#include <ctime>
#include <cstdio>
#include <sched.h>      // sched_setscheduler

#define NS_PER_SECOND 1000000000
#define PERIOD 2000000 // 2 ms

static void set_SCHED_RR()
{
  struct sched_param param = { 0 };
  param.sched_priority = 80;
  if (sched_setscheduler(0, SCHED_RR, &param) != 0) perror("SCHED_RR");
}

int main(void)
{
  set_SCHED_RR();

  struct timespec deadline, curr_spec;
  if (clock_gettime(CLOCK_MONOTONIC, &deadline) < 0) perror("clock_gettime");
  curr_spec = deadline;

  for (int i=0; i < 1000; ++i)
  {
    printf("CURRSPEC=%ld.%09ld\n", curr_spec.tv_sec, curr_spec.tv_nsec);
    printf("DEADLINE=%ld.%09ld\n", deadline.tv_sec, deadline.tv_nsec);
    puts("+++++");
    if ((deadline.tv_nsec += PERIOD) >= NS_PER_SECOND)
    {
      deadline.tv_nsec -= NS_PER_SECOND; ++deadline.tv_sec;
    }
    if (clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &deadline, NULL) < 0)
    {
      perror("clock_nanosleep");
    }
    clock_gettime(CLOCK_MONOTONIC, &curr_spec);
  }

  return 0;
}