nsa_select/nsa_socketpair is not working correctly

[ThuyThTruong]

neat nsa_poll (called by nsa_select) on this nsa_socketpair not able to detect writable/readable events on nsa_socketpair.

main.c
int main(int argc,char *argv[])
{


    int fd[2];
    pid_t pid;
    int cnt = 0;
    fd_set r_fds, e_fds, w_fds;

            FD_ZERO(&r_fds);
            FD_ZERO(&e_fds);
            FD_ZERO(&w_fds);

            struct timeval tv;
            tv.tv_sec = 5;
            tv.tv_usec = 0;

    nsa_socketpair(AF_UNIX, SOCK_STREAM, 0, fd, NULL);

    pid = fork();
    if (pid == 0) {
        close(fd[0]);
                const char hello[] = "hello parent, I am child";

                while(1)
                {
                            nsa_select(fd[1] + 1, 0, &w_fds, 0, &tv);   -> this does not detect the writable event to put on w_fds.

                            if (FD_ISSET(fd[1], &w_fds))
                            {
                                        nsa_write(socket, hello, sizeof(hello));
                                        printf("done nsa_write\n");
                                        break;
                            }
                }


    } else {
        close(fd[1]);
                char buf[1024];

                while (1)
                {
                            nsa_select(fd[0] + 1, &r_fds, 0, &e_fds, &tv);

                            if (FD_ISSET(fd[0], &r_fds))
                            {
                                        int n = nsa_read(socket, buf, sizeof(buf));
                                        printf("parent received '%.*s'\n", n, buf);
                                        break;
                            }
                }

    }
    return 0;
}

It seems that nsa_select on the child could not see the writable event to trigger the nsa_write.
I had a look into nsa_socketpair, there is no flow created and I’m wondering how the events (on_writable/readable/etc.) can be trigger in this nsa_sockepair case.