c Alarm() 和pause() 导致永远暂停

Question

在下面的程序中，暂停被中断一次，但随后暂停再也没有返回。我已设置闹钟来中断暂停，所以我很困惑为什么暂停永远不会返回？

#include <setjmp.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>

static void sig_alrm(int);
static jmp_buf env_alrm;


int main(int arc, char **argv)
{

    int x;
    x = setjmp(env_alrm);
    printf("setjmp was created with return value: %d\n", x);

    if(signal(SIGALRM, sig_alrm) == SIG_ERR)
    {
            printf("Error settting SIGALRM\n");
            exit(1);
    }


    if((x!= 0) && (x!=1))
    {

            printf("Error setting setjmp\n");
            exit(1);
    }

    printf("Line next to setjmp\n");
    x = alarm(2);
    printf("Alarm set for 2 seconds, remaning secs from previous alarm: %d\n");
    pause();
    printf("Line next to pause()\n");
    alarm(0);
    return 0;
}

static void sig_alrm(int signo)
{
    longjmp(env_alrm, 1);
}

这是输出，最后一行显示应用程序暂停的位置

setjmp was created with return value: 0
Line next to setjmp
Alarm set for 2 seconds, remaining secs from previous alarm: 0
setjmp was created with return value: 1
Line next to setjmp
Alarm set for 2 seconds, remaining secs from previous alarm: 0

Answer 1

使用 sigsetjmp() 和 siglongjmp() 来保存和恢复信号掩码(Linux 默认情况下不保存信号掩码)，以清除任何待处理的信号，来自男人setjmp() :

POSIX does not specify whether setjmp() will save the signal mask. In System V it will not.By default, Linux/glibc follows the System V behavior. If you want to portably save and restore signal masks, use sigsetjmp() and siglongjmp().

注意:我不确定您想要完成什么，但您的代码看起来应该在无限循环中运行，调用 longjmp() 恢复执行，就好像它刚刚执行一样从 setjmp() 返回并永远持续下去。