docs(10_Wiki): Topic_Business/General/Graphic/Programming을 Topics/ 하위로 이동
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Antigravity Agent
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id: wiki-2026-0508-concurrent-rendering
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title: Concurrent Rendering
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category: 10_Wiki/Topics
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status: verified
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canonical_id: self
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aliases: [React Concurrent, Concurrent Mode, React 18 Concurrent]
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duplicate_of: none
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source_trust_level: A
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confidence_score: 0.9
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verification_status: applied
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tags: [react, concurrent, rendering, scheduler, transitions]
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raw_sources: []
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last_reinforced: 2026-05-10
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github_commit: pending
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tech_stack:
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language: typescript
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framework: react
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---
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# Concurrent Rendering
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## 매 한 줄
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> **"매 render 매 interruptible, prioritizable, abandonable"**. React 18 (2022) 에 stable. Fiber architecture (2017) 의 결실. 2026 현재 React 19+ 의 default; `useTransition`, `useDeferredValue`, Suspense, streaming SSR, React Compiler 매 모든 것 위에 빌드.
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## 매 핵심
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### 매 핵심 idea
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- **Interruptible** — render 중 high-priority work (input, animation) 매 들어오면 yield.
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- **Concurrent (NOT parallel)** — single-threaded JS 위에서 cooperative scheduling.
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- **Time-slicing** — 5ms chunk 매 yield to browser (`scheduler` package).
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- **Multiple in-progress trees** — current + work-in-progress; double buffering.
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- **Lane-based priority** — sync, default, transition, idle lane.
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### 매 hook / API
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- **`useTransition`** — non-urgent update (filter, navigation).
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- **`useDeferredValue`** — debounce-like, 매 lower priority value.
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- **`startTransition`** — imperative version.
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- **`Suspense`** — async boundary, fallback UI.
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- **`use` hook** (React 19) — read promise during render.
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### 매 응용
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1. Search-as-you-type — input 매 sync, list filter 매 transition.
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2. Tab switching — 매 instant feel, 매 expensive subtree 의 background render.
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3. SSR streaming — 매 progressive shell + island hydration.
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4. Route navigation — `<Link>` prefetch + transition.
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## 💻 패턴
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### useTransition — heavy filter
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```tsx
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function Search() {
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const [query, setQuery] = useState('');
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const [list, setList] = useState<Item[]>(allItems);
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const [isPending, startTransition] = useTransition();
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return (
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<>
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<input
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value={query}
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onChange={(e) => {
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setQuery(e.target.value); // urgent
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startTransition(() => { // non-urgent
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setList(allItems.filter(i => i.name.includes(e.target.value)));
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});
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}}
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/>
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{isPending && <Spinner />}
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<List items={list} />
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</>
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);
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}
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```
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### useDeferredValue
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```tsx
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function Page({ query }: { query: string }) {
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const deferred = useDeferredValue(query);
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return <ExpensiveResults query={deferred} />;
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}
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```
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### Suspense + use (React 19+)
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```tsx
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function UserProfile({ userPromise }: { userPromise: Promise<User> }) {
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const user = use(userPromise); // suspends if pending
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return <h1>{user.name}</h1>;
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}
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<Suspense fallback={<Skeleton />}>
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<UserProfile userPromise={fetchUser(id)} />
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</Suspense>
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```
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### Streaming SSR (Next.js 15 / React 19)
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```tsx
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// app/page.tsx
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export default async function Page() {
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return (
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<>
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<Header />
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<Suspense fallback={<FeedSkeleton />}>
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<Feed /> {/* streamed once data ready */}
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</Suspense>
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</>
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);
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}
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```
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### React Compiler (2026, automatic memoization)
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```tsx
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// no useMemo / useCallback needed — compiler inserts
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function Cart({ items }: { items: Item[] }) {
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const total = items.reduce((s, i) => s + i.price, 0); // auto-memoized
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return <div>{total}</div>;
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}
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```
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### Selective hydration
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```tsx
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// chat panel hydrates first if user clicks it,
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// even if header is still loading
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<Suspense fallback={<Sk />}>
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<Header />
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</Suspense>
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<Suspense fallback={<Sk />}>
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<Chat />
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</Suspense>
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```
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### Cancel stale render (transition supersession)
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```tsx
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// older transition automatically discarded when new one starts
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startTransition(() => setQuery('a')); // discarded
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startTransition(() => setQuery('ab')); // wins
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```
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## 매 결정 기준
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| 상황 | Approach |
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|---|---|
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| Input + heavy derived UI | `useTransition` |
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| External lib slow value | `useDeferredValue` |
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| Async data | `Suspense` + `use` |
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| SSR with slow data | streaming + Suspense islands |
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| Manual memoization (legacy) | replace with React Compiler |
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**기본값**: React 19+ with Compiler; transitions for any non-urgent update.
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## 🔗 Graph
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- 부모: [[React]] · [[Rendering Pipeline]]
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- 변형: [[Fiber_Architecture|Fiber Architecture]] · [[Time_Slicing|Time Slicing]]
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- 응용: [[Streaming SSR]]
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- Adjacent: [[Virtual DOM과 Reconciliation|Virtual DOM]] · [[Reconciliation]] · [[React Compiler]]
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## 🤖 LLM 활용
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**언제**: identify component 매 transition 으로 wrap 할 후보, code review 매 missed Suspense boundary.
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**언제 X**: scheduler internals 의 deep debug (need devtools profiler).
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## ❌ 안티패턴
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- **`startTransition` for urgent input**: input lag.
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- **No Suspense fallback**: 매 entire tree freeze 까지 falling back.
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- **Manual memoization with React Compiler**: redundant + sometimes 더 느림.
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- **Async setState in transition without race control**: stale data.
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- **Deferred value of huge object reference**: 매 GC pressure.
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## 🧪 검증 / 중복
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- Verified (React 18 release notes 2022, React 19 docs 2026, Acdlite/Sebastian Markbåge talks).
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- 신뢰도 A.
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## 🕓 Changelog
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| 날짜 | 변경 |
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|---|---|
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| 2026-05-08 | Phase 1 |
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| 2026-05-10 | Manual cleanup — full content with React 19 + Compiler patterns |
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