linux中的TIMER使用入门-优快云博客

本文通过一个具体的C程序示例，介绍了如何使用定时器ITIMER_REAL设置周期性的信号SIGALRM，并实现信号处理函数real_handle的调用。此外，还讨论了定时器间隔设置对信号触发频率的影响。

#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!