Single instance of OPC client in WCF RIA Service

Question

I'm developing a simple Silverlight app. The application will display the information found in the tags of an OPC server, running in the same machine of the web server.

I implemented a domain service class with a method that let the client ask for the value of a tag. The problem is that every time I call the method from the client side it instantiate a new OPC Client, connect to the server, read the value and then disconnect. This can be a problem with a large number of calls.

How can I use a single OPC Client object on the server side?

Here's the code of the domain service class.

namespace BFLabClientSL.Web.Servizi
{
    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.ComponentModel.DataAnnotations;
    using System.Linq;
    using System.ServiceModel.DomainServices.Hosting;
    using System.ServiceModel.DomainServices.Server;
    using OpcClientX;
    using System.Configuration;

    // TODO: creare metodi contenenti la logica dell'applicazione.
    [EnableClientAccess()]
    public class DSCAccessoDati : DomainService
    {
        protected OPCItem itemOPC = null;

        /// <summary>
        /// Permette l'acceso al valore di un dato
        /// </summary>
        /// <param name="itemCode">Chiave del dato</param>
        /// <returns>Valore del dato</returns>
        public string GetDato(string itemCode)
        {
            string result = "";

            OPCServer clientOPC = new OPCServer();
            clientOPC.Connect(Properties.Settings.Default.OPCServer_ProgID);
            OPCGroup gruppoOPC = clientOPC.OPCGroups.Add("Gruppo1");

            OPCItem itemOPC = gruppoOPC.OPCItems.AddItem(itemCode, 0);

            try
            {
                object value = null;
                object quality = null;
                object timestamp = null;

                itemOPC.Read(1, out value, out quality, out timestamp);

                result = (string)value;
            }
            catch (Exception e)
            {
                throw new Exception("Errore durante Caricamento dato da OPCServer", e);
            }
            finally
            {
                try
                {
                    clientOPC.Disconnect();
                }
                catch { }
                clientOPC = null;
            }

            return result;
        }
    }
}

score 0 · Answer 1 · answered Jan 31 '13 at 07:36

A simple solution would be to define a static variable OPCServer in your class that you intialize once and reuse it in your methods

public class DSCAccessoDati : DomainService
{
    private static OPCServer clientOPC;

    static DSCAccessoDati() {
      clientOPC = new OPCServer();
      clientOPC.Connect(Properties.Settings.Default.OPCServer_ProgID);
    }

    public string GetDato(string itemCode) {

      OPCGroup gruppoOPC = clientOPC.OPCGroups.Add("Gruppo1");
      //your code without the disconnect of OPCServer
    }

Single instance of OPC client in WCF RIA Service

1 Answers1