2

这个程序应该使用fork()来创建进程，将子进程的PID存入一个单链表，fork失败后一次杀掉一个进程，然后释放链表中的节点，最后打印出多少个进程是在结束程序之前创建的。

目前它不做这些事情，我不知道该去哪里。它会正确编译，但是当我在必须使用的 Minix 终端中运行它时，它什么也没做。当我关闭终端时，我最终得到“关闭：不能 fork（）：资源暂时不可用”。所以出了点问题，我们将不胜感激。谢谢你。

/*
   Problem: Write a complete C-program to determine the number of
   simultaneous processes Minix can support for a single user. Be
   aware that a users' login shell is itself a process. Once this has
   been determined, any processes created will have to be terminated.
   Created processes will have to be kept track of in a singly linked list
   with node structure dynamically allocated at runtime.

   Solution: Create processes until fork() fails. Each child process will
   call pause(). The signal will be delivered by the parent process using
   kill() system call. When fork() fails, terminate the children processes
   one at a time using childs' PID and SIGKILL signal. You will have to
   keep track of children process PIDs in a singly linked list.

   Data-structure used: A singly linked list

   Accessing functions for the data structure: malloc() and free() to
   dynamically handle the node storage

   Errors handled: None.

   Limitations: None.

*/

#define _POSIX_SOURCE
#include <sys/types.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

struct lnode {
   int pid;
   struct lnode *next;
};

    /* Dynamically allocates node storage at runtime using
       malloc().
    */

struct lnode*
getnode(void)
{
   return malloc(sizeof(struct lnode));
}

/* Frees nodes dynamically allocated by getnode before
   the program is terminated.
*/

void
freenode(struct lnode *tmp)
{
   free(tmp);
}

/* Display the output of how many simultaneous processes Minix
   can support for a single user.
*/

void
printtotal(int count)
{
   fprintf(stdout, "For this user: %d\n", count);
}

int
main(int argc, char *argv[])
{
   struct lnode *curr;
   struct lnode *tmp;
   int count = 1;
   int pidholder = 1;

   tmp = NULL;

   while(pidholder > 0) {
      curr = getnode();

      pidholder = fork();

      if(pidholder < 0)
         exit(-1);
      else if(pidholder == 0)
         pause();
      else if(pidholder > 0) {
         curr->pid = pidholder;
         curr->next = tmp;
         tmp = curr;
      }
   }

   curr = tmp;

   while(curr) {
      pidholder = curr->pid;

      kill(pidholder, SIGKILL);

      tmp = curr;
      curr = curr->next;
      freenode(tmp);
   }

   printtotal(count);

   exit(0);
}
4

1 回答 1

0

在将程序单独留在晚上并在早上尝试新鲜之后，我发现了哪里出了问题。

当 fork() 在 while 循环中失败时，它会退出程序，这会导致问题，因为一旦我删除了这部分，程序就会正确执行。我相信这是因为程序的 kill 部分没有运行，而所有这些进程都在运行。此外，我意识到我忘记了包含一行代码来增加计数器以跟踪正在创建的进程数。

这是main的工作代码：

int
main(int argc, char *argv[])
{
   struct lnode *curr;
   struct lnode *tmp;
   int count = 1;
   int pidholder = 0;

   tmp = NULL;

   while(pidholder >= 0) {
      curr = getnode();

      pidholder = fork();

      if(pidholder == 0)
         pause();
      else if(pidholder > 0) {
         curr->pid = pidholder;
         curr->next = tmp;
         tmp = curr;
         count = count + 1;
      }
   }

   curr = tmp;

   while(curr) {
      pidholder = curr->pid;

      kill(pidholder, SIGKILL);

      tmp = curr;
      curr = curr->next;
      freenode(tmp);
   }

   printtotal(count);

   exit(0);
}
于 2014-09-26T13:35:17.437 回答