v0.4.0 — Performance, Verified

v0.4.0 — Performance, Verified

The "zero-overhead" claim that has been quietly sitting in the README since day one now ships with the numbers to back it up. clock-lib 0.4.0 adds a real benchmark suite and a docs/PERFORMANCE.md report that proves the wrapper costs the same as std::time — not "approximately the same", measurably the same.

Highlights

• Real benchmark suite. Seven criterion groups in benches/clock_bench.rs covering monotonic readings, wall readings, unix conversions, the unix helpers end-to-end, elapsed-time measurement, every ManualClock operation, and trait-object dispatch through &dyn Clock.
• Zero overhead, verified. docs/PERFORMANCE.md records the recorded median for every bench alongside the raw std::time call it forwards to. The wrapper functions sit on top of the bare std functions inside criterion's noise band.
• Committed baseline. Run cargo bench --bench clock_bench -- --save-baseline 0.4.0 to pin the current numbers, then cargo bench --bench clock_bench -- --baseline 0.4.0 after any change to detect regressions.
• Hot-path methodology written down. What was measured, how, on what hardware, and how to reproduce it locally — all in the performance doc.

What's New

Added

• benches/clock_bench.rs — real benchmarks across seven groups:
  • monotonic_now — Instant::now vs clock_lib::now, Monotonic::now, SystemClock::now.
  • wall_now — SystemTime::now vs clock_lib::wall, Wall::now.
  • unix_conversions — cost of Wall::unix_seconds / unix_millis / unix_nanos on a pre-captured reading.
  • unix_helpers — end-to-end cost of clock_lib::unix / unix_ms / unix_ns.
  • elapsed — Instant::elapsed vs Monotonic::elapsed vs clock_lib::elapsed.
  • manual_clock — now, wall, offset, advance(1ns).
  • dyn_dispatch — concrete SystemClock vs &dyn Clock.
• docs/PERFORMANCE.md — methodology, recorded numbers, the zero-overhead claim, and how to compare against the baseline.
• README link to the performance document.

Changed

• Replaced the placeholder bench function with the real suite.

Compatibility

• MSRV: Rust 1.85 (unchanged)
• Edition: 2024 (unchanged)
• Public API: unchanged — no migration required from 0.3.x.

Upgrading From 0.3.x

[dependencies]
clock-lib = "0.4"

No code changes required.

What's Next

• 0.5.0 — no_std hardening and the 1.0 release candidate.
• 1.0.0 — stable.

Full Changelog: v0.3.0...v0.4.0