kevy-ring

A lock-free, bounded single-producer / single-consumer (SPSC) ring buffer — pure Rust, zero dependencies.

One producer pushes, one consumer pops, with no locks and no per-message allocation: a fixed power-of-two slot array plus two cache-line-padded cursors. It is the cross-core transport primitive for [kevy-rt]'s shared-nothing, thread-per-core runtime (the Seastar/Scylla model) — each ordered pair of cores gets its own ring, so a hot reactor never contends a lock on the cross-core hop.

The SPSC contract is enforced by the type system: push/pop take &mut self on distinct owned Producer/Consumer halves, so the compiler guarantees at most one thread pushes and one pops. That keeps the synchronization to a single Release/Acquire pair per operation.

let (mut tx, mut rx) = kevy_ring::ring::<u32>(1024);
tx.push(1).unwrap();
assert_eq!(rx.pop(), Some(1));

push hands the value back as Err(val) when the ring is full, so the caller chooses the back-off policy (spin, yield, or — in kevy-rt — drain its own inbox and retry, which is what avoids deadlock in the all-to-all core mesh).

Safety

The lock-free buffer needs UnsafeCell + atomics, so this crate is not #![forbid(unsafe_code)]. Every unsafe block documents the SPSC invariant it relies on. It is still pure Rust with no C and no FFI, per the kevy project's pure-Rust principle.

Part of the kevy key–value server.

License

MIT OR Apache-2.0