#include 
     
      #include 
      
       static int count = 0;static struct itimerval oldtv;struct itimerval itv;void set_timer(){        itv.it_interval.tv_sec = 0;        itv.it_interval.tv_usec = 990000;  //启动后的定时器每隔990ms唤醒一次        itv.it_value.tv_sec = 0;        itv.it_value.tv_usec = 50000;   //定时器在50ms后启动        setitimer(ITIMER_REAL, &itv, &oldtv);            //ITIMER_REAL表示每次定时器唤醒时将会触发SIGALRM信号}void shut_timer(){        itv.it_value.tv_sec = 0;        //将启动参数设置为0,表示定时器不启动        itv.it_value.tv_usec = 0;        setitimer(ITIMER_REAL, &itv, &oldtv);}void signal_handler(int m){        count ++;        printf("%d\n", count);        if(count==4)     //调用4次后,关闭定时器          shut_timer();}int main(){        signal(SIGALRM, signal_handler);  //将SIGALRM信号与signal_handler函数建立关系,当信号触发时便会调用该函数.        set_timer();        while(count < 10000);        exit(0);        return 1;}