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ServiceBase Class

Provides a base class for a service that will exist as part of a service application. ServiceBase must be derived from when creating a new service class.

Namespace: System.ServiceProcess
Assembly: System.ServiceProcess (in system.serviceprocess.dll)

'Declaration
Public Class ServiceBase
	Inherits Component
'Usage
Dim instance As ServiceBase

public class ServiceBase extends Component
public class ServiceBase extends Component
Not applicable.

Derive from ServiceBase when defining your service class in a service application. Any useful service overrides the OnStart and OnStop methods. For additional functionality, you can override OnPause and OnContinue with specific behavior in response to changes in the service state.

A service is a long-running executable that does not support a user interface, and which might not run under the logged-on user account. The service can run without any user being logged on to the computer.

By default, services run under the System account, which is not the same as the Administrator account. You cannot change the rights of the System account. Alternatively, you can use a ServiceProcessInstaller to specify a user account under which the service will run.

An executable can contain more than one service but must contain a separate ServiceInstaller for each service. The ServiceInstaller instance registers the service with the system. The installer also associates each service with an event log that you can use to record service commands. The main() function in the executable defines which services should run. The current working directory of the service is the system directory, not the directory in which the executable is located.

When you start a service, the system locates the executable and runs the OnStart method for that service, contained within the executable. However, running the service is not the same as running the executable. The executable only loads the service. The service is accessed (for example, started and stopped) through the Service Control Manager.

The executable calls the ServiceBase derived class's constructor the first time you call Start on the service. The OnStart command-handling method is called immediately after the constructor executes. The constructor is not executed again after the first time the service has been loaded, so it is necessary to separate the processing performed by the constructor from that performed by OnStart. Any resources that can be released by OnStop should be created in OnStart. Creating resources in the constructor prevents them from being created properly if the service is started again after OnStop has released the resources.

The Service Control Manager (SCM) provides a way to interact with the service. You can use the SCM to pass Start, Stop, Pause, Continue, or custom commands into the service. The SCM uses the values of CanStop and CanPauseAndContinue to determine whether the service accepts Stop, Pause, or Continue commands. Stop, Pause, and Continue are enabled in the SCM's context menus only if the corresponding property CanStop or CanPauseAndContinue is true in the service class. If enabled, the command is passed to the service, and OnStop, OnPause, or OnContinue is called. If CanStop, CanShutdown, or CanPauseAndContinue is false, the corresponding command-handling method (such as OnStop) will not be processed, even if you have implemented the method.

You can use the ServiceController class to do programmatically what the SCM does using a user interface. You can automate the tasks available in the console. If CanStop, CanShutdown, or CanPauseAndContinue is true but you have not implemented a corresponding command-handling method (such as OnStop) the system throws an exception and ignores the command.

You do not have to implement OnStart, OnStop, or any other method in ServiceBase. However, the service's behavior is described in OnStart, so at minimum, this member should be overridden. The main() function of the executable registers the service in the executable with the Service Control Manager by calling the Run method. The ServiceName property of the ServiceBase object passed to the Run method must match the ServiceName property of the service installer for that service.

You can use InstallUtil.exe to install services on your system.

NoteNote:

You can specify a log other than the Application event log to receive notification of service calls, but neither the AutoLog nor the EventLog property can write to a custom log. Set AutoLog to false if you do not want to use automatic logging.

The following example derives a simple service implementation from the ServiceBase class. The service handles various service commands including Stop, Start, Pause, Continue and custom commands.


' Turn on the constant for logging to the event log.

#Const LOGEVENTS = True

Imports System
Imports System.IO
Imports System.Threading
Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Data
Imports System.Diagnostics
Imports System.ServiceProcess
Imports System.Text
Imports Microsoft.Win32
Imports System.Runtime.InteropServices


' Define custom commands for the SimpleService.

Public Enum SimpleServiceCustomCommands
    StopWorker = 128
    RestartWorker
    CheckWorker
End Enum 'SimpleServiceCustomCommands
<StructLayout(LayoutKind.Sequential)> _
Public Structure SERVICE_STATUS
    Public serviceType As Integer
    Public currentState As Integer
    Public controlsAccepted As Integer
    Public win32ExitCode As Integer
    Public serviceSpecificExitCode As Integer
    Public checkPoint As Integer
    Public waitHint As Integer
End Structure 'SERVICE_STATUS


Public Enum State
    SERVICE_STOPPED = &H1
    SERVICE_START_PENDING = &H2
    SERVICE_STOP_PENDING = &H3
    SERVICE_RUNNING = &H4
    SERVICE_CONTINUE_PENDING = &H5
    SERVICE_PAUSE_PENDING = &H6
    SERVICE_PAUSED = &H7
End Enum 'State

' Define a simple service implementation.

Public Class SimpleService
    Inherits System.ServiceProcess.ServiceBase
    Private Shared pause As New ManualResetEvent(False)

    Private Shared userCount As New Integer
    Public Declare Auto Function SetServiceStatus Lib "ADVAPI32.DLL" Alias "SetServiceStatus" (ByVal hServiceStatus As IntPtr, ByVal lpServiceStatus As SERVICE_STATUS) As Boolean
    Private myServiceStatus As SERVICE_STATUS

    Private workerThread As Thread = Nothing


    Public Sub New()
        CanPauseAndContinue = True
        CanHandleSessionChangeEvent = True
        ServiceName = "SimpleService"

    End Sub 'New

    Shared Sub Main()
#If LOGEVENTS Then
        System.Diagnostics.EventLog.WriteEntry("SimpleService.Main", DateTime.Now.ToLongTimeString() + _
        " - Service main method starting...")
#End If

        ' Load the service into memory.
        System.ServiceProcess.ServiceBase.Run(New SimpleService())

#If LOGEVENTS Then
        System.Diagnostics.EventLog.WriteEntry("SimpleService.Main", DateTime.Now.ToLongTimeString() + _
        " - Service main method exiting...")
#End If

    End Sub 'Main


    Private Sub InitializeComponent()
        ' Initialize the operating properties for the service.
        Me.CanPauseAndContinue = True
        Me.CanShutdown = True
        Me.CanHandleSessionChangeEvent = False
        Me.ServiceName = "SimpleService"

    End Sub 'InitializeComponent

    ' Start the service.
    Protected Overrides Sub OnStart(ByVal args() As String)
        Dim handle As IntPtr = Me.ServiceHandle
        myServiceStatus.currentState = Fix(State.SERVICE_START_PENDING)
        SetServiceStatus(handle, myServiceStatus)

        ' Start a separate thread that does the actual work.
        If workerThread Is Nothing OrElse (workerThread.ThreadState And System.Threading.ThreadState.Unstarted Or System.Threading.ThreadState.Stopped) <> 0 Then
#If LOGEVENTS Then
            System.Diagnostics.EventLog.WriteEntry("SimpleService.OnStart", DateTime.Now.ToLongTimeString() + _
                " - Starting the service worker thread.")
#End If

            workerThread = New Thread(New ThreadStart(AddressOf ServiceWorkerMethod))
            workerThread.Start()
        End If
        If Not (workerThread Is Nothing) Then
#If LOGEVENTS Then
            System.Diagnostics.EventLog.WriteEntry("SimpleService.OnStart", DateTime.Now.ToLongTimeString() + _
                " - Worker thread state = " + workerThread.ThreadState.ToString())
#End If
        End If
        myServiceStatus.currentState = Fix(State.SERVICE_RUNNING)
        SetServiceStatus(handle, myServiceStatus)

    End Sub 'OnStart

    ' Stop this service.
    Protected Overrides Sub OnStop()
        ' New in .NET Framework version 2.0.
        Me.RequestAdditionalTime(4000)
        ' Signal the worker thread to exit.
        If Not (workerThread Is Nothing) AndAlso workerThread.IsAlive Then
#If LOGEVENTS Then
            System.Diagnostics.EventLog.WriteEntry("SimpleService.OnStop", DateTime.Now.ToLongTimeString() + _
                " - Stopping the service worker thread.")
#End If
            pause.Reset()
            Thread.Sleep(5000)

            workerThread.Abort()
        End If
        If Not (workerThread Is Nothing) Then
#If LOGEVENTS Then
            System.Diagnostics.EventLog.WriteEntry("SimpleService.OnStop", DateTime.Now.ToLongTimeString() + _
                " - OnStop Worker thread state = " + workerThread.ThreadState.ToString())
#End If
        End If
        ' Indicate a successful exit.
        Me.ExitCode = 0

    End Sub 'OnStop

    ' Pause the service.
    Protected Overrides Sub OnPause()
        ' Pause the worker thread.
        If Not (workerThread Is Nothing) AndAlso workerThread.IsAlive AndAlso (workerThread.ThreadState And System.Threading.ThreadState.Suspended Or System.Threading.ThreadState.SuspendRequested) = 0 Then
#If LOGEVENTS Then
            System.Diagnostics.EventLog.WriteEntry("SimpleService.OnPause", DateTime.Now.ToLongTimeString() + _
                " - Pausing the service worker thread.")
#End If

            pause.Reset()
            Thread.Sleep(5000)
        End If

        If Not (workerThread Is Nothing) Then
#If LOGEVENTS Then
            System.Diagnostics.EventLog.WriteEntry("SimpleService.OnPause", DateTime.Now.ToLongTimeString() + _
                " OnPause - Worker thread state = " + workerThread.ThreadState.ToString())
#End If
        End If

    End Sub 'OnPause

    ' Continue a paused service.
    Protected Overrides Sub OnContinue()

        ' Signal the worker thread to continue.
        If Not (workerThread Is Nothing) AndAlso (workerThread.ThreadState And System.Threading.ThreadState.Suspended Or System.Threading.ThreadState.SuspendRequested) <> 0 Then
#If LOGEVENTS Then
            System.Diagnostics.EventLog.WriteEntry("SimpleService.OnContinue", DateTime.Now.ToLongTimeString() + " - Resuming the service worker thread.")

#End If
            pause.Set()
        End If
        If Not (workerThread Is Nothing) Then
#If LOGEVENTS Then
            System.Diagnostics.EventLog.WriteEntry("SimpleService.OnContinue", DateTime.Now.ToLongTimeString() + _
                " OnContinue - Worker thread state = " + workerThread.ThreadState.ToString())
#End If
        End If

    End Sub 'OnContinue

    ' Handle a custom command.
    Protected Overrides Sub OnCustomCommand(ByVal command As Integer)
#If LOGEVENTS Then
        System.Diagnostics.EventLog.WriteEntry("SimpleService.OnCustomCommand", DateTime.Now.ToLongTimeString() + _
            " - Custom command received: " + command.ToString())
#End If

        ' If the custom command is recognized,
        ' signal the worker thread appropriately.
        Select Case command
            Case Fix(SimpleServiceCustomCommands.StopWorker)
                ' Signal the worker thread to terminate.
                ' For this custom command, the main service
                ' continues to run without a worker thread.
                workerThread.Suspend()

            Case Fix(SimpleServiceCustomCommands.RestartWorker)

                ' Restart the worker thread if necessary.
                workerThread.Resume()

            Case Fix(SimpleServiceCustomCommands.CheckWorker)
#If LOGEVENTS Then
                ' Log the current worker thread state.
                System.Diagnostics.EventLog.WriteEntry("SimpleService.OnCustomCommand", _
                    DateTime.Now.ToLongTimeString() + _
                    " OnCustomCommand - Worker thread state = " + _
                    workerThread.ThreadState.ToString())
#End If


            Case Else
#If LOGEVENTS Then
                System.Diagnostics.EventLog.WriteEntry("SimpleService.OnCustomCommand", _
                DateTime.Now.ToLongTimeString())
#End If
        End Select

    End Sub 'OnCustomCommand

    ' Handle a session change notice
    Protected Overrides Sub OnSessionChange(ByVal changeDescription As SessionChangeDescription)
#If LOGEVENTS Then
        System.Diagnostics.EventLog.WriteEntry("SimpleService.OnSessionChange", _
        DateTime.Now.ToLongTimeString() + " - Session change notice recieved: " + _
        changeDescription.Reason.ToString() + "  Session ID: " + _
        changeDescription.SessionId.ToString())
#End If

        Select Case changeDescription.Reason
            Case SessionChangeReason.SessionLogon
                userCount += 1
#If LOGEVENTS Then
                System.Diagnostics.EventLog.WriteEntry("SimpleService.OnSessionChange", _
                DateTime.Now.ToLongTimeString() + " SessionLogon, total users: " + _
                userCount.ToString())
#End If

            Case SessionChangeReason.SessionLogoff

                userCount -= 1
#If LOGEVENTS Then
                System.Diagnostics.EventLog.WriteEntry("SimpleService.OnSessionChange", _
                DateTime.Now.ToLongTimeString() + " SessionLogoff, total users: " + _
                userCount.ToString())
#End If
            Case SessionChangeReason.RemoteConnect
                userCount += 1
#If LOGEVENTS Then
                System.Diagnostics.EventLog.WriteEntry("SimpleService.OnSessionChange", _
                DateTime.Now.ToLongTimeString() + " RemoteConnect, total users: " + _
                userCount.ToString())
#End If

            Case SessionChangeReason.RemoteDisconnect

                userCount -= 1
#If LOGEVENTS Then
                System.Diagnostics.EventLog.WriteEntry("SimpleService.OnSessionChange", _
                DateTime.Now.ToLongTimeString() + " RemoteDisconnect, total users: " + _
                userCount.ToString())
#End If
            Case SessionChangeReason.SessionLock
#If LOGEVENTS Then
                System.Diagnostics.EventLog.WriteEntry("SimpleService.OnSessionChange", _
                DateTime.Now.ToLongTimeString() + " SessionLock")
#End If

            Case SessionChangeReason.SessionUnlock
#If LOGEVENTS Then
                System.Diagnostics.EventLog.WriteEntry("SimpleService.OnSessionChange", _
                DateTime.Now.ToLongTimeString() + " SessionUnlock")
#End If

            Case Else
        End Select

    End Sub 'OnSessionChange

    ' Define a simple method that runs as the worker thread for 
    ' the service.  
    Public Sub ServiceWorkerMethod()
#If LOGEVENTS Then
        System.Diagnostics.EventLog.WriteEntry("SimpleService.WorkerThread", DateTime.Now.ToLongTimeString() + _
        " - Starting the service worker thread.")
#End If

        Try
            Do
                ' Simulate 4 seconds of work.
                Thread.Sleep(4000)
                ' Block if the service is pausing or shutting down.
                pause.WaitOne()
#If LOGEVENTS Then
                System.Diagnostics.EventLog.WriteEntry("SimpleService.WorkerThread", _
                DateTime.Now.ToLongTimeString() + " - heartbeat cycle.")
#End If
            Loop While True
        Catch
            ' Another thread has signalled that this worker
            ' thread must terminate.  Typically, this occurs when
            ' the main service thread receives a service stop 
            ' command.
            ' Write a trace line indicating that the worker thread
            ' is exiting.  Notice that this simple thread does
            ' not have any local objects or data to clean up.
#If LOGEVENTS Then
            System.Diagnostics.EventLog.WriteEntry("SimpleService.WorkerThread", DateTime.Now.ToLongTimeString() + _
            " - Thread abort signaled.")
#End If
        End Try
#If LOGEVENTS Then

        System.Diagnostics.EventLog.WriteEntry("SimpleService.WorkerThread", DateTime.Now.ToLongTimeString() + _
        " - Exiting the service worker thread.")
#End If

    End Sub 'ServiceWorkerMethod 
End Class 'SimpleService

System.Object
   System.MarshalByRefObject
     System.ComponentModel.Component
      System.ServiceProcess.ServiceBase

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows Server 2000 SP4, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0
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