CancellationToken Struktur

Definition

public value class CancellationToken

[System.Runtime.InteropServices.ComVisible(false)]
public struct CancellationToken

type CancellationToken = struct

Public Structure CancellationToken

Vererbung

Object

ValueType

CancellationToken

Attribute

ComVisibleAttribute

Beispiele

Im folgenden Beispiel wird ein Zufallszahlengenerator zum Emulieren einer Daten Sammlungs Anwendung verwendet, die 10 ganzzahlige Werte von elf verschiedenen Instrumenten liest.The following example uses a random number generator to emulate a data collection application that reads 10 integral values from eleven different instruments. Der Wert 0 (null) gibt an, dass die Messung für ein einziges Instrument fehlgeschlagen ist. in diesem Fall sollte der Vorgang abgebrochen werden, und es sollte kein allgemeiner Mittelwert berechnet werden.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.

Um den möglichen Abbruch des Vorgangs zu behandeln, instanziiert das Beispiel ein CancellationTokenSource -Objekt, das ein Abbruchtoken wird, die generiert an eine TaskFactory Objekt.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. Das TaskFactory Objekt übergibt wiederum das Abbruch Token an jede der Aufgaben, die für das Erfassen von Messungen für ein bestimmtes Instrument zuständig sind.The TaskFactory object in turn passes the cancellation token to each of the tasks responsible for collecting readings for a particular instrument. Die TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken)-Methode wird aufgerufen, um sicherzustellen, dass der Mittelwert nur berechnet wird, nachdem alle Messwerte erfolgreich erfasst wurden.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. Wenn eine Aufgabe nicht abgebrochen wurde, dann löst der Aufruf an die Methode TaskFactory.ContinueWhenAll eine Ausnahme aus.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.

Hinweise

Eine CancellationToken die den kooperativen Abbruch zwischen Threads, Arbeitsaufgaben im Thread Pool oder Task Objekten ermöglicht.A CancellationToken enables cooperative cancellation between threads, thread pool work items, or Task objects. Sie erstellen ein Abbruch Token, indem Sie ein CancellationTokenSource-Objekt instanziieren, das Abbruch Token verwaltet, die von seiner CancellationTokenSource.Token-Eigenschaft abgerufen werden.You create a cancellation token by instantiating a CancellationTokenSource object, which manages cancellation tokens retrieved from its CancellationTokenSource.Token property. Anschließend übergeben Sie das Abbruch Token an eine beliebige Anzahl von Threads, Tasks oder Vorgängen, die eine Benachrichtigung über den Abbruch erhalten sollen.You then pass the cancellation token to any number of threads, tasks, or operations that should receive notice of cancellation. Das Token kann nicht verwendet werden, um den Abbruch zu initiieren.The token cannot be used to initiate cancellation. Wenn das besitzende Objekt CancellationTokenSource.Cancelaufruft, wird die Eigenschaft IsCancellationRequested für jede Kopie des Abbruch Tokens auf truefestgelegt.When the owning object calls CancellationTokenSource.Cancel, the IsCancellationRequested property on every copy of the cancellation token is set to true. Die Objekte, die die Benachrichtigung empfangen, können auf jede beliebige Art und Weise reagieren.The objects that receive the notification can respond in whatever manner is appropriate.

Weitere Informationen und Codebeispiele finden Sie unter Abbruch in verwalteten Threads.For more information and code examples see Cancellation in Managed Threads.

Konstruktoren

Eigenschaften

Methoden

Operatoren

Gilt für:

Threadsicherheit

Alle öffentlichen und geschützten Member von CancellationToken sind Thread sicher und können gleichzeitig von mehreren Threads verwendet werden.All public and protected members of CancellationToken are thread-safe and may be used concurrently from multiple threads.

Siehe auch

• AbbruchCancellation
• AufgabenabbruchTask Cancellation