What is the use of "AsyncPattern" property of "OperationContractAttribute" + wcf?

Question

Thus for used ajax enabled wcf services to get records from DB and display it in client without using AsyncPattern property of OperationContractAttribute....

• When should i consider AsyncPattern property?

Sample of my operationcontract methods,

[OperationContract]
 public string GetDesignationData()
    {
        DataSet dt = GetDesignationViewData();
        return GetJSONString(dt.Tables[0]);
    }
    public string GetJSONString(DataTable Dt)
    {
        string[] StrDc = new string[Dt.Columns.Count];
        string HeadStr = string.Empty;
        for (int i = 0; i < Dt.Columns.Count; i++)
        {
            StrDc[i] = Dt.Columns[i].Caption;
            HeadStr += "\"" + StrDc[i] + "\" : \"" + StrDc[i] + i.ToString() + "¾" + "\",";
        }
        HeadStr = HeadStr.Substring(0, HeadStr.Length - 1);
        StringBuilder Sb = new StringBuilder();

        Sb.Append("{\"" + Dt.TableName + "\" : [");
        for (int i = 0; i < Dt.Rows.Count; i++)
        {
            string TempStr = HeadStr;
            Sb.Append("{");
            for (int j = 0; j < Dt.Columns.Count; j++)
            {
                if (Dt.Rows[i][j].ToString().Contains("'") == true)
                {
                    Dt.Rows[i][j] = Dt.Rows[i][j].ToString().Replace("'", "");
                }
                TempStr = TempStr.Replace(Dt.Columns[j] + j.ToString() + "¾", Dt.Rows[i][j].ToString());
            }
            Sb.Append(TempStr + "},");
        }
        Sb = new StringBuilder(Sb.ToString().Substring(0, Sb.ToString().Length - 1));
        Sb.Append("]}");
        return Sb.ToString();
    }
    public DataSet GetDesignationViewData()
    {
        try
        {
            string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["connectionString"].ConnectionString;
            return SqlHelper.ExecuteDataset(connectionString, CommandType.StoredProcedure, DataTemplate.spDesignation_View);
        }
        catch (Exception err)
        {
            throw err;
        }
    }

Answer 1

AsyncPattern has a few uses- it's mainly a server performance optimization that allows you to free up worker pool request threads on blocking operations. For example, when a long-running blocking operation like DB access occurs, if you're using an async DB API on the server with AsyncPattern, the worker thread can return to the pool and service other requests. The original request is "awakened" later on another worker thread when the DB access completes, and the rest of the work is done (the service client just patiently waits- this is all transparent to it unless you're using an AsyncPattern-aware client and binding). This CAN allow your service to process more requests, if done carefully. To take advantage, you need to be using APIs on the server that have native async implementations. The only one I see that might be a candidate is the DB call that's happening in your SQLHelper.ExecuteDataset method- you'd have to read up on the underlying API to make sure a TRUE asynchronous option is available (presence of BeginXXX/EndXXX methods doesn't necessarily mean it's a TRUE async impl). The System.SqlClient stuff is truly async.

A word of caution: you have to be processing a lot of requests to make this worthwhile- there's a significant cost to code complexity and readability to split things up this way. You also need to understand multi-threaded programming very well- there are numerous pitfalls around locking, error handling, etc, that are well outside the scope of a SO post.

Good luck!