setitimer 질문이요

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <time.h>
#include <string.h>
#include <signal.h>
 
#define TRUE 1
#define FALSE 0
 
#define PRINT_CTIME 0
 
void ptimer_handler(int signal)
{
	time_t now;
	if(signal == SIGPROF)
	{
#if PRINT_CTIME
		now = time(NULL);
		printf("get sig prof alarm:%s\n",ctime(&now));
#else
		printf("get sig prof alarm\n");
#endif
	}
}
 
void vtimer_handler(int signal)
{
	time_t now;
	if(signal == SIGVTALRM)
	{
#if PRINT_CTIME
		now = time(NULL);
		printf("get sig vt alarm:%s\n",ctime(&now));
#else
		printf("get sig vt alarm\n");
#endif
	}
 
}
 
void timer_handler(int signal)
{	
	time_t now;
	if(signal == SIGALRM)
	{
#if PRINT_CTIME
		now = time(NULL);
		printf("get sig alarm:%s\n",ctime(&now));
#else
		printf("get sig alarm\n");
#endif
	}
}
 
int risoo_prof_alarm(struct timeval *data)
{
	struct itimerval timer,old;
 
	memcpy(&timer.it_value,data,sizeof(struct timeval));
	timer.it_interval.tv_sec = 0;
	timer.it_interval.tv_usec = 0;
 
	if(setitimer(ITIMER_PROF,&timer,&old) < 0)
	{
		perror("setitimer() ");
		return FALSE;
	}
	return TRUE;
}
 
int risoo_vt_alarm(struct timeval *data)
{
	struct itimerval timer,old;
 
	memcpy(&timer.it_value,data,sizeof(struct timeval));
	timer.it_interval.tv_sec = 0;
	timer.it_interval.tv_usec = 0;
 
	if(setitimer(ITIMER_VIRTUAL,&timer,&old) < 0)
	{
		perror("setitimer() ");
		return FALSE;
	}
	return TRUE;
}
 
int risoo_real_alarm(struct timeval *data)
{
	struct itimerval timer,old;
 
	memcpy(&timer.it_value,data,sizeof(struct timeval));
	timer.it_interval.tv_sec = 0;
	timer.it_interval.tv_usec = 0;
 
	if(setitimer(ITIMER_REAL,&timer,&old) < 0)
	{
		perror("setitimer() ");
		return FALSE;
	}
	return TRUE;
}
 
int main(void)
{
	struct timeval timer;
 
	signal(SIGVTALRM,vtimer_handler);
	signal(SIGPROF,ptimer_handler);
	signal(SIGALRM,timer_handler);
 
	timer.tv_sec = 0;
	timer.tv_usec = 500000;
	if(!risoo_vt_alarm(&timer))
	{
		printf("set vt alarm fialed\n");
		return 0;
	}
	printf("set vt alarm ok\n");
 
	if(!risoo_prof_alarm(&timer))
	{
		printf("set prof alarm fialed\n");
		return 0;
	}
	printf("set prof alarm ok\n");
 
 
	if(!risoo_real_alarm(&timer))
	{
		printf("set real alarm fialed\n");
		return 0;
	}
	printf("set real alarm ok\n");
 
	while(1);
	return 0;
}