Using the ThreadPool - An example as simple as possible

I just posted a code sample using the ThreadPool on a forum so I thought I could also post it here. Who knows, it might prove usefull to someone someday. Basically it simply demonstrate how to create and start new threads with the ThreadPool and how to use delegates with parameters. Here it is :

Imports System.Threading

Public Class Form1

    Delegate Sub UpdateItemValueDelegate(ByVal index As Integer, ByVal value As Integer)
    Public UpdateListItem As UpdateItemValueDelegate = AddressOf UdateItemValue

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'Add some values to the listbox for the example
        For i As Integer = 0 To 10
            ListBox1.Items.Add(i.ToString())
        Next
    End Sub

    Private Sub UdateItemValue(ByVal index As Integer, ByVal value As Integer)
        'Set the new item's value
        ListBox1.Items(index) = value
    End Sub

    Private Sub CalculateNewValue(ByVal itemIndex As Integer)
        'Calculate a new value for the given item and call the delegate to set the new item's value
        Dim value As Integer
        value = ListBox1.Items(itemIndex) * 5
        If ListBox1.InvokeRequired Then
            Me.Invoke(UpdateListItem, {itemIndex, value})
        End If
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        'Run a thread for each item in the list
        For i As Integer = 0 To ListBox1.Items.Count - 1
            ThreadPool.QueueUserWorkItem(New WaitCallback(AddressOf CalculateNewValue), i)
        Next
    End Sub
End Class

Microsoft Press Books

For those interested in Microsoft Visual Studio 2010 MCTS or MCPD, the following MCTS book is suppose to be available december 16th :
MCTS Self-Paced Training Kit (Exam 70-515): Web Applications Development with Microsoft .NET Framework 4

Use VB on Windows Phone 7

For those of you VB coders who were interested by the new Windows Phone 7 platform, Visual Basic for Windows Phone Developer Tools - RTW is now available for download here.

.Net FW 4: Data Parallelism

I just started to look at the .NET Framework 4, yeah I know I’m late, and everything new it brings us so I thought I’d do a small post about the Data Paralellism and show a small example of Parallel.For loop and the comparison with a standard for loop. The code bellow is pretty simple, it additions integers from 0 to 2 million (exclusive) and put the result in a long variable and it displays the result and the elapsed time in milliseconds for each loop.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Diagnostics;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Stopwatch watch = new Stopwatch();

            int[] nums = Enumerable.Range(0, 2000000).ToArray();
            long total = 0;

            watch.Reset();
            watch.Start();
            for (int i = 0; i < nums.Count<int>(); i++ )
            {
                total += nums[i];
            }
            watch.Stop();

            Console.WriteLine("The total is {0}", total);
            Console.WriteLine("'For' loop completed in " + watch.ElapsedMilliseconds.ToString() + " milliseconds.");
            Console.WriteLine();

            total = 0;
            watch.Reset();
            watch.Start();

            Parallel.For<long>(0, nums.Length, () => 0, (j, loop, subtotal) =>
            {
                subtotal += nums[j];
                return subtotal;
            },
                (x) => Interlocked.Add(ref total, x)
            );

            watch.Stop();
            
            Console.WriteLine("The total is {0}", total);
            Console.WriteLine("'Parallel.For' loop completed in " + watch.ElapsedMilliseconds.ToString() + " milliseconds.");
            Console.WriteLine("Press any key to exit");
            Console.ReadKey();
        }
    }
}

As you can see in the following screenshot, The Parallel.For loop is much faster than the standard for loop.

Using Parallelism is usually faster but in case of very simple processing it can in fact be a little bit longer due to the parallelism layer that is added. I also suggest having a look at the other available classes from the System.Threading.Task Namespace as the TaskFactory, which is used to create asynchronous operations and can be a good alternative to the BackGroundWorker.

BackGroundWorker example

I’ve seen a lot of questions lately on forums about the BackGroundWorker (BGW) Class and how to use it. The BGW’s purpose is to execute an operation on a separate thread. Whenever you have a time-consuming operation that need to be executed you can use a BGW to avoid having your User Interface (UI) stop responding. It is a convenient solution if you only have a single time-consuming operation to execute. If you have multiple time-consuming operations that you would like to execute at the same time, then I suggest you have a look at the ThreadPool Class.

Here’s a small example in VB.NET that shows how to use the BGW to perform an SQL query while the first Form show a progress bar and then displays the second Form once the SQL operation as completed.

Imports System.Data.OleDb

Module Module1
    Public da As New OleDbDataAdapter
    Public ds As New DataSet
End Module

Imports System.Text
Imports System.Collections
Imports System.ComponentModel
Imports System.Data.OleDb


Public Class Form1
    Dim WithEvents bgw As New BackgroundWorker
    Delegate Sub HideButtonDelegate()
    Public HBD As HideButtonDelegate = AddressOf Me.HideButton

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        bgw.WorkerSupportsCancellation = True
        ProgressBar1.Show()
        bgw.RunWorkerAsync()
    End Sub

    Private Sub bgw_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs) Handles bgw.DoWork
        'Do your lenghty operations here

        Dim MyConnection As New System.Data.OleDb.OleDbConnection()
        Dim MyCommand As OleDbCommand


        Try
            MyConnection.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data source=" & Application.StartupPath & "\Database1.accdb"
            MyConnection.Open()
        Catch ex As Exception
            MessageBox.Show("Cannot connect to the specified database" & ex.Message)
        End Try

        Try
            MyCommand = New OleDbCommand("SELECT * FROM Table1", MyConnection)
            da.SelectCommand = MyCommand
            ds = New DataSet
            da.Fill(ds, "Table1")
        Catch ex As Exception
            MessageBox.Show("Cannot fetch data from the database" & ex.Message)
        End Try
        System.Threading.Thread.Sleep(2000)
        If Button1.InvokeRequired Then
            Me.Invoke(HBD)
        End If

        System.Threading.Thread.Sleep(2000)

    End Sub


    Private Sub bgw_Completed(ByVal sender As Object, ByVal e As AsyncCompletedEventArgs) Handles bgw.RunWorkerCompleted
        ProgressBar1.Hide()
        Me.Hide()
        Form2.Show()
    End Sub

    Private Sub HideButton()
        Button1.Visible = False
    End Sub
End Class

Public Class Form2

    Private Sub Form2_Disposed(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Disposed
        Form1.Close()
    End Sub

    Private Sub Form2_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        DataGridView1.DataSource = ds.Tables(0)
    End Sub
End Class

String replacement with Regular Expressions

I answered a question last week on a forum about using Regular Expressions for complex string replacements so I thought I might just post a small example. For simple string replacement there’s the String.Replace method, but whenever you need to manipulate the match you want to replace in order to build the replacement string, the RegEx.Replace method does the job. Here’s a small code sample that searches in a string for a parameter named “username” and its value and then builds a HTML link stirng with it.

private void button1_Click(object sender, EventArgs e)
{
 string s = "username=myusername";
 Regex patern = new Regex(@"\[(username=(\W+))\]");
 MatchEvaluator matchEval = new MatchEvaluator(GetReplacement);

 s = patern.Replace(s,GetReplacement);

 MessageBox.Show(s);

}
 
private string GetReplacement(Match m)
{
 return "" + m.Groups[2] + "";
} 

Using the StringBuilder class

In .NET I often see people use the plus ‘+’ operator in C# or the ampersand ‘&’ operator in VB.NET to concatenate strings. Whenever these operators are use for concatenation the Framework copies all the strings included in the operation into memory and then reads back those value as a new string. This, even if it doesn’t seem to be, is a costly operation. This is where the StringBuilder comes in. This class, as MSDN describes it is “ a string-like object whose value is a mutable sequence of characters. The value is said to be mutable because it can be modified once it has been created by appending, removing, replacing, or inserting characters.” And the important thing to know is that it is faster than using concatenation operators as you can see in the following example.

using System;
using System.Collections.Generic;
using System.Text;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Concatenation using string class and operators");
            string s = string.Empty;
            Console.WriteLine("Operation start time: " + DateTime.Now.ToLongTimeString());
            for (int i = 0; i < 100000; i++)
            {
                s += i.ToString();
            }
            Console.WriteLine("Operation stop time: " + DateTime.Now.ToLongTimeString());

            Console.WriteLine();

            Console.WriteLine("Concatenation using StringBuilder");
            StringBuilder sb = new StringBuilder(string.Empty);
            Console.WriteLine("Operation start time: " + DateTime.Now.ToLongTimeString());
            for (int i = 0; i < 100000; i++)
            {
                sb.Append(i);
            }
            Console.WriteLine("Operation stop time: " + DateTime.Now.ToLongTimeString());

            Console.WriteLine();
            Console.WriteLine("Press any key to close this window.");
            Console.ReadLine();
        }
    }
}

Sure if you only concatenate a couple of strings you won’t see the difference but still, I think that using the StringBuilder class whenever you need to manipulate a string is a good habit to take.