CSE2410 Fall 2014 Bounce

    TimeTicks highres_ticks = TimeTicks::HighResolutionNow();

template <typename T>

static void ResolutionTest(T (*Now)(), TimeDelta target_granularity) {

  // We're trying to measure that intervals increment in a VERY small amount

  // of time -- according to the specified target granularity. Unfortunately,

  // if we happen to have a context switch in the middle of our test, the

  // context switch could easily exceed our limit. So, we iterate on this

  // several times. As long as we're able to detect the fine-granularity

  // timers at least once, then the test has succeeded.

  static const TimeDelta kExpirationTimeout = TimeDelta::FromSeconds(1);

  ElapsedTimer timer;

  timer.Start();

  TimeDelta delta;

  do {

    T start = Now();

    T now = start;

    // Loop until we can detect that the clock has changed. Non-HighRes timers

    // will increment in chunks, i.e. 15ms. By spinning until we see a clock

    // change, we detect the minimum time between measurements.

    do {

      now = Now();

      delta = now - start;

    } while (now <= start);

    CHECK_NE(static_cast<int64_t>(0), delta.InMicroseconds());

  } while (delta > target_granularity && !timer.HasExpired(kExpirationTimeout));

  CHECK_LE(delta, target_granularity);

}

TEST(TimeNowResolution) {

  // We assume that Time::Now() has at least 16ms resolution.

  static const TimeDelta kTargetGranularity = TimeDelta::FromMilliseconds(16);

  ResolutionTest<Time>(&Time::Now, kTargetGranularity);

}

TEST(TimeTicksNowResolution) {

  // We assume that TimeTicks::Now() has at least 16ms resolution.

  static const TimeDelta kTargetGranularity = TimeDelta::FromMilliseconds(16);

  ResolutionTest<TimeTicks>(&TimeTicks::Now, kTargetGranularity);

}

TEST(TimeTicksHighResolutionNowResolution) {

  if (!TimeTicks::IsHighResolutionClockWorking()) return;

  // We assume that TimeTicks::HighResolutionNow() has sub-ms resolution.

  static const TimeDelta kTargetGranularity = TimeDelta::FromMilliseconds(1);

  ResolutionTest<TimeTicks>(&TimeTicks::HighResolutionNow, kTargetGranularity);

}