public void close(){
  if (running) {
    taskPool.clear();
    running=false;
    for (    PoolThread thread : threadPool) {
      thread.interrupt();
    }
  }
}

public void close ( ) { if ( running ) { taskPool . clear ( ) ; running = false ; for ( PoolThread thread : threadPool ) { thread . interrupt ( ) ; } } }
shutdown the pool of threads
