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// Copyright © 2020 Alexandra Frydl
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
//! A multi-producer, multi-consumer channel.
use crate::prelude::*;
use async_channel::TryRecvError;
/// A cloneable receiver for a channel.
pub struct Receiver<T> {
rx: async_channel::Receiver<T>,
}
/// A cloneable sender for a channel.
pub struct Sender<T> {
tx: async_channel::Sender<T>,
}
/// An error indicating that the channel is closed.
#[derive(Clone, Copy, Debug, Default, Error)]
#[error("Channel is closed.")]
pub struct ClosedError;
/// An error returned from a [`Sender::send()`] or [`Sender::try_send()`] call.
#[derive(Clone, Copy)]
pub struct SendError<M> {
/// The message that failed to send.
pub msg: M,
/// The reason for this error.
pub reason: SendErrorReason,
}
/// The reason a [`SendError`] was returned.
#[derive(Clone, Copy, Debug, Eq, Error, PartialEq)]
pub enum SendErrorReason {
#[error("Channel is closed.")]
Closed,
#[error("Channel is full.")]
Full,
}
/// Creates a channel with a buffer of a given capacity.
pub fn with_capacity<T>(capacity: usize) -> (Sender<T>, Receiver<T>) {
let (tx, rx) = async_channel::bounded(capacity);
(Sender { tx }, Receiver { rx })
}
/// Creates an channel whose buffer can grow unbounded.
pub fn unbounded<T>() -> (Sender<T>, Receiver<T>) {
let (tx, rx) = async_channel::unbounded();
(Sender { tx }, Receiver { rx })
}
impl<T> Receiver<T> {
/// Returns `true` if the channel is closed.
///
/// The channel is closed if all [`Sender`] clones are dropped.
pub fn is_closed(&self) -> bool {
self.rx.is_closed()
}
/// Waits for an available message in the channel and receives it.
pub async fn recv(&self) -> Result<T, ClosedError> {
self.rx.recv().await.map_err(|_| ClosedError)
}
/// Attempts to immediately receive an available message from the channel.
///
/// If the channel is empty, this function returns `None`.
pub fn try_recv(&self) -> Result<Option<T>, ClosedError> {
match self.rx.try_recv() {
Ok(msg) => Ok(Some(msg)),
Err(TryRecvError::Empty) => Ok(None),
Err(TryRecvError::Closed) => Err(ClosedError),
}
}
}
impl<T> Sender<T> {
/// Returns `true` if the channel is closed.
///
/// The channel is closed if all [`Receiver`] clones are dropped.
pub fn is_closed(&self) -> bool {
self.tx.is_closed()
}
/// Waits for available space in the channel and then sends a message.
///
/// If the channel is closed before the message can be sent, this function
/// returns a [`SendError`] containing the failed message.
pub async fn send(&self, message: T) -> Result<(), SendError<T>> {
self
.tx
.send(message)
.await
.map_err(|err| SendError { msg: err.0, reason: SendErrorReason::Closed })
}
/// Attempts to send a message to the channel immediately.
///
/// If the channel is closed or full, this function returns a [`SendError`]
/// containing the failed message.
pub fn try_send(&self, message: T) -> Result<(), SendError<T>> {
self.tx.try_send(message).map_err(|err| match err {
async_channel::TrySendError::Full(msg) => SendError { msg, reason: SendErrorReason::Full },
async_channel::TrySendError::Closed(msg) => {
SendError { msg, reason: SendErrorReason::Closed }
}
})
}
}
// Manually implement `Clone` for all `T`.
impl<T> Clone for Receiver<T> {
fn clone(&self) -> Self {
Self { rx: self.rx.clone() }
}
}
impl<T> Clone for Sender<T> {
fn clone(&self) -> Self {
Self { tx: self.tx.clone() }
}
}
// Implement SendError`.
impl<M> std::error::Error for SendError<M> {}
impl<M> Debug for SendError<M> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Debug::fmt(&self.reason, f)
}
}
impl<M> Display for SendError<M> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Display::fmt(&self.reason, f)
}
}