villa/src/concurrency.ts

Promise utilities for async/await-ready environment.

import {Resolvable, map} from '.';

let lockObjectToPromiseMapping = new Map<any, Promise<any>>();

export type LockHandler<T> = () => Resolvable<T>;

async function _lock<T>(object: any, handler: LockHandler<T>): Promise<T> {
  try {
    await lockObjectToPromiseMapping.get(object);
  } catch (error) {}

  return handler();
}

/**
 * A simple asynchronous lock that helps queueing operations.
 */
export async function lock<T>(
  object: any,
  handler: LockHandler<T>,
): Promise<T> {
  let ret = _lock(object, handler);
  lockObjectToPromiseMapping.set(object, ret);
  return ret;
}

export type ParallelHandler<T> = (
  value: T,
  index: number,
  values: T[],
) => Resolvable<void>;

/**
 * Run tasks in parallel, similar to `v.map` but not mean to transform.
 */
export async function parallel<T>(
  values: T[],
  handler: ParallelHandler<T>,
  concurrency?: number,
): Promise<void> {
  await map(values, handler, concurrency);
}

export type RaceTransformer<T, TResult> = (
  value: T,
  index: number,
  values: T[],
) => Resolvable<TResult>;

/**
 * Race tasks and fulfill or reject as soon as one of them fulfills or rejects.
 */
export async function race<T, TResult>(
  values: T[],
  transformer: RaceTransformer<T, TResult>,
): Promise<TResult> {
  return Promise.race(values.map(transformer));
}