[G1-Sync] Manual knowledge update

2026-05-09 21:08:02 +09:00
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+---
+id: native-anr-freeze-debugging
+title: ANR / Freeze — UI 블로킹 추적
+category: Coding
+status: draft
+source_trust_level: B
+verification_status: conceptual
+created_at: 2026-05-09
+updated_at: 2026-05-09
+tags: [native, anr, freeze, performance, vibe-coding]
+tech_stack: { language: "Swift / Kotlin", applicable_to: ["iOS", "Android"] }
+applied_in: []
+aliases: [ANR, Application Not Responding, hang, main thread block, freeze]
+---
+
+# ANR / Freeze Debugging
+
+> Android 5초 / iOS 250ms 이상 메인 스레드 블록 = 사용자 체감 freeze. Android = ANR dialog, iOS = Hang. 원인 = 동기 IO / 큰 JSON / Bitmap decode / 락 경합.
+
+## 📖 핵심 개념
+- ANR: Android — Activity 5s, Broadcast 10s, FG service 200s.
+- Hang (iOS): MetricKit `MXHangDiagnostic` / Xcode Organizer.
+- 원인: main thread 에서 disk / network / decode / DB.
+
+## 💻 코드 패턴
+
+### Android — StrictMode (개발용)
+```kotlin
+class App : Application() {
+    override fun onCreate() {
+        super.onCreate()
+        if (BuildConfig.DEBUG) {
+            StrictMode.setThreadPolicy(
+                StrictMode.ThreadPolicy.Builder()
+                    .detectDiskReads()
+                    .detectDiskWrites()
+                    .detectNetwork()
+                    .penaltyLog()
+                    .penaltyDialog() // dev: 다이얼로그
+                    .build()
+            )
+        }
+    }
+}
+```
+
+### Android — main thread → background
+```kotlin
+// ❌ main thread DB query
+val users = db.userDao().getAll()
+
+// ✅ Coroutine + Dispatchers.IO
+viewModelScope.launch {
+    val users = withContext(Dispatchers.IO) { db.userDao().getAll() }
+    _state.value = _state.value.copy(users = users)
+}
+```
+
+### iOS — Main Thread Checker
+```
+Xcode → Edit Scheme → Diagnostics → Main Thread Checker (default ON)
+실행 중 main 에서 UIKit 외 무거운 작업 시 즉시 stack 출력.
+```
+
+### iOS — async 로 빼기
+```swift
+// ❌ main 에서 큰 file decode
+let img = UIImage(contentsOfFile: path)
+
+// ✅ background queue
+Task.detached(priority: .userInitiated) {
+    let img = UIImage(contentsOfFile: path)
+    await MainActor.run { imageView.image = img }
+}
+```
+
+### Android — ANR trace
+```bash
+adb pull /data/anr/traces.txt
+# 또는 Logcat 에서 'ANR in com.app' 검색 → main thread stack 분석
+```
+
+### iOS — MetricKit
+```swift
+import MetricKit
+
+class MetricsObserver: NSObject, MXMetricManagerSubscriber {
+    func didReceive(_ payloads: [MXDiagnosticPayload]) {
+        for p in payloads {
+            for hang in (p.hangDiagnostics ?? []) {
+                print("Hang \(hang.hangDuration): \(hang.callStackTree)")
+            }
+        }
+    }
+}
+
+MXMetricManager.shared.add(observer)
+```
+
+### Lock 경합
+```kotlin
+// ❌ main thread synchronized 블록 → IO 가 들어가면 ANR
+synchronized(cache) {
+    cache.put(k, fetchFromNetwork()) // 네트워크 안에서 락 보유
+}
+
+// ✅ 락 안에서 short critical section 만
+val v = fetchFromNetwork()
+synchronized(cache) { cache.put(k, v) }
+```
+
+## 🤔 의사결정 기준
+| 증상 | 도구 |
+|---|---|
+| 화면 5초 정지 | Android: ANR trace, iOS: Hang Diagnostic |
+| 가끔 끊김 | StrictMode / Main Thread Checker |
+| Scroll jank | Systrace / Instruments Time Profiler |
+| 시작 느림 | App Startup tracing / Launch Time |
+| Background → FG 정지 | onResume 무거움 — async 로 |
+
+## ❌ 안티패턴
+- **runBlocking on main**: 코루틴 의의 무효, 즉시 ANR.
+- **main 에서 큰 JSON parse**: 1MB+ 면 hang.
+- **synchronized 가 IO 보유**: 다른 스레드도 같이 멈춤.
+- **main 에서 SharedPreferences.commit()**: synchronous disk write.
+- **이미지 main decode**: Glide/Coil 로 background.
+- **DB query 직접 Adapter 안**: Paging 또는 Room Flow.
+- **dispatchSemaphore wait main**: 죽음.
+
+## 🤖 LLM 활용 힌트
+- 모든 IO / decode / parse → background.
+- StrictMode + Main Thread Checker 항상 dev 켜기.
+
+## 🔗 관련 문서
+- [[Native_Memory_Profiling]]
+- [[Android_Coroutines_Concurrency]]