清单 5. 主循环

while (i < 1000) {
    FD_ZERO(&rfds);
    FD_SET(fd0, &rfds);
    FD_SET(fd1, &rfds);
    tv.tv_sec = 0;
    tv.tv_usec = 250000;

    retval = select(FD_SETSIZE, &rfds, NULL, NULL, &tv);
    if (retval > 0) {
          if (FD_ISSET(fd0, &rfds)) {
                  n = read(fd0, buf, BUFSIZE - 1);
                  buf[n] = 0;
                  printf("FIFO 1: %s\n",buf);
          }if (FD_ISSET(fd1, &rfds)) {
                  n = read(fd1, buf, BUFSIZE - 1);
                  buf[n] = 0;
                  printf("FIFO 2: %s\n",buf);
          }if (!(swap % 20)) {
                  msg.task = hello_thread?0:1;
                  msg.command = HELLO;
                  write(ctl, &msg, sizeof(msg));
                  msg.task = hello_thread?1:0;
                  msg.command = WORLD;
                  write(ctl, &msg, sizeof(msg));
                  hello_thread = hello_thread?0:1;
          }swap++;
          i++;
    }
}