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Thread Timers (C# and Visual Basic)

The System.Threading.Timer class is useful for periodically running a task on a separate thread. For example, you could use a thread timer to check the status and integrity of a database or to back up critical files.

The following example starts a task every two seconds and uses a flag to initiate the Dispose method that stops the timer. This example posts status to the output window.

Private Class StateObjClass
    ' Used to hold parameters for calls to TimerTask. 
    Public SomeValue As Integer 
    Public TimerReference As System.Threading.Timer
    Public TimerCanceled As Boolean 
End Class 

Public Sub RunTimer()
    Dim StateObj As New StateObjClass
    StateObj.TimerCanceled = False
    StateObj.SomeValue = 1
    Dim TimerDelegate As New System.Threading.TimerCallback(AddressOf TimerTask)
    ' Create a timer that calls a procedure every 2 seconds. 
    ' Note: There is no Start method; the timer starts running as soon as  
    ' the instance is created. 
    Dim TimerItem As New System.Threading.Timer(TimerDelegate, StateObj,
                                                2000, 2000)
    ' Save a reference for Dispose.
    StateObj.TimerReference = TimerItem

    ' Run for ten loops. 
    While StateObj.SomeValue < 10
        ' Wait one second.
        System.Threading.Thread.Sleep(1000)
    End While 

    ' Request Dispose of the timer object.
    StateObj.TimerCanceled = True 
End Sub 

Private Sub TimerTask(ByVal StateObj As Object)
    Dim State As StateObjClass = CType(StateObj, StateObjClass)
    ' Use the interlocked class to increment the counter variable.
    System.Threading.Interlocked.Increment(State.SomeValue)
    System.Diagnostics.Debug.WriteLine("Launched new thread  " & Now.ToString)
    If State.TimerCanceled Then 
        ' Dispose Requested.
        State.TimerReference.Dispose()
        System.Diagnostics.Debug.WriteLine("Done  " & Now)
    End If 
End Sub

Thread timers are particularly useful when the System.Windows.Forms.Timer object is unavailable, such as when you are developing console applications.

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