long prePoll(){
  lock.lock();
  try {
    long n=head;
    while (n != 0) {
      if (!polling(n)) {
        polling(n,true);
        break;
      }
      n=next(n);
    }
    return n;
  }
  finally {
    lock.unlock();
  }
}

long prePoll ( ) { lock . lock ( ) ; try { long n = head ; while ( n != 0 ) { if ( ! polling ( n ) ) { polling ( n , true ) ; break ; } n = next ( n ) ; } return n ; } finally { lock . unlock ( ) ; } }
polls oldest entry from the queue .
