fast 0.4.0

A helper library
Documentation 
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use alloc::sync::Arc;
use core::sync::atomic::{AtomicUsize, Ordering::*};

use super::q::Queue;
use crate::sync::{AtomicWaker, Closure, Flags, Signal, Waiters};

pub enum RecvError {
    Closed,
    Empty,
}

pub enum SendError<V> {
    Closed(V),
    Full(V),
}

struct Channel<T> {
    queue: Queue<T>,
    senders: Waiters,
    receivers: Waiters,
    is_closed: Flags<Closure>,
    capacity: Option<usize>,
}

impl<T: Send> Channel<T> {
    fn init(capacity: Option<usize>) -> Arc<Channel<T>> {
        Arc::new(Channel {
            queue: Queue::new(),
            senders: Waiters::new(),
            receivers: Waiters::new(),
            is_closed: Flags::default(),
            capacity,
        })
    }
}

#[derive()]
pub struct Sender<T>(Arc<Channel<T>>);
pub struct Receiver<T>(Arc<Channel<T>>);

impl<T: Send> Sender<T> {
    pub fn try_send(&self, value: T) -> Result<(), SendError<T>> {
        let Channel {
            queue,
            senders,
            receivers,
            is_closed,
            capacity,
        } = &*self.0;

        if is_closed.is_set(&Closure::Closed) {
            return Err(SendError::Closed(value));
        }

        if let Some(cap) = capacity
            && queue.len() >= cap - 1
        {
            return Err(SendError::Full(value));
        }

        let Some(waiter) = (unsafe {
            queue.enqueue(value);
            receivers.dequeue()
        }) else {
            unreachable!();
        };

        waiter.wake_by_ref();

        Ok(())
    }
}

impl<T: Send> Receiver<T> {
    pub fn try_recv(&self) -> Result<T, RecvError> {
        let Channel {
            queue,
            senders,
            receivers,
            is_closed,
            capacity,
        } = &*self.0;

        if let Some(value) = unsafe { queue.dequeue() } {
            if capacity.is_some()
                && let Some(waiter) = unsafe { senders.dequeue() }
            {
                waiter.wake_by_ref();
            }
            return Ok(value);
        }

        if is_closed.is_set(&Closure::Closed) {
            Err(RecvError::Closed)?
        }

        Err(RecvError::Empty)
    }
}

pub fn unbounded<T: Send>() -> (Sender<T>, Receiver<T>) {
    let channel = Channel::init(None);
    (Sender(channel.clone()), Receiver(channel))
}

pub fn bounded<T: Send>(capacity: usize) -> (Sender<T>, Receiver<T>) {
    let channel = Channel::init(Some(capacity));
    (Sender(channel.clone()), Receiver(channel))
}