vfork导致死循环 求解

Fatihyang

1. #include <unistd.h>
   
2. #include <stdio.h>
   
3. 
   
4. int main(void)
   
5. {
   
6.         if (vfork() == 0) {
   
7.                 printf("This is the child process!\n");
   
8.                 sleep(1);
   
9.         } else {
   
10.                 printf("This is the parent process!\n");
    
11.         }
    
12.         return 0;
    
13. }
    

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未加入sleep(1) :
This is the child process!
This is the parent process!
加入sleep(1)后 成为死循环:
This is the child process!
This is the parent process!
This is the child process!
This is the parent process!
This is the child process!
This is the parent process!
This is the child process!
This is the parent process!
This is the child process!
求解!!!!!

0506010237

你 把 return  改为 exit 还会出现不

Fatihyang

回复 2# 0506010237


    不会 退出了  改回return之后 我获取pid 尝试理解其中的过程 结果如下
This is the child process! 1965
This is the parent process! 1964
This is the child process! 1966
This is the parent process! 1964
This is the child process! 1967
This is the parent process! 1964
This is the child process! 1968
This is the parent process! 1964

父进程不断在循环  能解不?

Fatihyang

回复 2# 0506010237


    不会了  改回return之后  获取pid 尝试理解过程 结果如下
This is the child process! 1968
This is the parent process! 1964
This is the child process! 1969
This is the parent process! 1964
This is the child process! 1970
This is the parent process! 1964
This is the child process! 1971
This is the parent process! 1964
This is the child process! 1972
This is the parent process! 1964
This is the child process! 1973
This is the parent process! 1964
This is the child process! 1974

父进程不断循环  能解不?

zcheung

将

1. sleep(1);

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换成

1. exit(0);

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还有就是，你不判断出错的情况么？ 你真牛

雨过白鹭洲

The vfork() function shall be equivalent to fork(), 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 successfully calling _exit() or one of the exec family of functions.

调用vfork()之后，子进程要么_exit()，要么调用某个exec()，否则都是未定义行为！

另外：
This function is marked obsolescent.
别再纠结啦，放弃这个函数吧

729926317

虽然没看懂，但是记得APUE上不推荐这个函数，好像说那个什么unix标准也放弃了这个接口

zylthinking

This function is marked obsolescent. 有什么替代函数吗， 老实说， 在疯狂fork 然后 execl 的应用中， 这玩艺效率就算不是最高， 也肯定不是最低的。

至于为什么会循环， 很显然是vfork 修改了父进程的栈导致的。

Fatihyang

回复 5# zcheung


    这个仅仅用来测试vfork的导致的无限循环  目的非常明确  错误有没有 影响不大

Fatihyang

回复 7# 729926317


    fork 子进程   父子一起运行
  vfork 子进程   父等子之后再运行
当然  父价格wait 就等于 vfork了  .... 好吧  放弃vfork