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/**
 * Run `mapper` over `items` with at most `limit` concurrent in-flight
 * calls, preserving input order in the result. The git subprocess calls
 * this feeds are I/O-bound (fork+exec, not CPU), so running them
 * concurrently instead of one-at-a-time cuts wall-clock time roughly
 * proportional to `limit` on a multi-core machine.
 */
export const mapPool = async (items, limit, mapper) => {
  const results = new Array(items.length);
  let next = 0;
  const workers = Array.from({ length: Math.min(limit, items.length) }, async () => {
    while (next < items.length) {
      const i = next++;
      results[i] = await mapper(items[i], i);
    }
  });
  await Promise.all(workers);
  return results;
};