neon/types_impl/promise.rs
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use std::ptr;
use crate::{
context::{
internal::{ContextInternal, Env},
Context,
},
handle::{internal::TransparentNoCopyWrapper, Handle},
object::Object,
result::JsResult,
sys::{self, no_panic::FailureBoundary, raw},
types::{private::ValueInternal, Value},
};
#[cfg(feature = "napi-4")]
use crate::{
context::Cx,
event::{Channel, JoinHandle, SendError},
};
#[cfg(feature = "napi-6")]
use crate::{
lifecycle::{DropData, InstanceData},
sys::tsfn::ThreadsafeFunction,
};
#[cfg(all(feature = "napi-5", feature = "futures"))]
use {
crate::event::{JoinError, SendThrow},
crate::result::NeonResult,
crate::types::{JsFunction, JsValue},
std::future::Future,
std::pin::Pin,
std::sync::Mutex,
std::task::{self, Poll},
tokio::sync::oneshot,
};
#[cfg(any(feature = "napi-6", all(feature = "napi-5", feature = "futures")))]
use std::sync::Arc;
const BOUNDARY: FailureBoundary = FailureBoundary {
both: "A panic and exception occurred while resolving a `neon::types::Deferred`",
exception: "An exception occurred while resolving a `neon::types::Deferred`",
panic: "A panic occurred while resolving a `neon::types::Deferred`",
};
#[derive(Debug)]
#[repr(transparent)]
/// The type of JavaScript
/// [`Promise`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
/// objects.
///
/// [`JsPromise`] instances may be constructed with [`Context::promise`], which
/// produces both a promise and a [`Deferred`], which can be used to control
/// the behavior of the promise. A `Deferred` struct is similar to the `resolve`
/// and `reject` functions produced by JavaScript's standard
/// [`Promise`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/Promise)
/// constructor:
///
/// ```javascript
/// let deferred;
/// let promise = new Promise((resolve, reject) => {
/// deferred = { resolve, reject };
/// });
/// ```
///
/// # Example
///
/// ```
/// # use neon::prelude::*;
/// fn resolve_promise(mut cx: FunctionContext) -> JsResult<JsPromise> {
/// let (deferred, promise) = cx.promise();
/// let msg = cx.string("Hello, World!");
///
/// deferred.resolve(&mut cx, msg);
///
/// Ok(promise)
/// }
/// ```
///
/// # Example: Asynchronous task
///
/// This example uses the [linkify](https://crates.io/crates/linkify) crate in an
/// asynchronous task, i.e. a
/// [Node worker pool](https://nodejs.org/en/docs/guides/dont-block-the-event-loop/)
/// thread, to find all the links in a text string.
///
/// Alternate implementations might use a custom Rust thread or thread pool to avoid
/// blocking the worker pool; for more information, see the [`JsFuture`] example.
///
/// ```
/// # use neon::prelude::*;
/// use linkify::{LinkFinder, LinkKind};
/// # #[cfg(feature = "doc-dependencies")]
/// use easy_cast::Cast; // for safe numerical conversions
///
/// # #[cfg(feature = "doc-dependencies")]
/// fn linkify(mut cx: FunctionContext) -> JsResult<JsPromise> {
/// let text = cx.argument::<JsString>(0)?.value(&mut cx);
///
/// let promise = cx
/// .task(move || {
/// let (indices, kinds): (Vec<_>, Vec<_>) = LinkFinder::new()
/// // The spans() method fully partitions the text
/// // into a sequence of contiguous spans, some of which
/// // are plain text and some of which are links.
/// .spans(&text)
/// .map(|span| {
/// // The first span starts at 0 and the rest start
/// // at their preceding span's end index.
/// let end: u32 = span.end().cast();
///
/// let kind: u8 = match span.kind() {
/// Some(LinkKind::Url) => 1,
/// Some(LinkKind::Email) => 2,
/// _ => 0,
/// };
///
/// (end, kind)
/// })
/// .unzip();
/// (indices, kinds)
/// })
/// .promise(|mut cx, (indices, kinds)| {
/// let indices = JsUint32Array::from_slice(&mut cx, &indices)?;
/// let kinds = JsUint8Array::from_slice(&mut cx, &kinds)?;
/// Ok(cx.empty_object()
/// .prop(&mut cx, "indices")
/// .set(indices)?
/// .prop("kinds")
/// .set(kinds)?
/// .this())
/// });
///
/// Ok(promise)
/// }
/// ```
pub struct JsPromise(raw::Local);
impl JsPromise {
pub(crate) fn new<'a, C: Context<'a>>(cx: &mut C) -> (Deferred, Handle<'a, Self>) {
let (deferred, promise) = unsafe { sys::promise::create(cx.env().to_raw()) };
let deferred = Deferred {
internal: Some(NodeApiDeferred(deferred)),
#[cfg(feature = "napi-6")]
drop_queue: InstanceData::drop_queue(cx),
};
(deferred, Handle::new_internal(JsPromise(promise)))
}
/// Creates a new `Promise` immediately resolved with the given value. If the value is a
/// `Promise` or a then-able, it will be flattened.
///
/// `JsPromise::resolve` is useful to ensure a value that might not be a `Promise` or
/// might not be a native promise is converted to a `Promise` before use.
pub fn resolve<'a, C: Context<'a>, T: Value>(cx: &mut C, value: Handle<T>) -> Handle<'a, Self> {
let (deferred, promise) = cx.promise();
deferred.resolve(cx, value);
promise
}
/// Creates a nwe `Promise` immediately rejected with the given error.
pub fn reject<'a, C: Context<'a>, E: Value>(cx: &mut C, err: Handle<E>) -> Handle<'a, Self> {
let (deferred, promise) = cx.promise();
deferred.reject(cx, err);
promise
}
#[cfg(all(feature = "napi-5", feature = "futures"))]
#[cfg_attr(docsrs, doc(cfg(all(feature = "napi-5", feature = "futures"))))]
/// Creates a [`Future`](std::future::Future) that can be awaited to receive the result of a
/// JavaScript `Promise`.
///
/// A callback must be provided that maps a `Result` representing the resolution or rejection of
/// the `Promise` and returns a value as the `Future` output.
///
/// _Note_: Unlike `Future`, `Promise` are eagerly evaluated and so are `JsFuture`.
pub fn to_future<'a, O, C, F>(&self, cx: &mut C, f: F) -> NeonResult<JsFuture<O>>
where
O: Send + 'static,
C: Context<'a>,
F: FnOnce(Cx, Result<Handle<JsValue>, Handle<JsValue>>) -> NeonResult<O> + Send + 'static,
{
let then = self.get::<JsFunction, _, _>(cx, "then")?;
let (tx, rx) = oneshot::channel();
let take_state = {
// Note: If this becomes a bottleneck, `unsafe` could be used to avoid it.
// The promise spec guarantees that it will only be used once.
let state = Arc::new(Mutex::new(Some((f, tx))));
move || {
state
.lock()
.ok()
.and_then(|mut lock| lock.take())
// This should never happen because `self` is a native `Promise`
// and settling multiple times is a violation of the spec.
.expect("Attempted to settle JsFuture multiple times")
}
};
let resolve = JsFunction::new(cx, {
let take_state = take_state.clone();
move |mut cx| {
let (f, tx) = take_state();
let v = cx.argument::<JsValue>(0)?;
Cx::with_context(cx.env(), move |cx| {
// Error indicates that the `Future` has already dropped; ignore
let _ = tx.send(f(cx, Ok(v)).map_err(Into::into));
});
Ok(cx.undefined())
}
})?;
let reject = JsFunction::new(cx, {
move |mut cx| {
let (f, tx) = take_state();
let v = cx.argument::<JsValue>(0)?;
Cx::with_context(cx.env(), move |cx| {
// Error indicates that the `Future` has already dropped; ignore
let _ = tx.send(f(cx, Err(v)).map_err(Into::into));
});
Ok(cx.undefined())
}
})?;
then.exec(
cx,
Handle::new_internal(Self(self.0)),
[resolve.upcast(), reject.upcast()],
)?;
Ok(JsFuture { rx })
}
}
unsafe impl TransparentNoCopyWrapper for JsPromise {
type Inner = raw::Local;
fn into_inner(self) -> Self::Inner {
self.0
}
}
impl ValueInternal for JsPromise {
fn name() -> &'static str {
"Promise"
}
fn is_typeof<Other: Value>(cx: &mut Cx, other: &Other) -> bool {
unsafe { sys::tag::is_promise(cx.env().to_raw(), other.to_local()) }
}
fn to_local(&self) -> raw::Local {
self.0
}
unsafe fn from_local(_env: Env, h: raw::Local) -> Self {
Self(h)
}
}
impl Value for JsPromise {}
impl Object for JsPromise {}
/// A controller struct that can be used to resolve or reject a [`JsPromise`].
///
/// It is recommended to settle a [`Deferred`] with [`Deferred::settle_with`] to ensure
/// exceptions are caught.
///
/// On Node-API versions less than 6, dropping a [`Deferred`] without settling will
/// cause a panic. On Node-API 6+, the associated [`JsPromise`] will be automatically
/// rejected.
///
/// # Examples
///
/// See [`JsPromise`], [`JsFuture`].
pub struct Deferred {
internal: Option<NodeApiDeferred>,
#[cfg(feature = "napi-6")]
drop_queue: Arc<ThreadsafeFunction<DropData>>,
}
impl Deferred {
/// Resolve a [`JsPromise`] with a JavaScript value
pub fn resolve<'a, V, C>(self, cx: &mut C, value: Handle<V>)
where
V: Value,
C: Context<'a>,
{
unsafe {
sys::promise::resolve(cx.env().to_raw(), self.into_inner(), value.to_local());
}
}
/// Reject a [`JsPromise`] with a JavaScript value
pub fn reject<'a, V, C>(self, cx: &mut C, value: Handle<V>)
where
V: Value,
C: Context<'a>,
{
unsafe {
sys::promise::reject(cx.env().to_raw(), self.into_inner(), value.to_local());
}
}
#[cfg(feature = "napi-4")]
#[cfg_attr(docsrs, doc(cfg(feature = "napi-4")))]
/// Settle the [`JsPromise`] by sending a closure across a [`Channel`][`crate::event::Channel`]
/// to be executed on the main JavaScript thread.
///
/// Usage is identical to [`Deferred::settle_with`].
///
/// Returns a [`SendError`][crate::event::SendError] if sending the closure to the main JavaScript thread fails.
/// See [`Channel::try_send`][crate::event::Channel::try_send] for more details.
pub fn try_settle_with<V, F>(
self,
channel: &Channel,
complete: F,
) -> Result<JoinHandle<()>, SendError>
where
V: Value,
F: FnOnce(Cx) -> JsResult<V> + Send + 'static,
{
channel.try_send(move |cx| {
self.try_catch_settle(cx, complete);
Ok(())
})
}
#[cfg(feature = "napi-4")]
#[cfg_attr(docsrs, doc(cfg(feature = "napi-4")))]
/// Settle the [`JsPromise`] by sending a closure across a [`Channel`][crate::event::Channel]
/// to be executed on the main JavaScript thread.
///
/// Panics if there is a libuv error.
///
/// ```
/// # use neon::prelude::*;
/// # fn example(mut cx: FunctionContext) -> JsResult<JsPromise> {
/// let channel = cx.channel();
/// let (deferred, promise) = cx.promise();
///
/// deferred.settle_with(&channel, move |mut cx| Ok(cx.number(42)));
///
/// # Ok(promise)
/// # }
/// ```
pub fn settle_with<V, F>(self, channel: &Channel, complete: F) -> JoinHandle<()>
where
V: Value,
F: FnOnce(Cx) -> JsResult<V> + Send + 'static,
{
self.try_settle_with(channel, complete).unwrap()
}
pub(crate) fn try_catch_settle<'a, C, V, F>(self, cx: C, f: F)
where
C: Context<'a>,
V: Value,
F: FnOnce(C) -> JsResult<'a, V>,
{
unsafe {
BOUNDARY.catch_failure(
cx.env().to_raw(),
Some(self.into_inner()),
move |_| match f(cx) {
Ok(value) => value.to_local(),
Err(_) => ptr::null_mut(),
},
);
}
}
pub(crate) fn into_inner(mut self) -> sys::Deferred {
self.internal.take().unwrap().0
}
}
#[repr(transparent)]
pub(crate) struct NodeApiDeferred(sys::Deferred);
unsafe impl Send for NodeApiDeferred {}
#[cfg(feature = "napi-6")]
impl NodeApiDeferred {
pub(crate) unsafe fn leaked(self, env: raw::Env) {
sys::promise::reject_err_message(
env,
self.0,
"`neon::types::Deferred` was dropped without being settled",
);
}
}
impl Drop for Deferred {
#[cfg(not(feature = "napi-6"))]
fn drop(&mut self) {
// If `None`, the `Deferred` has already been settled
if self.internal.is_none() {
return;
}
// Destructors are called during stack unwinding, prevent a double
// panic and instead prefer to leak.
if std::thread::panicking() {
eprintln!("Warning: neon::types::JsPromise leaked during a panic");
return;
}
// Only panic if the event loop is still running
if let Ok(true) = crate::context::internal::IS_RUNNING.try_with(|v| *v.borrow()) {
panic!("Must settle a `neon::types::JsPromise` with `neon::types::Deferred`");
}
}
#[cfg(feature = "napi-6")]
fn drop(&mut self) {
// If `None`, the `Deferred` has already been settled
if let Some(internal) = self.internal.take() {
let _ = self.drop_queue.call(DropData::Deferred(internal), None);
}
}
}
#[cfg(all(feature = "napi-5", feature = "futures"))]
#[cfg_attr(docsrs, doc(cfg(all(feature = "napi-5", feature = "futures"))))]
/// A type of JavaScript
/// [`Promise`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
/// object that acts as a [`Future`](std::future::Future).
///
/// Unlike typical `Future` implementations, `JsFuture`s are eagerly executed
/// because they are backed by a `Promise`.
///
/// # Example
///
/// This example uses a `JsFuture` to take asynchronous binary data and perform
/// potentially expensive computations on that data in a Rust thread.
///
/// The example uses a [Tokio](https://tokio.rs) thread pool (allocated and
/// stored on demand with a [`OnceCell`](https://crates.io/crates/once_cell))
/// to run the computations.
///
/// ```
/// # use neon::prelude::*;
/// use neon::types::buffer::TypedArray;
/// use once_cell::sync::OnceCell;
/// use tokio::runtime::Runtime;
///
/// // Lazily allocate a Tokio runtime to use as the thread pool.
/// fn runtime(cx: &mut Cx) -> NeonResult<&'static Runtime> {
/// static RUNTIME: OnceCell<Runtime> = OnceCell::new();
///
/// RUNTIME
/// .get_or_try_init(Runtime::new)
/// .or_else(|err| cx.throw_error(&err.to_string()))
/// }
///
/// // async_compute: Promise<Float64Array> -> Promise<number>
/// //
/// // Takes a promise that produces a typed array and returns a promise that:
/// // - awaits the typed array from the original promise;
/// // - computes a value from the contents of the array in a background thread; and
/// // - resolves once the computation is completed
/// pub fn async_compute(mut cx: FunctionContext) -> JsResult<JsPromise> {
/// let nums: Handle<JsPromise> = cx.argument(0)?;
///
/// // Convert the JS Promise to a Rust Future for use in a compute thread.
/// let nums = nums.to_future(&mut cx, |mut cx, result| {
/// // Get the promise's result value (or throw if it was rejected).
/// let value = result.or_throw(&mut cx)?;
///
/// // Downcast the result value to a Float64Array.
/// let array: Handle<JsFloat64Array> = value.downcast_or_throw(&mut cx)?;
///
/// // Convert the typed array to a Rust vector.
/// let vec = array.as_slice(&cx).to_vec();
/// Ok(vec)
/// })?;
///
/// // Construct a result promise which will be fulfilled when the computation completes.
/// let (deferred, promise) = cx.promise();
/// let channel = cx.channel();
/// let runtime = runtime(&mut cx)?;
///
/// // Perform the computation in a background thread using the Tokio thread pool.
/// runtime.spawn(async move {
/// // Await the JsFuture, which yields Result<Vec<f64>, JoinError>.
/// let result = match nums.await {
/// // Perform the computation. In this example, we just calculate the sum
/// // of all values in the array; more involved examples might be running
/// // compression or decompression algorithms, encoding or decoding media
/// // codecs, image filters or other media transformations, etc.
/// Ok(nums) => Ok(nums.into_iter().sum::<f64>()),
/// Err(err) => Err(err)
/// };
///
/// // Resolve the result promise with the result of the computation.
/// deferred.settle_with(&channel, |mut cx| {
/// let result = result.or_throw(&mut cx)?;
/// Ok(cx.number(result))
/// });
/// });
///
/// Ok(promise)
/// }
/// ```
pub struct JsFuture<T> {
// `Err` is always `Throw`, but `Throw` cannot be sent across threads
rx: oneshot::Receiver<Result<T, SendThrow>>,
}
#[cfg(all(feature = "napi-5", feature = "futures"))]
#[cfg_attr(docsrs, doc(cfg(all(feature = "napi-5", feature = "futures"))))]
impl<T> Future for JsFuture<T> {
type Output = Result<T, JoinError>;
fn poll(mut self: Pin<&mut Self>, cx: &mut task::Context) -> Poll<Self::Output> {
match Pin::new(&mut self.rx).poll(cx) {
Poll::Ready(result) => {
// Flatten `Result<Result<T, SendThrow>, RecvError>` by mapping to
// `Result<T, JoinError>`. This can be simplified by replacing the
// closure with a try-block after stabilization.
// https://doc.rust-lang.org/beta/unstable-book/language-features/try-blocks.html
let get_result = move || Ok(result??);
Poll::Ready(get_result())
}
Poll::Pending => Poll::Pending,
}
}
}