protected void purge(){
  Reference<?> ref=queue.poll();
  while (ref != null) {
    purge(ref);
    ref=queue.poll();
  }
}

protected void purge ( ) { Reference < ? > ref = queue . poll ( ) ; while ( ref != null ) { purge ( ref ) ; ref = queue . poll ( ) ; } }
purges stale mappings from this map . < p > note that this method is not synchronized ! special care must be taken if , for instance , you want stale mappings to be removed on a periodic basis by some background thread .
