/**
 *	PromisePool limits the number of concurrent executions for any given task.
 *
 *	@example
 * ```ts
 *
 *  const pool = new PromisePool(4);
 *
 *  for (let idx = 0; idx < 7) {
 * 		// Runs the fetch request 4 times,
 * 		// halting on the 5th call.
 * 		// Waits until at least 1 or more promise resolves
 * 		// before resolving
 * 		await pool.add(() => {
 * 			return fetch(SOME_URL).then((r) => r.json());
 * 		});
 * 	}
 * ```
 */
export declare class PromisePool {
    private readonly concurrency;
    private pendingTasks;
    private activeTasks;
    private drainScheduled;
    constructor(concurrency: number);
    private runTask;
    private scheduleDrain;
    private drain;
    /**
     * Adds a task to the pool.
     * @param task The task to add to the pool.
     */
    add<T>(task: () => Promise<T>): Promise<T>;
}