2nd/10_Wiki/Topic_Programming/DevOps_and_Security/High Resolution Time.md

id, title, category, status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, verification_status, tags, raw_sources, last_reinforced, github_commit, tech_stack

id	title	category	status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	verification_status	tags	raw_sources	last_reinforced	github_commit	tech_stack
wiki-2026-0508-high-resolution-time	High Resolution Time	10_Wiki/Topics	verified	self	performance.now Monotonic Time HR Time Hi-Res Timer	none	A	0.9	applied	web-api performance timing security		2026-05-10	pending	language framework JavaScript/C W3C-HRTime/POSIX

High Resolution Time

매 한 줄

"매 sub-millisecond 정밀도의 매 monotonic clock". W3C High Resolution Time spec — performance.now() 가 매 Date.now() 의 ms 한계 + wall-clock jitter 를 매 해결. 매 Spectre 후 — 모든 brower 가 매 timer 정밀도를 매 100µs ~ 1ms 로 매 reduce + cross-origin isolation 으로 매 5µs 회복.

매 핵심

매 vs Date.now

• Date.now(): wall clock, ms 단위, NTP 으로 점프 가능 (음수 delta!).
• performance.now(): monotonic, fractional ms, navigation start 기준.

매 timer attack mitigation

• Spectre/Meltdown (2018) → 매 brower 가 timer fuzz/round.
• Default: 100µs ~ 1ms rounding + jitter.
• COOP+COEP (cross-origin isolated) 시 → 5µs 정밀 + SharedArrayBuffer.

매 응용

1. Animation frame timing (rAF callback).
2. Performance profiling (User Timing API).
3. WebGL/WebGPU frame budget tracking.
4. Audio scheduling (AudioContext.currentTime 동기).

💻 패턴

Basic timing

const t0 = performance.now();
heavyWork();
const elapsed = performance.now() - t0;
console.log(`took ${elapsed.toFixed(3)} ms`);  // 12.345 ms

User Timing API (DevTools 표시)

performance.mark('render-start');
render();
performance.mark('render-end');
performance.measure('render', 'render-start', 'render-end');
const [m] = performance.getEntriesByName('render');
console.log(m.duration);
// Visible in Chrome DevTools Performance panel.

Frame budget tracker

let lastT = performance.now();
function frame(now) {
  const dt = now - lastT;
  lastT = now;
  if (dt > 16.7) console.warn(`slow frame: ${dt.toFixed(1)}ms`);
  requestAnimationFrame(frame);
}
requestAnimationFrame(frame);

Cross-origin isolated (max precision)

# Server response headers
Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: require-corp

if (crossOriginIsolated) {
  // performance.now() granularity ~5µs
  // SharedArrayBuffer 가능
}

POSIX equivalent (C)

#include <time.h>
struct timespec t0, t1;
clock_gettime(CLOCK_MONOTONIC, &t0);
do_work();
clock_gettime(CLOCK_MONOTONIC, &t1);
double elapsed_ns = (t1.tv_sec - t0.tv_sec) * 1e9 + (t1.tv_nsec - t0.tv_nsec);

Rust std (cross-platform)

use std::time::Instant;
let t0 = Instant::now();
heavy_work();
println!("took {:?}", t0.elapsed());  // sub-ns precision on modern HW

Debounce slow timers

// If you measure dt < 0.1ms repeatedly, you're in fuzzed timer mode.
function isolatedPrecisionAvailable() {
  const samples = Array.from({length: 100}, () => {
    const a = performance.now(); const b = performance.now();
    return b - a;
  });
  return samples.some(d => d > 0 && d < 0.05);  // sub-100µs visible
}

매 결정 기준

상황	Approach
Wall-clock event log	Date.now() / Date.toISOString()
Profile / micro-bench	performance.now() + User Timing
Frame loop	rAF callback timestamp (매 monotonic)
Audio sync	AudioContext.currentTime
Cross-origin iframe	postMessage with monotonic delta
Native (Linux/macOS)	clock_gettime(CLOCK_MONOTONIC)
Native (Windows)	QueryPerformanceCounter

기본값: Duration 측정엔 매 monotonic. 매 Date 는 user-facing timestamp 만.

🔗 Graph

• 변형: Long Tasks
• 응용: Core Web Vitals Optimization (INP, LCP, CLS)
• Adjacent: Spectre · Cross-Origin Isolation · SharedArrayBuffer

🤖 LLM 활용

언제: 성능 측정 코드 작성, profiling, frame budget 분석. 언제 X: Persistent timestamp / event log 매 wall-clock 필요 시.

❌ 안티패턴

• Date.now() for delta: NTP step 시 음수 / 점프 가능.
• new Date() 매 hot loop: allocation cost + ms 한계.
• Assuming sub-ms precision: COOP/COEP 없으면 매 1ms rounded.
• Cross-origin worker timing: postMessage 의 매 ms 단위 transmit overhead.
• setTimeout 으로 정밀 timing: 매 4ms+ minimum, jittery.

🧪 검증 / 중복

• Verified (W3C HR Time Level 3, MDN performance.now, Chrome timer reduction notes).
• 신뢰도 A.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — performance.now + Spectre mitigation + COOP/COEP 5µs