Optimizing a Lock-Free Ring Buffer

March 24, 2026

A single-producer single-consumer (SPSC) queue is a great example of how far constraints can take a design. In this post, you will learn how to implement a ring buffer from scratch: start with the simplest design, make it thread-safe, and then gradually remove overhead while preserving FIFO behavior and predictable latency. This pattern is widely used to share data between threads in the lowest-latency environments.

What is a ring buffer? §

You might have run into the term circular buffer, or perhaps cyclic queue. These are simply other names for a ring buffer: a queue where a producer generates data and inserts it into the buffer, and a consumer later pulls it back out, in first-in-first-out order.

What makes a ring buffer distinctive is how it stores data and the constraints it enforces. It has a fixed capacity; it neither expands nor shrinks. As a result, when the buffer fills up, the producer must either wait until space becomes available or overwrite entries that have not been read yet, depending on what the application expects.

The consumer’s job is straightforward: read items as they arrive. When the ring buffer is empty, the consumer has to block, spin, or move on to other work. Each successful read releases a slot the producer can reuse. In the ideal case, the producer stays just a bit ahead, and the system turns into a quiet game of “catch me if you can,” with minimal waiting on both sides.

Single-threaded ring buffer §

Let’s start with a single-threaded ring buffer, which is just an array2 and two indices. We leave one slot permanently unused to distinguish “full” from “empty.” Push writes to head and advances it; pop reads from tail and advances it.

template < typename T , std :: size_t N > class RingBufferV1 { std :: array < T , N > buffer_ ; std :: size_t head_ { 0 }; std :: size_t tail_ { 0 }; };

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