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Merge pull request #1514 from ibaryshnikov/threadsafe-futures

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Threadsafe futures
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Alex Crichton 2019-07-19 09:38:04 -05:00 committed by GitHub
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11 changed files with 658 additions and 416 deletions
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9
crates/futures/Cargo.toml
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@ -11,6 +11,7 @@ version = "0.3.25"
edition = "2018"
[dependencies]
cfg-if = "0.1.9"
futures = "0.1.20"
js-sys = { path = "../js-sys", version = '0.3.25' }
wasm-bindgen = { path = "../..", version = '0.2.48' }
@ -18,6 +19,14 @@ futures-util-preview = { version = "0.3.0-alpha.15", optional = true }
futures-channel-preview = { version = "0.3.0-alpha.15", optional = true }
lazy_static = { version = "1.3.0", optional = true }
[target.'cfg(target_feature = "atomics")'.dependencies.web-sys]
path = "../web-sys"
version = "0.3.24"
features = [
"MessageEvent",
"Worker",
]
[target.'cfg(target_arch = "wasm32")'.dev-dependencies]
wasm-bindgen-test = { path = '../test', version = '0.2.48' }

204
crates/futures/src/legacy.rs Normal file
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@ -0,0 +1,204 @@
use futures::executor::{self, Notify, Spawn};
use futures::prelude::*;
use js_sys::{Function, Promise};
use std::cell::{Cell, RefCell};
use std::rc::Rc;
use std::sync::Arc;
use wasm_bindgen::prelude::*;
/// Converts a Rust `Future` into a JavaScript `Promise`.
///
/// This function will take any future in Rust and schedule it to be executed,
/// returning a JavaScript `Promise` which can then be passed back to JavaScript
/// to get plumbed into the rest of a system.
///
/// The `future` provided must adhere to `'static` because it'll be scheduled
/// to run in the background and cannot contain any stack references. The
/// returned `Promise` will be resolved or rejected when the future completes,
/// depending on whether it finishes with `Ok` or `Err`.
///
/// # Panics
///
/// Note that in wasm panics are currently translated to aborts, but "abort" in
/// this case means that a JavaScript exception is thrown. The wasm module is
/// still usable (likely erroneously) after Rust panics.
///
/// If the `future` provided panics then the returned `Promise` **will not
/// resolve**. Instead it will be a leaked promise. This is an unfortunate
/// limitation of wasm currently that's hoped to be fixed one day!
pub fn future_to_promise<F>(future: F) -> Promise
where
F: Future<Item = JsValue, Error = JsValue> + 'static,
{
_future_to_promise(Box::new(future))
}
// Implementation of actually transforming a future into a JavaScript `Promise`.
//
// The only primitive we have to work with here is `Promise::new`, which gives
// us two callbacks that we can use to either reject or resolve the promise.
// It's our job to ensure that one of those callbacks is called at the
// appropriate time.
//
// Now we know that JavaScript (in general) can't block and is largely
// notification/callback driven. That means that our future must either have
// synchronous computational work to do, or it's "scheduled a notification" to
// happen. These notifications are likely callbacks to get executed when things
// finish (like a different promise or something like `setTimeout`). The general
// idea here is thus to do as much synchronous work as we can and then otherwise
// translate notifications of a future's task into "let's poll the future!"
//
// This isn't necessarily the greatest future executor in the world, but it
// should get the job done for now hopefully.
fn _future_to_promise(future: Box<dyn Future<Item = JsValue, Error = JsValue>>) -> Promise {
let mut future = Some(executor::spawn(future));
return Promise::new(&mut |resolve, reject| {
Package::poll(&Arc::new(Package {
spawn: RefCell::new(future.take().unwrap()),
resolve,
reject,
notified: Cell::new(State::Notified),
}));
});
struct Package {
// Our "spawned future". This'll have everything we need to poll the
// future and continue to move it forward.
spawn: RefCell<Spawn<Box<dyn Future<Item = JsValue, Error = JsValue>>>>,
// The current state of this future, expressed in an enum below. This
// indicates whether we're currently polling the future, received a
// notification and need to keep polling, or if we're waiting for a
// notification to come in (and no one is polling).
notified: Cell<State>,
// Our two callbacks connected to the `Promise` that we returned to
// JavaScript. We'll be invoking one of these at the end.
resolve: Function,
reject: Function,
}
// The possible states our `Package` (future) can be in, tracked internally
// and used to guide what happens when polling a future.
enum State {
// This future is currently and actively being polled. Attempting to
// access the future will result in a runtime panic and is considered a
// bug.
Polling,
// This future has been notified, while it was being polled. This marker
// is used in the `Notify` implementation below, and indicates that a
// notification was received that the future is ready to make progress.
// If seen, however, it probably means that the future is also currently
// being polled.
Notified,
// The future is blocked, waiting for something to happen. Stored here
// is a self-reference to the future itself so we can pull it out in
// `Notify` and continue polling.
//
// Note that the self-reference here is an Arc-cycle that will leak
// memory unless the future completes, but currently that should be ok
// as we'll have to stick around anyway while the future is executing!
//
// This state is removed as soon as a notification comes in, so the leak
// should only be "temporary"
Waiting(Arc<Package>),
}
// No shared memory right now, wasm is single threaded, no need to worry
// about this!
unsafe impl Send for Package {}
unsafe impl Sync for Package {}
impl Package {
// Move the future contained in `me` as far forward as we can. This will
// do as much synchronous work as possible to complete the future,
// ensuring that when it blocks we're scheduled to get notified via some
// callback somewhere at some point (vague, right?)
//
// TODO: this probably shouldn't do as much synchronous work as possible
// as it can starve other computations. Rather it should instead
// yield every so often with something like `setTimeout` with the
// timeout set to zero.
fn poll(me: &Arc<Package>) {
loop {
match me.notified.replace(State::Polling) {
// We received a notification while previously polling, or
// this is the initial poll. We've got work to do below!
State::Notified => {}
// We've gone through this loop once and no notification was
// received while we were executing work. That means we got
// `NotReady` below and we're scheduled to receive a
// notification. Block ourselves and wait for later.
//
// When the notification comes in it'll notify our task, see
// our `Waiting` state, and resume the polling process
State::Polling => {
me.notified.set(State::Waiting(me.clone()));
break;
}
State::Waiting(_) => panic!("shouldn't see waiting state!"),
}
let (val, f) = match me.spawn.borrow_mut().poll_future_notify(me, 0) {
// If the future is ready, immediately call the
// resolve/reject callback and then return as we're done.
Ok(Async::Ready(value)) => (value, &me.resolve),
Err(value) => (value, &me.reject),
// Otherwise keep going in our loop, if we weren't notified
// we'll break out and start waiting.
Ok(Async::NotReady) => continue,
};
drop(f.call1(&JsValue::undefined(), &val));
break;
}
}
}
impl Notify for Package {
fn notify(&self, _id: usize) {
let me = match self.notified.replace(State::Notified) {
// we need to schedule polling to resume, so keep going
State::Waiting(me) => me,
// we were already notified, and were just notified again;
// having now coalesced the notifications we return as it's
// still someone else's job to process this
State::Notified => return,
// the future was previously being polled, and we've just
// switched it to the "you're notified" state. We don't have
// access to the future as it's being polled, so the future
// polling process later sees this notification and will
// continue polling. For us, though, there's nothing else to do,
// so we bail out.
// later see
State::Polling => return,
};
// Use `Promise.then` on a resolved promise to place our execution
// onto the next turn of the microtask queue, enqueueing our poll
// operation. We don't currently poll immediately as it turns out
// `futures` crate adapters aren't compatible with it and it also
// helps avoid blowing the stack by accident.
//
// Note that the `Rc`/`RefCell` trick here is basically to just
// ensure that our `Closure` gets cleaned up appropriately.
let promise = Promise::resolve(&JsValue::undefined());
let slot = Rc::new(RefCell::new(None));
let slot2 = slot.clone();
let closure = Closure::wrap(Box::new(move |_| {
let myself = slot2.borrow_mut().take();
debug_assert!(myself.is_some());
Package::poll(&me);
}) as Box<dyn FnMut(JsValue)>);
promise.then(&closure);
*slot.borrow_mut() = Some(closure);
}
}
}

166
crates/futures/src/legacy_atomics.rs Normal file
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@ -0,0 +1,166 @@
use futures::executor::{self, Notify, Spawn};
use futures::prelude::*;
use js_sys::Function;
use std::sync::atomic::{AtomicI32, Ordering};
use std::sync::Arc;
use wasm_bindgen::prelude::*;
use wasm_bindgen::JsCast;
// Duplicate a bit here because `then` takes a `JsValue` instead of a `Closure`.
#[wasm_bindgen]
extern "C" {
type Promise;
#[wasm_bindgen(method)]
fn then(this: &Promise, cb: &JsValue) -> Promise;
type Atomics;
#[wasm_bindgen(static_method_of = Atomics, js_name = waitAsync)]
fn wait_async(buf: &JsValue, index: i32, value: i32) -> js_sys::Promise;
#[wasm_bindgen(static_method_of = Atomics, js_name = waitAsync, getter)]
fn get_wait_async() -> JsValue;
}
/// Converts a Rust `Future` into a JavaScript `Promise`.
///
/// This function will take any future in Rust and schedule it to be executed,
/// returning a JavaScript `Promise` which can then be passed back to JavaScript
/// to get plumbed into the rest of a system.
///
/// The `future` provided must adhere to `'static` because it'll be scheduled
/// to run in the background and cannot contain any stack references. The
/// returned `Promise` will be resolved or rejected when the future completes,
/// depending on whether it finishes with `Ok` or `Err`.
///
/// # Panics
///
/// Note that in wasm panics are currently translated to aborts, but "abort" in
/// this case means that a JavaScript exception is thrown. The wasm module is
/// still usable (likely erroneously) after Rust panics.
///
/// If the `future` provided panics then the returned `Promise` **will not
/// resolve**. Instead it will be a leaked promise. This is an unfortunate
/// limitation of wasm currently that's hoped to be fixed one day!
pub fn future_to_promise<F>(future: F) -> js_sys::Promise
where
F: Future<Item = JsValue, Error = JsValue> + 'static,
{
_future_to_promise(Box::new(future))
}
// Implementation of actually transforming a future into a JavaScript `Promise`.
//
// The main primitives used here are `Promise::new` to actually create a JS
// promise to return as well as `Atomics.waitAsync` to create a promise that we
// can asynchronously wait on. The general idea here is that we'll create a
// promise to return and schedule work to happen in `Atomics.waitAsync`
// callbacks.
//
// After we've created a promise we start polling a future, and whenever it's
// not ready we'll execute `Atomics.waitAsync`. When that resolves we'll keep
// polling the future, and this happens until the future is done. Finally
// when it's all finished we call either resolver or reject depending on the
// result of the future.
fn _future_to_promise(future: Box<dyn Future<Item = JsValue, Error = JsValue>>) -> js_sys::Promise {
let mut future = Some(executor::spawn(future));
return js_sys::Promise::new(&mut |resolve, reject| {
Package {
spawn: future.take().unwrap(),
resolve,
reject,
waker: Arc::new(Waker {
value: AtomicI32::new(1), // 1 == "notified, ready to poll"
}),
}
.poll();
});
struct Package {
// Our "spawned future". This'll have everything we need to poll the
// future and continue to move it forward.
spawn: Spawn<Box<dyn Future<Item = JsValue, Error = JsValue>>>,
// Our two callbacks connected to the `Promise` that we returned to
// JavaScript. We'll be invoking one of these at the end.
resolve: Function,
reject: Function,
// Shared state used to communicate waking up this future, this is the
// `Send + Sync` piece needed by the async task system.
waker: Arc<Waker>,
}
struct Waker {
value: AtomicI32,
};
impl Notify for Waker {
fn notify(&self, _id: usize) {
// Attempt to notify us by storing 1. If we're already 1 then we
// were previously notified and there's nothing to do. Otherwise
// we execute the native `notify` instruction to wake up the
// corresponding `waitAsync` that was waiting for the transition
// from 0 to 1.
let prev = self.value.swap(1, Ordering::SeqCst);
if prev == 1 {
return;
}
debug_assert_eq!(prev, 0);
unsafe {
core::arch::wasm32::atomic_notify(
&self.value as *const AtomicI32 as *mut i32,
1, // number of threads to notify
);
}
}
}
impl Package {
fn poll(mut self) {
// Poll in a loop waiting for the future to become ready. Note that
// we probably shouldn't maximize synchronous work here but rather
// we should occasionally yield back to the runtime and schedule
// ourselves to resume this future later on.
//
// Note that 0 here means "need a notification" and 1 means "we got
// a notification". That means we're storing 0 into the `notified`
// slot and we're trying to read 1 to keep on going.
while self.waker.value.swap(0, Ordering::SeqCst) == 1 {
let (val, f) = match self.spawn.poll_future_notify(&self.waker, 0) {
// If the future is ready, immediately call the
// resolve/reject callback and then return as we're done.
Ok(Async::Ready(value)) => (value, &self.resolve),
Err(value) => (value, &self.reject),
// ... otherwise let's break out and wait
Ok(Async::NotReady) => break,
};
// Call the resolution function, and then when we're done
// destroy ourselves through `drop` since our future is no
// longer needed.
drop(f.call1(&JsValue::undefined(), &val));
return;
}
// Create a `js_sys::Promise` using `Atomics.waitAsync` (or our
// polyfill) and then register its completion callback as simply
// calling this function again.
let promise = wait_async(&self.waker.value, 0).unchecked_into::<Promise>();
let closure = Closure::once_into_js(move || {
self.poll();
});
promise.then(&closure);
}
}
}
fn wait_async(ptr: &AtomicI32, val: i32) -> js_sys::Promise {
// If `Atomics.waitAsync` isn't defined (as it isn't defined anywhere today)
// then we use our fallback, otherwise we use the native function.
if Atomics::get_wait_async().is_undefined() {
crate::wait_async_polyfill::wait_async(ptr, val)
} else {
let mem = wasm_bindgen::memory().unchecked_into::<js_sys::WebAssembly::Memory>();
Atomics::wait_async(&mem.buffer(), ptr as *const AtomicI32 as i32 / 4, val)
}
}

108
crates/futures/src/legacy_shared.rs Normal file
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@ -0,0 +1,108 @@
use std::cell::RefCell;
use futures::future;
use std::fmt;
use std::rc::Rc;
use futures::prelude::*;
use futures::sync::oneshot;
use js_sys::Promise;
use wasm_bindgen::prelude::*;
/// A Rust `Future` backed by a JavaScript `Promise`.
///
/// This type is constructed with a JavaScript `Promise` object and translates
/// it to a Rust `Future`. This type implements the `Future` trait from the
/// `futures` crate and will either succeed or fail depending on what happens
/// with the JavaScript `Promise`.
///
/// Currently this type is constructed with `JsFuture::from`.
pub struct JsFuture {
rx: oneshot::Receiver<Result<JsValue, JsValue>>,
}
impl fmt::Debug for JsFuture {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "JsFuture {{ ... }}")
}
}
impl From<Promise> for JsFuture {
fn from(js: Promise) -> JsFuture {
// Use the `then` method to schedule two callbacks, one for the
// resolved value and one for the rejected value. We're currently
// assuming that JS engines will unconditionally invoke precisely one of
// these callbacks, no matter what.
//
// Ideally we'd have a way to cancel the callbacks getting invoked and
// free up state ourselves when this `JsFuture` is dropped. We don't
// have that, though, and one of the callbacks is likely always going to
// be invoked.
//
// As a result we need to make sure that no matter when the callbacks
// are invoked they are valid to be called at any time, which means they
// have to be self-contained. Through the `Closure::once` and some
// `Rc`-trickery we can arrange for both instances of `Closure`, and the
// `Rc`, to all be destroyed once the first one is called.
let (tx, rx) = oneshot::channel();
let state = Rc::new(RefCell::new(None));
let state2 = state.clone();
let resolve = Closure::once(move |val| finish(&state2, Ok(val)));
let state2 = state.clone();
let reject = Closure::once(move |val| finish(&state2, Err(val)));
js.then2(&resolve, &reject);
*state.borrow_mut() = Some((tx, resolve, reject));
return JsFuture { rx };
fn finish(
state: &RefCell<
Option<(
oneshot::Sender<Result<JsValue, JsValue>>,
Closure<dyn FnMut(JsValue)>,
Closure<dyn FnMut(JsValue)>,
)>,
>,
val: Result<JsValue, JsValue>,
) {
match state.borrow_mut().take() {
// We don't have any guarantee that anyone's still listening at this
// point (the Rust `JsFuture` could have been dropped) so simply
// ignore any errors here.
Some((tx, _, _)) => drop(tx.send(val)),
None => wasm_bindgen::throw_str("cannot finish twice"),
}
}
}
}
impl Future for JsFuture {
type Item = JsValue;
type Error = JsValue;
fn poll(&mut self) -> Poll<JsValue, JsValue> {
match self.rx.poll() {
Ok(Async::Ready(val)) => val.map(Async::Ready),
Ok(Async::NotReady) => Ok(Async::NotReady),
Err(_) => wasm_bindgen::throw_str("cannot cancel"),
}
}
}
/// Converts a Rust `Future` on a local task queue.
///
/// The `future` provided must adhere to `'static` because it'll be scheduled
/// to run in the background and cannot contain any stack references.
///
/// # Panics
///
/// This function has the same panic behavior as `future_to_promise`.
pub fn spawn_local<F>(future: F)
where
F: Future<Item = (), Error = ()> + 'static,
{
crate::future_to_promise(
future
.map(|()| JsValue::undefined())
.or_else(|()| future::ok::<JsValue, JsValue>(JsValue::undefined())),
);
}

337
crates/futures/src/lib.rs
View File

@ -101,317 +101,34 @@
//! }
//! ```
#![cfg_attr(target_feature = "atomics", feature(stdsimd))]
#![deny(missing_docs)]
use cfg_if::cfg_if;
mod legacy_shared;
pub use legacy_shared::*;
cfg_if! {
if #[cfg(target_feature = "atomics")] {
/// Contains a thread-safe version of this crate, with Futures 0.1
mod legacy_atomics;
pub use legacy_atomics::*;
/// Polyfill for `Atomics.waitAsync` function
mod wait_async_polyfill;
} else {
mod legacy;
pub use legacy::*;
}
}
#[cfg(feature = "futures_0_3")]
/// Contains a Futures 0.3 implementation of this crate.
pub mod futures_0_3;
use std::cell::{Cell, RefCell};
use std::fmt;
use std::rc::Rc;
use std::sync::Arc;
use futures::executor::{self, Notify, Spawn};
use futures::future;
use futures::prelude::*;
use futures::sync::oneshot;
use js_sys::{Function, Promise};
use wasm_bindgen::prelude::*;
/// A Rust `Future` backed by a JavaScript `Promise`.
///
/// This type is constructed with a JavaScript `Promise` object and translates
/// it to a Rust `Future`. This type implements the `Future` trait from the
/// `futures` crate and will either succeed or fail depending on what happens
/// with the JavaScript `Promise`.
///
/// Currently this type is constructed with `JsFuture::from`.
pub struct JsFuture {
rx: oneshot::Receiver<Result<JsValue, JsValue>>,
}
impl fmt::Debug for JsFuture {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "JsFuture {{ ... }}")
}
}
impl From<Promise> for JsFuture {
fn from(js: Promise) -> JsFuture {
// Use the `then` method to schedule two callbacks, one for the
// resolved value and one for the rejected value. We're currently
// assuming that JS engines will unconditionally invoke precisely one of
// these callbacks, no matter what.
//
// Ideally we'd have a way to cancel the callbacks getting invoked and
// free up state ourselves when this `JsFuture` is dropped. We don't
// have that, though, and one of the callbacks is likely always going to
// be invoked.
//
// As a result we need to make sure that no matter when the callbacks
// are invoked they are valid to be called at any time, which means they
// have to be self-contained. Through the `Closure::once` and some
// `Rc`-trickery we can arrange for both instances of `Closure`, and the
// `Rc`, to all be destroyed once the first one is called.
let (tx, rx) = oneshot::channel();
let state = Rc::new(RefCell::new(None));
let state2 = state.clone();
let resolve = Closure::once(move |val| finish(&state2, Ok(val)));
let state2 = state.clone();
let reject = Closure::once(move |val| finish(&state2, Err(val)));
js.then2(&resolve, &reject);
*state.borrow_mut() = Some((tx, resolve, reject));
return JsFuture { rx };
fn finish(
state: &RefCell<
Option<(
oneshot::Sender<Result<JsValue, JsValue>>,
Closure<dyn FnMut(JsValue)>,
Closure<dyn FnMut(JsValue)>,
)>,
>,
val: Result<JsValue, JsValue>,
) {
match state.borrow_mut().take() {
// We don't have any guarantee that anyone's still listening at this
// point (the Rust `JsFuture` could have been dropped) so simply
// ignore any errors here.
Some((tx, _, _)) => drop(tx.send(val)),
None => wasm_bindgen::throw_str("cannot finish twice"),
}
}
}
}
impl Future for JsFuture {
type Item = JsValue;
type Error = JsValue;
fn poll(&mut self) -> Poll<JsValue, JsValue> {
match self.rx.poll() {
Ok(Async::Ready(val)) => val.map(Async::Ready),
Ok(Async::NotReady) => Ok(Async::NotReady),
Err(_) => wasm_bindgen::throw_str("cannot cancel"),
}
}
}
/// Converts a Rust `Future` into a JavaScript `Promise`.
///
/// This function will take any future in Rust and schedule it to be executed,
/// returning a JavaScript `Promise` which can then be passed back to JavaScript
/// to get plumbed into the rest of a system.
///
/// The `future` provided must adhere to `'static` because it'll be scheduled
/// to run in the background and cannot contain any stack references. The
/// returned `Promise` will be resolved or rejected when the future completes,
/// depending on whether it finishes with `Ok` or `Err`.
///
/// # Panics
///
/// Note that in wasm panics are currently translated to aborts, but "abort" in
/// this case means that a JavaScript exception is thrown. The wasm module is
/// still usable (likely erroneously) after Rust panics.
///
/// If the `future` provided panics then the returned `Promise` **will not
/// resolve**. Instead it will be a leaked promise. This is an unfortunate
/// limitation of wasm currently that's hoped to be fixed one day!
pub fn future_to_promise<F>(future: F) -> Promise
where
F: Future<Item = JsValue, Error = JsValue> + 'static,
{
_future_to_promise(Box::new(future))
}
// Implementation of actually transforming a future into a JavaScript `Promise`.
//
// The only primitive we have to work with here is `Promise::new`, which gives
// us two callbacks that we can use to either reject or resolve the promise.
// It's our job to ensure that one of those callbacks is called at the
// appropriate time.
//
// Now we know that JavaScript (in general) can't block and is largely
// notification/callback driven. That means that our future must either have
// synchronous computational work to do, or it's "scheduled a notification" to
// happen. These notifications are likely callbacks to get executed when things
// finish (like a different promise or something like `setTimeout`). The general
// idea here is thus to do as much synchronous work as we can and then otherwise
// translate notifications of a future's task into "let's poll the future!"
//
// This isn't necessarily the greatest future executor in the world, but it
// should get the job done for now hopefully.
fn _future_to_promise(future: Box<dyn Future<Item = JsValue, Error = JsValue>>) -> Promise {
let mut future = Some(executor::spawn(future));
return Promise::new(&mut |resolve, reject| {
Package::poll(&Arc::new(Package {
spawn: RefCell::new(future.take().unwrap()),
resolve,
reject,
notified: Cell::new(State::Notified),
}));
});
struct Package {
// Our "spawned future". This'll have everything we need to poll the
// future and continue to move it forward.
spawn: RefCell<Spawn<Box<dyn Future<Item = JsValue, Error = JsValue>>>>,
// The current state of this future, expressed in an enum below. This
// indicates whether we're currently polling the future, received a
// notification and need to keep polling, or if we're waiting for a
// notification to come in (and no one is polling).
notified: Cell<State>,
// Our two callbacks connected to the `Promise` that we returned to
// JavaScript. We'll be invoking one of these at the end.
resolve: Function,
reject: Function,
}
// The possible states our `Package` (future) can be in, tracked internally
// and used to guide what happens when polling a future.
enum State {
// This future is currently and actively being polled. Attempting to
// access the future will result in a runtime panic and is considered a
// bug.
Polling,
// This future has been notified, while it was being polled. This marker
// is used in the `Notify` implementation below, and indicates that a
// notification was received that the future is ready to make progress.
// If seen, however, it probably means that the future is also currently
// being polled.
Notified,
// The future is blocked, waiting for something to happen. Stored here
// is a self-reference to the future itself so we can pull it out in
// `Notify` and continue polling.
//
// Note that the self-reference here is an Arc-cycle that will leak
// memory unless the future completes, but currently that should be ok
// as we'll have to stick around anyway while the future is executing!
//
// This state is removed as soon as a notification comes in, so the leak
// should only be "temporary"
Waiting(Arc<Package>),
}
// No shared memory right now, wasm is single threaded, no need to worry
// about this!
unsafe impl Send for Package {}
unsafe impl Sync for Package {}
impl Package {
// Move the future contained in `me` as far forward as we can. This will
// do as much synchronous work as possible to complete the future,
// ensuring that when it blocks we're scheduled to get notified via some
// callback somewhere at some point (vague, right?)
//
// TODO: this probably shouldn't do as much synchronous work as possible
// as it can starve other computations. Rather it should instead
// yield every so often with something like `setTimeout` with the
// timeout set to zero.
fn poll(me: &Arc<Package>) {
loop {
match me.notified.replace(State::Polling) {
// We received a notification while previously polling, or
// this is the initial poll. We've got work to do below!
State::Notified => {}
// We've gone through this loop once and no notification was
// received while we were executing work. That means we got
// `NotReady` below and we're scheduled to receive a
// notification. Block ourselves and wait for later.
//
// When the notification comes in it'll notify our task, see
// our `Waiting` state, and resume the polling process
State::Polling => {
me.notified.set(State::Waiting(me.clone()));
break;
}
State::Waiting(_) => panic!("shouldn't see waiting state!"),
}
let (val, f) = match me.spawn.borrow_mut().poll_future_notify(me, 0) {
// If the future is ready, immediately call the
// resolve/reject callback and then return as we're done.
Ok(Async::Ready(value)) => (value, &me.resolve),
Err(value) => (value, &me.reject),
// Otherwise keep going in our loop, if we weren't notified
// we'll break out and start waiting.
Ok(Async::NotReady) => continue,
};
drop(f.call1(&JsValue::undefined(), &val));
break;
}
}
}
impl Notify for Package {
fn notify(&self, _id: usize) {
let me = match self.notified.replace(State::Notified) {
// we need to schedule polling to resume, so keep going
State::Waiting(me) => me,
// we were already notified, and were just notified again;
// having now coalesced the notifications we return as it's
// still someone else's job to process this
State::Notified => return,
// the future was previously being polled, and we've just
// switched it to the "you're notified" state. We don't have
// access to the future as it's being polled, so the future
// polling process later sees this notification and will
// continue polling. For us, though, there's nothing else to do,
// so we bail out.
// later see
State::Polling => return,
};
// Use `Promise.then` on a resolved promise to place our execution
// onto the next turn of the microtask queue, enqueueing our poll
// operation. We don't currently poll immediately as it turns out
// `futures` crate adapters aren't compatible with it and it also
// helps avoid blowing the stack by accident.
//
// Note that the `Rc`/`RefCell` trick here is basically to just
// ensure that our `Closure` gets cleaned up appropriately.
let promise = Promise::resolve(&JsValue::undefined());
let slot = Rc::new(RefCell::new(None));
let slot2 = slot.clone();
let closure = Closure::wrap(Box::new(move |_| {
let myself = slot2.borrow_mut().take();
debug_assert!(myself.is_some());
Package::poll(&me);
}) as Box<dyn FnMut(JsValue)>);
promise.then(&closure);
*slot.borrow_mut() = Some(closure);
}
}
}
/// Converts a Rust `Future` on a local task queue.
///
/// The `future` provided must adhere to `'static` because it'll be scheduled
/// to run in the background and cannot contain any stack references.
///
/// # Panics
///
/// This function has the same panic behavior as `future_to_promise`.
pub fn spawn_local<F>(future: F)
where
F: Future<Item = (), Error = ()> + 'static,
{
future_to_promise(
future
.map(|()| JsValue::undefined())
.or_else(|()| future::ok::<JsValue, JsValue>(JsValue::undefined())),
);
cfg_if! {
if #[cfg(target_feature = "atomics")] {
compile_error!("futures 0.3 support is not implemented with atomics yet");
} else {
/// Contains a Futures 0.3 implementation of this crate.
pub mod futures_0_3;
}
}

104
crates/futures/src/wait_async_polyfill.rs Normal file
View File

@ -0,0 +1,104 @@
//!
//! The polyfill was kindly borrowed from https://github.com/tc39/proposal-atomics-wait-async
//! and ported to Rust
//!
/* 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 http://mozilla.org/MPL/2.0/.
*
* Author: Lars T Hansen, lhansen@mozilla.com
*/
/* Polyfill for Atomics.waitAsync() for web browsers.
*
* Any kind of agent that is able to create a new Worker can use this polyfill.
*
* Load this file in all agents that will use Atomics.waitAsync.
*
* Agents that don't call Atomics.waitAsync need do nothing special.
*
* Any kind of agent can wake another agent that is sleeping in
* Atomics.waitAsync by just calling Atomics.wake for the location being slept
* on, as normal.
*
* The implementation is not completely faithful to the proposed semantics: in
* the case where an agent first asyncWaits and then waits on the same location:
* when it is woken, the two waits will be woken in order, while in the real
* semantics, the sync wait will be woken first.
*
* In this polyfill Atomics.waitAsync is not very fast.
*/
/* Implementation:
*
* For every wait we fork off a Worker to perform the wait. Workers are reused
* when possible. The worker communicates with its parent using postMessage.
*/
use js_sys::{encode_uri_component, Array, Promise};
use std::cell::RefCell;
use std::sync::atomic::AtomicI32;
use wasm_bindgen::prelude::*;
use wasm_bindgen::JsCast;
use web_sys::{MessageEvent, Worker};
const HELPER_CODE: &'static str = "
onmessage = function (ev) {
let [ia, index, value] = ev.data;
ia = new Int32Array(ia.buffer);
let result = Atomics.wait(ia, index, value);
postMessage(result);
};
";
thread_local! {
static HELPERS: RefCell<Vec<Worker>> = RefCell::new(vec![]);
}
fn alloc_helper() -> Worker {
HELPERS.with(|helpers| {
if let Some(helper) = helpers.borrow_mut().pop() {
return helper;
}
let mut initialization_string = "data:application/javascript,".to_owned();
let encoded: String = encode_uri_component(HELPER_CODE).into();
initialization_string.push_str(&encoded);
Worker::new(&initialization_string).unwrap_or_else(|js| wasm_bindgen::throw_val(js))
})
}
fn free_helper(helper: Worker) {
HELPERS.with(move |helpers| {
let mut helpers = helpers.borrow_mut();
helpers.push(helper.clone());
helpers.truncate(10); // random arbitrary limit chosen here
});
}
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));
})
}

2
crates/futures/tests/tests.rs
View File

@ -6,6 +6,8 @@ extern crate wasm_bindgen;
extern crate wasm_bindgen_futures;
extern crate wasm_bindgen_test;
wasm_bindgen_test::wasm_bindgen_test_configure!(run_in_browser);
use futures::unsync::oneshot;
use futures::Future;
use wasm_bindgen::prelude::*;

11
crates/js-sys/src/lib.rs
View File

@ -598,10 +598,19 @@ pub mod Atomics {
/// The static `Atomics.notify()` method notifies up some agents that
/// are sleeping in the wait queue.
/// Note: This operation works with a shared `Int32Array` only.
/// If `count` is not provided, notifies all the agents in the queue.
///
/// [MDN documentation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Atomics/notify)
#[wasm_bindgen(js_namespace = Atomics, catch)]
pub fn notify(typed_array: &Int32Array, index: u32, count: u32) -> Result<u32, JsValue>;
pub fn notify(typed_array: &Int32Array, index: u32) -> Result<u32, JsValue>;
/// Notifies up to `count` agents in the wait queue.
#[wasm_bindgen(js_namespace = Atomics, catch, js_name = notify)]
pub fn notify_with_count(
typed_array: &Int32Array,
index: u32,
count: u32,
) -> Result<u32, JsValue>;
/// The static `Atomics.or()` method computes a bitwise OR with a given value
/// at a given position in the array, and returns the old value at that position.

2
examples/raytrace-parallel/Cargo.toml
View File

@ -18,7 +18,7 @@ wasm-bindgen = { version = "0.2.48", features = ['serde-serialize'] }
wasm-bindgen-futures = "0.3.25"
[dependencies.web-sys]
version = "0.3.4"
version = "0.3.23"
features = [
'CanvasRenderingContext2d',
'ErrorEvent',

42
examples/raytrace-parallel/src/lib.rs
View File

@ -1,3 +1,4 @@
use futures::sync::oneshot;
use futures::Future;
use js_sys::{Promise, Uint8ClampedArray, WebAssembly};
use rayon::prelude::*;
@ -69,27 +70,28 @@ impl Scene {
// threads so we don't lock up the main thread, so we ship off a thread
// which actually does the whole rayon business. When our returned
// future is resolved we can pull out the final version of the image.
let done = pool
.run_notify(move || {
thread_pool.install(|| {
rgb_data
.par_chunks_mut(4)
.enumerate()
.for_each(|(i, chunk)| {
let i = i as u32;
let x = i % width;
let y = i / width;
let ray = raytracer::Ray::create_prime(x, y, &scene);
let result = raytracer::cast_ray(&scene, &ray, 0).to_rgba();
chunk[0] = result.data[0];
chunk[1] = result.data[1];
chunk[2] = result.data[2];
chunk[3] = result.data[3];
});
});
let (tx, rx) = oneshot::channel();
pool.run(move || {
thread_pool.install(|| {
rgb_data
})?
.map(move |_data| image_data(base, len, width, height).into());
.par_chunks_mut(4)
.enumerate()
.for_each(|(i, chunk)| {
let i = i as u32;
let x = i % width;
let y = i / width;
let ray = raytracer::Ray::create_prime(x, y, &scene);
let result = raytracer::cast_ray(&scene, &ray, 0).to_rgba();
chunk[0] = result.data[0];
chunk[1] = result.data[1];
chunk[2] = result.data[2];
chunk[3] = result.data[3];
});
});
drop(tx.send(rgb_data));
})?;
let done = rx.map(move |_data| image_data(base, len, width, height).into())
.map_err(|_| JsValue::undefined());
Ok(RenderingScene {
promise: wasm_bindgen_futures::future_to_promise(done),

89
examples/raytrace-parallel/src/pool.rs
View File

@ -1,13 +1,8 @@
//! A small module that's intended to provide an example of creating a pool of
//! web workers which can be used to execute `rayon`-style work.
use futures::sync::oneshot;
use futures::Future;
use std::cell::{RefCell, UnsafeCell};
use std::mem;
use std::cell::RefCell;
use std::rc::Rc;
use std::sync::atomic::{AtomicBool, Ordering::SeqCst};
use std::sync::Arc;
use wasm_bindgen::prelude::*;
use wasm_bindgen::JsCast;
use web_sys::{DedicatedWorkerGlobalScope, MessageEvent};
@ -141,12 +136,11 @@ impl WorkerPool {
/// whatn it's done the worker is ready to execute more work. This method is
/// used for all spawned workers to ensure that when the work is finished
/// the worker is reclaimed back into this pool.
fn reclaim_on_message(&self, worker: Worker, on_finish: impl FnOnce() + 'static) {
fn reclaim_on_message(&self, worker: Worker) {
let state = Rc::downgrade(&self.state);
let worker2 = worker.clone();
let reclaim_slot = Rc::new(RefCell::new(None));
let slot2 = reclaim_slot.clone();
let mut on_finish = Some(on_finish);
let reclaim = Closure::wrap(Box::new(move |event: Event| {
if let Some(error) = event.dyn_ref::<ErrorEvent>() {
console_log!("error in worker: {}", error.message());
@ -155,11 +149,9 @@ impl WorkerPool {
return;
}
// If this is a completion event then we can execute our `on_finish`
// callback and we can also deallocate our own callback by clearing
// out `slot2` which contains our own closure.
// If this is a completion event then can deallocate our own
// callback by clearing out `slot2` which contains our own closure.
if let Some(_msg) = event.dyn_ref::<MessageEvent>() {
on_finish.take().unwrap()();
if let Some(state) = state.upgrade() {
state.push(worker2.clone());
}
@ -193,80 +185,9 @@ impl WorkerPool {
/// a web worker, that error is returned.
pub fn run(&self, f: impl FnOnce() + Send + 'static) -> Result<(), JsValue> {
let worker = self.execute(f)?;
self.reclaim_on_message(worker, || {});
self.reclaim_on_message(worker);
Ok(())
}
/// Executes the closure `f` in a web worker, returning a future of the
/// value that `f` produces.
///
/// This method is the same as `run` execept that it allows recovering the
/// return value of the closure `f` in a nonblocking fashion with the future
/// returned.
///
/// # Errors
///
/// If an error happens while spawning a web worker or sending a message to
/// a web worker, that error is returned.
pub fn run_notify<T>(
&self,
f: impl FnOnce() -> T + Send + 'static,
) -> Result<impl Future<Item = T, Error = JsValue> + 'static, JsValue>
where
T: Send + 'static,
{
// FIXME(#1379) we should just use the `oneshot` directly as the future,
// but we have to use JS callbacks to ensure we don't have futures cross
// threads as that's currently not safe to do so.
let (tx, rx) = oneshot::channel();
let storage = Arc::new(AtomicValue::new(None));
let storage2 = storage.clone();
let worker = self.execute(move || {
assert!(storage2.replace(Some(f())).is_ok());
})?;
self.reclaim_on_message(worker, move || match storage.replace(None) {
Ok(Some(val)) => drop(tx.send(val)),
_ => unreachable!(),
});
Ok(rx.map_err(|_| JsValue::undefined()))
}
}
/// A small helper struct representing atomic access to an internal value `T`
///
/// This struct only supports one API, `replace`, which will either succeed and
/// replace the internal value with another (returning the previous one), or it
/// will fail returning the value passed in. Failure happens when two threads
/// try to `replace` at the same time.
///
/// This is only really intended to help safely transfer information between
/// threads, it doesn't provide any synchronization capabilities itself other
/// than a guaranteed safe API.
struct AtomicValue<T> {
modifying: AtomicBool,
slot: UnsafeCell<T>,
}
unsafe impl<T: Send> Send for AtomicValue<T> {}
unsafe impl<T: Send> Sync for AtomicValue<T> {}
impl<T> AtomicValue<T> {
fn new(val: T) -> AtomicValue<T> {
AtomicValue {
modifying: AtomicBool::new(false),
slot: UnsafeCell::new(val),
}
}
fn replace(&self, val: T) -> Result<T, T> {
if self.modifying.swap(true, SeqCst) {
return Err(val);
}
let ret = unsafe { mem::replace(&mut *self.slot.get(), val) };
self.modifying.store(false, SeqCst);
Ok(ret)
}
}
impl PoolState {