mirror of https://github.com/smol-rs/async-task
146 lines
3.7 KiB
Rust
146 lines
3.7 KiB
Rust
//! A single threaded executor that uses shortest-job-first scheduling.
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use std::cell::RefCell;
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use std::collections::BinaryHeap;
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use std::pin::Pin;
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use std::task::{Context, Poll};
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use std::thread;
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use std::time::{Duration, Instant};
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use std::{cell::Cell, future::Future};
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use async_task::{Builder, Runnable, Task};
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use pin_project_lite::pin_project;
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use smol::{channel, future};
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struct ByDuration(Runnable<DurationMetadata>);
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impl ByDuration {
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fn duration(&self) -> Duration {
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self.0.metadata().inner.get()
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}
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}
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impl PartialEq for ByDuration {
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fn eq(&self, other: &Self) -> bool {
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self.duration() == other.duration()
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}
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}
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impl Eq for ByDuration {}
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impl PartialOrd for ByDuration {
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fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
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Some(self.cmp(other))
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}
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}
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impl Ord for ByDuration {
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fn cmp(&self, other: &Self) -> std::cmp::Ordering {
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self.duration().cmp(&other.duration()).reverse()
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}
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}
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pin_project! {
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#[must_use = "futures do nothing unless you `.await` or poll them"]
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struct MeasureRuntime<'a, F> {
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#[pin]
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f: F,
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duration: &'a Cell<Duration>
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}
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}
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impl<'a, F: Future> Future for MeasureRuntime<'a, F> {
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type Output = F::Output;
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fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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let this = self.project();
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let duration_cell: &Cell<Duration> = this.duration;
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let start = Instant::now();
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let res = F::poll(this.f, cx);
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let new_duration = Instant::now() - start;
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duration_cell.set(duration_cell.get() / 2 + new_duration / 2);
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res
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}
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}
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pub struct DurationMetadata {
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inner: Cell<Duration>,
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}
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thread_local! {
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// A queue that holds scheduled tasks.
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static QUEUE: RefCell<BinaryHeap<ByDuration>> = RefCell::new(BinaryHeap::new());
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}
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fn make_future_fn<'a, F>(
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future: F,
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) -> impl (FnOnce(&'a DurationMetadata) -> MeasureRuntime<'a, F>) {
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move |duration_meta| MeasureRuntime {
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f: future,
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duration: &duration_meta.inner,
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}
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}
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fn ensure_safe_schedule<F: Send + Sync + 'static>(f: F) -> F {
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f
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}
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/// Spawns a future on the executor.
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pub fn spawn<F, T>(future: F) -> Task<T, DurationMetadata>
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where
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F: Future<Output = T> + 'static,
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T: 'static,
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{
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let spawn_thread_id = thread::current().id();
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// Create a task that is scheduled by pushing it into the queue.
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let schedule = ensure_safe_schedule(move |runnable| {
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if thread::current().id() != spawn_thread_id {
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panic!("Task would be run on a different thread than spawned on.");
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}
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QUEUE.with(move |queue| queue.borrow_mut().push(ByDuration(runnable)));
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});
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let future_fn = make_future_fn(future);
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let (runnable, task) = unsafe {
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Builder::new()
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.metadata(DurationMetadata {
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inner: Cell::new(Duration::default()),
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})
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.spawn_unchecked(future_fn, schedule)
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};
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// Schedule the task by pushing it into the queue.
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runnable.schedule();
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task
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}
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pub fn block_on<F>(future: F)
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where
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F: Future<Output = ()> + 'static,
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{
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let task = spawn(future);
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while !task.is_finished() {
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let Some(runnable) = QUEUE.with(|queue| queue.borrow_mut().pop()) else {
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thread::yield_now();
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continue;
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};
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runnable.0.run();
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}
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}
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fn main() {
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// Spawn a future and await its result.
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block_on(async {
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let (sender, receiver) = channel::bounded(1);
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let world = spawn(async move {
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receiver.recv().await.unwrap();
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println!("world.")
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});
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let hello = spawn(async move {
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sender.send(()).await.unwrap();
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print!("Hello, ")
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});
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future::zip(hello, world).await;
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});
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}
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