# Kotlin Coroutines & Flow

> Structured Concurrency, Flow patterns, and Asynchronous programming standards.

- Skill: `majiayu000/kotlin-coroutines-flow` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add majiayu000/kotlin-coroutines-flow`
- Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/kotlin-coroutines-flow/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: majiayu000 (https://skillmd.com/u/majiayu000)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/majiayu000/kotlin-coroutines-flow

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# Kotlin Coroutines & Flow

## **Priority: P1 (HIGH)**

Standard for safe, structured asynchronous programming.

## Implementation Guidelines

- **Structured Concurrency**: Always launch coroutines within a `CoroutineScope` (e.g., `viewModelScope`, `lifecycleScope`). Never use `GlobalScope`.
- **Dispatchers**: Inject `DispatcherProvider` or `CoroutineDispatcher` to simplify testing. Do not hardcode `Dispatchers.IO` in classes.
- **Suspend Functions**: Mark blocking/long-running operations as `suspend`. They should be "main-safe" (handle their own context switching).
- **Flow**: Prefer `StateFlow` (state holder) and `SharedFlow` (events) over `LiveData`.
- **Collection**: Use `collectLatest` for restartable upstream updates. Use `flowWithLifecycle` in UI.
- **Error Handling**: Use `CoroutineExceptionHandler` for top-level launch, `try/catch` for code blocks within coroutines.

## Anti-Patterns

- **GlobalScope**: Leaks memory and breaks structure.
- **Blocking Calls**: Never use `Thread.sleep` or blocking I/O in coroutines. Use `delay` or proper suspend functions.
- **Async/Await Abuse**: Don't use `async` unless you need parallel execution. Use linear code in `launch`.
- **Mutable State in Flow**: Don't expose `MutableStateFlow` publicly. Cast to `StateFlow`.

## Code

For detailed `ViewModel` + `StateFlow` and `Parallel Async` examples:
[references/advanced-patterns.md](references/advanced-patterns.md)

```kotlin
// Structured Scope + Main-safe Suspend
viewModelScope.launch {
    val data = withContext(Dispatchers.IO) { repo.fetch() }
    _state.value = UiState.Success(data)
}
```

## Related Topics

best-practices | language | android