86 lines
3.0 KiB
Rust
86 lines
3.0 KiB
Rust
use super::assert_future;
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use crate::future::TryFutureExt;
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use alloc::vec::Vec;
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use core::iter::FromIterator;
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use core::mem;
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use core::pin::Pin;
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use futures_core::future::{Future, TryFuture};
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use futures_core::task::{Context, Poll};
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/// Future for the [`select_ok`] function.
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#[derive(Debug)]
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#[must_use = "futures do nothing unless you `.await` or poll them"]
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pub struct SelectOk<Fut> {
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inner: Vec<Fut>,
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}
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impl<Fut: Unpin> Unpin for SelectOk<Fut> {}
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/// Creates a new future which will select the first successful future over a list of futures.
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///
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/// The returned future will wait for any future within `iter` to be ready and Ok. Unlike
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/// `select_all`, this will only return the first successful completion, or the last
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/// failure. This is useful in contexts where any success is desired and failures
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/// are ignored, unless all the futures fail.
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///
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/// This function is only available when the `std` or `alloc` feature of this
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/// library is activated, and it is activated by default.
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///
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/// # Panics
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///
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/// This function will panic if the iterator specified contains no items.
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pub fn select_ok<I>(iter: I) -> SelectOk<I::Item>
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where
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I: IntoIterator,
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I::Item: TryFuture + Unpin,
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{
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let ret = SelectOk { inner: iter.into_iter().collect() };
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assert!(!ret.inner.is_empty(), "iterator provided to select_ok was empty");
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assert_future::<
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Result<(<I::Item as TryFuture>::Ok, Vec<I::Item>), <I::Item as TryFuture>::Error>,
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_,
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>(ret)
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}
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impl<Fut: TryFuture + Unpin> Future for SelectOk<Fut> {
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type Output = Result<(Fut::Ok, Vec<Fut>), Fut::Error>;
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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// loop until we've either exhausted all errors, a success was hit, or nothing is ready
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loop {
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let item =
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self.inner.iter_mut().enumerate().find_map(|(i, f)| match f.try_poll_unpin(cx) {
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Poll::Pending => None,
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Poll::Ready(e) => Some((i, e)),
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});
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match item {
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Some((idx, res)) => {
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// always remove Ok or Err, if it's not the last Err continue looping
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drop(self.inner.remove(idx));
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match res {
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Ok(e) => {
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let rest = mem::replace(&mut self.inner, Vec::new());
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return Poll::Ready(Ok((e, rest)));
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}
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Err(e) => {
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if self.inner.is_empty() {
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return Poll::Ready(Err(e));
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}
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}
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}
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}
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None => {
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// based on the filter above, nothing is ready, return
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return Poll::Pending;
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}
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}
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}
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}
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}
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impl<Fut: TryFuture + Unpin> FromIterator<Fut> for SelectOk<Fut> {
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fn from_iter<T: IntoIterator<Item = Fut>>(iter: T) -> Self {
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select_ok(iter)
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}
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}
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