crossbeam-ring-channel

A small Rust crate that adds a ring-buffer channel alongside crossbeam-channel, plus a Select wrapper that can mix ring receivers with standard crossbeam-channel send/recv operations.

What it provides

ring_bounded(capacity): a bounded, ring-buffer channel.
RingSender / RingReceiver: sender/receiver halves with familiar methods.
Select + select! / select_biased!: crossbeam-style selection that works with ring receivers and crossbeam-channel send/recv operations.

Semantics

The ring channel is bounded and non-blocking on send.
When full, send evicts the oldest item in the buffer to make room for the new one.
recv blocks until an item is available or all senders are dropped.

Installation

Add to your Cargo.toml:

[dependencies]
crossbeam-ring-channel = "0.1"
crossbeam-channel = "0.5" # needed if you use crossbeam-channel receivers/senders in Select

Usage

Basic ring channel:

use crossbeam_ring_channel::ring_bounded;

let (tx, rx) = ring_bounded(2);

// Sends never block; the oldest item is dropped when full.
tx.send("a").unwrap();
tx.send("b").unwrap();
tx.send("c").unwrap();

assert_eq!(rx.recv().unwrap(), "b");
assert_eq!(rx.recv().unwrap(), "c");

Selecting over ring receivers and crossbeam-channel receivers:

use crossbeam_channel::unbounded;
use crossbeam_ring_channel::{ring_bounded, Select};

let (ring_tx, ring_rx) = ring_bounded::<i32>(1);
let (tx, rx) = unbounded::<i32>();

ring_tx.send(1).unwrap();
tx.send(2).unwrap();

let mut sel = Select::new();
let ring_idx = sel.recv(&ring_rx);
let cb_idx = sel.recv(&rx);

let oper = sel.select();
match oper.index() {
    i if i == ring_idx => {
        let value = oper.recv(&ring_rx).unwrap();
        assert_eq!(value, 1);
    }
    i if i == cb_idx => {
        let value = oper.recv(&rx).unwrap();
        assert_eq!(value, 2);
    }
    _ => unreachable!(),
}

Macro selection:

use crossbeam_ring_channel::{ring_bounded, select};

let (tx, rx) = ring_bounded::<i32>(1);
tx.send(42).unwrap();

select! {
    recv(rx) -> msg => {
        assert_eq!(msg.unwrap(), 42);
    },
}

API overview