test-usleep.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>

// from <sys/time.h>
// used timersub macro, changed timeval to timespec
// kept the order of operands the same, that is a - b = result
# define timespec_diff_macro(a, b, result)                  \
  do {                                                \
    (result)->tv_sec = (a)->tv_sec - (b)->tv_sec;     \
    (result)->tv_nsec = (a)->tv_nsec - (b)->tv_nsec;  \
    if ((result)->tv_nsec < 0) {                      \
      --(result)->tv_sec;                             \
      (result)->tv_nsec += 1000000000;                \
    }                                                 \
  } while (0)

int main(int argc, char **argv)
{
  struct timespec start, stop, delta;
  struct timespec duration, remaining;
  struct timezone tz;
  int continuations = 0;

  duration.tv_sec = 0;
  duration.tv_nsec = 1000;

  clock_gettime(CLOCK_MONOTONIC, &start);
  for (int x = 0; x < 1000; x++) {
    while ( nanosleep(&duration, &remaining) == -1) {
      duration.tv_sec = remaining.tv_sec;
      duration.tv_nsec = remaining.tv_nsec;
      continuations++;
    }
  }

  clock_gettime(CLOCK_MONOTONIC, &stop);

  timespec_diff_macro(&stop, &start, &delta);
  printf("%ld.%09ld\n", start.tv_sec, start.tv_nsec);
  printf("%ld.%09ld\n", stop.tv_sec, stop.tv_nsec);
  printf("%ld.%09ld\n", delta.tv_sec, delta.tv_nsec);
  printf("%d\n", continuations);
}