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use std::future::Future;
use std::pin::Pin;
use std::sync::{Arc, RwLock};
use std::task::{Context, Poll, Waker};
pub struct Promise<Env, T> {
inner: Arc<RwLock<Inner<T>>>,
waiters: Arc<RwLock<Vec<Box<dyn Fn(&mut Env, &T)>>>>,
}
pub struct Complete<T> {
inner: Arc<RwLock<Inner<T>>>,
}
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct Cancelled;
struct Inner<T> {
value: Option<Arc<T>>,
waker: Option<Waker>,
}
pub fn promise<Env, T>() -> (Complete<T>, Promise<Env, T>) {
let inner = Arc::new(RwLock::new(Inner {
value: None,
waker: None,
}));
let promise = Promise {
inner: inner.clone(),
waiters: Arc::new(RwLock::new(Vec::new())),
};
let complete = Complete { inner: inner };
(complete, promise)
}
impl<T> Complete<T> {
pub fn fulfill(&self, val: T) {
let mut inner = self.inner.write().unwrap();
inner.value = Some(Arc::new(val));
if let Some(waker) = inner.waker.take() {
waker.wake()
}
}
}
impl<T> Complete<Result<T, Cancelled>> {
pub fn cancel(&mut self) {
self.fulfill(Err(Cancelled))
}
}
impl<E, T> Complete<Result<T, E>> {
pub fn ok(&mut self, val: T) {
self.fulfill(Ok(val))
}
pub fn err(&mut self, e: E) {
self.fulfill(Err(e))
}
}
impl<Env, T> Promise<Env, T> {
pub fn on_fulfill<F: Fn(&mut Env, &T) + 'static>(&mut self, f: F) {
let mut waiters = self.waiters.write().unwrap();
waiters.push(Box::new(f));
}
}
impl<Env, T> Promise<Env, Result<T, Cancelled>> {
pub fn on_cancel<F: Fn(&mut Env) + 'static>(&mut self, f: F) {
self.on_err(move |env, _| f(env))
}
}
impl<Env, E, T> Promise<Env, Result<T, E>> {
pub fn on_ok<F: Fn(&mut Env, &T) + 'static>(&mut self, f: F) {
self.on_fulfill(move |env, r| {
if let Ok(val) = r {
f(env, val)
}
})
}
pub fn on_err<F: Fn(&mut Env, &E) + 'static>(&mut self, f: F) {
self.on_fulfill(move |env, r| {
if let Err(e) = r {
f(env, e)
}
})
}
}
pub trait Give<Env> {
fn give(&self, env: &mut Env) -> bool;
}
impl<Env, T> Give<Env> for Promise<Env, T> {
fn give(&self, env: &mut Env) -> bool {
let inner = self.inner.read().unwrap();
if let Some(value) = &inner.value {
let mut waiters = self.waiters.write().unwrap();
for waiter in waiters.iter() {
waiter(env, value);
}
waiters.clear();
true
} else {
false
}
}
}
impl<Env, T> Clone for Promise<Env, T> {
fn clone(&self) -> Self {
Promise {
inner: self.inner.clone(),
waiters: self.waiters.clone(),
}
}
}
impl<Env, P: Give<Env>> Give<Env> for &P {
fn give(&self, env: &mut Env) -> bool {
(*self).give(env)
}
}
impl<Env, T> Future for Promise<Env, T> {
type Output = Arc<T>;
fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
let mut inner = self.inner.write().unwrap();
match inner.value {
Some(ref v) => Poll::Ready(v.clone()),
None => {
inner.waker = Some(cx.waker().clone());
Poll::Pending
}
}
}
}
pub struct Promises<'a, Env> {
ps: Vec<Box<dyn Give<Env> + 'a>>,
}
impl<'a, Env> Promises<'a, Env> {
pub fn new() -> Self {
Promises { ps: Vec::new() }
}
pub fn push(&mut self, p: Box<dyn Give<Env> + 'a>) {
self.ps.push(p);
}
pub fn give_all(&mut self, env: &mut Env) {
self.ps.retain(|p| !p.give(env));
}
}
|
