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|
// compile-flags: -C opt-level=3
// edition:2018
use std::future::Future;
use std::marker::PhantomData;
use std::pin::Pin;
use std::sync::atomic::AtomicUsize;
use std::sync::Arc;
use std::task::Poll::{Pending, Ready};
use std::task::Waker;
use std::task::{Context, Poll};
use std::{
ptr,
task::{RawWaker, RawWakerVTable},
};
/// Future for the [`poll_fn`] function.
pub struct PollFn<F> {
f: F,
}
impl<F> Unpin for PollFn<F> {}
/// Creates a new future wrapping around a function returning [`Poll`].
pub fn poll_fn<T, F>(f: F) -> PollFn<F>
where
F: FnMut(&mut Context<'_>) -> Poll<T>,
{
PollFn { f }
}
impl<T, F> Future for PollFn<F>
where
F: FnMut(&mut Context<'_>) -> Poll<T>,
{
type Output = T;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
(&mut self.f)(cx)
}
}
pub fn run<F: Future>(future: F) -> F::Output {
BasicScheduler.block_on(future)
}
pub(crate) struct BasicScheduler;
impl BasicScheduler {
pub(crate) fn block_on<F>(&mut self, mut future: F) -> F::Output
where
F: Future,
{
let waker = unsafe { Waker::from_raw(raw_waker()) };
let mut cx = std::task::Context::from_waker(&waker);
let mut future = unsafe { Pin::new_unchecked(&mut future) };
loop {
if let Ready(v) = future.as_mut().poll(&mut cx) {
return v;
}
}
}
}
// ===== impl Spawner =====
fn raw_waker() -> RawWaker {
RawWaker::new(ptr::null(), waker_vtable())
}
fn waker_vtable() -> &'static RawWakerVTable {
&RawWakerVTable::new(
clone_arc_raw,
wake_arc_raw,
wake_by_ref_arc_raw,
drop_arc_raw,
)
}
unsafe fn clone_arc_raw(_: *const ()) -> RawWaker {
raw_waker()
}
unsafe fn wake_arc_raw(_: *const ()) {}
unsafe fn wake_by_ref_arc_raw(_: *const ()) {}
unsafe fn drop_arc_raw(_: *const ()) {}
struct AtomicWaker {}
impl AtomicWaker {
/// Create an `AtomicWaker`
fn new() -> AtomicWaker {
AtomicWaker {}
}
fn register_by_ref(&self, _waker: &Waker) {}
}
#[allow(dead_code)]
struct Tx<T> {
inner: Arc<Chan<T>>,
}
struct Rx<T> {
inner: Arc<Chan<T>>,
}
#[allow(dead_code)]
struct Chan<T> {
tx: PhantomData<T>,
semaphore: Sema,
rx_waker: AtomicWaker,
rx_closed: bool,
}
fn channel<T>() -> (Tx<T>, Rx<T>) {
let chan = Arc::new(Chan {
tx: PhantomData,
semaphore: Sema(AtomicUsize::new(0)),
rx_waker: AtomicWaker::new(),
rx_closed: false,
});
(
Tx {
inner: chan.clone(),
},
Rx { inner: chan },
)
}
// ===== impl Rx =====
impl<T> Rx<T> {
/// Receive the next value
fn recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<T>> {
self.inner.rx_waker.register_by_ref(cx.waker());
if self.inner.rx_closed && self.inner.semaphore.is_idle() {
Ready(None)
} else {
Pending
}
}
}
struct Sema(AtomicUsize);
impl Sema {
fn is_idle(&self) -> bool {
false
}
}
pub struct UnboundedReceiver<T> {
chan: Rx<T>,
}
pub fn unbounded_channel<T>() -> UnboundedReceiver<T> {
let (tx, rx) = channel();
drop(tx);
let rx = UnboundedReceiver { chan: rx };
rx
}
impl<T> UnboundedReceiver<T> {
pub async fn recv(&mut self) -> Option<T> {
poll_fn(|cx| self.chan.recv(cx)).await
}
}
|
