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//! An unbounded set of streams
use core::{
fmt::{self, Debug},
iter::FromIterator,
pin::Pin,
};
use std::task::{Context, Poll};
use futures_util::stream::{FusedStream, FuturesUnordered, StreamExt, StreamFuture};
use futures_util::{ready, stream::Stream};
/// An unbounded set of streams
///
/// This "combinator" provides the ability to maintain a set of streams
/// and drive them all to completion.
///
/// Streams are pushed into this set and their realized values are
/// yielded as they become ready. Streams will only be polled when they
/// generate notifications. This allows to coordinate a large number of streams.
///
/// Note that you can create a ready-made `SelectAll` via the
/// `select_all` function in the `stream` module, or you can start with an
/// empty set with the `SelectAll::new` constructor.
#[must_use = "streams do nothing unless polled"]
pub struct SelectAll<St> {
inner: FuturesUnordered<StreamFuture<St>>,
}
impl<St: Debug> Debug for SelectAll<St> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "SelectAll {{ ... }}")
}
}
impl<St: Stream + Unpin> SelectAll<St> {
/// Constructs a new, empty `SelectAll`
///
/// The returned `SelectAll` does not contain any streams and, in this
/// state, `SelectAll::poll` will return `Poll::Ready(None)`.
pub fn new() -> Self {
Self {
inner: FuturesUnordered::new(),
}
}
/// Returns the number of streams contained in the set.
///
/// This represents the total number of in-flight streams.
pub fn len(&self) -> usize {
self.inner.len()
}
/// Returns `true` if the set contains no streams
pub fn is_empty(&self) -> bool {
self.inner.is_empty()
}
/// Push a stream into the set.
///
/// This function submits the given stream to the set for managing. This
/// function will not call `poll` on the submitted stream. The caller must
/// ensure that `SelectAll::poll` is called in order to receive task
/// notifications.
pub fn push(&self, stream: St) {
self.inner.push(stream.into_future());
}
}
impl<St: Stream + Unpin> Default for SelectAll<St> {
fn default() -> Self {
Self::new()
}
}
impl<St: Stream + Unpin> Stream for SelectAll<St> {
type Item = St::Item;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
loop {
match ready!(self.inner.poll_next_unpin(cx)) {
Some((Some(item), remaining)) => {
self.push(remaining);
return Poll::Ready(Some(item));
}
Some((None, _)) => {
// `FuturesUnordered` thinks it isn't terminated
// because it yielded a Some.
// We do not return, but poll `FuturesUnordered`
// in the next loop iteration.
}
None => return Poll::Ready(None),
}
}
}
}
impl<St: Stream + Unpin> FusedStream for SelectAll<St> {
fn is_terminated(&self) -> bool {
self.inner.is_terminated()
}
}
/// Convert a list of streams into a `Stream` of results from the streams.
///
/// This essentially takes a list of streams (e.g. a vector, an iterator, etc.)
/// and bundles them together into a single stream.
/// The stream will yield items as they become available on the underlying
/// streams internally, in the order they become available.
///
/// Note that the returned set can also be used to dynamically push more
/// futures into the set as they become available.
///
/// This function is only available when the `std` or `alloc` feature of this
/// library is activated, and it is activated by default.
pub fn select_all<I>(streams: I) -> SelectAll<I::Item>
where
I: IntoIterator,
I::Item: Stream + Unpin,
{
let set = SelectAll::new();
for stream in streams {
set.push(stream);
}
set
}
impl<St: Stream + Unpin> FromIterator<St> for SelectAll<St> {
fn from_iter<T: IntoIterator<Item = St>>(iter: T) -> Self {
select_all(iter)
}
}
impl<St: Stream + Unpin> Extend<St> for SelectAll<St> {
fn extend<T: IntoIterator<Item = St>>(&mut self, iter: T) {
for st in iter {
self.push(st)
}
}
}
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