使用fork（）后，父进程中的无限循环不会更新屏幕

Question

I need to write UNIX appplication that creates 2 processes using fork(), both of these processes prints current time in different positions on the screen. Parent process must stop its work after the child process is over. I've written this code:

#include <ncurses.h>
#include <unistd.h>
#include <time.h>
#include <wait.h>
#include <sys/types.h>

struct Point2
{
    int X;
    int Y;
};

int kbhit()
{
    //getch() implementation
}

void printTime(const struct Point2 pt, const char* st)
{
    char buf[255];
    time_t rawtime;
    struct tm * timeinfo;

    time (&rawtime);
    timeinfo = localtime(&rawtime);
    sprintf(buf, "%s: %02d:%02d:%02d", st, timeinfo->tm_hour,
            timeinfo->tm_min, timeinfo->tm_sec);
    mvaddstr(pt.Y, pt.X, buf);
    refresh();
}

void childp(pid_t pid, const struct Point2 pt)
{
    while(kbhit() != 27)
    {
        printTime(pt, "CHLD");
        usleep(1000);
    }
}

void parentp(pid_t pid, const struct Point2 pt)
{
    struct Point2 newp = {pt.X, pt.Y + 1};
    while(1)
    {
        int stat;
        waitpid(pid, &stat, WNOHANG);
        if(WIFEXITED(stat) != 0)
            break;

        printTime(newp, "PARN");
            usleep(1000);
    }
}

int main(int argc, char* argv[])
{
    if(argc != 3)
    {
        printf("unable to load XY position for clock.\n");
        return 1;
    }

    initscr();
    refresh(); // <-- this refresh

    struct Point2 opt;
    opt.X = atoi(argv[1]);
    opt.Y = atoi(argv[2]);

    pid_t pid;
    pid = fork();

    switch(pid)
    {
        case -1:
            printw("Error");
            _exit(0);
        case 0:
            childp(pid, opt);
            break;
        default:
        parentp(pid, opt);
            break;

    }
    endwin();
    return 0;
}

Once the program is started, it outputs once "CHLD" and "PARN" time, and then correctly updates "CHLD" time from the child proccess, but the output from the parent process does not change. Moreover, if I comment the refresh() call in main() "PARN" time string does not show up at all. So my question is: why the parent process does not updates the screen?

upd. I have deleted almost all code in parent function's cycle, now it looks like:

void parentp(pid_t pid, const struct Point2 pt)
{
    struct Point2 newp = {pt.X, pt.Y + 1};
    while(1)
    {
        printTime(newp, "PARN");
    }
}

but it still not working

Answer 1

waitpid(pid, &stat, WNOHANG); worked correctly. I don't know why, but the problem was in mvaddstr(); I changed it to printw() and voila, it worked! Maybe that's happening because mvaddstr(); does not updates the whole screen. Another way is to draw PARN and CHLD time before calling fork(), but I think this is neither simple nor elegant solution. Used printw().