c - 从 parent 向 child 发送信号，反之亦然

Question

我正在尝试练习信号并尝试实现以下目标

1) child 和家长打印10个数字并将接力棒传递给其他人

2)父/子通过sigsuspend等待轮流

3) sigaction 只是为了捕获信号

4)kill用于发送带有各自进程ID的信号

然而，输出受到竞争条件的影响，我发现一旦父级从子级控件获得信号，就永远不会将其返回给子级

我还期望 sigaction 也能捕获信号，但这似乎没有发生。

你能指出我做错了什么吗？

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

static volatile int count = 0;

void sighandler(int sig)
{
    if (sig == SIGUSR1)
    {
        printf(" \n child sends parent signal - \n ");
    }

    if (sig == SIGUSR2)
    {
        printf("\n parent sends child signal - \n ");
    }
}

int main(void)
{
    //pid_t pid, cid;
    sigset_t block_csignal, block_psignal, empty_signal;
    struct sigaction ccatch, pcatch;

    setbuf(stdout, NULL);

    /* Creating signal set for suspending process till
       it receives below signal */
    sigfillset(&block_csignal);
    sigdelset(&block_csignal, SIGUSR2);

    sigfillset(&block_psignal);
    sigdelset(&block_psignal, SIGUSR1);

    /* Creating signal set for catching the signal
       and changing signal disposition */
    sigemptyset(&ccatch.sa_mask);   /* ccatch for catching signal from parent */
    ccatch.sa_flags = 0;
    ccatch.sa_handler = sighandler;

    sigemptyset(&pcatch.sa_mask);  /*  pcatch for catching signal from child */
    pcatch.sa_flags = 0;
    pcatch.sa_handler = sighandler;

    sigaction(SIGUSR2, &ccatch, NULL); /* catch signal from parent for child */
    sigaction(SIGUSR1, &pcatch, NULL); /* catch signal from child for parent */

    switch(fork())
    {
        case -1:
            printf("error in child creation \n ");
            exit(-1);
        case 0:
            printf(" \n Control in hand of child \n ");

            while(count < 50)
            {
                int temp = 0;
                printf(" \n c count ---  \n ");
                while (temp < 10)
                {
                    printf(" %d ", count);
                    temp++;
                    count++;
                }
                printf(" \n parent id in child process --- %d \n ", getppid());
                kill(getppid(), SIGUSR1);  /* send signal to parent */
                sigsuspend(&block_csignal); /* wait till you get signal from parent */

            }
            exit(1);
        default:
            printf("\n Control in hand of parent \n ");
            sigsuspend(&block_psignal); /*wait till you get signal from child*/
            printf("\n Control back in hand of parent \n ");
            while (count < 50)
            {
                int temp = 0;
                printf(" \n p count ---  \n ");
                while (temp < 10)
                {
                    printf(" %d ", count);
                    temp++;
                    count++;
                }
                kill(getpid(), SIGUSR2); /* send signal to child */
            }
            break;
    }

    printf("\n ");
    return EXIT_SUCCESS;
}

Answer 1

为了从父进程向子进程发送信号，您首先需要存储子进程的 pid(它是成功 fork 的返回值)。在父代码中，您使用 getpid() 来返回当前正在运行的进程的 ID，即父进程。

尝试如下:

  int cid = fork();
  if(cid == 0) //child
  if(cid > 0){ // parent
    //... 
    kill(cid,... 
}