private void RegisterHandler(IPacketHandler handler)
    {
        Int32 messageId = handler.GetMessageId();

        if (m_PacketHandlers.ContainsKey(messageId))
        {
            Debug.LogWarning("Exist same handler (MessageId=" + messageId + ") already!");
            return;
        }
        m_PacketHandlers.Add(messageId, handler);
    }