holders.put(serverId, h);
holders.put(in, h);
   public synchronized MessageIdGenerator checkOutGenerator(String serverId,                                                            ConnectionFactoryDelegate cfd)      throws JMSException   {      Holder h = (Holder)holders.get(serverId);      if (h == null)      {         h = new Holder(new MessageIdGenerator(cfd, BLOCK_SIZE));         holders.put(serverId, h);      }      else      {         h.refCount++;      }      log.debug("checked out MessageIdGenerator for " + serverId +                ", reference count is " + h.refCount);      return h.generator;   }