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use std::{
fmt,
future::{poll_fn, Future},
pin::Pin,
task::{ready, Context, Poll},
};
use futures_core::Stream;
use tokio_util::sync::ReusableBoxFuture;
use super::{Next, Subscriber};
use crate::{state::ObservableState, AsyncLock, ObservableReadGuard};
pub struct AsyncSubscriberState<S> {
inner: readlock_tokio::SharedReadLock<S>,
get_lock: ReusableBoxFuture<'static, readlock_tokio::OwnedSharedReadGuard<S>>,
}
impl<S: Send + Sync + 'static> Clone for AsyncSubscriberState<S> {
fn clone(&self) -> Self {
Self {
inner: self.inner.clone(),
get_lock: ReusableBoxFuture::new(self.inner.clone().lock_owned()),
}
}
}
impl<S: fmt::Debug> fmt::Debug for AsyncSubscriberState<S> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.inner.fmt(f)
}
}
impl<T: Send + Sync + 'static> Subscriber<T, AsyncLock> {
pub(crate) fn new_async(
inner: readlock_tokio::SharedReadLock<ObservableState<T>>,
version: u64,
) -> Self {
let get_lock = ReusableBoxFuture::new(inner.clone().lock_owned());
Self { state: AsyncSubscriberState { inner, get_lock }, observed_version: version }
}
/// Wait for an update and get a clone of the updated value.
///
/// Awaiting returns `Some(_)` after an update happened, or `None` after the
/// `Observable` (and all clones for `shared::Observable`) is dropped.
///
/// This method is a convenience so you don't have to import a `Stream`
/// extension trait such as `futures::StreamExt` or
/// `tokio_stream::StreamExt`.
#[allow(clippy::should_implement_trait)]
pub async fn next(&mut self) -> Option<T>
where
T: Clone,
{
self.next_ref().await.map(|read_guard| read_guard.clone())
}
/// Get a clone of the inner value without waiting for an update.
///
/// If the returned value has not been observed by this subscriber before,
/// it is marked as observed such that a subsequent call of
/// [`next`][Self::next] or [`next_ref`][Self::next_ref] won't return the
/// same value again. See [`get`][Self::get] for a function that doesn't
/// mark the value as observed.
#[must_use]
pub async fn next_now(&mut self) -> T
where
T: Clone,
{
let lock = self.state.inner.lock().await;
self.observed_version = lock.version();
lock.get().clone()
}
/// Get a clone of the inner value without waiting for an update.
///
/// If the returned value has not been observed by this subscriber before,
/// it is **not** marked as observed such that a subsequent call of
/// [`next`][Self::next] or [`next_ref`][Self::next_ref] will return the
/// same value again.
#[must_use]
pub async fn get(&self) -> T
where
T: Clone,
{
self.read().await.clone()
}
/// Wait for an update and get a read lock for the updated value.
///
/// Awaiting returns `Some(_)` after an update happened, or `None` after the
/// `Observable` (and all clones for `shared::Observable`) is dropped.
///
/// You can use this method to get updates of an `Observable` where the
/// inner type does not implement `Clone`. However, the `Observable`
/// will be locked (not updateable) while any read locks are alive.
#[must_use]
pub async fn next_ref(&mut self) -> Option<ObservableReadGuard<'_, T, AsyncLock>> {
// Unclear how to implement this as a named future.
poll_fn(|cx| self.poll_update(cx)).await?;
Some(self.next_ref_now().await)
}
/// Lock the inner value for reading without waiting for an update.
///
/// Note that as long as the returned [`ObservableReadGuard`] is kept alive,
/// the associated `Observable` is locked and can not be updated.
///
/// If the returned value has not been observed by this subscriber before,
/// it is marked as observed such that a subsequent call of
/// [`next`][Self::next] or [`next_ref`][Self::next_ref] won't return the
/// same value again. See [`get`][Self::get] for a function that doesn't
/// mark the value as observed.
pub async fn next_ref_now(&mut self) -> ObservableReadGuard<'_, T, AsyncLock> {
let lock = self.state.inner.lock().await;
self.observed_version = lock.version();
ObservableReadGuard::new(lock)
}
/// Lock the inner value for reading without waiting for an update.
///
/// Note that as long as the returned [`ObservableReadGuard`] is kept alive,
/// the associated `Observable` is locked and can not be updated.
///
/// If the returned value has not been observed by this subscriber before,
/// it is **not** marked as observed such that a subsequent call of
/// [`next`][Self::next] or [`next_ref`][Self::next_ref] will return the
/// same value again.
pub async fn read(&self) -> ObservableReadGuard<'_, T, AsyncLock> {
ObservableReadGuard::new(self.state.inner.lock().await)
}
fn poll_update(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
let state = ready!(self.state.get_lock.poll(cx));
self.state.get_lock.set(self.state.inner.clone().lock_owned());
let version = state.version();
if version == 0 {
Poll::Ready(None)
} else if self.observed_version < version {
self.observed_version = version;
Poll::Ready(Some(()))
} else {
state.add_waker(cx.waker().clone());
Poll::Pending
}
}
fn poll_next_nopin(&mut self, cx: &mut Context<'_>) -> Poll<Option<T>>
where
T: Clone,
{
let state = ready!(self.state.get_lock.poll(cx));
self.state.get_lock.set(self.state.inner.clone().lock_owned());
let version = state.version();
if version == 0 {
Poll::Ready(None)
} else if self.observed_version < version {
self.observed_version = version;
Poll::Ready(Some(state.get().clone()))
} else {
state.add_waker(cx.waker().clone());
Poll::Pending
}
}
}
impl<T: Clone + Send + Sync + 'static> Stream for Subscriber<T, AsyncLock> {
type Item = T;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
self.poll_next_nopin(cx)
}
}
impl<T: Clone + Send + Sync + 'static> Future for Next<'_, T, AsyncLock> {
type Output = Option<T>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
self.subscriber.poll_next_nopin(cx)
}
}