Synchronised block of code in node.js - Example inspired by rabbit-queue implementation of prefetch

prefetch.js

let globalPrefetch = 10;
async function changePrefetch(prefetchNum) {
  await new Promise(r => setTimeout(r, 10));
  globalPrefetch = prefetchNum;
}

async function subscribeToQueue(name, prefetch) {
  await changePrefetch(prefetch);
  await new Promise(r => setTimeout(r, 20));
  console.log(`subscribing to queue ${name} with prefetch ${globalPrefetch}`);
}

let lock;
async function subscribeToQueueWithLock(name, prefetch) {
  await lock;
  lock = changePrefetch(prefetch).then(async () => {
    await new Promise(r => setTimeout(r, 20));
    console.log(`subscribing to queue ${name} with prefetch ${globalPrefetch}`);
  });
}

/** The correct solution is this */
async function subscribeToQueueWithLocalLock(name, prefetch) {
  let localLock;
  do {
    localLock = lock;
    await lock;
  } while (localLock !== lock);
  lock = changePrefetch(prefetch).then(async () => {
    await new Promise(r => setTimeout(r, 20));
    console.log(`subscribing to queue ${name} with prefetch ${globalPrefetch}`);
  });
}

async function subscribeToManyQueues() {
  subscribeToQueueWithLocalLock('one', 1);
  subscribeToQueueWithLocalLock('two', 2);
  subscribeToQueueWithLocalLock('three', 3);
}

module.exports = subscribeToManyQueues;