/**
 * @internal
 * WorkerPool, T is is post message type, U is return type.
 */
export declare class WorkerPool<T = any, U = any> {
    readonly limitedCount: number;
    private readonly _workerCreator;
    private _taskQueue;
    private _workerStatus;
    private _workerItems;
    /**
     * Constructor of WorkerPool.
     * @param limitedCount - worker limit count
     * @param _workerCreator - creator of worker
     */
    constructor(limitedCount: number, _workerCreator: () => Worker | Promise<Worker>);
    prepareWorker(): Promise<Worker[]>;
    /**
     * Post message to worker.
     * @param message - Message which posted to worker
     * @returns Return a promise of message
     */
    postMessage(message: T): Promise<U>;
    /**
     * Destroy the worker pool.
     */
    destroy(): void;
    private _initWorker;
    private _getIdleWorkerId;
    private _onMessage;
    private _nextTask;
}