code: func (ps *peerSet) Close() {
  	ps.lock.Lock()
  	defer ps.lock.Unlock()
  
  	for _, p := range ps.peers {
  		p.Disconnect(p2p.DiscQuitting)
  	}
  	ps.closed = true
  }
docs: // Close disconnects all peers.
  // No new peers can be registered after Close has returned.