import { Log } from 'ts-tiny-log';
import { Worker } from './worker';
export interface PoolOptions<TIn, TOut> {
    /**
     * Number of workers. Default is 4
     */
    nWorkers?: number;
    /**
     * Worker entry file. Must be a relative/absolute path/file
     */
    workerEntry: string;
    /**
     * Queue name that this pool serves
     */
    queueName: string;
    /**
     * Class for communicating Parent -> Worker
     */
    workerType?: typeof Worker;
    /**
     * Error handler callback
     */
    error?: (err: Error) => void | Promise<void>;
}
/**
 * Worker pool that manages a set of workers for a queue
 *
 * @typeParam TIn Queue task input type
 * @typeParam TOut Queue task output type
 */
export declare class Pool<TIn, TOut> {
    protected log: Log;
    protected workers: Worker<TIn, TOut>[];
    protected options: PoolOptions<TIn, TOut>;
    constructor(options: PoolOptions<TIn, TOut>);
    /**
     * Initialize the pool by spawning the initial worker set
     *
     * @returns Promise that resolves when all workers are spawned
     */
    initialize(): Promise<void>;
    /**
     * Reserve and return a free worker
     *
     * @returns The worker, or null if none are available
     */
    reserve(): Promise<null | Worker<TIn, TOut>>;
    /**
     * Mark a worker as free (available for next task)
     *
     * @param worker Worker to release
     */
    release(worker: Worker<TIn, TOut>): void;
    /**
     * Get the current number of workers in the pool
     *
     * @returns Number of workers
     */
    getWorkerCount(): number;
    /**
     * Spawn a new worker thread
     *
     * @returns The spawned worker
     */
    protected spawnWorker(): Promise<Worker<TIn, TOut>>;
}