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Diffstat (limited to 'third_party/rust/futures-util/src/abortable.rs')
| -rw-r--r-- | third_party/rust/futures-util/src/abortable.rs | 185 |
1 files changed, 185 insertions, 0 deletions
diff --git a/third_party/rust/futures-util/src/abortable.rs b/third_party/rust/futures-util/src/abortable.rs new file mode 100644 index 0000000000..e0afd47218 --- /dev/null +++ b/third_party/rust/futures-util/src/abortable.rs @@ -0,0 +1,185 @@ +use crate::task::AtomicWaker; +use alloc::sync::Arc; +use core::fmt; +use core::pin::Pin; +use core::sync::atomic::{AtomicBool, Ordering}; +use futures_core::future::Future; +use futures_core::task::{Context, Poll}; +use futures_core::Stream; +use pin_project_lite::pin_project; + +pin_project! { + /// A future/stream which can be remotely short-circuited using an `AbortHandle`. + #[derive(Debug, Clone)] + #[must_use = "futures/streams do nothing unless you poll them"] + pub struct Abortable<T> { + #[pin] + task: T, + inner: Arc<AbortInner>, + } +} + +impl<T> Abortable<T> { + /// Creates a new `Abortable` future/stream using an existing `AbortRegistration`. + /// `AbortRegistration`s can be acquired through `AbortHandle::new`. + /// + /// When `abort` is called on the handle tied to `reg` or if `abort` has + /// already been called, the future/stream will complete immediately without making + /// any further progress. + /// + /// # Examples: + /// + /// Usage with futures: + /// + /// ``` + /// # futures::executor::block_on(async { + /// use futures::future::{Abortable, AbortHandle, Aborted}; + /// + /// let (abort_handle, abort_registration) = AbortHandle::new_pair(); + /// let future = Abortable::new(async { 2 }, abort_registration); + /// abort_handle.abort(); + /// assert_eq!(future.await, Err(Aborted)); + /// # }); + /// ``` + /// + /// Usage with streams: + /// + /// ``` + /// # futures::executor::block_on(async { + /// # use futures::future::{Abortable, AbortHandle}; + /// # use futures::stream::{self, StreamExt}; + /// + /// let (abort_handle, abort_registration) = AbortHandle::new_pair(); + /// let mut stream = Abortable::new(stream::iter(vec![1, 2, 3]), abort_registration); + /// abort_handle.abort(); + /// assert_eq!(stream.next().await, None); + /// # }); + /// ``` + pub fn new(task: T, reg: AbortRegistration) -> Self { + Self { task, inner: reg.inner } + } + + /// Checks whether the task has been aborted. Note that all this + /// method indicates is whether [`AbortHandle::abort`] was *called*. + /// This means that it will return `true` even if: + /// * `abort` was called after the task had completed. + /// * `abort` was called while the task was being polled - the task may still be running and + /// will not be stopped until `poll` returns. + pub fn is_aborted(&self) -> bool { + self.inner.aborted.load(Ordering::Relaxed) + } +} + +/// A registration handle for an `Abortable` task. +/// Values of this type can be acquired from `AbortHandle::new` and are used +/// in calls to `Abortable::new`. +#[derive(Debug)] +pub struct AbortRegistration { + pub(crate) inner: Arc<AbortInner>, +} + +/// A handle to an `Abortable` task. +#[derive(Debug, Clone)] +pub struct AbortHandle { + inner: Arc<AbortInner>, +} + +impl AbortHandle { + /// Creates an (`AbortHandle`, `AbortRegistration`) pair which can be used + /// to abort a running future or stream. + /// + /// This function is usually paired with a call to [`Abortable::new`]. + pub fn new_pair() -> (Self, AbortRegistration) { + let inner = + Arc::new(AbortInner { waker: AtomicWaker::new(), aborted: AtomicBool::new(false) }); + + (Self { inner: inner.clone() }, AbortRegistration { inner }) + } +} + +// Inner type storing the waker to awaken and a bool indicating that it +// should be aborted. +#[derive(Debug)] +pub(crate) struct AbortInner { + pub(crate) waker: AtomicWaker, + pub(crate) aborted: AtomicBool, +} + +/// Indicator that the `Abortable` task was aborted. +#[derive(Copy, Clone, Debug, Eq, PartialEq)] +pub struct Aborted; + +impl fmt::Display for Aborted { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + write!(f, "`Abortable` future has been aborted") + } +} + +#[cfg(feature = "std")] +impl std::error::Error for Aborted {} + +impl<T> Abortable<T> { + fn try_poll<I>( + mut self: Pin<&mut Self>, + cx: &mut Context<'_>, + poll: impl Fn(Pin<&mut T>, &mut Context<'_>) -> Poll<I>, + ) -> Poll<Result<I, Aborted>> { + // Check if the task has been aborted + if self.is_aborted() { + return Poll::Ready(Err(Aborted)); + } + + // attempt to complete the task + if let Poll::Ready(x) = poll(self.as_mut().project().task, cx) { + return Poll::Ready(Ok(x)); + } + + // Register to receive a wakeup if the task is aborted in the future + self.inner.waker.register(cx.waker()); + + // Check to see if the task was aborted between the first check and + // registration. + // Checking with `is_aborted` which uses `Relaxed` is sufficient because + // `register` introduces an `AcqRel` barrier. + if self.is_aborted() { + return Poll::Ready(Err(Aborted)); + } + + Poll::Pending + } +} + +impl<Fut> Future for Abortable<Fut> +where + Fut: Future, +{ + type Output = Result<Fut::Output, Aborted>; + + fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { + self.try_poll(cx, |fut, cx| fut.poll(cx)) + } +} + +impl<St> Stream for Abortable<St> +where + St: Stream, +{ + type Item = St::Item; + + fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> { + self.try_poll(cx, |stream, cx| stream.poll_next(cx)).map(Result::ok).map(Option::flatten) + } +} + +impl AbortHandle { + /// Abort the `Abortable` stream/future associated with this handle. + /// + /// Notifies the Abortable task associated with this handle that it + /// should abort. Note that if the task is currently being polled on + /// another thread, it will not immediately stop running. Instead, it will + /// continue to run until its poll method returns. + pub fn abort(&self) { + self.inner.aborted.store(true, Ordering::Relaxed); + self.inner.waker.wake(); + } +} |