CODEWITHSUNDEEP
c++chromium
lokippc
lokippc

Reputation: 13

why did the chromium implement Time::Now ? what is the benefit?

code segment as follows, code come frome chromium, why?

// Initilalize initial_ticks and initial_time
void InitializeClock() {
  initial_ticks = TimeTicks::Now();
  // Initilalize initial_time 
  initial_time = CurrentWallclockMicroseconds();
}// static
Time Time::Now() {
  if (initial_time == 0)
    InitializeClock();

  // We implement time using the high-resolution timers so that we can get
  // timeouts which are smaller than 10-15ms.  If we just used
  // CurrentWallclockMicroseconds(), we'd have the less-granular timer.
  //
  // To make this work, we initialize the clock (initial_time) and the
  // counter (initial_ctr).  To compute the initial time, we can check
  // the number of ticks that have elapsed, and compute the delta.
  //
  // To avoid any drift, we periodically resync the counters to the system
  // clock.
  while (true) {
    TimeTicks ticks = TimeTicks::Now();

    // Calculate the time elapsed since we started our timer
    TimeDelta elapsed = ticks - initial_ticks;

    // Check if enough time has elapsed that we need to resync the clock.
    if (elapsed.InMilliseconds() > kMaxMillisecondsToAvoidDrift) {
      InitializeClock();
      continue;
    }

    return Time(elapsed + Time(initial_time));
  }
}

Upvotes: 0

Views: 183

Answers (1)

Johann Gerell
Johann Gerell

Reputation: 25591

I assume your answer lies in the comment of the code you pasted:

// We implement time using the high-resolution timers so that we can get
// timeouts which are smaller than 10-15ms.  If we just used
// CurrentWallclockMicroseconds(), we'd have the less-granular timer.

So Now gives a time value of high resolution, which is beneficial when you need higher resolution than 10-15ms, as they state in the comment. For instance, if you want to reschedule a task every 100 ns, you need the higher resolution, or if you want to measure the execution time of something - 10-15 ms is an eternity.

Upvotes: 2

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