在fork（）进程中没有针对父进程的操作时会发生什么？

Question

I have the following example code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>

int main (){
    printf("hello world (pid:%d)\n", (int)getpid());
    int rc = fork();

    if(rc < 0){ //fork failed; exit
        fprintf(stderr, "fork failed\n");
        exit(1);

    } else if (rc == 0) { //child new process
        printf("hello, i am child (pid:%d)\n", (int)getpid());
        char *myargs[3];
        myargs[0] = strdup("wc"); //program: "wc" (word count)
        myargs[1] = strdup("p3.c"); //argument: file to count
        myargs[2] = NULL; //marks end of array
        execvp(myargs[0],myargs); //runs word count
        printf("this shouldn't print out");

    } else {//parent process
        // int wc = wait(NULL);
        // printf("hello, i am parent of %d (wc: %d) (pid: %d)\n", rc, wc, (int) getpid());
    }

    return 0;
}

So I have commented out the else statement (the arguments or the actions of the parent process. I was wondering what would happen, or would the outputs remain the same if the parent process does not have to wait for the child process? If so, why?

I was thinking, since the child process is its own independent process from the parent, the output would remain the same but is that the only reason why?

Some pointers would be nice, thanks!

Answer 1

This can be understood in two contexts.

1. Execution time of parent < execution time of child
2. Execution time of parent > execution time of child

In case 1, the parent process exits before the child and hence, the init process (pid 1) becomes the parent of the child; child process continues execution.

Normally, a child process (resources of child process) cannot be released until the parent process completes. In case 2, the child process is released only after the completion of parent process; till that time the child process becomes a zombie (defunct in ps -al command).

In this particular context, when the parent process has nothing to execute, the execution time of child > execution time of parent , which is nothing but execution time of parent < execution time of child . This is case 1. Hence, the parent process exits and init process becomes the parent of the child process.