Kotlin Coroutines

Kotlin Coroutines

Treat cancellation, ownership, and lifecycle as public contracts, not implementation details.

Core rules

• Every launched coroutine must have an owner whose lifetime is explicit. Avoid GlobalScope.
• Prefer coroutineScope for fail-together work and supervisorScope only when sibling failure isolation is required by contract.
• Re-throw CancellationException; broad exception handlers must not consume cancellation.
• Move blocking calls to an appropriate dispatcher or replace them with cancellable asynchronous APIs.
• Do not expose a cold Flow as if it were shared state. Choose cold Flow, StateFlow, or SharedFlow from subscriber and replay semantics.
• Bound channels and queues. Define overflow, fairness, ordering, and shutdown behavior.
• Preserve context intentionally; do not pass request-scoped mutable state through globals or thread locals.
• Make cleanup run on success, failure, timeout, and cancellation. Use finally and cancellable resource APIs.

Review sequence

1. Map coroutine creation sites to scope owners.
2. Trace cancellation from caller through child work and adapters.
3. Identify blocking calls and dispatcher assumptions.
4. Record ordering, buffering, retry, timeout, and supervision contracts.
5. Write deterministic tests using virtual time or event-driven synchronization.
6. Stress lifecycle transitions and repeated cancellation.

Testing expectations

Assert emitted values, ordering, terminal errors, cancellation cleanup, no post-cancel work, and resource closure. Avoid fixed sleeps and tests that only assert completion.

./gradlew --no-daemon test
./gradlew --no-daemon check