Awesome-android-agent-skills kotlin-concurrency-expert

Kotlin Coroutines review and remediation for Android. Use when asked to review concurrency usage, fix coroutine-related bugs, improve thread safety, or resolve lifecycle issues in Kotlin/Android code.

install

source · Clone the upstream repo

git clone https://github.com/new-silvermoon/awesome-android-agent-skills

Claude Code · Install into ~/.claude/skills/

T=$(mktemp -d) && git clone --depth=1 https://github.com/new-silvermoon/awesome-android-agent-skills "$T" && mkdir -p ~/.claude/skills && cp -r "$T/.github/skills/concurrency_and_networking/kotlin-concurrency-expert" ~/.claude/skills/new-silvermoon-awesome-android-agent-skills-kotlin-concurrency-expert && rm -rf "$T"

manifest: .github/skills/concurrency_and_networking/kotlin-concurrency-expert/SKILL.md

source content

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-android

version,

lifecycle-runtime-ktx

version.

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)
```
or
```
Dispatchers.Default
```
; ensure suspend functions are main-safe.
Memory leaks / zombie coroutines: Replace
```
GlobalScope
```
with a lifecycle-bound scope (
```
viewModelScope
```
,
```
lifecycleScope
```
, or injected
```
applicationScope
```
).

Lifecycle collection issues: Replace deprecated

launchWhenStarted

with

repeatOnLifecycle(Lifecycle.State.STARTED)

State exposure: Encapsulate
```
MutableStateFlow
```
/
```
MutableSharedFlow
```
; expose read-only
```
StateFlow
```
or
```
Flow
```
.
CancellationException swallowing: Ensure generic
```
catch (e: Exception)
```
blocks rethrow
```
CancellationException
```
.
Non-cooperative cancellation: Add
```
ensureActive()
```
or
```
yield()
```
in tight loops for cooperative cancellation.
Callback APIs: Convert listeners to
```
callbackFlow
```
with proper
```
awaitClose
```
cleanup.
Hardcoded Dispatchers: Inject
```
CoroutineDispatcher
```
via constructor for testability.

Critical Rules

Dispatcher Injection (Testability)

// 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

// 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

// 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

// 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

// 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

// 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

@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)
}