检查子进程的状态

Question

您好，我对 C 编程有点陌生。我有以下代码，基本上程序需要检查子进程的状态，父进程等待子进程终止，然后打印“子进程已终止”。但我尝试了 WNOHANG，但不知何故我的第二次检查不起作用/或者我无法停止子进程。有什么想法吗？提前致谢。

代码:

#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>

int main()
{
    int pid;
    int ppid;
    int status;
    pid=vfork();
    pid_t return_pid = waitpid(pid, &status, WNOHANG);

    if (pid<0) {
        printf("\n Error ");
        exit(1);
    } else if (pid==0) {
        printf("\n Hello I am the child process ");
        printf("\n My pid is %d %d ",return_pid, getpid());
        exit(0);
    } else if (return_pid == pid) {
            printf("child is finished %d %d", return_pid, pid);
            exit(0);
    } else {
        printf("\n Hello I am the parent process %d %d", return_pid, pid);
        printf("\n My actual pid is %d %d \n ",return_pid, getpid());
        exit(1);
    }
}

Answer 1

我想知道您的 waitpid 是否在错误的位置。检查 man 2 wait 并阅读 pid 的参数代表什么

The pid parameter specifies the set of child processes for which to wait. If pid is -1, the call waits for any child process. If pid is 0, the call waits for any child process in the process group of the caller. If pid is greater than zero, the call waits for the process with process id pid. If pid is less than -1, the call waits for any process whose process group id equals the absolute value of pid.

对我来说，粗体文本表示 child 可能正在等待自己？ vfork 的值将为 child 返回 0。

此外，WNOHANG 选项将导致 waitpid 在子进程未退出时立即返回，这意味着父进程不会等待子进程完成。如果子进程已经完成，那么它将返回子进程的 pid。