(C# e Visual Basic) de Timers de segmento
A classe System.Threading.Timer é útil para executar uma tarefa periodicamente em uma thread separada. Por exemplo, você poderia utilizar um timer de segmento para verificar o status e a integridade do banco de dados ou para fazer backup de arquivos críticos.
Exemplo de timer de segmento
O exemplo a seguir inicia uma tarefa a cada dois segundos e usa um sinalizador para iniciar o método Dispose que interrompe o cronômetro. Este exemplo envia o status para a janela de saída.
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
private class StateObjClass
{
// Used to hold parameters for calls to TimerTask.
public int SomeValue;
public System.Threading.Timer TimerReference;
public bool TimerCanceled;
}
public void RunTimer()
{
StateObjClass StateObj = new StateObjClass();
StateObj.TimerCanceled = false;
StateObj.SomeValue = 1;
System.Threading.TimerCallback TimerDelegate =
new System.Threading.TimerCallback(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.
System.Threading.Timer TimerItem =
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);
}
// Request Dispose of the timer object.
StateObj.TimerCanceled = true;
}
private void TimerTask(object StateObj)
{
StateObjClass State = (StateObjClass)StateObj;
// Use the interlocked class to increment the counter variable.
System.Threading.Interlocked.Increment(ref State.SomeValue);
System.Diagnostics.Debug.WriteLine("Launched new thread " + DateTime.Now.ToString());
if (State.TimerCanceled)
// Dispose Requested.
{
State.TimerReference.Dispose();
System.Diagnostics.Debug.WriteLine("Done " + DateTime.Now.ToString());
}
}
Timers de thread são particularmente úteis quando o objeto System.Windows.Forms.Timer estiver indisponível, como quando você estiver desenvolvendo aplicativos do console.