Worker-postMessage-happens-in-parallel.https.html

<!DOCTYPE html>
<title>Test that calling "worker.postMessage()" will occur truly in parallel to the main JS thread performing other computation.</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
promise_test(t => {
  return new Promise(resolve => {
    let worker = new Worker("support/Worker-postMessage-happens-in-parallel.js");
    worker.postMessage('init');
    worker.onmessage = () => {
      let sab = new Uint8Array(new SharedArrayBuffer(16));
      worker.postMessage(sab);
      let end = performance.now() + 30*1000;
      while(sab[0] != 1 && performance.now() < end) /*wait to join with the result*/;
      assert_true(sab[0] == 1);
      resolve();
    };
  });
}, 'Tests that calling "worker.postMessage()" will occur truly in parallel to the main JS thread');
</script>

chromium/third_party/blink/web_tests/external/wpt/workers/Worker-postMessage-happens-in-parallel.https.html