CancellationTokenSource.Cancel Méthode

public:
 void Cancel();

public void Cancel ();

member this.Cancel : unit -> unit

Public Sub Cancel ()

Exceptions

Exemples

L’exemple suivant utilise un générateur de nombres aléatoires pour émuler une application de collecte de données qui lit 10 valeurs intégrales à partir de onze instruments différents. Une valeur de zéro indique que la mesure a échoué pour un instrument, auquel cas l’opération doit être annulée et aucune moyenne globale ne doit être calculée.

Pour gérer l’annulation possible de l’opération, l’exemple instancie un CancellationTokenSource objet qui génère un jeton d’annulation passé à un TaskFactory objet. L’objet TaskFactory transmet à son tour le jeton d’annulation à chacune des tâches responsables de la collecte de lectures pour un instrument particulier. La TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken) méthode est appelée pour s’assurer que la moyenne est calculée uniquement après que toutes les lectures ont été collectées avec succès. Si une tâche n’a pas été annulée, l’appel à la TaskFactory.ContinueWhenAll méthode lève une 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.

Remarques

L’associé CancellationToken est informé de l’annulation et passe à un état où IsCancellationRequested retourne true.

Tous les rappels ou opérations annulables inscrits auprès de l’objet CancellationToken seront exécutés.

Nous vous recommandons d’annuler des opérations et des rappels inscrits sans CancellationToken lever d’exceptions.

Cette surcharge d’Cancel agrège les exceptions levées dans un AggregateException, de sorte qu’un rappel lève une exception n’empêche pas les autres rappels inscrits d’être exécutés.

L’appel de cette méthode a le même effet que l’appel Cancel(false).

Voir aussi

• Annulation
• Annulation de tâches

public:
 void Cancel(bool throwOnFirstException);

public void Cancel (bool throwOnFirstException);

member this.Cancel : bool -> unit

Public Sub Cancel (throwOnFirstException As Boolean)

Paramètres

Exceptions

Remarques

L’associé CancellationToken est informé de l’annulation et passe à un état où IsCancellationRequested retourne true.

Tous les rappels ou opérations annulables inscrits auprès de l’objet CancellationToken seront exécutés. Les rappels seront exécutés de façon synchrone dans l’ordre LIFO.

Nous vous recommandons d’annuler des opérations et des rappels inscrits sans CancellationToken lever d’exceptions.

Si throwOnFirstException c’est truele cas, une exception se propage immédiatement hors de l’appel Cancel, empêchant les rappels restants et les opérations annulables d’être traitées.

Si throwOnFirstException c’est falsele cas, cette surcharge agrège les exceptions levées dans un AggregateException, de sorte qu’un rappel lève une exception n’empêche pas les autres rappels inscrits d’être exécutés.

Voir aussi

• Annulation
• Annulation de tâches