Implement promise queue with concurrency limit

Medium

You need to implement a promise queue that limits concurrent operations. What's the correct implementation of the missing methods?

Choose an option below

async add(promiseFactory) {
  if (this.running >= this.concurrency) {
    await new Promise(resolve => this.queue.push(resolve));
  }
  this.running++;
  try {
    return await promiseFactory();
  } finally {
    this.running--;
    if (this.queue.length > 0) {
      this.queue.shift()();
    }
  }
}

add(promiseFactory) {
  return new Promise((resolve, reject) => {
    this.queue.push({ promiseFactory, resolve, reject });
    this.processQueue();
  });
}

async processQueue() {
  if (this.running >= this.concurrency) return;
  
  const next = this.queue.shift();
  if (!next) return;
  
  this.running++;
  try {
    const result = await next.promiseFactory();
    next.resolve(result);
  } catch (error) {
    next.reject(error);
  } finally {
    this.running--;
    this.processQueue();
  }
}

add(promiseFactory) {
  if (this.running < this.concurrency) {
    this.running++;
    return promiseFactory().finally(() => {
      this.running--;
      this.processQueue();
    });
  } else {
    return new Promise(resolve => {
      this.queue.push(() => resolve(promiseFactory()));
    });
  }
}

processQueue() {
  while (this.queue.length > 0 &amp;&amp; this.running < this.concurrency) {
    this.queue.shift()();
  }
}

async add(promiseFactory) {
  while (this.running >= this.concurrency) {
    await Promise.resolve();
  }
  this.running++;
  try {
    return await promiseFactory();
  } finally {
    this.running--;
  }
}

JavascriptPromisesConcurrencyQueueAsync

1class PromiseQueue {
2  constructor(concurrency = 3) {
3    this.concurrency = concurrency;
4    this.running = 0;
5    this.queue = [];
6  }
7
8  // Missing implementation
9  ____________________
10  ____________________
11  ____________________
12  ____________________
13}
14
15// Usage:
16const queue = new PromiseQueue(2);
17const urls = ['url1', 'url2', 'url3', 'url4', 'url5'];
18
19urls.forEach(url => {
20  queue.add(() => fetch(url))
21    .then(response => console.log(`Completed: ${url}`));
22});

You need to implement a promise queue that limits concurrent operations. What's the correct implementation of the missing methods?

Hint