timing_a.c

/*
 * timing_a.c
 *
 * Timing the process with SIGALRM and itmer.
 *
 * 2016-12-11 Frank Jeschke <frank@fjes.de>
 */

#if __STDC_VERSION__ >= 199901L
#define  _XOPEN_SOURCE    600
#else
#define  _XOPEN_SOURCE    700
#endif /* __STDC_VERSION__ */

#include "commons.h"

#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <sys/time.h>
#include <sys/types.h>
#include <time.h>

static unsigned int g_sig_alarm = 0;
static int          g_running;

static int setup_timer(struct itimerval *tv)
{
	tv->it_interval.tv_sec  = 0;
	tv->it_interval.tv_usec = 1000;
	tv->it_value.tv_sec     = 0;
	tv->it_value.tv_usec    = 1000;

	if (setitimer(ITIMER_REAL, tv, NULL)) {
		fprintf(stderr, "Error setup itimer\n");
		return -1;
	}

	return 0;
}

void signal_handler(int signum)
{
	switch (signum) {
	case SIGALRM:
		g_sig_alarm++;
		break;
	case SIGINT:
		g_running = 0;
		break;
	}
}

static int setup_sig_handler(struct sigaction *sa)
{
	sa->sa_handler = signal_handler;
	sigemptyset(&(sa->sa_mask));
	sa->sa_flags = 0;

	if (sigaction(SIGALRM, sa, 0)) {
		fprintf(stderr, "Error setup signal handler\n");
		return -1;
	}

	if (sigaction(SIGINT, sa, 0)) {
		fprintf(stderr, "Error setup signal handler\n");
		return -1;
	}

	return 0;
}

int main(int argc, char *argv[])
{
	(void)argc;
	(void)argv;

	struct sigaction sa;
	struct itimerval tv;

	if (setup_sig_handler(&sa))
		return -1;

	if (setup_timer(&tv))
		return -1;

	g_running = 1;
	clock_t start = clock();

	unsigned int user_alarm = 0;
	struct timespec previous;
	struct timespec current;
	struct timespec difference;

	double mean = 0;  /* mean value in nanoseconds (ns) */
	size_t mean_count = 0;
	double max = 0, min = 1000000000;

	const size_t MaxDifference = 1500000;
	size_t values_miss = 0;

	clock_gettime(CLOCK_MONOTONIC, &previous);

	while (g_running) {
		pause();

		while (g_sig_alarm != user_alarm) {
			user_alarm++;

			clock_gettime(CLOCK_MONOTONIC, &current);
			timespec_diff(&previous, &current, &difference);

			double cur = (double)difference.tv_nsec;
			mean = calc_mean(mean, cur, mean_count++);

			max = (cur > max) ?  cur : max;
			min = (cur < min) ?  cur : min;

			if (difference.tv_nsec > MaxDifference) {
//				printf("%u: %u\n", user_alarm, difference.tv_nsec / 1000);
				values_miss++;
			}

			previous.tv_sec = current.tv_sec;
			previous.tv_nsec = current.tv_nsec;
		}
	}

	clock_t end = clock();
	double runtime = (double)(end - start) / CLOCKS_PER_SEC;

	printf("Summary:\n");
	printf("Processortime: %f s\n", runtime);
	printf("mean: %f ns; min: %f ns; max: %f ns\n", mean, min, max);
	printf(" on %u iterations with %u values larger %d ns\n", mean_count, values_miss, MaxDifference);

	return 0;
}