子进程和父进程ID [英] child and parent process id

问题描述

只是在子进程块中与父pid值混淆了.我的程序如下:

Just got confused with parent pid value in child process block. My program is given below:

 int main(int argc, char *argv[])
  {
    pid_t pid;
    pid=fork();
    if(pid==-1){
            perror("fork failure");
            exit(EXIT_FAILURE);
    }
    else if(pid==0){
            printf("pid in child=%d and parent=%d\n",getpid(),getppid()); 
    }
    else{
            printf("pid in parent=%d and childid=%d\n",getpid(),pid);
    }
    exit(EXIT_SUCCESS);
  }

输出: parent = 2642和childid = 2643中的pid

Output: pid in parent=2642 and childid=2643

pid = child = 2643 and parent = 1

pid in child=2643 and parent=1

在高级Unix编程"中，它表示子进程可以使用getppid()函数获取父进程ID.但是在这里，我得到的是"1"，它是"init"进程ID.

In "Advanced Unix programming" it says that child process can get parent process id using getppid() function. But here I am getting "1" which is "init" process id.

如何在子进程块中获取父pid值.请帮助我获取输出.

How can I get the parent pid value in the child process block.. Please help me in getting output.

我在"Linux Mint OS"中执行，但是在"WindRiver" OS中我没有遇到这个问题.该程序会根据操作系统更改行为吗?

I executed in "Linux Mint OS" but in "WindRiver" OS I am not getting this problem. Does this program change behaviour according to OS?

推荐答案

这是因为父亲可以/将在儿子之前退出.如果一个父亲存在而没有请求其孩子的返回值，则该孩子将被pid = 1的进程所拥有.在经典UNIX或GNU系统SystemV init上是什么.

That's because the father can / will exit before the son. If a father exists without having requested the return value of it's child, the child will get owned by the process with pid=1. What is on classic UNIX or GNU systems SystemV init.

解决方案是在父亲中使用waitpid():

The solution is to use waitpid() in father:

int main(int argc, char *argv[])
{
    pid_t pid;
    pid=fork();
    if(pid==-1){
        perror("fork failure");
        exit(EXIT_FAILURE);
    }
    else if(pid==0){
        printf("pid in child=%d and parent=%d\n",getpid(),getppid()); 
    }
    else{
        printf("pid in parent=%d and childid=%d\n",getpid(),pid);
    }

    int status = -1;
    waitpid(pid, &status, WEXITED);

    printf("The child exited with return code %d\n", status);
    exit(EXIT_SUCCESS);
}

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