c - 彼得森临界区问题的解决方案

Question

#include<stdio.h>
#include<sys/types.h>
#include<stdlib.h>
int turn;
int flag[2];
int main(void)
{
        int pid,parent=1;
        printf("before vfork\n");
        if((pid=vfork())<0)
        {
                perror("vfork error\n");
                return 1;

        }
        while(1)
        {
                if(pid==0)
                {
                     while(parent==1)
                     {
                      sleep(2);
                     }
                     parent=0;
                     flag[0]=1;
                     turn=1;
                     while(flag[1]&&turn==1);
                     printf("This is critical section:parent process\n");
                     flag[0]=0;
                }
                else
                {
                        parent=2;
                        printf("This is parent");
                        flag[1]=1;
                        turn=0;
                        while(flag[0]&&turn==0);
                        printf("This is critical section:child process %d \n",pid);
                        flag[1]=0;
                }
        }

}

这是我的代码。谁能告诉我为什么控制权没有进入我的父进程。

Answer 1

man 2 vfork 说:

   (From  POSIX.1)  The  vfork()  function has the same effect as fork(2),
   except that the behavior is undefined if the process created by vfork()
   either  modifies  any  data other than a variable of type pid_t used to
   store the return value from vfork(), or returns from  the  function  in
   which  vfork()  was called, or calls any other function before success-
   fully calling _exit(2) or one of the exec(3) family of functions.

因为您正在子进程中修改数据，所以 vfork() 行为未定义，因此无论它做什么都是正确的(这里的“正确”是指“符合规范”)。