<!DOCTYPE HTML>
<html>
<head>
  <title>Test for High Resolution Timer</title>
  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
  <script src="/tests/SimpleTest/SimpleTest.js"></script>
  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
</head>
<body>
  <script>
    ok(window.performance, "Performance object should exist.");
    ok(typeof window.performance.now == 'function', "Performance object should have a 'now' method.");
    var n = window.performance.now(), d = Date.now();
    ok(n >= 0, "The value of now() should be equal to or greater than 0.");
    ok(window.performance.now() >= n, "The value of now() should monotonically increase.");

    SimpleTest.waitForExplicitFinish();
    SimpleTest.requestFlakyTimeout("using setTimeout() to measure performance.now()");

    // Spin on setTimeout() until performance.now() increases. Due to recent
    // security developments, the hr-time working group has not yet reached
    // consensus on what the recommend minimum clock resolution should be:
    // https://w3c.github.io/hr-time/#clock-resolution
    // Since setTimeout might return too early/late, our goal is for
    // performance.now() to increase before a 2 ms deadline rather than specific
    // number of setTimeout(N) invocations.
    // See bug 749894 (intermittent failures of this test)
    var checks = 0;

    function checkAfterTimeout() {
      checks++;
      var d2 = Date.now();
      var n2 = window.performance.now();

      // Spin on setTimeout() until performance.now() increases. Abort the
      // test if it runs for more than 2 ms or 50 timeouts.
      let elapsedTime = d2 - d;
      let elapsedPerf = n2 - n;
      if (elapsedPerf == 0 && elapsedTime < 2 && checks < 50) {
        setTimeout(checkAfterTimeout, 1);
        return;
      }

      // Our implementation provides 1 ms resolution (bug 1451790).
      ok(elapsedPerf >= 1,
         `Loose - the value of now() should increase by no less than 1 ms ` +
         `after 2 ms. delta now(): ${elapsedPerf} ms`);

      // If we need more than 1 iteration, then either performance.now()
      // resolution is shorter than 1 ms or setTimeout() is returning too early.
      ok(checks == 1,
         `Strict - the value of now() should increase after one setTimeout. ` +
         `iters: ${checks}, dt: ${elapsedTime}, now(): ${n2}`);

      SimpleTest.finish();
    };
    setTimeout(checkAfterTimeout, 1);
  </script>
</body>
</html>
