Function HighResClockTest

test/time_unittest.cc:648–685

}

static void HighResClockTest(TimeTicks (*GetTicks)()) {
#if defined(OS_WIN)
  // HighResNow doesn't work on some systems.  Since the product still works
  // even if it doesn't work, it makes this entire test questionable.
  if (!TimeTicks::IsHighResClockWorking())
    return;
#endif

  // Why do we loop here?
  // We're trying to measure that intervals increment in a VERY small amount
  // of time --  less than 15ms.  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.

  const int kTargetGranularityUs = 15000;  // 15ms

  bool success = false;
  int retries = 100;  // Arbitrary.
  TimeDelta delta;
  while (!success && retries--) {
    TimeTicks ticks_start = GetTicks();
    // Loop until we can detect that the clock has changed.  Non-HighRes timers
    // will increment in chunks, e.g. 15ms.  By spinning until we see a clock
    // change, we detect the minimum time between measurements.
    do {
      delta = GetTicks() - ticks_start;
    } while (delta.InMilliseconds() == 0);

    if (delta.InMicroseconds() <= kTargetGranularityUs)
      success = true;
  }

  // In high resolution mode, we expect to see the clock increment
  // in intervals less than 15ms.
  EXPECT_TRUE(success);
}

TEST(TimeTicks, HighResNow) {
  HighResClockTest(&TimeTicks::HighResNow);