def update_polling_pool(key, thread)
      unless @pool.size < @max_threads
        _, thread = @pool.shift
        Thread.kill(thread)
      end
      @pool[key] = thread
    end
def update_polling_pool(key, thread)
      unless @pool.size < @max_threads
        _, thread = @pool.shift
        Thread.kill(thread)
      end
      @pool[key] = thread
    end
update polling threads pool
 param [String] key
 param [Thread] thread