Developing Windows Services

by Wei-Meng Lee
08/18/2003

A Windows Service is an application that does not have a user interface. It commonly runs without human intervention and can be automatically started when the computer starts up. Examples of Windows Services are the Internet Information Server (IIS), Telnet, and FTP. Windows Services were formerly known as NT Services. In this article, I will illustrate how to create a Windows Service using Visual Studio .NET 2003.

Developing the TimeService Windows Service

In this article, I will develop a simple Windows Service that returns the current date and time. I will use the network example as illustrated in my earlier article. When this Windows Service is started, the server will start listening for all incoming network connections at port 500. Regardless of what the client sends, the Windows Service will return the current date and time.

Let's now build our Windows Service:

1. Launch Visual Studio .NET 2003 and create a New Project.
2. Select the Project Types (Visual Basic Projects) and the templates (Windows Service).
3. Name the project TimeService (see Figure 1).

Figure 1. Creating a new Windows Service project

4. Right-click on the design surface and select Properties.
5. Change the ServiceName property to TimeService. Also, set the CanPauseAndContinue property to True (see Figure 2). You want to be able to pause and resume the Windows Service after you have started it.

Figure 2. Naming the Windows Service

6. Right-click on the design surface and select Add Installer (see Figure 3).

Figure 3. Adding the Installer

7. Two installers will be added: ServiceProcessInstaller1 and ServiceInstaller1 (see Figure 4). These two controls are used by the InstallUtil.exe utility when installing the Windows Service (more on this in the next section).

Figure 4. Adding the two Installer controls

8. Right-click on ServiceProcessInstaller1 and select Properties. Set the Account property to LocalSystem.
9. Right-click on ServiceInstaller1 and select Properties. Set the StartType to Manual.
10. Finally, double-click on the design surface to reveal the two default methods, OnStart() and OnStop() (see Figure 5).

Figure 5. The default OnStart() and OnStop() methods

Now for the coding. First, import the following namespaces:

Imports System.Net.Sockets
Imports System.Net
Imports System.Text
Imports System.Threading

You have also need to declare the following global variables:

Dim t1 As New Thread(AddressOf Listen)
Dim canStopListening As Boolean = False
Dim pause As Boolean = False
Dim log As New System.Diagnostics.EventLog

I have a subroutine named Listen() that repeatedly listens for incoming network requests. When a client is connected, it will send the current date and time. The global variables canStopListening and pause control the status of the loop.

Private Sub Listen()
  Const portNo As Integer = 500
  Dim localAdd As System.Net.IPAddress = _
    IPAddress.Parse("127.0.0.1")
  Dim listener As New TcpListener(localAdd, portNo)
  listener.Start()
  Do
    If Not pause Then
      Dim tcpClient As TcpClient = listener.AcceptTcpClient()
      Dim NWStream As NetworkStream = tcpClient.GetStream
      Dim bytesToRead(tcpClient.ReceiveBufferSize) As Byte
      '---read incoming stream
      Dim numBytesRead As Integer = _
        NWStream.Read(bytesToRead, 0, _
        CInt(tcpClient.ReceiveBufferSize))
      '---write to event log
      log.WriteEntry("Received :" & _
        Encoding.ASCII.GetString(bytesToRead, _
        0, numBytesRead) & " @ " & Now)
      '---write time back to client
      Dim time() As Byte = _
        Encoding.ASCII.GetBytes(Now.ToString)
      NWStream.Write(time, 0, time.Length)
      tcpClient.Close()
    End If
  Loop Until canStopListening
  listener.Stop()
End Sub

Pages: 1, 2, 3

Next Page