workers.js

let mutex = Promise.resolve();

let counter = 0;

const read = async () => counter;

const write = async (value) => {
  counter = value;
}

const sleep = (ms) =>
  new Promise(accept => setTimeout(accept, ms));

const criticalSection = async (f) => {
  mutex = mutex.then(f);
  await mutex;
}

const numWorkers = 200;
const incsPerWorker = 3000;
const expected = numWorkers * incsPerWorker;

const worker = async () => {
  for (let i = 0; i < incsPerWorker; i++) {
    await criticalSection(async () => {
      let x = await read();
      await sleep(Math.random() * 50);
      await write(x + 1);
    });
  }
};

const main = async () => {
  const workers = [];
  for (let i = 0; i < numWorkers; i++) {
    workers.push(worker());
  }
  await Promise.all(workers);
  if (expected === counter) {
    console.log('ok');
  } else {
    console.log('expected:', expected);
    console.log('got:', counter);
  }
};

void main();