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// notification was received that the future is ready to make progress.
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// If seen, however, it probably means that the future is also currently
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// being polled.
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Notified,
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// The future is blocked, waiting for something to happen. Stored here
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// is a self-reference to the future itself so we can pull it out in
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// `Notify` and continue polling.
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//
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// Note that the self-reference here is an Arc-cycle that will leak
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// memory unless the future completes, but currently that should be ok
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// as we'll have to stick around anyway while the future is executing!
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//
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// This state is removed as soon as a notification comes in, so the leak
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// should only be "temporary"
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Waiting(Arc<Package>),
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}
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#[derive(Default)]
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struct Waker {
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// worker will be waiting on this value
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// 0 by default, which means not notified
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value: AtomicI32,
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};
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impl Notify for Waker {
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fn notify(&self, _id: usize) {
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// since we have only value field here
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// let it be 1 if notified, 0 if not
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if self.value.swap(1, Ordering::SeqCst) == 0 {
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let _ = unsafe {
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core::arch::wasm32::atomic_notify(
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&self.value as *const AtomicI32 as *mut i32,
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std::u32::MAX, // number of threads to notify
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)
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};
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// Attempt to notify us by storing 1. If we're already 1 then we
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// were previously notified and there's nothing to do. Otherwise
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// we execute the native `notify` instruction to wake up the
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// corresponding `waitAsync` that was waiting for the transition
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// from 0 to 1.
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let prev = self.value.swap(1, Ordering::SeqCst);
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if prev == 1 {
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return;
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}
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debug_assert_eq!(prev, 0);
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unsafe {
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core::arch::wasm32::atomic_notify(
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&self.value as *const AtomicI32 as *mut i32,
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1, // number of threads to notify
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);
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}
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}
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}
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fn poll_again(package: Arc<Package>) {
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let me = match package.notified.replace(State::Notified) {
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// we need to schedule polling to resume, so keep going
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State::Waiting(me) => {
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me
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}
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// we were already notified, and were just notified again;
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// having now coalesced the notifications we return as it's
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// still someone else's job to process this
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State::Notified => {
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return;
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}
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// the future was previously being polled, and we've just
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// switched it to the "you're notified" state. We don't have
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// access to the future as it's being polled, so the future
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// polling process later sees this notification and will
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// continue polling. For us, though, there's nothing else to do,
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// so we bail out.
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// later see
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State::Polling => {
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return;
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}
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};
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// Use `Promise.then` on a resolved promise to place our execution
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// onto the next turn of the microtask queue, enqueueing our poll
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// operation. We don't currently poll immediately as it turns out
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// `futures` crate adapters aren't compatible with it and it also
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// helps avoid blowing the stack by accident.
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let promise =
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crate::polyfill::wait_async(&package.waker.value).expect("Should create a Promise");
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let closure = Closure::once(move |_| {
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Package::poll(&me);
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});
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promise.then(&closure);
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closure.forget();
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}
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impl Package {
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// Move the future contained in `me` as far forward as we can. This will
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// do as much synchronous work as possible to complete the future,
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// ensuring that when it blocks we're scheduled to get notified via some
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// callback somewhere at some point (vague, right?)
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//
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// TODO: this probably shouldn't do as much synchronous work as possible
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// as it can starve other computations. Rather it should instead
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// yield every so often with something like `setTimeout` with the
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// timeout set to zero.
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fn poll(me: &Arc<Package>) {
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loop {
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match me.notified.replace(State::Polling) {
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// We received a notification while previously polling, or
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// this is the initial poll. We've got work to do below!
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State::Notified => {}
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// We've gone through this loop once and no notification was
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// received while we were executing work. That means we got
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// `NotReady` below and we're scheduled to receive a
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// notification. Block ourselves and wait for later.
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//
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// When the notification comes in it'll notify our task, see
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// our `Waiting` state, and resume the polling process
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State::Polling => {
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me.notified.set(State::Waiting(me.clone()));
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poll_again(me.clone());
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break;
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}
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State::Waiting(_) => panic!("shouldn't see waiting state!"),
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}
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let (val, f) = match me.spawn.borrow_mut().poll_future_notify(&me.waker, 0) {
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fn poll(mut self) {
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// Poll in a loop waiting for the future to become ready. Note that
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// we probably shouldn't maximize synchronous work here but rather
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// we should occasionally yield back to the runtime and schedule
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// ourselves to resume this future later on.
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//
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// Note that 0 here means "need a notification" and 1 means "we got
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// a notification". That means we're storing 0 into the `notified`
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// slot and we're trying to read 1 to keep on going.
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while self.waker.value.swap(0, Ordering::SeqCst) == 1 {
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let (val, f) = match self.spawn.poll_future_notify(&self.waker, 0) {
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// If the future is ready, immediately call the
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// resolve/reject callback and then return as we're done.
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Ok(Async::Ready(value)) => (value, &me.resolve),
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Err(value) => (value, &me.reject),
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Ok(Async::Ready(value)) => (value, &self.resolve),
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Err(value) => (value, &self.reject),
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// Otherwise keep going in our loop, if we weren't notified
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// we'll break out and start waiting.
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Ok(Async::NotReady) => continue,
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// ... otherwise let's break out and wait
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Ok(Async::NotReady) => break,
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};
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// Call the resolution function, and then when we're done
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// destroy ourselves through `drop` since our future is no
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// longer needed.
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drop(f.call1(&JsValue::undefined(), &val));
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break;
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return;
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}
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// Create a `js_sys::Promise` using `Atomics.waitAsync` (or our
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// polyfill) and then register its completion callback as simply
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// calling this function again.
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let promise = wait_async(&self.waker.value, 0).unchecked_into::<Promise>();
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let closure = Closure::once_into_js(move || {
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self.poll();
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});
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promise.then(&closure);
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}
|
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}
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}
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fn wait_async(ptr: &AtomicI32, val: i32) -> js_sys::Promise {
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// If `Atomics.waitAsync` isn't defined (as it isn't defined anywhere today)
|
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// then we use our fallback, otherwise we use the native function.
|
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if Atomics::get_wait_async().is_undefined() {
|
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crate::polyfill::wait_async(ptr, val)
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} else {
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let mem = wasm_bindgen::memory().unchecked_into::<js_sys::WebAssembly::Memory>();
|
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Atomics::wait_async(&mem.buffer(), ptr as *const AtomicI32 as i32 / 4, val)
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}
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|
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}
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|
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/// Converts a Rust `Future` on a local task queue.
|
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///
|
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/// The `future` provided must adhere to `'static` because it'll be scheduled
|
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@ -320,8 +262,8 @@ fn _future_to_promise(future: Box<dyn Future<Item = JsValue, Error = JsValue>>)
|
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///
|
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/// This function has the same panic behavior as `future_to_promise`.
|
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pub fn spawn_local<F>(future: F)
|
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where
|
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F: Future<Item = (), Error = ()> + 'static,
|
||||
where
|
||||
F: Future<Item = (), Error = ()> + 'static,
|
||||
{
|
||||
future_to_promise(
|
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future
|
||||
|
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@ -36,38 +36,21 @@
|
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* when possible. The worker communicates with its parent using postMessage.
|
||||
*/
|
||||
|
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use js_sys::{encode_uri_component, Array, Promise};
|
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use std::cell::RefCell;
|
||||
use std::sync::atomic::{AtomicI32, Ordering};
|
||||
|
||||
use js_sys::{
|
||||
encode_uri_component, Array, Function, Int32Array, JsString, Promise, Reflect,
|
||||
WebAssembly,
|
||||
};
|
||||
use std::sync::atomic::AtomicI32;
|
||||
use wasm_bindgen::prelude::*;
|
||||
use wasm_bindgen::JsCast;
|
||||
use web_sys::{MessageEvent, Worker};
|
||||
|
||||
const DEFAULT_TIMEOUT: f64 = std::f64::INFINITY;
|
||||
|
||||
const HELPER_CODE: &'static str = "
|
||||
onmessage = function (ev) {
|
||||
try {
|
||||
switch (ev.data[0]) {
|
||||
case 'wait': {
|
||||
let [_, ia, index, value, timeout] = ev.data;
|
||||
let result = Atomics.wait(ia, index, value, timeout);
|
||||
postMessage(['ok', result]);
|
||||
break;
|
||||
}
|
||||
default: {
|
||||
throw new Error('Wrong message sent to wait helper: ' + ev.data.join(','));
|
||||
}
|
||||
}
|
||||
} catch (e) {
|
||||
console.log('Exception in wait helper', e);
|
||||
postMessage(['error', 'Exception']);
|
||||
}
|
||||
}
|
||||
let [ia, index, value] = ev.data;
|
||||
ia = new Int32Array(ia.buffer);
|
||||
let result = Atomics.wait(ia, index, value);
|
||||
console.log('done', result);
|
||||
postMessage(result);
|
||||
};
|
||||
";
|
||||
|
||||
thread_local! {
|
||||
@ -84,103 +67,39 @@ fn alloc_helper() -> Worker {
|
||||
let encoded: String = encode_uri_component(HELPER_CODE).into();
|
||||
initialization_string.push_str(&encoded);
|
||||
|
||||
Worker::new(&initialization_string).expect("Should create a Worker")
|
||||
Worker::new(&initialization_string).unwrap_or_else(|js| wasm_bindgen::throw_val(js))
|
||||
})
|
||||
}
|
||||
|
||||
fn free_helper(helper: Worker) {
|
||||
HELPERS.with(move |helpers| {
|
||||
helpers.borrow_mut().push(helper.clone());
|
||||
let mut helpers = helpers.borrow_mut();
|
||||
helpers.push(helper.clone());
|
||||
helpers.truncate(10); // random arbitrary limit chosen here
|
||||
});
|
||||
}
|
||||
|
||||
pub fn wait_async(value: &AtomicI32) -> Result<Promise, JsValue> {
|
||||
wait_async_with_timeout(value, DEFAULT_TIMEOUT)
|
||||
}
|
||||
|
||||
fn get_array_item(array: &JsValue, index: u32) -> JsValue {
|
||||
Reflect::get(array, &JsValue::from(index))
|
||||
.expect(&format!("Array should contain the index {}", index))
|
||||
}
|
||||
|
||||
// Atomics.waitAsync always returns a promise. Throws standard errors
|
||||
// for parameter validation. The promise is resolved with a string as from
|
||||
// Atomics.wait, or, in the case something went completely wrong, it is
|
||||
// rejected with an error string.
|
||||
pub fn wait_async_with_timeout(value: &AtomicI32, timeout: f64) -> Result<Promise, JsValue> {
|
||||
let memory_buffer = wasm_bindgen::memory()
|
||||
.dyn_into::<WebAssembly::Memory>()
|
||||
.expect("Should cast a memory to WebAssembly::Memory")
|
||||
.buffer();
|
||||
|
||||
let indexed_array = Int32Array::new(&memory_buffer);
|
||||
|
||||
let index = value as *const AtomicI32 as u32 / 4;
|
||||
let value_i32 = value.load(Ordering::SeqCst);
|
||||
|
||||
// General case, we must wait.
|
||||
|
||||
Ok(Promise::new(
|
||||
&mut move |resolve: Function, reject: Function| {
|
||||
let helper = alloc_helper();
|
||||
let helper_ref = helper.clone();
|
||||
|
||||
let onmessage_callback = Closure::once_into_js(move |e: MessageEvent| {
|
||||
// Free the helper early so that it can be reused if the resolution
|
||||
// needs a helper.
|
||||
free_helper(helper_ref);
|
||||
match String::from(
|
||||
get_array_item(&e.data(), 0)
|
||||
.as_string()
|
||||
.expect("data[0] should return a String"),
|
||||
)
|
||||
.as_str()
|
||||
{
|
||||
"ok" => {
|
||||
resolve
|
||||
.call1(&JsValue::NULL, &get_array_item(&e.data(), 1))
|
||||
.expect("Should successfully call a resolve callback");
|
||||
}
|
||||
"error" => {
|
||||
// Note, rejection is not in the spec, it is an artifact of the polyfill.
|
||||
// The helper already printed an error to the console.
|
||||
reject
|
||||
.call1(&JsValue::NULL, &get_array_item(&e.data(), 1))
|
||||
.expect("Should successfully call a reject callback");
|
||||
}
|
||||
// it's not specified in the proposal yet
|
||||
_ => (),
|
||||
}
|
||||
});
|
||||
helper.set_onmessage(Some(onmessage_callback.as_ref().unchecked_ref()));
|
||||
|
||||
// onmessage_callback.forget();
|
||||
|
||||
// It's possible to do better here if the ia is already known to the
|
||||
// helper. In that case we can communicate the other data through
|
||||
// shared memory and wake the agent. And it is possible to make ia
|
||||
// known to the helper by waking it with a special value so that it
|
||||
// checks its messages, and then posting the ia to the helper. Some
|
||||
// caching / decay scheme is useful no doubt, to improve performance
|
||||
// and avoid leaks.
|
||||
//
|
||||
// In the event we wake the helper directly, we can micro-wait here
|
||||
// for a quick result. We'll need to restructure some code to make
|
||||
// that work out properly, and some synchronization is necessary for
|
||||
// the helper to know that we've picked up the result and no
|
||||
// postMessage is necessary.
|
||||
|
||||
let data = Array::of5(
|
||||
&JsString::from("wait"),
|
||||
&indexed_array,
|
||||
&JsValue::from(index),
|
||||
&JsValue::from(value_i32),
|
||||
&JsValue::from(timeout),
|
||||
);
|
||||
|
||||
helper
|
||||
.post_message(&data)
|
||||
.expect("Should successfully post data to a Worker");
|
||||
},
|
||||
))
|
||||
pub fn wait_async(ptr: &AtomicI32, value: i32) -> Promise {
|
||||
Promise::new(&mut |resolve, _reject| {
|
||||
let helper = alloc_helper();
|
||||
let helper_ref = helper.clone();
|
||||
|
||||
let onmessage_callback = Closure::once_into_js(move |e: MessageEvent| {
|
||||
// Our helper is done waiting so it's available to wait on a
|
||||
// different location, so return it to the free list.
|
||||
free_helper(helper_ref);
|
||||
drop(resolve.call1(&JsValue::NULL, &e.data()));
|
||||
});
|
||||
helper.set_onmessage(Some(onmessage_callback.as_ref().unchecked_ref()));
|
||||
|
||||
let data = Array::of3(
|
||||
&wasm_bindgen::memory(),
|
||||
&JsValue::from(ptr as *const AtomicI32 as i32 / 4),
|
||||
&JsValue::from(value),
|
||||
);
|
||||
|
||||
helper
|
||||
.post_message(&data)
|
||||
.unwrap_or_else(|js| wasm_bindgen::throw_val(js));
|
||||
})
|
||||
}
|
||||
|
||||
Reference in New Issue
Block a user