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

#define MAX_INTERVAL 5000
#define MIN_INTERVAL 500

#define SLEEP_TIME 0
#define IO_SIZE 1024

#define MTOUS(x)    ((x)*1000)
#define msleep(x)   usleep(MTOUS(x));

volatile enum {CPU_STATE, IO_STATE, SLEEP_STATE} state;

void sig_handler(int signum)
{
	state++;
	if(state > 2)
		state = 0;
}

int do_cpuhog(int msec)
{
	unsigned long long v1,v2,v3;
	int i;

	v1 = 42;
	v2 = v3 = -1;
	while(state == CPU_STATE)
	{
		i++;
		v1 += i;
		v2 = v1*i + v3;
		v3 = v1 ^ v2;
	}
	if (msec)
		msleep(msec);
	return 0;
}

int do_syshog(int size, int msec)
{
	static void *buffer = NULL;
	int fd;

	if (!buffer)
		buffer = realloc(buffer, size);

	fd = open("/dev/zero", O_RDWR);
	if (fd>=0)
	{
		while(state == IO_STATE)
		{
			read(fd, buffer, size);
			write(fd, buffer, size);
		}
		close(fd);
	}
	if (msec)
		msleep(msec);
	return 0;
}

int main(int argc, char **argv)
{
	struct sigaction action;
	struct itimerval period;

	action.sa_handler = &sig_handler;
	action.sa_flags = 0;
	if(sigaction(SIGALRM, &action, NULL))
		perror("siga");

	for(;;)
	{
		int interval = random() % MAX_INTERVAL;
		if(interval < MIN_INTERVAL)
			interval = MIN_INTERVAL;
		period.it_value.tv_sec = period.it_interval.tv_sec = interval / 1000;
		period.it_value.tv_usec = period.it_interval.tv_usec = interval * 1000;
		if(setitimer(ITIMER_REAL, &period, NULL))
			perror("seti");
		switch(state)
		{
			case CPU_STATE:
				do_cpuhog(SLEEP_TIME);
				break;
			case IO_STATE:
				do_syshog(IO_SIZE, SLEEP_TIME);
				break;
			case SLEEP_STATE:
				pause();
				break;
		}
	}

	return 0;
}