perf(circular-buffer): add lock-free SPSC variant#491
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Add SPSCCircularBuffer<T, Capacity> alongside the existing mutex-based CircularBuffer. Uses std::atomic head/tail with acquire/release memory ordering for lock-free operation when there is exactly one producer and one consumer thread. Key design decisions: - Internal buffer has Capacity+1 slots to distinguish full from empty without an extra counter - head_ and tail_ are cache-line aligned (alignas(64)) to avoid false sharing between producer and consumer threads - Existing CircularBuffer class is unchanged Includes 9 new tests covering basic ops, wraparound, move semantics, capacity-of-one edge case, and a 100k-element concurrent SPSC stress test.
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Summary
SPSCCircularBuffer<T, Capacity>class for lock-free single-producer single-consumer scenariosstd::atomic<size_t>head/tail with acquire/release ordering instead of mutexalignas(64)) head/tail to prevent false sharingCircularBufferclass is unchangedWhy
The mutex-based
CircularBufferhas unnecessary synchronization overhead for SPSC use cases (e.g., logger batch processor queue, event pipelines). Lock-free SPSC eliminates mutex contention entirely.Closes #485
Test plan