int preSend(int fd, int timeout){
   fd_set rfds;
   struct timeval tv;
   int retval;
   FD_ZERO(&rfds);
   FD_SET(fd, &rfds);
   tv.tv_sec = timeout;
   tv.tv_usec = 0;
   retval = select(fd+1, NULL, &rfds, NULL, &tv);
   if(retval == -1){
      return -1;
   }else if(retval){
      return 0;
   }else{
      return -1;
   }
}