code: @Override
      public boolean close() {
          this.open = false;
  
          for (int i = 0; i < listeningStreams.get(); i++) {
             try{
                this.queue.offer((T) POISON_PILL);
             }catch(Exception e){
  
             }
  
          }
  
          return true;
      }
docs: Close this Queue
  Poison Pills are used to communicate closure to connected Streams
  A Poison Pill is added per connected Stream to the Queue
  If a BlockingQueue is backing this async.Queue it will block until
  able to add to the Queue.
  
  @return true if closed