ringbuffers

A ring buffer, also known as a circular buffer, is a fixed-size data structure that uses a contiguous block of memory as if it were arranged in a circle. It is designed for efficient, low-latency data transfer between producers and consumers without dynamic memory allocation. The buffer’s constant size makes it predictable in worst-case latency and memory usage.

The structure typically maintains two indices: a head for reading and a tail for writing. Elements are written at the tail and read from the head. When either index reaches the end of the block, it wraps around to the beginning. To distinguish full from empty, implementations commonly reserve one slot and treat the buffer as full when (tail + 1) mod capacity equals head, or they keep an explicit count of elements.

Operations are simple: enqueue writes at the current tail position and advances the tail; dequeue reads from the current head position and advances the head. The buffer is empty when head equals tail, and full when advancing the tail would collide with the head. Some designs allow an overwrite policy, where new data overwrites the oldest data on overflow, while others signal overflow to the producer.

Concurrency considerations vary by use case. In single-producer, single-consumer scenarios, non-atomic indices suffice and straightforward synchronization is often unnecessary. In multi-producer or multi-consumer contexts, careful synchronization or lock-free algorithms using atomic operations and memory barriers are required to prevent data races and ensure visibility across threads or cores.

Common uses include streaming I/O, audio processing, inter-thread communication, network buffering, and event logging. Benefits include a bounded memory footprint, constant-time operations, and cache-friendly access patterns. Drawbacks include a fixed capacity that can lead to overflow or data loss if not managed, and increased complexity when supporting concurrent access. Variants may optimize for power-of-two capacities or provide explicit element counts to simplify full/empty checks.