/**
 *
 * queue pending size out of limit
 *
 * @internal
 * @private
 * @ignore
 */
export declare class QueueOverFlowError extends Error {
}
/**
 * BlockedQueue
 *
 * a blocked queue for async operations
 *
 * @since 5.19.0
 * @category Functional
 */
export declare class BlockedQueue<I = any> {
    private _capacity;
    private _notifyQueue;
    private _maxPending;
    private _container;
    /**
     * @param capacity default 1000
     * @param maxPending default 10 * capacity, the max allowed number of pending items
     */
    constructor(capacity?: number, maxPending?: number);
    /**
     * push an item to the queue, blocked when the queue is full
     *
     * @throws {QueueOverFlowError} throw when pending items are too much
     * @param item
     * @returns
     */
    enQueue(item: I): Promise<void>;
    /**
     * retrieve an item from queue
     *
     * @returns
     */
    deQueue(): Promise<I>;
}
export default BlockedQueue;