emscripten/tests/emscripten_get_now.cpp

#include <stdio.h>
#include "emscripten.h"

#ifndef REPORT_RESULT
// To be able to run this test outside the browser harness in node.js/spidermonkey:
#define REPORT_RESULT int dummy
#endif

int result = 0;

int main() {
  // This code tests three things:
  // a) Calling emscripten_get_now(), time actually proceeds.
  // b) Values returned by emscripten_get_now() are strictly nondecreasing.
  // c) emscripten_get_now() is able to return sub-millisecond precision timer values.
  bool detected_good_timer_precision = false;
  double smallest_delta = 0.f;
  for(int x = 0; x < 1000; ++x) { // Have several attempts to find a good small delta, i.e. give time to JS engine to warm up the code and so on.
    double t = emscripten_get_now();
    double t2 = emscripten_get_now();
    for(int i = 0; i < 100 && t == t2; ++i) {
      t2 = emscripten_get_now();
    }

    if (t2 < t && t2 - t < 1000.f) { // Timer must be monotonous.
      printf("Timer is not monotonous!\\n");
      smallest_delta = t2 - t;
      break;
    }
    if (t2 > t && t2 - t < 0.7f) { // Must pass less than a millisecond between two calls.
      detected_good_timer_precision = true;
      smallest_delta = t2 - t;
      break;
    }
  }
  
  if (detected_good_timer_precision) {
    printf("Timer resolution is good. (%f msecs)\\n", smallest_delta);
    result = 1;
  } else {
    printf("Error: Bad timer precision: Smallest timer delta: %f msecs\\n", smallest_delta);
    result = 0;
  }
  REPORT_RESULT();
  return 0;
}