CancellationTokenSource Clase

Definición

public ref class CancellationTokenSource : IDisposable

public ref class CancellationTokenSource sealed : IDisposable

public class CancellationTokenSource : IDisposable

[System.Runtime.InteropServices.ComVisible(false)]
public sealed class CancellationTokenSource : IDisposable

[System.Runtime.InteropServices.ComVisible(false)]
public class CancellationTokenSource : IDisposable

type CancellationTokenSource = class
    interface IDisposable

[<System.Runtime.InteropServices.ComVisible(false)>]
type CancellationTokenSource = class
    interface IDisposable

Public Class CancellationTokenSource
Implements IDisposable

Public NotInheritable Class CancellationTokenSource
Implements IDisposable

Herencia

Object

CancellationTokenSource

Atributos

ComVisibleAttribute

Implementaciones

IDisposable

Ejemplos

En el ejemplo siguiente se utiliza un generador de números aleatorios para emular una aplicación de recopilación de datos que lee 10 valores enteros de once instrumentos diferentes.The following example uses a random number generator to emulate a data collection application that reads 10 integral values from eleven different instruments. Un valor de cero indica que se ha producido un error en la medida para un instrumento, en cuyo caso se debe cancelar la operación y no se debe calcular la media global.A value of zero indicates that the measurement has failed for one instrument, in which case the operation should be cancelled and no overall mean should be computed.

Para controlar la posible cancelación de la operación, en el ejemplo se crea una instancia de un CancellationTokenSource objeto que genera un token de cancelación que se pasa a un TaskFactory objeto.To handle the possible cancellation of the operation, the example instantiates a CancellationTokenSource object that generates a cancellation token which is passed to a TaskFactory object. TaskFactoryA su vez, el objeto pasa el token de cancelación a cada una de las tareas responsables de recopilar las lecturas de un instrumento determinado.The TaskFactory object in turn passes the cancellation token to each of the tasks responsible for collecting readings for a particular instrument. TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken)Se llama al método para asegurarse de que la media se calcula solo después de que todas las lecturas se hayan recopilado correctamente.The TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken) method is called to ensure that the mean is computed only after all readings have been gathered successfully. Si una tarea no se ha cancelado porque se ha cancelado, la llamada al TaskFactory.ContinueWhenAll método produce una excepción.If a task has not because it has been cancelled, the call to the TaskFactory.ContinueWhenAll method throws an exception.

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      // Define the cancellation token.
      CancellationTokenSource source = new CancellationTokenSource();
      CancellationToken token = source.Token;

      Random rnd = new Random();
      Object lockObj = new Object();
      
      List<Task<int[]>> tasks = new List<Task<int[]>>();
      TaskFactory factory = new TaskFactory(token);
      for (int taskCtr = 0; taskCtr <= 10; taskCtr++) {
         int iteration = taskCtr + 1;
         tasks.Add(factory.StartNew( () => {
                                       int value;
                                       int[] values = new int[10];
                                       for (int ctr = 1; ctr <= 10; ctr++) {
                                          lock (lockObj) {
                                             value = rnd.Next(0,101);
                                          }
                                          if (value == 0) { 
                                             source.Cancel();
                                             Console.WriteLine("Cancelling at task {0}", iteration);
                                             break;
                                          }   
                                          values[ctr-1] = value; 
                                       }
                                       return values;
                                    }, token));   
      }
      try {
         Task<double> fTask = factory.ContinueWhenAll(tasks.ToArray(), 
                                                      (results) => {
                                                         Console.WriteLine("Calculating overall mean...");
                                                         long sum = 0;
                                                         int n = 0; 
                                                         foreach (var t in results) {
                                                            foreach (var r in t.Result) {
                                                                  sum += r;
                                                                  n++;
                                                               }
                                                         }
                                                         return sum/(double) n;
                                                      } , token);
         Console.WriteLine("The mean is {0}.", fTask.Result);
      }   
      catch (AggregateException ae) {
         foreach (Exception e in ae.InnerExceptions) {
            if (e is TaskCanceledException)
               Console.WriteLine("Unable to compute mean: {0}", 
                                 ((TaskCanceledException) e).Message);
            else
               Console.WriteLine("Exception: " + e.GetType().Name);
         }
      }
      finally {
         source.Dispose();
      }
   }
}
// Repeated execution of the example produces output like the following:
//       Cancelling at task 5
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 10
//       Unable to compute mean: A task was canceled.
//       
//       Calculating overall mean...
//       The mean is 5.29545454545455.
//       
//       Cancelling at task 4
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 5
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 6
//       Unable to compute mean: A task was canceled.
//       
//       Calculating overall mean...
//       The mean is 4.97363636363636.
//       
//       Cancelling at task 4
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 5
//       Unable to compute mean: A task was canceled.
//       
//       Cancelling at task 4
//       Unable to compute mean: A task was canceled.
//       
//       Calculating overall mean...
//       The mean is 4.86545454545455.

Imports System.Collections.Generic
Imports System.Threading
Imports System.Threading.Tasks

Module Example
   Public Sub Main()
      ' Define the cancellation token.
      Dim source As New CancellationTokenSource()
      Dim token As CancellationToken = source.Token

      Dim lockObj As New Object()
      Dim rnd As New Random

      Dim tasks As New List(Of Task(Of Integer()))
      Dim factory As New TaskFactory(token)
      For taskCtr As Integer = 0 To 10
         Dim iteration As Integer = taskCtr + 1
         tasks.Add(factory.StartNew(Function()
                                       Dim value, values(9) As Integer
                                       For ctr As Integer = 1 To 10
                                          SyncLock lockObj
                                             value = rnd.Next(0,101)
                                          End SyncLock
                                          If value = 0 Then 
                                             source.Cancel
                                             Console.WriteLine("Cancelling at task {0}", iteration)
                                             Exit For
                                          End If   
                                          values(ctr-1) = value 
                                       Next
                                       Return values
                                    End Function, token))   
         
      Next
      Try
         Dim fTask As Task(Of Double) = factory.ContinueWhenAll(tasks.ToArray(), 
                                                         Function(results)
                                                            Console.WriteLine("Calculating overall mean...")
                                                            Dim sum As Long
                                                            Dim n As Integer 
                                                            For Each t In results
                                                               For Each r In t.Result
                                                                  sum += r
                                                                  n+= 1
                                                               Next
                                                            Next
                                                            Return sum/n
                                                         End Function, token)
         Console.WriteLine("The mean is {0}.", fTask.Result)
      Catch ae As AggregateException
         For Each e In ae.InnerExceptions
            If TypeOf e Is TaskCanceledException
               Console.WriteLine("Unable to compute mean: {0}", 
                                 CType(e, TaskCanceledException).Message)
            Else
               Console.WriteLine("Exception: " + e.GetType().Name)
            End If   
         Next
      Finally
         source.Dispose()
      End Try                                                          
   End Sub
End Module
' Repeated execution of the example produces output like the following:
'       Cancelling at task 5
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 10
'       Unable to compute mean: A task was canceled.
'       
'       Calculating overall mean...
'       The mean is 5.29545454545455.
'       
'       Cancelling at task 4
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 5
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 6
'       Unable to compute mean: A task was canceled.
'       
'       Calculating overall mean...
'       The mean is 4.97363636363636.
'       
'       Cancelling at task 4
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 5
'       Unable to compute mean: A task was canceled.
'       
'       Cancelling at task 4
'       Unable to compute mean: A task was canceled.
'       
'       Calculating overall mean...
'       The mean is 4.86545454545455.

Comentarios

A partir de la .NET Framework 4, el .NET Framework usa un modelo unificado para la cancelación cooperativa de operaciones asincrónicas o sincrónicas de ejecución prolongada que implican dos objetos:Starting with the .NET Framework 4, the .NET Framework uses a unified model for cooperative cancellation of asynchronous or long-running synchronous operations that involves two objects:

• CancellationTokenSourceObjeto, que proporciona un token de cancelación a través Token de su propiedad y envía un mensaje de cancelación llamando a su Cancel CancelAfter método o.A CancellationTokenSource object, which provides a cancellation token through its Token property and sends a cancellation message by calling its Cancel or CancelAfter method.

• CancellationTokenObjeto, que indica si se solicita la cancelación.A CancellationToken object, which indicates whether cancellation is requested.

El patrón general para implementar el modelo de cancelación cooperativa es:The general pattern for implementing the cooperative cancellation model is:

• Crear una instancia de un objeto CancellationTokenSource, que administra y envía una notificación de cancelación a los tokens de cancelación individuales.Instantiate a CancellationTokenSource object, which manages and sends cancellation notification to the individual cancellation tokens.

• Pasar el token devuelto por la propiedad CancellationTokenSource.Token para cada tarea o el subproceso que realiza escuchas de cancelación.Pass the token returned by the CancellationTokenSource.Token property to each task or thread that listens for cancellation.

• Llame al CancellationToken.IsCancellationRequested método desde las operaciones que reciben el token de cancelación.Call the CancellationToken.IsCancellationRequested method from operations that receive the cancellation token. Proporcione un mecanismo para que cada tarea o subproceso responda a una solicitud de cancelación.Provide a mechanism for each task or thread to respond to a cancellation request. Tanto si decide cancelar una operación como si lo hace exactamente, depende de la lógica de la aplicación.Whether you choose to cancel an operation, and exactly how you do it, depends on your application logic.

• Llamar al método CancellationTokenSource.Cancel para proporcionar una notificación de cancelación.Call the CancellationTokenSource.Cancel method to provide notification of cancellation. Esto establece la CancellationToken.IsCancellationRequested propiedad en cada copia del token de cancelación en true .This sets the CancellationToken.IsCancellationRequested property on every copy of the cancellation token to true.

• Llame al Dispose método cuando termine con el CancellationTokenSource objeto.Call the Dispose method when you are finished with the CancellationTokenSource object.

Para más información, consulte el tema sobre la cancelación en subprocesos administrados.For more information, see Cancellation in Managed Threads.

Constructores

Propiedades

Métodos

Se aplica a

Seguridad para subprocesos

Todos los miembros públicos y protegidos de CancellationTokenSource son seguros para subprocesos y se pueden usar simultáneamente desde varios subprocesos, con la excepción de Dispose() , que solo se debe usar cuando todas las demás operaciones del CancellationTokenSource objeto se hayan completado.All public and protected members of CancellationTokenSource are thread-safe and may be used concurrently from multiple threads, with the exception of Dispose(), which must only be used when all other operations on the CancellationTokenSource object have completed.