CancellationTokenSource.Cancel Método

Definição

Comunica uma solicitação de cancelamento.Communicates a request for cancellation.

Sobrecargas

Cancel()

Comunica uma solicitação de cancelamento.Communicates a request for cancellation.

Cancel(Boolean)

Comunica uma solicitação de cancelamento e especifica se as operações canceláveis e os retornos de chamada restantes deverão ser processados se ocorrer uma exceção.Communicates a request for cancellation, and specifies whether remaining callbacks and cancelable operations should be processed if an exception occurs.

Cancel()

Comunica uma solicitação de cancelamento.Communicates a request for cancellation.

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

Exceções

Uma exceção de agregação que contém todas as exceções geradas pelos retornos de chamada registrados no CancellationToken associado.An aggregate exception containing all the exceptions thrown by the registered callbacks on the associated CancellationToken.

Exemplos

O exemplo a seguir usa um gerador de números aleatórios para emular um aplicativo de coleta de dados que lê 10 valores integrais de onze 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. Um valor de zero indica que a medição falhou para um instrumento; nesse caso, a operação deve ser cancelada e nenhuma média geral deve ser computada.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 lidar com o cancelamento possível da operação, o exemplo instancia um CancellationTokenSource objeto que gera um token de cancelamento que é passado para um 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. O TaskFactory objeto, por sua vez, passa o token de cancelamento para cada uma das tarefas responsáveis pela coleta de leituras de um instrumento específico.The TaskFactory object in turn passes the cancellation token to each of the tasks responsible for collecting readings for a particular instrument. O TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken) método é chamado para garantir que a média seja calculada somente depois que todas as leituras tiverem sido reunidas com êxito.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 uma tarefa não tiver sido cancelada, a chamada para o TaskFactory.ContinueWhenAll método lançará uma exceção.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.

Comentários

O associado CancellationToken será notificado sobre o cancelamento e passará para um estado em que IsCancellationRequested retorna true.The associated CancellationToken will be notified of the cancellation and will transition to a state where IsCancellationRequested returns true.

Quaisquer retornos de chamada ou operações canceláveis registradas com o CancellationToken serão executados.Any callbacks or cancelable operations registered with the CancellationToken will be executed.

Recomendamos que operações canceláveis e retornos de chamada sejam registrados com CancellationToken exceções not throw.We recommend that cancelable operations and callbacks registered with CancellationToken not throw exceptions.

Essa sobrecarga de Cancel agregará quaisquer exceções geradas em um AggregateException , de modo que um retorno de chamada gerando uma exceção não impedirá que outros retornos de chamada registrados sejam executados.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.

Confira também

Aplica-se a

Cancel(Boolean)

Comunica uma solicitação de cancelamento e especifica se as operações canceláveis e os retornos de chamada restantes deverão ser processados se ocorrer uma exceção.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)

Parâmetros

throwOnFirstException
Boolean

true se exceções devem propagar imediatamente; caso contrário, false.true if exceptions should immediately propagate; otherwise, false.

Exceções

Uma exceção de agregação que contém todas as exceções geradas pelos retornos de chamada registrados no CancellationToken associado.An aggregate exception containing all the exceptions thrown by the registered callbacks on the associated CancellationToken.

Comentários

O associado CancellationToken será notificado sobre o cancelamento e passará para um estado em que o IsCancellationRequested retorna true .The associated CancellationToken will be notified of the cancellation and will transition to a state where IsCancellationRequested returns true.

Quaisquer retornos de chamada ou operações canceláveis registradas com o CancellationToken serão executados.Any callbacks or cancelable operations registered with the CancellationToken will be executed. Os retornos de chamada serão executados de forma síncrona na ordem de UEPS.Callbacks will be executed synchronously in LIFO order.

Recomendamos que operações canceláveis e retornos de chamada sejam registrados com CancellationToken exceções not throw.We recommend that cancelable operations and callbacks registered with CancellationToken not throw exceptions.

Se throwOnFirstException for true , uma exceção será propagada imediatamente para fora da chamada para Cancel , impedindo que os retornos de chamada e as operações canceláveis restantes sejam processados.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 for false , essa sobrecarga agregará quaisquer exceções geradas em um AggregateException , de modo que um retorno de chamada gerando uma exceção não impedirá a execução de outros retornos de chamada registrados.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.

Confira também

Aplica-se a