sleeptest.c

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

int
timeval_subtract(struct timeval *result, struct timeval *x,
		 struct timeval *y)
{
	if (x->tv_usec < y->tv_usec) {
		int		nsec = (y->tv_usec - x->tv_usec) / 1000000 + 1;
		y->tv_usec -= 1000000 * nsec;
		y->tv_sec += nsec;
	}
	if (x->tv_usec - y->tv_usec > 1000000) {
		int		nsec = (x->tv_usec - y->tv_usec) / 1000000;
		y->tv_usec += 1000000 * nsec;
		y->tv_sec -= nsec;
	}
	result->tv_sec = x->tv_sec - y->tv_sec;
	result->tv_usec = x->tv_usec - y->tv_usec;

	return x->tv_sec < y->tv_sec;
}

int
main(int argc, char **argv)
{
	struct timeval	start;
	struct timeval	end;
	struct timeval	duration;
	struct timeval	timeout;
	uint64_t	uduration;
	uint64_t	i;
	uint64_t	maxduration = 0;

	for (i = 0; i < 5000; i++) {
		gettimeofday(&start, NULL);

		timeout.tv_sec = 0;
		timeout.tv_usec = 5000;
		select(0, NULL, NULL, NULL, &timeout);

		gettimeofday(&end, NULL);

		timeval_subtract(&duration, &end, &start);
		uduration = (uint64_t) duration.tv_usec + (uint64_t) duration.tv_sec * (uint64_t) 1000000;
		if (uduration > maxduration)
			maxduration = uduration;

	}

	printf("Maximum duration was %" PRIu64 " usecs\n", maxduration);

	exit(0);
}