如何在C中将信号从一个孩子发送到另一个孩子？

Question

如何将乘客-儿童的信号发送给出租车-儿童？
我有以下 C 代码：

 passengerPid = fork()
 if(passengerPid) { //passenger-parents 

                taxiPid = fork();   
                if(taxiPid) { //taxi - parents      
                } else { //taxi - children  
                } 
        }       
        else { //passenger - children  
        }

Answer 1

我怎样才能将乘客-儿童的信号发送给出租车 - 儿童？ 是的可以，但这里的问题是你如何在 @ 中获得 taxi-children pid 987654322@进程？一旦你得到了那个出租车孩子的pid，为了从另一个进程向一个进程发送信号，你可以使用kill()函数。使用任何IPC 机制将一个进程的pid（任何int 数据）发送到另一个进程。

这是我的解决方案，在此之前通过 wait() 和 waitpid() 的手册页：

/**How can I send a signal form passenger-children to the taxi - children? **/
#include<stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main() {
    int passengerPid, taxiPid;
    passengerPid = fork();
    if(passengerPid) { //passenger-parents 

        taxiPid = fork();   
        if(taxiPid) { 
            //taxi - parents   

            printf("taxi parents or main parent process : pid = %d ppid = %d\n",getpid(),getppid());
            /** parents should wait until all children's got finish 
               use wait() or waitpid() to collect the children's status **/  
            int s,ret;
            while((ret = wait(&s))!=-1)//if there is no further child, wait returns 
            {
                if(ret == passengerPid) {
                    if(WIFEXITED(s)) {
                    printf("passenger children removed after sleep, status is : %d\n",WEXITSTATUS(s));
                    } else if(WIFSIGNALED(s)) {
                        printf("passenger children removed forcefully because of signal no : %d \n",WTERMSIG(s));
                    }
                } else if(ret == taxiPid) {
                    if(WIFEXITED(s)) {
                    printf("taxi children removed after sleep, status is : %d\n",WEXITSTATUS(s));
                    } else if(WIFSIGNALED(s)) {
                        printf("taxi children removed forcefully because of signal no : %d \n",WTERMSIG(s));
                    }

                }
            }
            printf("all done !! parents is also going to complete \n"); 
        } 
        else {
            //for sending pid of this process

        #if 0   
            int fd = open("data",O_WRONLY | 0664);
            if(fd == -1) {
                perror("open");
                return 0;
            }
            int w_pid = getpid();
            write(fd,&w_pid,4); 
            close(fd);
        #endif
            //taxi - children  
            printf("taxi children : pid = %d ppid = %d\n",getpid(),getppid());
            sleep(10);//random delay to observe whether this process got any signal or not ?
            exit(1);//sends it's exit status to it's parent process whether it's terminated normally or by any external signal
        } 
    }       
    else { 
        //passenger - children  
        printf("passenger children : pid = %d ppid = %d\n",getpid(),getppid());
        printf("sending signal from passenger children to taxi children :\n");
        sleep(5);   
        int pid;
    #if 0
        int fd = open("data",O_RDONLY | 0664);
        if(fd == -1) {
            perror("open");
            return 0;
        }
        read(fd,&pid,4);
        close(fd);
    #endif
        printf("pid of child received : %d \n",pid);
        kill(pid,SIGKILL);//sending signal no 2 to taxi child, bydefault action of SIGINT will be performed 
        perror("kill");
        printf("passenger children dies after sending signal & completion of delay\n");
        exit(0); 
    }
}

上述代码的工作原理在 cmets 中进行了说明。在两个过程中使用macro(#if 0) 部分是为了将taxi-child process 中的pid 发送到passenger-child process。 启用用于观察输出的宏。

希望对你有帮助。