CancellationToken Struct

Definizione

public value class CancellationToken

public struct CancellationToken

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

type CancellationToken = struct

[<System.Runtime.InteropServices.ComVisible(false)>]
type CancellationToken = struct

Public Structure CancellationToken

Ereditarietà

Object

ValueType

CancellationToken

Attributi

ComVisibleAttribute

Esempio

Nell'esempio seguente viene usato un generatore di numeri casuali per emulare un'applicazione di raccolta dati che legge 10 valori integrali da undici strumenti diversi.The following example uses a random number generator to emulate a data collection application that reads 10 integral values from eleven different instruments. Un valore pari a zero indica che la misura non è riuscita per uno strumento, nel qual caso l'operazione deve essere annullata e non deve essere calcolata alcuna media complessiva.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.

Per gestire l'eventuale annullamento dell'operazione, l'esempio crea un'istanza di un CancellationTokenSource oggetto che genera un token di annullamento passato a un TaskFactory oggetto.To handle the possible cancellation of the operation, the example instantiates a CancellationTokenSource object that generates a cancellation token that's passed to a TaskFactory object. A sua volta, l' TaskFactory oggetto passa il token di annullamento a ognuna delle attività responsabili della raccolta di letture per un determinato strumento.In turn, the TaskFactory object passes the cancellation token to each of the tasks responsible for collecting readings for a particular instrument. Il TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken) metodo viene chiamato per garantire che il valore medio venga calcolato solo dopo che tutte le letture sono state raccolte correttamente.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. Se un'attività non è stata completata perché è stata annullata, il TaskFactory.ContinueWhenAll metodo genera un'eccezione.If a task has not completed because it was cancelled, 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.

Commenti

Un oggetto CancellationToken consente l'annullamento cooperativo tra thread, elementi di lavoro del pool di thread o Task oggetti.A CancellationToken enables cooperative cancellation between threads, thread pool work items, or Task objects. Si crea un token di annullamento creando un'istanza di un CancellationTokenSource oggetto che gestisce i token di annullamento recuperati dalla relativa CancellationTokenSource.Token Proprietà.You create a cancellation token by instantiating a CancellationTokenSource object, which manages cancellation tokens retrieved from its CancellationTokenSource.Token property. Si passa quindi il token di annullamento a un numero qualsiasi di thread, attività o operazioni che dovrebbero ricevere l'avviso di annullamento.You then pass the cancellation token to any number of threads, tasks, or operations that should receive notice of cancellation. Non è possibile usare il token per avviare l'annullamento.The token cannot be used to initiate cancellation. Quando l'oggetto proprietario chiama CancellationTokenSource.Cancel , la IsCancellationRequested proprietà di ogni copia del token di annullamento viene impostata su true .When the owning object calls CancellationTokenSource.Cancel, the IsCancellationRequested property on every copy of the cancellation token is set to true. Gli oggetti che ricevono la notifica possono rispondere in qualsiasi modo appropriato.The objects that receive the notification can respond in whatever manner is appropriate.

Per ulteriori informazioni ed esempi di codice, vedere annullamento nei thread gestiti.For more information and code examples see Cancellation in Managed Threads.

Costruttori

Proprietà

Metodi

Operatori

Si applica a

Thread safety

Tutti i membri pubblici e protetti di CancellationToken sono thread-safe e possono essere usati contemporaneamente da più thread.All public and protected members of CancellationToken are thread-safe and may be used concurrently from multiple threads.

Vedi anche

• AnnullamentoCancellation
• Annullamento delle attivitàTask Cancellation