kotlin-coroutines

name	kotlin-coroutines
promoted_to	kotlin
description	Kotlin structured concurrency, Flow, and Channel patterns.
user-invocable	false
context	fork
agent	kotlin-general-engineer
routing	{"triggers":["kotlin coroutines","kotlin structured concurrency","kotlin Flow","kotlin Channel","suspend function","structured concurrency kotlin"],"category":"kotlin","pairs_with":["kotlin-testing"]}

Kotlin Coroutines Patterns

Umbrella skill for Kotlin coroutine development: structured concurrency, cancellation, Flow, StateFlow/SharedFlow, Channels, exception handling, and dispatchers. Routes to the correct reference based on the task at hand.

Reference Loading Table

Signal	Load These Files	Why
Concurrency	concurrency-patterns.md	Scopes, cancellation, dispatchers, exception handling
Flow	flow-patterns.md	Flow builders, StateFlow, SharedFlow, operators
Channels	channel-patterns.md	Producer-consumer, fan-in/fan-out patterns
Failure modes	preferred-patterns.md	GlobalScope, unstructured launch, CancellationException

Instructions

Step 1: Identify the Domain

Classify the task into one or more domains, then load the corresponding reference files. Only load what is needed -- do not load all references for every task.

Domain	Load Reference	When
Concurrency	references/concurrency-patterns.md	Scopes, cancellation, dispatchers, exception handling
Flow	references/flow-patterns.md	Flow builders, StateFlow, SharedFlow, operators
Channels	references/channel-patterns.md	Producer-consumer, fan-in/fan-out patterns
Failure modes	references/preferred-patterns.md	GlobalScope, unstructured launch, CancellationException

Multiple domains may apply. For example, reviewing code that uses both Flow and Channels should load both flow-patterns.md and channel-patterns.md.

Step 2: Load and Follow the Reference

Read the selected reference file(s) using ${CLAUDE_SKILL_DIR}/references/<name>.md. Each reference contains the full patterns, code examples, and decision matrices for that domain. Follow the instructions in the reference as if they were this skill's instructions.

Step 3: Execute

Apply the loaded reference patterns to the task. Use the code examples as templates for implementation guidance.

Key Principles

1. Structured concurrency is non-negotiable -- every coroutine must have a parent scope that defines its lifetime.
2. Inject dispatchers -- accept CoroutineDispatcher as a parameter so callers (and tests) can control threading.
3. Always rethrow CancellationException -- rethrow it immediately or use specific exception types instead of catching Exception.
4. Prefer Flow over Channel -- Flow is cold, composable, and handles backpressure. Channels are lower-level; reach for them only when Flow cannot express the pattern.
5. Use supervisorScope for partial failure tolerance -- when independent tasks should not cancel each other, wrap them in supervisorScope.
6. Use scoped coroutines instead of GlobalScope -- it has no lifecycle, no cancellation, and no structured concurrency. Pass a scope from your application framework instead.