redisx 0.0.2

Minimal and Asynchronous Redis client for Rust.
Documentation 
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use crate::connection::Connection;
use crate::raw::RawConnection;
use async_std::sync::Arc;
use crossbeam_queue::{ArrayQueue, SegQueue};
use futures_channel::oneshot;
use std::sync::atomic::{AtomicU32, Ordering};
use std::time::Instant;

#[derive(Clone)]
pub struct Pool(Arc<SharedPool>);

impl Pool {
    pub fn builder() -> Builder {
        Builder::new()
    }

    pub async fn acquire(&self) -> crate::Result<Connection> {
        let raw = self.0.acquire().await?;
        Ok(Connection {
            raw: Some(raw),
            pool: Some(self.0.clone()),
        })
    }

    // Client

    pub async fn get(&self, key: &str) -> crate::Result<Option<String>> {
        self.acquire().await?.get(key).await
    }
}

pub struct Builder {
    max_size: u32,
}

impl Builder {
    pub fn new() -> Self {
        Self { max_size: 1 }
    }

    pub fn max_size(mut self, size: u32) -> Self {
        self.max_size = size;
        self
    }

    pub fn build(self, url: &str) -> Pool {
        Pool(Arc::new(SharedPool {
            max_size: self.max_size,
            url: url.to_owned(),
            size: AtomicU32::new(0),
            idle: ArrayQueue::new(self.max_size as usize),
            waiters: SegQueue::new(),
        }))
    }
}

pub(crate) struct SharedPool {
    max_size: u32,
    size: AtomicU32,
    url: String,
    idle: ArrayQueue<Idle>,
    waiters: SegQueue<oneshot::Sender<RawConnection>>,
}

impl SharedPool {
    #[inline]
    fn try_acquire(&self) -> Option<RawConnection> {
        if let Ok(idle) = self.idle.pop() {
            return Some(idle.raw);
        }

        None
    }

    async fn acquire(&self) -> crate::Result<RawConnection> {
        if let Some(live) = self.try_acquire() {
            return Ok(live);
        }

        loop {
            let size = self.size.load(Ordering::Acquire);

            if size >= self.max_size {
                // Too many open connections
                // Wait until one is available

                let (sender, receiver) = oneshot::channel();

                self.waiters.push(sender);

                // Waiters are not dropped unless the pool is dropped
                // which would drop this future
                return Ok(receiver
                    .await
                    .expect("waiter dropped without dropping pool"));
            }

            if self.size.compare_and_swap(size, size + 1, Ordering::AcqRel) == size {
                // Open a new connection and return directly
                return RawConnection::open(&self.url).await;
            }
        }
    }

    pub(crate) fn release(&self, mut raw: RawConnection) {
        while let Ok(waiter) = self.waiters.pop() {
            raw = match waiter.send(raw) {
                Ok(()) => {
                    return;
                }

                Err(raw) => raw,
            };
        }

        let _ = self.idle.push(Idle {
            raw,
            since: Instant::now(),
        });
    }
}

struct Idle {
    raw: RawConnection,
    #[allow(unused)]
    since: Instant,
}