如何/为什么可以fork（）失败 [英] How/Why can fork() fail

问题描述

我目前就读于C.叉（）函数，我理解它做什么（我认为）。我的问题是，为什么我们在下面的程序检查吗？

I'm currently studying the fork() function in C. I understand what it does (I think). My question is why do we check it in the following program?

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
int main()
{
  int pid;
  pid=fork();

  if(pid<0)/* why is this here? */
  {
    fprintf(stderr, "Fork failed");
    exit(-1);
  }
  else if (pid == 0)
  {
    printf("Printed from the child process\n");
  }
  else
  {
    printf("Printed from the parent process\n");
    wait(pid);
  }
}

在这个程序中，我们检查PID返回为＆lt; 0，这将指示失败。为什么可以fork（）失败？

In this program we check if the PID returned is < 0, which would indicate a failure. Why can fork() fail?

推荐答案

从手册页：

 Fork() will fail and no child process will be created if:
 [EAGAIN]           The system-imposed limit on the total number of pro-
                    cesses under execution would be exceeded.  This limit
                    is configuration-dependent.

 [EAGAIN]           The system-imposed limit MAXUPRC (<sys/param.h>) on the
                    total number of processes under execution by a single
                    user would be exceeded.

 [ENOMEM]           There is insufficient swap space for the new process.

（这是从OS X的手册页，但在其它系统上的原因是相似的。）

(This is from the OS X man page, but the reasons on other systems are similar.)

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