CancellationToken.IsCancellationRequested Propriedade

Definição

Especifica se o cancelamento foi solicitado para esse token.Gets whether cancellation has been requested for this token.

public:
 property bool IsCancellationRequested { bool get(); };
public bool IsCancellationRequested { get; }
member this.IsCancellationRequested : bool
Public ReadOnly Property IsCancellationRequested As Boolean

Valor da propriedade

Boolean

true se o cancelamento tiver sido solicitado para esse token; caso contrário, false.true if cancellation has been requested for this token; otherwise, false.

Exemplos

Veja a seguir um exemplo simples que executa um processo de servidor até que a IsCancellationRequested Propriedade retorne true .The following is a simple example that executes a server process until the IsCancellationRequested property returns true.

using System;
using System.Threading;

public class ServerClass
{
   public static void StaticMethod(object obj)
   {
      CancellationToken ct = (CancellationToken)obj;
      Console.WriteLine("ServerClass.StaticMethod is running on another thread.");

      // Simulate work that can be canceled.
      while (!ct.IsCancellationRequested) {
         Thread.SpinWait(50000);
      }
      Console.WriteLine("The worker thread has been canceled. Press any key to exit.");
      Console.ReadKey(true);
   }
}

public class Simple
{
   public static void Main()
   {
      // The Simple class controls access to the token source.
      CancellationTokenSource cts = new CancellationTokenSource();

      Console.WriteLine("Press 'C' to terminate the application...\n");
      // Allow the UI thread to capture the token source, so that it
      // can issue the cancel command.
      Thread t1 = new Thread(() => { if (Console.ReadKey(true).KeyChar.ToString().ToUpperInvariant() == "C")
                                     cts.Cancel(); } );

      // ServerClass sees only the token, not the token source.
      Thread t2 = new Thread(new ParameterizedThreadStart(ServerClass.StaticMethod));
      // Start the UI thread.

      t1.Start();

      // Start the worker thread and pass it the token.
      t2.Start(cts.Token);

      t2.Join();
      cts.Dispose();
   }
}
// The example displays the following output:
//       Press 'C' to terminate the application...
//
//       ServerClass.StaticMethod is running on another thread.
//       The worker thread has been canceled. Press any key to exit.
Imports System.Threading

Public Class ServerClass
   Public Shared Sub StaticMethod(obj As Object)
      Dim ct AS CancellationToken = CType(obj, CancellationToken)
      Console.WriteLine("ServerClass.StaticMethod is running on another thread.")

      ' Simulate work that can be canceled.
      While Not ct.IsCancellationRequested
         Thread.SpinWait(50000)
      End While
      Console.WriteLine("The worker thread has been canceled. Press any key to exit.")
      Console.ReadKey(True)
   End Sub
End Class

Public Class Simple
   Public Shared Sub Main()
      ' The Simple class controls access to the token source.
      Dim cts As New CancellationTokenSource()

      Console.WriteLine("Press 'C' to terminate the application..." + vbCrLf)
      ' Allow the UI thread to capture the token source, so that it
      ' can issue the cancel command.
      Dim t1 As New Thread( Sub()
                               If Console.ReadKey(true).KeyChar.ToString().ToUpperInvariant() = "C" Then
                                  cts.Cancel()
                               End If
                            End Sub)

      ' ServerClass sees only the token, not the token source.
      Dim t2 As New Thread(New ParameterizedThreadStart(AddressOf ServerClass.StaticMethod))

      ' Start the UI thread.
      t1.Start()

      ' Start the worker thread and pass it the token.
      t2.Start(cts.Token)

      t2.Join()
      cts.Dispose()
   End Sub
End Class
' The example displays the following output:
'       Press 'C' to terminate the application...
'
'       ServerClass.StaticMethod is running on another thread.
'       The worker thread has been canceled. Press any key to exit.

O exemplo cria uma instância de um CancellationTokenSource objeto, que controla o acesso ao token de cancelamento.The example instantiates a CancellationTokenSource object, which controls access to the cancellation token. Em seguida, ele define dois procedimentos de thread.It then defines two thread procedures. O primeiro é definido como uma expressão lambda que agrupa o teclado e, quando a tecla "C" é pressionada, chama CancellationTokenSource.Cancel para definir o token de cancelamento para o estado cancelado.The first is defined as a lambda expression that pools the keyboard and, when the "C" key is pressed, calls CancellationTokenSource.Cancel to set the cancellation token to the cancelled state. O segundo é um método com parâmetros, ServerClass.StaticMethod , que executa um loop até que a IsCancellationRequested propriedade seja true .The second is a parameterized method, ServerClass.StaticMethod, that executes a loop until the IsCancellationRequested property is true.

Em seguida, o thread principal inicia os dois threads e blocos até que o thread que executa o ServerClass.StaticMethod método seja encerrado.The main thread then starts the two threads and blocks until the thread that executes the ServerClass.StaticMethod method terminates.

Comentários

Esta propriedade indica se o cancelamento foi solicitado para esse token, por meio do token inicialmente sendo construído em um estado cancelado ou por meio da chamada do Cancel token associado CancellationTokenSource .This property indicates whether cancellation has been requested for this token, either through the token initially being constructed in a canceled state, or through calling Cancel on the token's associated CancellationTokenSource.

Se essa propriedade for true , ela só garante que o cancelamento tenha sido solicitado.If this property is true, it only guarantees that cancellation has been requested. Ele não garante que todos os manipuladores registrados concluíram a execução, nem que as solicitações de cancelamento concluíram a propagação para todos os manipuladores registrados.It does not guarantee that every registered handler has finished executing, nor that cancellation requests have finished propagating to all registered handlers. A sincronização adicional pode ser necessária, particularmente em situações em que os objetos relacionados estão sendo cancelados simultaneamente.Additional synchronization may be required, particularly in situations where related objects are being canceled concurrently.

Aplica-se a

Confira também