How to execute the threadpool after Queueing user work items in C#?

Question

I am new to C# programming and I have a task to make a process from single thread to multithreaded. I am using C#3.5 version and implementing threadpool in the code. I have searched about threadpool and did some changes but it is not working. When I again searched in the internet I think I wrote partial code upto only queueing user workitems, I am not understanding how to execute the threads.

Shown here is the code I wrote, please don't hesitate to correct me if the code is wrong, I am very new to C# coding.

ThreadPool.SetMaxThreads(6, 6);

try
{
    // Assign the values to the report parameters
    for (int i = 0; i < aq.Count; i++)
    {
        object j = aq[i];
        ThreadPool.QueueUserWorkItem(new WaitCallback(process), j);
    }
}            
   private void process(object i)
    {

        List<Report> aq = new List<Report>();
        ReportEnv env = null;
        ParameterValue[] paramval;

        List<Report> list = new List<Report>();
        Report al = null;

        using (OleDbDataAdapter oleDA = new OleDbDataAdapter())
        using (DataTable dt = new DataTable())
        {
            oleDA.Fill(dt, i);

            foreach (DataRow _row in dt.Rows)
            {
                al = new Report();

                al.EmailAttachmentMsg = _row["AttachmentMsg"].ToString();
                al.reportName = _row["Repo"].ToString();
                al.AccountNumber = _row["Number"].ToString();
                al.AccountGroupCode = _row["GroupCode"].ToString();
                al.EmailTo = _row["To"].ToString().Split(';');
                al.ReportScheduleId = _row["ReportScheduleId"].ToString();
                al.Frequency = _row["Frequency"].ToString();
                al.ColcoContactTelephone = _row["ColcoContactTelephone"].ToString();

                list.Add(al);
            }
        }
        // aq = Populatereport(Dts.Variables["vnSource_SQL_Result"].Value);
        env = PopulateEnvironment(Dts.Variables["vnEnvironment"].Value);
        aq = list;


        paramval = new ParameterValue[2];
        paramval[0] = new ParameterValue();
        paramval[0].Name = "PRM_CustomerDetails";
        paramval[0].Value = aq[0].AccountNumber;
        paramval[1] = new ParameterValue();
        paramval[1].Name = "PRM_Startdate";
        paramval[1].Value = aq[0].StartDate;


        //Rendering the report begins

        ReportExecutionService rs = new ReportExecutionService();
        rs.Credentials = System.Net.CredentialCache.DefaultCredentials;
        rs.Url = env.SSRSServerUrl.ToString();


        //Load the report options
        rs.LoadReport(aq[0].ReportPath, null);
        rs.SetExecutionParameters(paramval, aq[0].CultureCode);



        // Set the filename

        String filename = aq[0]. Number + "_" + env.Code + "_" + "_" + aq[0].Name +
            DateTime.UtcNow.ToString("_dd-MM-yyyy_hh-mm-ss.fff");

        //Render the report and generate pdf
        Byte[] results;
        string encoding = String.Empty;
        string mimeType = String.Empty;
        string extension = String.Empty;
        Warning[] warnings = null;
        string[] streamIDs = null;
        string deviceInfo = null;
        results = rs.Render(aq[0].ReportFormat, deviceInfo, out extension, out encoding, out mimeType, out warnings, out streamIDs);


        //Write the file into the directory
        using (FileStream stream = File.OpenWrite(@env.wipPath + filename))
        {

            stream.Write(results, 0, results.Length);
         }


            if (SendEmail(env.From, aq[0].To,  env.Subject, aq[0].Attachment, env.Server, false,  filename, env.TimeOut) == true)
            {
                // Move report file from WIP to Processed
                File.Move(@env.oldPath + filename, @env.newPath + filename);
                }


            }

Answer 1

You don't have to do anything more. By calling QueueUserWorkItem you are saying that you want to execute a give method in a thread that is managed by a thread pool. However, you don't have any guarantee that it will be executed immediately and it is how a thread pool works. Your method will be executed when a thread pool thread is available.

In the first line of your code you call ThreadPool.SetMaxThreads(6, 6); Because of that no more than 6 thread pool threads will be active at the same time. All requests, to execute something in a thread pool, above this limit will be queued. So, maybe you made so many requests that some of them are simply waiting for their turn.

Besides you have to keep in mind that there might be another code that also uses a thread pool. In this case your requests need to compete for thread pool threads.

UPDATE (after discussion):

Try to put a breakpoint inside a process method. A debugger will stop there and it will prove that process method is really executed. However, there is probably some bug in your code and it is why you don't see e-mails being set

Answer 2

One reason I think that your code may not execute is that you have a race condition of some sort between the thread executing and your program ending. How long is your code? If you're just beginning to learn C#, I have a feeling you are coding a console app and your code is mostly on the Main() method and consists of a few lines. If you do ThreadPool.QueueUserWorkItem() on a short application and the end of the Main() method is reached immediately, your code may never execute!

To avoid this, you can add a sleep for a second before the Main() method ends, e.g.:

Thread.Sleep(1000);