posix_time.cpp

#include "posix_time.h"

#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
int
nanosleep (const struct timespec *requested_delay,
           struct timespec *remaining_delay)
{
  static bool initialized;
  /* Number of performance counter increments per nanosecond,
     or zero if it could not be determined.  */
  static double ticks_per_nanosecond;

  if (requested_delay->tv_nsec < 0 || BILLION <= requested_delay->tv_nsec)
    {
      errno = EINVAL;
      return -1;
    }

  /* For requested delays of one second or more, 15ms resolution is
     sufficient.  */
  if (requested_delay->tv_sec == 0)
    {
      if (!initialized)
        {
          /* Initialize ticks_per_nanosecond.  */
          LARGE_INTEGER ticks_per_second;

          if (QueryPerformanceFrequency (&ticks_per_second))
            ticks_per_nanosecond =
              (double) ticks_per_second.QuadPart / 1000000000.0;

          initialized = true;
        }
      if (ticks_per_nanosecond)
        {
          /* QueryPerformanceFrequency worked.  We can use
             QueryPerformanceCounter.  Use a combination of Sleep and
             busy-looping.  */
          /* Number of milliseconds to pass to the Sleep function.
             Since Sleep can take up to 8 ms less or 8 ms more than requested
             (or maybe more if the system is loaded), we subtract 10 ms.  */
          int sleep_millis = (int) requested_delay->tv_nsec / 1000000 - 10;
          /* Determine how many ticks to delay.  */
          LONGLONG wait_ticks = requested_delay->tv_nsec * ticks_per_nanosecond;
          /* Start.  */
          LARGE_INTEGER counter_before;
          if (QueryPerformanceCounter (&counter_before))
            {
              /* Wait until the performance counter has reached this value.
                 We don't need to worry about overflow, because the performance
                 counter is reset at reboot, and with a frequency of 3.6E6
                 ticks per second 63 bits suffice for over 80000 years.  */
              LONGLONG wait_until = counter_before.QuadPart + wait_ticks;
              /* Use Sleep for the longest part.  */
              if (sleep_millis > 0)
                Sleep (sleep_millis);
              /* Busy-loop for the rest.  */
              for (;;)
                {
                  LARGE_INTEGER counter_after;
                  if (!QueryPerformanceCounter (&counter_after))
                    /* QueryPerformanceCounter failed, but succeeded earlier.
                       Should not happen.  */
                    break;
                  if (counter_after.QuadPart >= wait_until)
                    /* The requested time has elapsed.  */
                    break;
                }
              goto done;
            }
        }
    }
  /* Implementation for long delays and as fallback.  */
  Sleep (requested_delay->tv_sec * 1000 + requested_delay->tv_nsec / 1000000);

 done:
  /* Sleep is not interruptible.  So there is no remaining delay.  */
  if (remaining_delay != NULL)
    {
      remaining_delay->tv_sec = 0;
      remaining_delay->tv_nsec = 0;
    }
  return 0;
}
#endif