master.js

'use strict';

(function() {

  const shmem = new SharedArrayBuffer(1024 * 100000); // 25600000
  const sync = new Int32Array(shmem);
  const cores = [...new Array(navigator.hardwareConcurrency)];
  const sync_shift = cores.length;
  const core_shift = (sync.length - sync_shift) / sync_shift;
  let doneCount = 0;

  console.time('main thread')
  for (let i = 0, ln = sync.length; i < ln; i++) {
    sync[i] = Math.round(Math.random() * 100);
  }
  console.timeEnd('main thread')

  cores
    .map((core, idx) => {
      const worker = new Worker('/js/worker.js');
      worker.postMessage([shmem, idx, sync_shift, core_shift], [shmem]);
      worker.onmessage = ({ data }) => {
        if (data === 'done') {
          doneCount++;
          if (doneCount === sync_shift) {
            console.timeEnd(sync_shift + ' workers')
          }
        }
      };
      return worker;
    })
    .forEach((worker, idx) => {
      if (idx === 0) {
        console.time(sync_shift + ' workers')
      }
      Atomics.store(sync, idx, 1);
      Atomics.wake(sync, idx, 1);
    });

})();

worker.js

'use strict';

onmessage = ({ data }) => runWorker(...data);

function runWorker(shmem, idx, sync_shift, core_shift) {

  const sync = new Int32Array(shmem);

  while (true) {

    Atomics.wait(sync, idx, 0);
    Atomics.store(sync, idx, 0);

    for (let i = core_shift * idx + sync_shift; i < core_shift * (idx + 1) + sync_shift; i++) {
      sync[i] = Math.round(Math.random() * 100);
    }

    postMessage('done');
  }
}