可以从父进程的子进程中获取退出状态

Question

I try to get the exit code from a child of a child process in the parent process. If the process goes in the while loop to fork again i don't get the exit code. I tried some options for waitpid like WNOHANG but then the program hangs. Maybe what i wan't is not possible because it's some like a zombie child?

This is my code.

void    parrent_process(t_token *token, t_info *info)
{
    pid_t   pid;
    int     wstatus;

    pid = fork();
    if (pid == -1)
        return (print_error_msg(FORK_FAIL, NULL, NULL));
    if (pid == 0)
    {
        child_process(token);
    }
    if (info->in)
        close(info->in);
    waitpid(pid, &wstatus, 0);
    if (WIFEXITED(wstatus))
        info->exit_code = WEXITSTATUS(wstatus);
}

void    child_process(t_token *token)
{
    t_token *cmd_token;
    pid_t       pid;

    pid = 0;
    cmd_token = token;
    while (token->next && ((token->next)->type == GREAT))
    {
        pid = fork();
        if (pid == -1)
            return (print_error_msg(FORK_FAIL, NULL, NULL));
        if (pid == 0)
        {
            redirect_output(token);
            break;
        }
        token = token->next->next;
    }
    if (execve(cmd_token->path, cmd_token->args, cmd_token->envp) == -1)
    {
        print_error_msg(CMD_NOT_FOUND, "minishell", cmd_token->args[0]);
        exit(127);
    }
}

Answer 1

In most POSIX-like systems, the answer is "No — a process can only wait on its own children, those it created directly with fork() ¹ ".

However, on Linux, there is the prctl(2) system call. The option PR_SET_CHILD_SUBREAPER allows a process to wait for more distant descendants (grandchildren, great-grandchildren, …) too. However, if the direct parent of a process waits for it, the ancestral process will not get the exit status information.

¹ Or posix_spawn()