2nd/10_Wiki/Topics/Programming & Language/Scheduler API.md

---
id: wiki-2026-0508-scheduler-api
title: Scheduler API
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [scheduler.postTask, Prioritized Task Scheduling]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [web, performance, scheduling, browser-api]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: JavaScript
  framework: Web Platform
---

# Scheduler API

## 매 한 줄
> **"매 priority-aware task scheduling for the main thread"**. Scheduler API (`scheduler.postTask`, `scheduler.yield`) 는 long task breakup + priority hint (user-blocking / user-visible / background) 로 INP/responsiveness 최적화. 2026 Chromium + Firefox stable.

## 매 핵심

### 매 Priorities
- `user-blocking`: 매 immediate UI response (input handler post-work).
- `user-visible`: 매 default — visible 하지만 non-blocking.
- `background`: 매 lazy work (analytics, prefetch).

### 매 vs setTimeout(0) / requestIdleCallback
- 매 setTimeout(0): no priority, no abort.
- 매 rIC: idle only, deadline-based.
- 매 postTask: explicit priority + AbortSignal + delay.

### 매 응용
1. 매 long list rendering 분할.
2. 매 input handler 후 heavy work 양보.
3. 매 background data prefetch.

## 💻 패턴

### postTask 기본
```js
scheduler.postTask(() => doWork(), { priority: 'background' });
```

### scheduler.yield (long task breakup)
```js
async function processItems(items) {
  for (const item of items) {
    process(item);
    if (navigator.scheduling?.isInputPending?.() || items.indexOf(item) % 50 === 0) {
      await scheduler.yield();
    }
  }
}
```

### TaskController로 abort
```js
const controller = new TaskController({ priority: 'user-visible' });
scheduler.postTask(longJob, { signal: controller.signal });
// 매 cancel
controller.abort();
// 매 priority 동적 변경
controller.setPriority('background');
```

### Delay
```js
scheduler.postTask(refresh, { priority: 'background', delay: 5000 });
```

### Polyfill fallback
```js
const yield_ = () =>
  globalThis.scheduler?.yield?.() ??
  new Promise(r => setTimeout(r, 0));
```

### React + Scheduler API
```js
// React 19+ 의 useTransition + scheduler integration
startTransition(() => {
  scheduler.postTask(() => setState(heavy), { priority: 'background' });
});
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Heavy work after input | `scheduler.yield()` mid-loop |
| Lazy prefetch | `postTask({priority:'background'})` |
| Cancel-able task | `TaskController` |
| Idle-only callback | `requestIdleCallback` |
| 매 simple deferral | `queueMicrotask` |

**기본값**: 매 long loops 의 `scheduler.yield()` + 매 background work `postTask({priority:'background'})`.

## 🔗 Graph
- 부모: [[Core Web Vitals Optimization (INP, LCP, CLS)|Core_Web_Vitals]]
- 응용: [[INP_Optimization]]
- Adjacent: [[AbortController]] · [[React_useTransition]]

## 🤖 LLM 활용
**언제**: 매 INP regression 발견 + 매 long task (>50ms) breakup 필요 시. 매 prioritized background work.
**언제 X**: 매 worker offload 가 더 적합한 CPU-heavy work, 또는 매 framework scheduler (React) 가 이미 처리.

## ❌ 안티패턴
- **postTask 안 yield**: 매 single long callback 은 여전히 long task. 매 internally yield 필요.
- **user-blocking 남용**: 매 priority inversion 의. 매 진짜 input-critical 만.
- **Polyfill 없는 production deploy**: 매 Safari 일부 버전 미지원.

## 🧪 검증 / 중복
- Verified (W3C Prioritized Task Scheduling, web.dev/optimize-inp).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — postTask + yield patterns |