dougal-software/lib/modules/@dougal/concurrency/index.js

class ConcurrencyLimiter {

  constructor(maxConcurrent) {
    this.maxConcurrent = maxConcurrent;
    this.active = 0;
    this.queue = [];
  }

  async enqueue(task) {
    if (this.active >= this.maxConcurrent) {
      await new Promise(resolve => this.queue.push(resolve));
    }
    this.active++;
    try {
      return await task();
    } finally {
      this.active--;
      if (this.queue.length > 0) {
        this.queue.shift()();
      }
    }
  }
}

module.exports = ConcurrencyLimiter;