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use crate::{
common::*, config::BufSize, index_stream::IndexStreamExt as _, rt, stream::StreamExt as _,
utils,
};
use tokio::sync::{oneshot, watch};
/// The build type returned from [broadcast()](crate::par_stream::ParStreamExt::broadcast).
///
/// It is used to register new broadcast receivers. Each receiver consumes copies
/// of items of the stream. The builder is finished by `guard.build()` so that
/// registered receivers can start consuming data. Otherwise, the receivers
/// take empty input.
#[derive(Debug)]
pub struct BroadcastBuilder<T> {
pub(super) buf_size: Option<usize>,
pub(super) ready_rx: watch::Receiver<()>,
pub(super) senders_tx: Option<oneshot::Sender<Vec<flume::Sender<(usize, T)>>>>,
pub(super) senders: Option<Vec<flume::Sender<(usize, T)>>>,
}
impl<T> BroadcastBuilder<T>
where
T: 'static + Send + Clone,
{
pub fn new<B, St>(stream: St, buf_size: B, send_all: bool) -> BroadcastBuilder<T>
where
St: 'static + Send + Stream<Item = T>,
B: Into<BufSize>,
{
let (senders_tx, senders_rx) = oneshot::channel();
let (ready_tx, ready_rx) = watch::channel(());
rt::spawn(async move {
// wait for receiver list to be ready
let senders: Vec<flume::Sender<(usize, T)>> = match senders_rx.await {
Ok(senders) => senders,
Err(_) => return,
};
// tell subscribers to be ready
if ready_tx.send(()).is_err() {
return;
}
let num_senders = senders.len();
match num_senders {
0 => {
// fall through for zero senders
}
1 => {
// fast path for single sender
let sender = senders.into_iter().next().unwrap();
let _ = stream.enumerate().map(Ok).forward(sender.into_sink()).await;
}
_ => {
// merge senders into a sink
let sink =
futures::sink::unfold(senders, |senders, item: (usize, T)| async move {
// let each sender sends a copy of the item
let futures: stream::FuturesUnordered<_> = senders
.into_iter()
.map(|tx| {
let item = item.clone();
async move {
let result = tx.send_async(item).await;
// if sending is successful, return the sender back
result.map(move |()| tx)
}
})
.collect();
// collect senders back
let senders: Vec<_> = futures
.filter_map(|tx| future::ready(tx.ok()))
.collect()
.await;
// finish sink if
// case 1: send_all == true, no senders fail
// case 2: send_all == false, there are successful sender(s)
let n_remaining_senders = senders.len();
if (!send_all && n_remaining_senders > 0)
|| (send_all && (n_remaining_senders == num_senders))
{
Ok(senders)
} else {
Err(flume::SendError(()))
}
});
let _ = stream.enumerate().map(Ok).forward(sink).await;
}
}
});
BroadcastBuilder {
buf_size: buf_size.into().get(),
ready_rx,
senders_tx: Some(senders_tx),
senders: Some(vec![]),
}
}
/// Creates a new receiver.
pub fn register(&mut self) -> BroadcastStream<T> {
let Self {
buf_size,
ref ready_rx,
ref mut senders,
..
} = *self;
let senders = senders.as_mut().unwrap();
let mut ready_rx = ready_rx.clone();
let (tx, rx) = utils::channel(buf_size);
senders.push(tx);
let stream = rx
.into_stream()
.reorder_enumerated()
.wait_until(async move { ready_rx.changed().await.is_ok() })
.boxed();
BroadcastStream { stream }
}
/// Finish the builder to start broadcasting.
pub fn build(mut self) {
let senders_tx = self.senders_tx.take().unwrap();
let senders = self.senders.take().unwrap();
senders_tx.send(senders).unwrap();
}
}
/// The receiver that consumes broadcasted messages from the stream.
#[pin_project]
pub struct BroadcastStream<T> {
#[pin]
pub(super) stream: BoxStream<'static, T>,
}
impl<T> Stream for BroadcastStream<T> {
type Item = T;
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
self.project().stream.poll_next(cx)
}
}
// tests
#[cfg(test)]
mod tests {
use super::*;
use crate::{par_stream::ParStreamExt as _, utils::async_test};
use itertools::izip;
async_test! {
async fn broadcast_test() {
let mut builder = stream::iter(0..).broadcast(2, true);
let rx1 = builder.register();
let rx2 = builder.register();
builder.build();
let (ret1, ret2): (Vec<_>, Vec<_>) =
join!(rx1.take(100).collect(), rx2.take(100).collect());
izip!(ret1, 0..100).for_each(|(lhs, rhs)| {
assert_eq!(lhs, rhs);
});
izip!(ret2, 0..100).for_each(|(lhs, rhs)| {
assert_eq!(lhs, rhs);
});
}
async fn broadcast_and_drop_receiver_test() {
{
let mut builder = stream::iter(0..).broadcast(2, false);
let rx1 = builder.register();
let rx2 = builder.register();
builder.build();
drop(rx2);
let vec: Vec<_> = rx1.take(100).collect().await;
izip!(vec, 0..100).for_each(|(lhs, rhs)| {
assert_eq!(lhs, rhs);
});
}
{
let mut builder = stream::iter(0..).broadcast(2, true);
let mut rx1 = builder.register();
let rx2 = builder.register();
builder.build();
drop(rx2);
assert_eq!(rx1.next().await, Some(0));
assert!(rx1.next().await.is_none());
}
}
}
}