c - 如何一次又一次地生成相同的信号(SIGALRM)？

Question

我们正在尝试使用 sigaction 和 setitimer 从我们的三个函数中的 while(1) 循环中获取控制权，我们现在面临的问题是仅生成一次 SIGALRM，而下一次它不会生成，即我们能够从 fun1() 的 while(1) 控制，但不能从 fun2() 的 while(1) 控制。您能否提出解决此问题的方法。请在下面找到代码。

#define INTERVAL 500
void fun1();
void fun2();
void fun3();
void timer_handler(int );
struct itimerval it_val;
int count=0;
void timer_handler (int signum)
{

    L1:
        printf(“\nScheduler Called .. Calling Fun1″);

        if(count==0){
            count++;
            fun1();
        }
        printf(“\nScheduler Called .. Calling Fun2″);
        if(count==1){
            count++;
            fun2();
         }
     printf(“\nScheduler Called .. Calling Fun3″);
         if(count==2){
             count++;
             fun3();
         }
         count=0;
     goto L1;
}

void fun1()
{

    struct sigaction sa;

    /* Install timer_handler as the signal handler for SIGVTALRM. */
    memset (&sa, 0, sizeof (sa));
    sa.sa_handler = &timer_handler;

    /* Configure the timer to expire  */
    it_val.it_value.tv_sec = INTERVAL/1000;
    it_val.it_value.tv_usec = (INTERVAL*1000) % 1000000;

    it_val.it_interval.tv_sec = INTERVAL/1000;;
    it_val.it_interval.tv_usec=(INTERVAL*1000) % 1000000;
    /* Start a timer. It counts down whenever this process is*/

    sigaction (SIGALRM, &sa, NULL);
    setitimer (ITIMER_REAL, &it_val, NULL);
    while (1){
        printf(“\nfun1″);
    }

}

 void fun2()
{

    struct sigaction sa;

    /* Install timer_handler as the signal handler for SIGVTALRM. */
    memset (&sa, 0, sizeof (sa));
    sa.sa_handler = &timer_handler;

    /* Configure the timer to expire  */
    it_val.it_value.tv_sec = INTERVAL/1000;
    it_val.it_value.tv_usec = (INTERVAL*1000) % 1000000;

    it_val.it_interval.tv_sec = INTERVAL/1000;;
    it_val.it_interval.tv_usec=(INTERVAL*1000) % 1000000;
    /* Start a timer. It counts down whenever this process is*/

    sigaction (SIGALRM, &sa, NULL);
    setitimer (ITIMER_REAL, &it_val, NULL);
    while (1){
        printf(“\nfun2″);
    }

}


 void fun3()
{

    struct sigaction sa;

    /* Install timer_handler as the signal handler for SIGVTALRM. */
    memset (&sa, 0, sizeof (sa));
    sa.sa_handler = &timer_handler;

    /* Configure the timer to expire  */
    it_val.it_value.tv_sec = INTERVAL/1000;
    it_val.it_value.tv_usec = (INTERVAL*1000) % 1000000;

    it_val.it_interval.tv_sec = INTERVAL/1000;;
    it_val.it_interval.tv_usec=(INTERVAL*1000) % 1000000;
    /* Start a timer. It counts down whenever this process is*/

    sigaction (SIGALRM, &sa, NULL);
    setitimer (ITIMER_REAL, &it_val, NULL);
    while (1){
        printf(“\nfun3″);
    }

}
int main(){
    timer_handler(1);
    return 0;
}

Answer 1

当传递信号时，它会自动屏蔽，直到操作函数返回。

一般来说，你希望你的信号 Action 函数做到绝对最小。你所写的实际上是一个递归 Action 函数，其中包含你的大部分程序。即使它确实有效，你也会一直吃到吃完为止!

---

章节和诗句:来自 sigaction() for POSIX:

When a signal is caught by a signal-catching function installed by sigaction(), a new signal mask is calculated and installed for the duration of the signal-catching function (or until a call to either sigprocmask() or sigsuspend() is made). This mask is formed by taking the union of the current signal mask and the value of the sa_mask for the signal being delivered, and unless SA_NODEFER or SA_RESETHAND is set, then including the signal being delivered. If and when the user's signal handler returns normally, the original signal mask is restored.