futures: add select_slice, rename select_all to select_array.

This commit is contained in:
Dario Nieuwenhuis 2022-08-28 21:15:30 +02:00
parent 1ee2dfa03e
commit 3763baf8fa
2 changed files with 57 additions and 8 deletions

View File

@ -5,5 +5,6 @@ Utilities for working with futures:
- [`select`](select::select) - waiting for one out of two futures to complete. - [`select`](select::select) - waiting for one out of two futures to complete.
- [`select3`](select::select3) - waiting for one out of three futures to complete. - [`select3`](select::select3) - waiting for one out of three futures to complete.
- [`select4`](select::select4) - waiting for one out of four futures to complete. - [`select4`](select::select4) - waiting for one out of four futures to complete.
- [`select_all`](select::select_all) - waiting for one future in a list of futures to complete. - [`select_array`](select::select_array) - waiting for one future in an array of futures to complete.
- [`select_slice`](select::select_slice) - waiting for one future in a slice of futures to complete.
- [`yield_now`](yield_now::yield_now) - yielding the current task. - [`yield_now`](yield_now::yield_now) - yielding the current task.

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@ -186,28 +186,76 @@ where
// ==================================================================== // ====================================================================
/// Future for the [`select_all`] function. /// Future for the [`select_array`] function.
#[derive(Debug)] #[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"] #[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct SelectAll<Fut, const N: usize> { pub struct SelectArray<Fut, const N: usize> {
inner: [Fut; N], inner: [Fut; N],
} }
/// Creates a new future which will select over a list of futures. /// Creates a new future which will select over an array of futures.
/// ///
/// The returned future will wait for any future within `iter` to be ready. Upon /// The returned future will wait for any future to be ready. Upon
/// completion the item resolved will be returned, along with the index of the /// completion the item resolved will be returned, along with the index of the
/// future that was ready. /// future that was ready.
/// ///
/// # Panics /// # Panics
/// ///
/// This function will panic if the array specified contains no items. /// This function will panic if the array specified contains no items.
pub fn select_all<Fut: Future, const N: usize>(arr: [Fut; N]) -> SelectAll<Fut, N> { pub fn select_array<Fut: Future, const N: usize>(arr: [Fut; N]) -> SelectArray<Fut, N> {
assert!(N > 0); assert!(N > 0);
SelectAll { inner: arr } SelectArray { inner: arr }
} }
impl<Fut: Future, const N: usize> Future for SelectAll<Fut, N> { impl<Fut: Future, const N: usize> Future for SelectArray<Fut, N> {
type Output = (Fut::Output, usize);
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
// Safety: Since `self` is pinned, `inner` cannot move. Since `inner` cannot move,
// its elements also cannot move. Therefore it is safe to access `inner` and pin
// references to the contained futures.
let item = unsafe {
self.get_unchecked_mut()
.inner
.iter_mut()
.enumerate()
.find_map(|(i, f)| match Pin::new_unchecked(f).poll(cx) {
Poll::Pending => None,
Poll::Ready(e) => Some((i, e)),
})
};
match item {
Some((idx, res)) => Poll::Ready((res, idx)),
None => Poll::Pending,
}
}
}
// ====================================================================
/// Future for the [`select_slice`] function.
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct SelectSlice<'a, Fut> {
inner: &'a mut [Fut],
}
/// Creates a new future which will select over a slice of futures.
///
/// The returned future will wait for any future to be ready. Upon
/// completion the item resolved will be returned, along with the index of the
/// future that was ready.
///
/// # Panics
///
/// This function will panic if the slice specified contains no items.
pub fn select_slice<'a, Fut: Future>(slice: &'a mut [Fut]) -> SelectSlice<'a, Fut> {
assert!(!slice.is_empty());
SelectSlice { inner: slice }
}
impl<'a, Fut: Future> Future for SelectSlice<'a, Fut> {
type Output = (Fut::Output, usize); type Output = (Fut::Output, usize);
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {