c - vfork 永不返回

Question

为什么这个程序永远不会返回并继续创建子进程？

int main()
{
    pid_t pid;
    int foo1 = 1, foo2 = 2;
    printf("before fork()\n");

    if ((pid = vfork()) < 0 ) {
            printf("fork failed.\n");
    }else if (pid == 0) {
            foo1++;
            foo2++;
            printf("child process: pid is %d, my parent pid is  %d\n", getpid(), getppid());
    }else if (pid > 0){
            printf("parent process: pid is %d\n", getpid());
    }

    printf("%s: foo1 is %d, foo2 is %d\n",pid == 0 ? "child process" : "parent process", foo1, foo2);
    return 0;
}

输出如下:

before fork()
child process: pid is 17244, my parent pid is  15839
child process: foo1 is 2, foo2 is 3
parent process: pid is 15839
parent process: foo1 is -1079005816, foo2 is -1218256081
before fork()
child process: pid is 17245, my parent pid is  15839
child process: foo1 is 2, foo2 is 3
parent process: pid is 15839
parent process: foo1 is -1079005816, foo2 is -1218256081
before fork()
.....
.....

如果在第二个 if block 中添加一个 _exit 就可以了。我知道 vfork 与父进程共享相同的地址空间，但如果程序以崩溃而不是无限循环结束则更合理。

Answer 1

vfork 是一个非常棘手的系统调用，它的唯一用途是立即在子系统中拥有一个 execve - 对于其他类型的用途，它是危险且不可预测的。

另请注意，与 fork 不同，父级会暂停，直到子级退出或调用 execve。