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use super::publisher::*;
use super::subscriber::*;
use super::message_publisher::*;
use futures::*;
use futures::future::{BoxFuture};
use futures::channel::oneshot;
///
/// A blocking publisher is a publisher that blocks messages until it has enough subscribers
///
/// This is useful for cases where a publisher is being used asynchronously and wants to ensure that
/// its messages are sent to at least one subscriber. Once the required number of subscribers is
/// reached, this will not block again even if some subscribers are dropped.
///
pub struct BlockingPublisher<Message> {
/// True if there are not currently enouogh subscribers in this publisher
insufficient_subscribers: bool,
/// The number of required subscribers
required_subscribers: usize,
/// The publisher where messages will be relayed
publisher: Publisher<Message>,
/// Futures to be notified when there are enough subscribers for this publisher
notify_futures: Vec<oneshot::Sender<()>>
}
impl<Message: Clone> BlockingPublisher<Message> {
///
/// Creates a new blocking publisher
///
/// This publisher will refuse to receive any items until at least required_subscribers are connected.
/// The buffer size indicates the number of queued items permitted per buffer.
///
pub fn new(required_subscribers: usize, buffer_size: usize) -> BlockingPublisher<Message> {
BlockingPublisher {
insufficient_subscribers: required_subscribers != 0,
required_subscribers: required_subscribers,
publisher: Publisher::new(buffer_size),
notify_futures: vec![]
}
}
///
/// Returns a future that will complete when this publisher has enough subscribers
///
/// This is useful as a way to avoid blocking with `wait_send` when setting up the publisher
///
pub fn when_fully_subscribed(&mut self) -> impl Future<Output=Result<(), oneshot::Canceled>>+Send {
let receiver = if self.insufficient_subscribers {
// Return a future that will be notified when we have enough subscribers
let (sender, receiver) = oneshot::channel();
// Notify when there are enough subscribers
self.notify_futures.push(sender);
Some(receiver)
} else {
None
};
async {
if let Some(receiver) = receiver {
receiver.await
} else {
Ok(())
}
}
}
}
impl<Message: 'static+Send+Clone> MessagePublisher for BlockingPublisher<Message> {
type Message = Message;
fn subscribe(&mut self) -> Subscriber<Message> {
// Create the subscription
let subscription = self.publisher.subscribe();
// Wake the sink if we get enough subscribers
if self.insufficient_subscribers && self.publisher.count_subscribers() >= self.required_subscribers {
// We now have enough subscribers
self.insufficient_subscribers = false;
// Notify any futures that are waiting on this publisher
self.notify_futures.drain(..)
.for_each(|sender| { sender.send(()).ok(); });
}
// Result is our new subscription
subscription
}
///
/// Reserves a space for a message with the subscribers, returning when it's ready
///
fn when_ready(&mut self) -> BoxFuture<'static, MessageSender<Message>> {
// If there are not enough subscribers, wait for there to be enough subscribers
let when_subscribed = if self.insufficient_subscribers {
Some(self.when_fully_subscribed())
} else {
None
};
let when_ready = self.publisher.when_ready();
// Wait for there to be enough subscribers before waiting for the publisher to become ready
Box::pin(async move {
if let Some(when_subscribed) = when_subscribed {
when_subscribed.await.ok();
}
when_ready.await
})
}
///
/// Waits until all subscribers have consumed all pending messages
///
fn when_empty(&mut self) -> BoxFuture<'static, ()> {
let when_subscribed = if self.insufficient_subscribers {
Some(self.when_fully_subscribed())
} else {
None
};
let when_empty = self.publisher.when_empty();
Box::pin(async move {
if let Some(when_subscribed) = when_subscribed {
when_subscribed.await.ok();
}
when_empty.await
})
}
///
/// Returns true if this publisher is closed (will not publish any further messages to its subscribers)
///
fn is_closed(&self) -> bool { self.publisher.is_closed() }
///
/// Future that returns when this publisher is closed
///
fn when_closed(&self) -> BoxFuture<'static, ()> {
self.publisher.when_closed()
}
}