c10-22 how to handle sigtstp--apue

#include "apue.h"
#define BUFFSIZE 1024
static void sig_tstp(int );
int main(void)
{
    int n;
    char buf[BUFFSIZE];

    /*
     *Only catch sigtstp if we're running with a job-control  shell
     */
    if (signal(SIGTSTP,SIG_IGN) == SIG_DFL)
        signal(SIGTSTP,sig_tstp);
    while( (n =read(STDIN_FILENO,buf,BUFFSIZE) ) > 0)
        if (write(STDOUT_FILENO,buf,n) !=n )
            err_sys("write error");
    if (n < 0)
        err_sys("read error");
    exit(0);
}
static void
sig_tstp(int signo)
{
    sigset_t mask;
    /*
     *...move cursor to lower left corner,reset tty mode ....
     */
    /*
     *Unblock sigtstp,since it't block while we're handling it.
     */
    sigemptyset(&mask);
    sigaddset(&mask,SIGTSTP);
    sigprocmask(SIG_UNBLOCK,&mask,NULL);
    signal(SIGTSTP,SIG_DFL);/* RESET disposition to default */
    kill(getpid(),SIGTSTP);  /* and send the signalto ourself */
    /*
     * we won't return form the kill until we're continued
     */
    signal(SIGTSTP,sig_tstp); /* reestablish signal handler */
    /*
     * reset tty mode,redraw window
     *...................
     */
}