linux中的TIMER使用入门

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

#define MAXSEC 1
#define MAXUSEC 0

void real_handle()
{
printf("this is real_handl ");
}

long unsigned int fibonacci(unsigned int n)

{

if(n==0)

return 0;

else if(n==1 || n==2)

return 1;

else

return (fibonacci(n-1) + fibonacci(n-2));

}

static struct itimerval p_realt;

main()
{
p_realt.it_interval.tv_sec = MAXSEC;
p_realt.it_interval.tv_usec = MAXUSEC;
p_realt.it_value.tv_sec = MAXSEC;
p_realt.it_value.tv_usec = MAXUSEC;

signal(SIGALRM,real_handle);

if(setitimer(ITIMER_REAL,&p_realt,(struct itimerval *)0) == -1)
perror("setitimer error! ");
fibonacci(40);
}

/////////////////////////////////////////////////////////////////////////
THE OUTPUT IS:
[root@localhost Lab03]# ./a.out
this is real_handl
this is real_handl
this is real_handl

EXPLAINATION:
the value of p_realt is given to ITIMER_REAL,a timer.When this timer expired,signal SIGALRM will be send out and function real_handle() will be invoked.
if it_interval is set too big,like 100 sec,real_handl() won't be invoked.because SIGALRM is send out every 100 seconds.
if it_interval is set too small,like 1000 usec,real_handle() will be invoked too frequently!