/**
 * If this token is returned in the results from a batchingFunction, the corresponding requests will be placed back
 * into the the head of the queue.
 */
export declare const BATCHER_RETRY_TOKEN: unique symbol;
export declare type BatchingResult<T> = T | Error | typeof BATCHER_RETRY_TOKEN;
export interface BatcherOptions<I, O> {
    /**
     * The maximum number of requests that can be combined in a single batch.
     */
    readonly maxBatchSize?: number;
    /**
     * The number of milliseconds to wait before running a batch of requests.
     *
     * This is used to allow time for the requests to queue up. Defaults to 1ms.
     * This delay does not apply if the limit set by options.maxBatchSize is reached.
     */
    readonly queuingDelay?: number;
    /**
     * An array containing the number of requests that must be queued in order to trigger a batch request at each level
     * of concurrency.
     *
     * For example [1, 5], would require at least 1 queued request when no batch requests are active,
     * and 5 queued requests when 1 (or more) batch requests are active. Defaults to [1]. Note that the delay imposed
     * by options.queuingDelay still applies when a batch request is triggered.
     */
    readonly queuingThresholds?: readonly number[];
    /**
     * A function which is passed an array of request values, returning a promise which resolves to an array of
     * response values.
     *
     * The request and response arrays must be of equal length. To reject an individual request, return an Error object
     * (or class which extends Error) at the corresponding element in the response array.
     */
    readonly batchingFunction: (this: Batcher<I, O>, inputs: readonly I[]) => ReadonlyArray<BatchingResult<O>> | PromiseLike<ReadonlyArray<BatchingResult<O>>>;
    /**
     * A function which can delay a batch by returning a promise which resolves when the batch should be run.
     * If the function does not return a promise, no delay will be applied.
     */
    readonly delayFunction?: () => PromiseLike<void> | undefined | null | void;
}
export declare class Batcher<I, O> {
    private readonly _maxBatchSize;
    private readonly _queuingDelay;
    private readonly _queuingThresholds;
    private readonly _inputQueue;
    private readonly _outputQueue;
    private readonly _delayFunction?;
    private readonly _batchingFunction;
    private _waitTimeout?;
    private _waiting;
    private _activePromiseCount;
    private _immediateCount;
    constructor(options: BatcherOptions<I, O>);
    /**
     * Returns a promise which resolves or rejects with the individual result returned from the batching function.
     */
    getResult(input: I): Promise<O>;
    /**
     * Triggers a batch to run, bypassing the queuingDelay while respecting other imposed delays.
     */
    send(): void;
    /**
     * Triggers a batch to run, adhering to the maxBatchSize, queueingThresholds, and queuingDelay
     */
    private _trigger;
    /**
     * Runs the batch, while respecting delays imposed by the supplied delayFunction
     */
    private _run;
    /**
     * Runs the batch immediately without further delay
     */
    private _runImmediately;
}