CancellationTokenSource.Cancel CancellationTokenSource.Cancel CancellationTokenSource.Cancel CancellationTokenSource.Cancel Method

Definizione

Comunica una richiesta di annullamento.Communicates a request for cancellation.

Overload

Cancel() Cancel() Cancel() Cancel()

Comunica una richiesta di annullamento.Communicates a request for cancellation.

Cancel(Boolean) Cancel(Boolean) Cancel(Boolean) Cancel(Boolean)

Passa una richiesta di annullamento e specifica se i callback restanti e le operazioni annullabili devono essere elaborati se si verifica un'eccezione.Communicates a request for cancellation, and specifies whether remaining callbacks and cancelable operations should be processed if an exception occurs.

Cancel() Cancel() Cancel() Cancel()

Comunica una richiesta di annullamento.Communicates a request for cancellation.

public:
 void Cancel();
public void Cancel ();
member this.Cancel : unit -> unit
Public Sub Cancel ()

Eccezioni

Eccezione di aggregazione che contiene tutte le eccezioni generate dai callback registrati sull'oggetto CancellationToken associato.An aggregate exception containing all the exceptions thrown by the registered callbacks on the associated CancellationToken.

Esempi

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 CancellationTokenSource un oggetto che genera un token di annullamento che viene passato TaskFactory a un oggetto.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. L' TaskFactory oggetto passa a sua volta il token di annullamento a ognuna delle attività responsabili della raccolta di letture per un determinato strumento.The TaskFactory object in turn 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 annullata, la chiamata al TaskFactory.ContinueWhenAll metodo genera un'eccezione.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.

Commenti

L'oggetto CancellationToken associato riceverà una notifica dell'annullamento e passerà a uno stato IsCancellationRequested in cui restituisce true.The associated CancellationToken will be notified of the cancellation and will transition to a state where IsCancellationRequested returns true.

Verranno eseguiti eventuali callback o operazioni annullabili registrate CancellationToken con.Any callbacks or cancelable operations registered with the CancellationToken will be executed.

È consigliabile che le operazioni e i callback annullabili CancellationToken registrati con eccezioni non generino eccezioni.We recommend that cancelable operations and callbacks registered with CancellationToken not throw exceptions.

Questo overload di Cancel aggrega tutte le eccezioni generate in AggregateExceptionun oggetto, in modo tale che un callback che genera un'eccezione non impedirà l'esecuzione di altri callback registrati.This overload of Cancel will aggregate any exceptions thrown into an AggregateException, such that one callback throwing an exception will not prevent other registered callbacks from being executed.

Vedi anche

Cancel(Boolean) Cancel(Boolean) Cancel(Boolean) Cancel(Boolean)

Passa una richiesta di annullamento e specifica se i callback restanti e le operazioni annullabili devono essere elaborati se si verifica un'eccezione.Communicates a request for cancellation, and specifies whether remaining callbacks and cancelable operations should be processed if an exception occurs.

public:
 void Cancel(bool throwOnFirstException);
public void Cancel (bool throwOnFirstException);
member this.Cancel : bool -> unit
Public Sub Cancel (throwOnFirstException As Boolean)

Parametri

throwOnFirstException
Boolean Boolean Boolean Boolean

true se le eccezioni devono essere propagate immediatamente; in caso contrario, false.true if exceptions should immediately propagate; otherwise, false.

Eccezioni

Eccezione di aggregazione che contiene tutte le eccezioni generate dai callback registrati sull'oggetto CancellationToken associato.An aggregate exception containing all the exceptions thrown by the registered callbacks on the associated CancellationToken.

Commenti

L'oggetto CancellationToken associato riceverà una notifica dell'annullamento e passerà a uno stato IsCancellationRequested in truecui restituisce.The associated CancellationToken will be notified of the cancellation and will transition to a state where IsCancellationRequested returns true.

Verranno eseguiti eventuali callback o operazioni annullabili registrate CancellationToken con.Any callbacks or cancelable operations registered with the CancellationToken will be executed. I callback verranno eseguiti in modo sincrono nell'ordine LIFO.Callbacks will be executed synchronously in LIFO order.

È consigliabile che le operazioni e i callback annullabili CancellationToken registrati con eccezioni non generino eccezioni.We recommend that cancelable operations and callbacks registered with CancellationToken not throw exceptions.

Se throwOnFirstException Cancelè true, un'eccezione verrà immediatamente propagata all'esterno della chiamata a, evitando che vengano elaborati i callback restanti e le operazioni annullabili.If throwOnFirstException is true, an exception will immediately propagate out of the call to Cancel, preventing the remaining callbacks and cancelable operations from being processed.

Se throwOnFirstException AggregateExceptionè false, questo overload aggrega tutte le eccezioni generate in un oggetto, in modo tale che un callback che genera un'eccezione non impedirà l'esecuzione di altri callback registrati.If throwOnFirstException is false, this overload will aggregate any exceptions thrown into an AggregateException, such that one callback throwing an exception will not prevent other registered callbacks from being executed.

Vedi anche

Si applica a