Class Throttler

src/vs/base/common/async.ts:183–245

 * 		}
 */
export class Throttler implements IDisposable {

	private activePromise: Promise<any> | null;
	private queuedPromise: Promise<any> | null;
	private queuedPromiseFactory: ITask<Promise<any>> | null;

	private isDisposed = false;

	constructor() {
		this.activePromise = null;
		this.queuedPromise = null;
		this.queuedPromiseFactory = null;
	}

	queue<T>(promiseFactory: ITask<Promise<T>>): Promise<T> {
		if (this.isDisposed) {
			return Promise.reject(new Error('Throttler is disposed'));
		}

		if (this.activePromise) {
			this.queuedPromiseFactory = promiseFactory;

			if (!this.queuedPromise) {
				const onComplete = () => {
					this.queuedPromise = null;

					if (this.isDisposed) {
						return;
					}

					const result = this.queue(this.queuedPromiseFactory!);
					this.queuedPromiseFactory = null;

					return result;
				};

				this.queuedPromise = new Promise(resolve => {
					this.activePromise!.then(onComplete, onComplete).then(resolve);
				});
			}

			return new Promise((resolve, reject) => {
				this.queuedPromise!.then(resolve, reject);
			});
		}

		this.activePromise = promiseFactory();

		return new Promise((resolve, reject) => {
			this.activePromise!.then((result: T) => {
				this.activePromise = null;
				resolve(result);
			}, (err: unknown) => {
				this.activePromise = null;
				reject(err);
			});
		});
	}