사용 방법
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npx skills add https://github.com/new-silvermoon/awesome-android-agent-skills --skill kotlin-concurrency-expert시작 전 확인
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원본 Skill 문서
원본 저장소의 제목, 예시, 코드, 표, 링크, 이미지를 유지해 표시합니다.
Kotlin Concurrency Expert
Overview
Review and fix Kotlin Coroutines issues in Android codebases by applying structured concurrency, lifecycle safety, proper scoping, and modern best practices with minimal behavior changes.
Workflow
1. Triage the Issue
- Capture the exact error, crash, or symptom (ANR, memory leak, race condition, incorrect state).
- Check project coroutines setup:
kotlinx-coroutines-androidversion,lifecycle-runtime-ktxversion. - Identify the current scope context (
viewModelScope,lifecycleScope, custom scope, or none). - Confirm whether the code is UI-bound (
Dispatchers.Main) or intended to run off the main thread (Dispatchers.IO,Dispatchers.Default). - Verify Dispatcher injection patterns for testability.
2. Apply the Smallest Safe Fix
Prefer edits that preserve existing behavior while satisfying structured concurrency and lifecycle safety.
Common fixes:
- ANR / Main thread blocking: Move heavy work to
withContext(Dispatchers.IO)orDispatchers.Default; ensure suspend functions are main-safe. - Memory leaks / zombie coroutines: Replace
GlobalScopewith a lifecycle-bound scope (viewModelScope,lifecycleScope, or injectedapplicationScope). - Lifecycle collection issues: Replace deprecated
launchWhenStartedwithrepeatOnLifecycle(Lifecycle.State.STARTED). - State exposure: Encapsulate
MutableStateFlow/MutableSharedFlow; expose read-onlyStateFloworFlow. - CancellationException swallowing: Ensure generic
catch (e: Exception)blocks rethrowCancellationException. - Non-cooperative cancellation: Add
ensureActive()oryield()in tight loops for cooperative cancellation. - Callback APIs: Convert listeners to
callbackFlowwith properawaitClosecleanup. - Hardcoded Dispatchers: Inject
CoroutineDispatchervia constructor for testability.
Critical Rules
Dispatcher Injection (Testability)
kotlin
// CORRECT: Inject dispatcher
class UserRepository(
private val ioDispatcher: CoroutineDispatcher = Dispatchers.IO
) {
suspend fun fetchUser() = withContext(ioDispatcher) { ... }
}
// INCORRECT: Hardcoded dispatcher
class UserRepository {
suspend fun fetchUser() = withContext(Dispatchers.IO) { ... }
}Lifecycle-Aware Collection
kotlin
// CORRECT: Use repeatOnLifecycle
viewLifecycleOwner.lifecycleScope.launch {
viewLifecycleOwner.repeatOnLifecycle(Lifecycle.State.STARTED) {
viewModel.uiState.collect { state -> updateUI(state) }
}
}
// INCORRECT: Direct collection (unsafe, deprecated)
lifecycleScope.launchWhenStarted {
viewModel.uiState.collect { state -> updateUI(state) }
}State Encapsulation
kotlin
// CORRECT: Expose read-only StateFlow
class MyViewModel : ViewModel() {
private val _uiState = MutableStateFlow(UiState())
val uiState: StateFlow<UiState> = _uiState.asStateFlow()
}
// INCORRECT: Exposed mutable state
class MyViewModel : ViewModel() {
val uiState = MutableStateFlow(UiState()) // Leaks mutability
}Exception Handling
kotlin
// CORRECT: Rethrow CancellationException
try {
doSuspendWork()
} catch (e: CancellationException) {
throw e // Must rethrow!
} catch (e: Exception) {
handleError(e)
}
// INCORRECT: Swallows cancellation
try {
doSuspendWork()
} catch (e: Exception) {
handleError(e) // CancellationException swallowed!
}Cooperative Cancellation
kotlin
// CORRECT: Check for cancellation in tight loops
suspend fun processLargeList(items: List<Item>) {
items.forEach { item ->
ensureActive() // Check cancellation
processItem(item)
}
}
// INCORRECT: Non-cooperative (ignores cancellation)
suspend fun processLargeList(items: List<Item>) {
items.forEach { item ->
processItem(item) // Never checks cancellation
}
}Callback Conversion
kotlin
// CORRECT: callbackFlow with awaitClose
fun locationUpdates(): Flow<Location> = callbackFlow {
val listener = LocationListener { location ->
trySend(location)
}
locationManager.requestLocationUpdates(listener)
awaitClose { locationManager.removeUpdates(listener) }
}Scope Guidelines
| Scope | Use When | Lifecycle |
|---|---|---|
viewModelScope | ViewModel operations | Cleared with ViewModel |
lifecycleScope | UI operations in Activity/Fragment | Destroyed with lifecycle owner |
repeatOnLifecycle | Flow collection in UI | Started/Stopped with lifecycle state |
applicationScope (injected) | App-wide background work | Application lifetime |
GlobalScope | NEVER USE | Breaks structured concurrency |
Testing Pattern
kotlin
@Test
fun `loading data updates state`() = runTest {
val testDispatcher = StandardTestDispatcher(testScheduler)
val repository = FakeRepository()
val viewModel = MyViewModel(repository, testDispatcher)
viewModel.loadData()
advanceUntilIdle()
assertEquals(UiState.Success(data), viewModel.uiState.value)
}
