Effect Concurrency And Lifecycle

Use this skill for concurrent work, background processes, and resource lifecycles.

Fiber Ownership

Pick the lifecycle intentionally.

const fiber = yield* Effect.forkDetach({ startImmediately: true })(work)
yield* Fiber.interrupt(fiber)

Rules:

• Use Effect.forkScoped for work that must stop when the current scope closes.
• Use Effect.forkIn(effect, scope) when scope ownership is explicit.
• Use Effect.forkDetach({ startImmediately: true })(effect) only when work must outlive the parent fiber.
• Use Deferred for cross-fiber result delivery, especially from detached work.
• Use Effect.onExit or Effect.ensuring for cleanup that must run on success, failure, or interrupt.
• Use Effect.acquireUseRelease or scoped layers for real resources.
• Background work must have an owner: scope, registry, runtime service, or explicit detached lifecycle.
• Queues, streams, subscriptions, and detached fibers must have a shutdown story. If it cannot be interrupted or drained, it is not ready for runtime code.

Bounded Work

• Limit parallelism with Effect.all(..., { concurrency: n }) or Effect.forEach(..., { concurrency: n }).
• Use "unbounded" only when the collection and cost are bounded by design.
• Effect.race interrupts the losing effect. Make sure both sides are interruption-safe.
• Prefer deterministic shutdown signals over sleeps.

Queues, PubSub, Streams

Queues encode pressure policy. Choose it deliberately:

• Queue.bounded<A>(n) - backpressure; producer waits when full.
• Queue.sliding<A>(n) - keep latest, drop oldest.
• Queue.dropping<A>(n) - keep current, drop new when full.
• Queue.unbounded<A>() - only when memory growth is impossible or bounded elsewhere.

Rules:

• Use explicit type parameters for queues.
• Use PubSub when one event must be broadcast to multiple subscribers.
• Bridge queues to streams with Stream.fromQueue(queue).
• End queue-backed streams by offering a terminal event plus Stream.takeUntil(...), or by Queue.shutdown(queue) when shutdown semantics are correct.
• Do not leave background consumers without interruption or shutdown.

Checks

• Who owns this fiber?
• What interrupts it?
• Where is shutdown/drain handled?
• Can producers outrun consumers?
• What happens when the consumer fails?
• Are failures logged, surfaced, or intentionally ignored?