c++ - 如何忽略前 50 秒的信号？

Question

void signal_handler(int signo)
{
    struct sigaction act;

    if ((sigaction(signo, NULL, &act) == -1) || (act.sa_handler != SIG_IGN))
    {
        alarm(50);
    }

}

int main()
{
    sigaction(SIGINT,signal_handler);
    sigaction(SIGALAM,signal_handler);
    alarm(50);

    while (1)
    {
    }
     return 0;
}

我想在前 50 秒内忽略 Ctrl + C 信号。我用警报试了一下，但它并没有忽略信号。

Answer 1

这些是您实现目标需要遵循的步骤:

• 当 main 启动时，将 SIGINT 设置为 SIG_IGN。
• 然后设置 SIGALARM 以调用一个不同的 处理程序(50 秒后)。
• 在该处理程序中，更改 SIGINT 使其现在指向实际的处理程序。

这应该在前五十秒左右忽略 SIGINT 中断，然后再对它们采取行动。

---

这是一个完整的程序，展示了这一点。它基本上执行上面详述的步骤，但对测试程序稍作修改:

• 开始忽略 INT。
• 将 ALRM 设置为在十秒后激活。
• 开始每秒生成 INT 信号，持续二十秒。
• 当警报激活时，停止忽略 INT。

程序是:

#include <stdio.h>
#include <time.h>
#include <unistd.h>
#include <signal.h>

static time_t base, now; // Used for tracking time.

// Signal handlers.

void int_handler(int unused) {
    // Just log the event.

    printf("  - Handling INT at t=%ld\n", now - base);
}

void alarm_handler(int unused) {
    // Change SIGINT handler from ignore to actual.

    struct sigaction actn;
    actn.sa_flags = 0;
    actn.sa_handler = int_handler;
    sigaction(SIGINT, &actn, NULL);
}

int main(void)
{
    base = time(0);

    struct sigaction actn;

    // Initially ignore INT.

    actn.sa_flags = 0;
    actn.sa_handler = SIG_IGN;
    sigaction(SIGINT, &actn, NULL);

    // Set ALRM so that it enables INT handling, then start timer.

    actn.sa_flags = 0;
    actn.sa_handler = alarm_handler;
    sigaction(SIGALRM, &actn, NULL);
    alarm(10);

    // Just loop, generating one INT per second.

    for (int i = 0; i < 20; ++i)
    {
        now = time(0);
        printf("Generating INT at t=%ld\n", now - base);
        raise(SIGINT);
        sleep(1);
    }

    return 0;
}

这是我盒子上的输出，所以你可以看到它的运行情况，前十秒忽略 INT 信号，然后对它们采取行动:

Generating INT at t=0
Generating INT at t=1
Generating INT at t=2
Generating INT at t=3
Generating INT at t=4
Generating INT at t=5
Generating INT at t=6
Generating INT at t=7
Generating INT at t=8
Generating INT at t=9
Generating INT at t=10
  - Handling INT at t=10
Generating INT at t=11
  - Handling INT at t=11
Generating INT at t=12
  - Handling INT at t=12
Generating INT at t=13
  - Handling INT at t=13
Generating INT at t=14
  - Handling INT at t=14
Generating INT at t=15
  - Handling INT at t=15
Generating INT at t=16
  - Handling INT at t=16
Generating INT at t=17
  - Handling INT at t=17
Generating INT at t=18
  - Handling INT at t=18
Generating INT at t=19
  - Handling INT at t=19