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