Async Pool

async function asyncPool<T, R>(

  items: readonly T[],

  concurrency: number,

  fn: (item: T) => Promise<R>

): Promise<R[]> {

  const results: R[] = [];

  const executing = new Set<Promise<void>>();

  for (const item of items) {

    const p = fn(item).then((r) => { results.push(r); });