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use std::ops::DerefMut;
use super::change::{ChangeReader, ChangeValNoWake};
use super::shared_state::SharedState;
use super::*;
use crate::IntoReader;
use futures::channel::oneshot;
use futures::never::Never;
use tokio::select;
pub struct Eventual<T> {
state: Arc<SharedState<T>>,
}
impl<T> Eventual<T>
where
T: Value,
{
pub fn new() -> (EventualWriter<T>, Self) {
let (sender, receiver) = oneshot::channel();
let state = Arc::new(SharedState::new(sender));
(EventualWriter::new(&state, receiver), Eventual { state })
}
pub fn from_value(value: T) -> Self {
let (mut writer, eventual) = Eventual::new();
writer.write(value);
eventual
}
pub fn spawn<F, Fut>(f: F) -> Self
where
F: 'static + Send + FnOnce(EventualWriter<T>) -> Fut,
Fut: Future<Output = Result<Never, Closed>> + Send,
{
let (writer, eventual) = Eventual::new();
tokio::spawn(async move {
select!(
_ = writer.closed() => {}
_ = async { f(writer).await } => {}
);
});
eventual
}
pub fn subscribe(&self) -> EventualReader<T> {
EventualReader::new(self.state.clone())
}
pub fn value(&self) -> ValueFuture<T> {
let change = self.state.clone().subscribe();
ValueFuture {
change: Some(change),
}
}
pub fn value_immediate(&self) -> Option<T> {
match self.state.last_write.lock().unwrap().deref_mut() {
ChangeValNoWake::None => None,
ChangeValNoWake::Value(t) => Some(t.clone()),
ChangeValNoWake::Finalized(t) => t.clone(),
}
}
#[cfg(feature = "trace")]
pub fn subscriber_count(&self) -> usize {
self.state.subscribers.lock().unwrap().len()
}
}
pub struct ValueFuture<T> {
change: Option<ChangeReader<T>>,
}
impl<T> Future for ValueFuture<T>
where
T: Value,
{
type Output = Result<T, Closed>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let update = self.change.as_mut().unwrap().change.poll(&None, cx);
match update {
None => Poll::Pending,
Some(value) => {
self.change = None;
Poll::Ready(value)
}
}
}
}
impl<T> Clone for Eventual<T> {
#[inline]
fn clone(&self) -> Self {
Self {
state: self.state.clone(),
}
}
}
impl<T> IntoReader for &'_ Eventual<T>
where
T: Value,
{
type Output = T;
#[inline]
fn into_reader(self) -> EventualReader<Self::Output> {
self.subscribe()
}
}
impl<T> IntoReader for Eventual<T>
where
T: Value,
{
type Output = T;
#[inline]
fn into_reader(self) -> EventualReader<Self::Output> {
self.subscribe()
}
}