class FBClient : IDisposable
{
    FbConnection    fbConnection;
    FbTransaction   fbTransaction;
    string          fbConString;

    public FBClient(string conString)
    {
        fbConString = conString;
    }

    public void Dispose()
    {
        fbConnection.Dispose();
    }

    public void Open()
    {
        fbConnection = new FbConnection(fbConString);
        fbConnection.Open();
    }

    public void Close()
    {
        fbConnection.Close();
        fbConnection.Dispose();
    }

    public void TransactionBegin()
    {
        fbTransaction = fbConnection.BeginTransaction();
    }

    public void TransactionCommit()
    {
        fbTransaction.Commit();
    }

    public void TransactionRollback()
    {
        fbTransaction.Rollback();
    }

    public void ExecuteQuery(string commandStr, List<string> parameters, bool isQuery)
    {
        using (FbCommand cmd = new FbCommand(commandStr, fbConnection, fbTransaction))
        {
            for(int i=0; i<parameters.Count; i++)
            {
                if (parameters[i] == "<NULL>")
                {
                    cmd.Parameters.Add(string.Format("@param{0}", i), null);
                }
                else
                {
                    cmd.Parameters.Add(string.Format("@param{0}", i), parameters[i]);
                }
            }

            if (isQuery)
            {
                var reader = cmd.ExecuteReader();
            }
            else
            {
                cmd.ExecuteNonQuery();
            }
        }
    }
}

        public static string BuildConnectionString(string server, string db, string user, string psw)
        {
            FbConnectionStringBuilder cs = new FbConnectionStringBuilder();
            cs.DataSource   = server;
            cs.Database     = db;
            cs.UserID       = user;
            cs.Password     = psw;
            cs.Charset      = "win1251";
            return cs.ToString();
        }

        public void Open()
        {
            if (isOpen) return;
            try
            {
                fbConnection = new FbConnection(fbConString);
                fbConnection.Open();
                isOpen = true;
            }
            catch (System.Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

		private void CheckMaxPoolSize()
		{
			lock (this.syncObject)
			{
				if (this.options.MaxPoolSize > 0 &&
					(this.Count + 1) >= this.options.MaxPoolSize)
				{
					long timeout = this.options.ConnectionTimeout * TimeSpan.TicksPerSecond;
					long start = DateTime.Now.Ticks;

					while (true)
					{
						if ((this.Count + 1) >= this.options.MaxPoolSize)
						{
							if ((DateTime.Now.Ticks - start) > timeout)
							{
								throw new SystemException("Timeout exceeded.");
							}

							Thread.Sleep(100);
						}
						else
						{
							break;
						}
					}
				}
			}
		}

var reader = cmd.ExecuteReader();