Kotlin Concurrency And Flow

Kotlin concurrency and Flow

Core principle

Give asynchronous work an explicit owner and lifetime, then model durable state and transient events with primitives whose delivery and replay semantics match the product contract.

Procedure

1. Identify each coroutine owner, cancellation boundary, producer, consumer, durable state, and transient event.
2. Before changing an API, compare its existing caller-visible contract with the required owner and lifetime. If a suspend API already gives its caller cancellation, result, and failure ownership, finish with no change; do not add a scope, launch, callback, or deferred wrapper merely for convenience.
3. Select a scope whose lifecycle owns the work; do not retain arbitrary scopes or hide unstructured launches behind non-suspending APIs.
4. Model renderable, current data as state and imperative one-shot work as an event only when its loss and replay behavior are explicitly acceptable.
5. Choose Flow sharing and buffering semantics from the producer and consumer lifetimes rather than from a default.
6. Read the focused reference for the material concern below.
7. Finish when cancellation, restart, replay, and failure behavior are all observable from the public API and no caller must guess who owns the work.

Topic router

RED/GREEN agent scenarios

1. RED stores a long-lived CoroutineScope in a service and launches from arbitrary callers. GREEN makes ownership and cancellation follow a defined lifecycle boundary.
2. Novel case: a screen needs replayable loading state and non-replayable navigation. GREEN uses distinct state and event contracts with documented delivery semantics.
3. Counterexample: a suspend function already has a caller-owned scope. GREEN reports that no code change is necessary rather than adding an internal scope merely to make the API look asynchronous.