public void free( int frameNo ) throws PagePinnedException
  {
  
      if ( (mgr.frameTable())[frameNo].pin_count() > 1 ) {
    
	 throw new PagePinnedException (null, "BUFMGR: PAGE_PINNED.");

      }

    (mgr.frameTable())[frameNo].unpin();
    state_bit[frameNo].state = Available;

  }