fork()系统以哪种方式调用制作子进程? [英] In what manner, fork() system call making child process?

问题描述

这是我的fork()系统调用代码，

Here is my code for fork() system call,

#include<stdio.h>
#include<stdlib.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<unistd.h>
#include<errno.h>
int main(int argc, char *argv[])
{
 pid_t pid;
 pid=fork();
 printf("1st Fork\n");
 printf("Process ID : %d, Parent Process ID : %d\n",getpid(),getppid());
 pid=fork();
 printf("2nd Fork\n");
 printf("Process ID : %d, Parent Process ID : %d\n",getpid(),getppid());
 pid=fork();
 printf("3rd Fork\n");
 printf("Process ID : %d, Parent Process ID : %d\n",getpid(),getppid());
 return 0;
}

运行代码时，我得到的输出类似

While running the code, i am getting output like

1st Fork
Process ID : 3393, Parent Process ID : 3392
2nd Fork
Process ID : 3394, Parent Process ID : 3393
3rd Fork
Process ID : 3395, Parent Process ID : 3394
3rd Fork
Process ID : 3394, Parent Process ID : 3393
2nd Fork
Process ID : 3393, Parent Process ID : 3392
3rd Fork
Process ID : 3397, Parent Process ID : 3393
3rd Fork
Process ID : 3393, Parent Process ID : 3392
1st Fork
Process ID : 3392, Parent Process ID : 3440
2nd Fork
Process ID : 3398, Parent Process ID : 3392
3rd Fork
Process ID : 3400, Parent Process ID : 3398
3rd Fork
Process ID : 3398, Parent Process ID : 3392
2nd Fork
Process ID : 3392, Parent Process ID : 3440
3rd Fork
Process ID : 3401, Parent Process ID : 3392
3rd Fork
Process ID : 3392, Parent Process ID : 3440

为什么这个fork()系统调用进行8处理，以及如何进行?

Why this fork() system call making 8 process and how?

我也正在执行14个printf()语句执行.为什么?

Also i am getting 14 printf() statement executions. Why?

推荐答案

每次调用fork时，它将返回两次.一次进入父级，一次进入新流程.然后继续进行操作，它们又重新分叉.

Each time you call fork it returns twice. Once in the parent, once in a new process. Then as they go on, they both fork again.

您很有可能没想到孩子再次分叉.对于每个fork，您通常具有:

It's most likely you didn't expect the children to fork again. With each fork you usually have:

switch (fork()) {
case -1:
    /* ERROR. */
    break;
case 0:
    /* Child process. */
    break;
default:
    /* Parent. */
    break;
}

在您的代码中是这样的:

In your code it's like this:

• 您有一个流程，然后它分叉
• 您现在有两个流程，并且两个都是 fork
• 您现在有4个流程，并且所有流程都分叉
• 您现在有8个流程，您正在就SO提出问题

• You have one process, then it forks
• You now have two processes and both fork
• You now have 4 processes and all of them fork
• You now have 8 processes and you're asking questions on SO

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