如何在 C 中将信号从 children 发送到另一个 children？

Question

如何向出租车发送信号表 passenger-children - children？
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？是的这是可能的，但这里的问题是如何你在 passenger-children 进程中得到 taxi-children pid？一旦你得到了那个 taxi-children 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，在此之前先阅读 wait() & 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); 
    }
}

上面的代码是如何工作的，在评论中有解释。 macro(#if 0) 部分在两个过程中的用法是将 taxi-child process 的 pid 发送到 passenger-child process。启用宏以观察输出。

希望对您有所帮助。

如何在 C 中将信号从 children 发送到另一个 children？

How to send signal from a children to another children in C?

c

fork

signals

pid