Vyuh CDX

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Service Tasks ​

A service task is automated, side-effecting work. The workflow schedules it; a leased worker executes a versioned ActivityHandler.

dart
final reservation = await flow.serviceTask(
  reserve,
  order,
  id: 'reserve',
  retry: RetryPolicy(maxAttempts: 3),
);

id is the replay identity. activity is a compatibility alias for serviceTask.

Handler ​

dart
final class ReservationHandler implements ActivityHandler<Order, Reservation> {
  @override
  Future<Reservation> handle(ActivityContext context, Order order) {
    return reservations.reserve(
      order,
      idempotencyKey: context.idempotencyKey,
    );
  }
}

ActivityContext exposes runId, commandId, operationKey, attempt, idempotencyKey, and heartbeat(). Long work must heartbeat before the lease expires.

Timeouts and Retries ​

Activities have no timeout unless configured. Retryable failures use backoff and keep the same idempotency key. Permanent failures fail the command. Manual retry creates a new attempt and retains the key.

Prefer this shape for work that lasts days:

  1. The activity starts an external job and returns its ID.
  2. The workflow waits for a signal or a durable poll timer.
  3. A callback records completion and wakes replay.

See Also ​