/* Test the idea of whether a bunch of threads continuously calling
 * pthread_yield() actually raises the system load or not. */

/* Oh, yes, it certainly does. */

#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

#define __USE_GNU

void *only_yield(void *arg)
{
	for (;;)
		pthread_yield();
}

int main(int argc, char **argv)
{
	int i, threads;
	pthread_t tids[256];
	double avg[3];

	if (argc == 2)
		threads = atoi(argv[1]);
	else
		threads = 5;

	if (getloadavg(avg, 3) < 0) {
		fprintf(stderr, "Can't get load average?\n");
		exit(1);
	}
	printf("Initial load averages for %d threads are %.2lf %.2lf %.2lf\n", threads, avg[0], avg[1], avg[2]);

	for (i = 0; i < threads; i++) {
		if (pthread_create(&tids[i], NULL, only_yield, NULL)) {
			fprintf(stderr, "Failed to create thread number %d\n", i + 1);
			exit(1);
		}
	}

	for (i = 0; i < 60; i++) {
		sleep(15);
		if (getloadavg(avg, 3) < 0) {
			fprintf(stderr, "Can't get load average?\n");
			exit(1);
		}
		printf("After %.2f minute%s, for %d threads, the load averages are %.2lf %.2lf %.2lf\n", (i + 1) / 4.0, i != 3 ? "s" : "", threads, avg[0], avg[1], avg[2]);
	}
	exit(0);
}