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#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);
}
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/////////////////////////////////////////////////////////////////////////
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!
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