fork（）和父/子进程ID [英] fork() and parent/child process ids

问题描述

我对以下两个程序中的子进程为什么显示不同的父代id感到困惑。

I am a bit confused about why the child process in the following two programs is showing different parents ids.

 int main ( void ) {
   int pid, fpid, ppid;
   fpid = fork ();
   pid = getpid();
   ppid = getppid();
   printf ("fpid is %d\n", fpid);
   sleep(5);
   if (fpid > 0){
       printf ("\nThis is Parent. My pid %d. My parent's pid %d\n",pid,ppid);
   }
   else if (fpid ==0){
       sleep(1);
       printf ("\nThis is Child. My pid %d. My parent's pid %d\n",pid,ppid);
   }
   else
       printf ("fork failed\n");
   return (0);
}

输出：

fpid is 53560
fpid is 0

This is Parent. My pid 53559. My parent's pid 44632

MacBook-Pro:~/Desktop/$ 

This is Child. My pid 53560. My parent's pid 53559

第二程序：

Second program:

int main ( void ) {
   int pid, fpid, ppid;
   fpid = fork ();
   printf ("fpid is is %d\n", fpid);
   sleep(5);
   if (fpid > 0){
       pid = getpid();
       ppid = getppid();
       printf ("\nThis is Parent. My pid %d. My parent's pid %d\n",pid,ppid);
   }
   else if (fpid ==0){
       sleep(1);
       pid = getpid();
       ppid = getppid();
       printf ("\nThis is Child. My pid %d. My parent's pid %d\n",pid,ppid);
   }
   else
       printf ("fork failed\n");
   return (0);
}

输出：

fpid is is 53635
fpid is is 0

This is Parent. My pid 53634. My parent's pid 44632

MacBook-Pro:~/Desktop$ 

This is Child. My pid 53635. My parent's pid 1

我知道流程1是接管流程原始父级终止后，其父级会终止。我想我想知道的是：在两种情况下，子进程都不能先完成父进程，然后子进程才能处理其 printf 吗？输出不应该相同吗？

I understand that process 1 is the process that takes over as a parent once the original parent terminates. I guess what I want to know is: isn't the parent process being finished before the child process can process its printf in both cases? Shouldn't the outputs be the same?

推荐答案

由于父进程和子进程同时运行，因此执行顺序取决于运行时。其中之一可以提前完成。当父项在子项到达其 getppid（）之前完成时，子进程将由 init 采用。因此，父ID为1。

要查看孩子的实际父进程ID：

Since parent and child processes run concurrently, the order of execution depends on runtime. One of them can finish earlier. When parent finishes before child reaches its getppid(), child process would be adopted by init. Hence the parent id 1.
To see child's actual parent process id:

1. 让父级等待其子级使用 wait（）或 waitpid（）或


2. 父级终止在这是父母 printf（）之后，以一些可感知的量睡眠，例如 sleep（120）。

1. Let the parent wait for its child termination using wait() or waitpid(), or
2. Let parent sleep for some perceivable amount like sleep(120) after 'This is parent' printf().

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