CancellationToken CancellationToken CancellationToken CancellationToken Struct

Definição

Propaga a notificação de que as operações devem ser canceladas.Propagates notification that operations should be canceled.

public value class CancellationToken
[System.Runtime.InteropServices.ComVisible(false)]
public struct CancellationToken
type CancellationToken = struct
Public Structure CancellationToken
Herança
CancellationTokenCancellationTokenCancellationTokenCancellationToken
Atributos

Exemplos

O exemplo a seguir usa um gerador de número aleatório para emular um aplicativo de coleta de dados que lê os 10 valores de 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, caso em que a operação deve ser cancelada e nenhum média geral devem ser calculados.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 possíveis cancelamento da operação, o exemplo cria uma instância de 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 responsável por coletar leituras para um determinado instrumento.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 é computada somente depois que todas as leituras foram compiladas 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 tiver não porque ele foi cancelado, 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

Um CancellationToken permite que o cancelamento cooperativo entre threads, itens de trabalho do pool de thread, ou Task objetos.A CancellationToken enables cooperative cancellation between threads, thread pool work items, or Task objects. Criar um token de cancelamento pela instanciação de um CancellationTokenSource recuperado do objeto, que gerencia tokens de cancelamento do seu CancellationTokenSource.Token propriedade.You create a cancellation token by instantiating a CancellationTokenSource object, which manages cancellation tokens retrieved from its CancellationTokenSource.Token property. Você, em seguida, passar o token de cancelamento para qualquer número de threads, tarefas ou operações que devem receber a notificação de cancelamento.You then pass the cancellation token to any number of threads, tasks, or operations that should receive notice of cancellation. O token não pode ser usado para iniciar o cancelamento.The token cannot be used to initiate cancellation. Quando o objeto proprietário chama CancellationTokenSource.Cancel, o IsCancellationRequested propriedade em todas as cópias do token de cancelamento é definida como true.When the owning object calls CancellationTokenSource.Cancel, the IsCancellationRequested property on every copy of the cancellation token is set to true. Os objetos que recebem a notificação podem responder de maneira que for apropriada.The objects that receive the notification can respond in whatever manner is appropriate.

Para obter mais informações e exemplos de código, consulte cancelamento em Threads gerenciados.For more information and code examples see Cancellation in Managed Threads.

Construtores

CancellationToken(Boolean) CancellationToken(Boolean) CancellationToken(Boolean) CancellationToken(Boolean)

Inicializa o CancellationToken.Initializes the CancellationToken.

Propriedades

CanBeCanceled CanBeCanceled CanBeCanceled CanBeCanceled

Determina se esse token pode estar no estado cancelado.Gets whether this token is capable of being in the canceled state.

IsCancellationRequested IsCancellationRequested IsCancellationRequested IsCancellationRequested

Especifica se o cancelamento foi solicitado para esse token.Gets whether cancellation has been requested for this token.

None None None None

Retorna um valor CancellationToken vazio.Returns an empty CancellationToken value.

WaitHandle WaitHandle WaitHandle WaitHandle

Obtém um WaitHandle que é sinalizado quando o token é cancelado.Gets a WaitHandle that is signaled when the token is canceled.

Métodos

Equals(Object) Equals(Object) Equals(Object) Equals(Object)

Determina se a instância CancellationToken atual é igual ao Object especificado.Determines whether the current CancellationToken instance is equal to the specified Object.

Equals(CancellationToken) Equals(CancellationToken) Equals(CancellationToken) Equals(CancellationToken)

Determina se a instância CancellationToken atual é igual ao token especificado.Determines whether the current CancellationToken instance is equal to the specified token.

GetHashCode() GetHashCode() GetHashCode() GetHashCode()

Serve como uma função de hash para CancellationToken.Serves as a hash function for a CancellationToken.

Register(Action) Register(Action) Register(Action) Register(Action)

Registra um delegado que será chamado quando este CancellationToken for cancelado.Registers a delegate that will be called when this CancellationToken is canceled.

Register(Action, Boolean) Register(Action, Boolean) Register(Action, Boolean) Register(Action, Boolean)

Registra um delegado que será chamado quando este CancellationToken for cancelado.Registers a delegate that will be called when this CancellationToken is canceled.

Register(Action<Object>, Object) Register(Action<Object>, Object) Register(Action<Object>, Object) Register(Action<Object>, Object)

Registra um delegado que será chamado quando este CancellationToken for cancelado.Registers a delegate that will be called when this CancellationToken is canceled.

Register(Action<Object>, Object, Boolean) Register(Action<Object>, Object, Boolean) Register(Action<Object>, Object, Boolean) Register(Action<Object>, Object, Boolean)

Registra um delegado que será chamado quando este CancellationToken for cancelado.Registers a delegate that will be called when this CancellationToken is canceled.

ThrowIfCancellationRequested() ThrowIfCancellationRequested() ThrowIfCancellationRequested() ThrowIfCancellationRequested()

Gera um OperationCanceledException se esse token tiver tido o cancelamento solicitado.Throws a OperationCanceledException if this token has had cancellation requested.

UnsafeRegister(Action<Object>, Object) UnsafeRegister(Action<Object>, Object) UnsafeRegister(Action<Object>, Object) UnsafeRegister(Action<Object>, Object)

Operadores

Equality(CancellationToken, CancellationToken) Equality(CancellationToken, CancellationToken) Equality(CancellationToken, CancellationToken) Equality(CancellationToken, CancellationToken)

Determina se duas instâncias CancellationToken são iguais.Determines whether two CancellationToken instances are equal.

Inequality(CancellationToken, CancellationToken) Inequality(CancellationToken, CancellationToken) Inequality(CancellationToken, CancellationToken) Inequality(CancellationToken, CancellationToken)

Determina se duas instâncias CancellationToken não são iguais.Determines whether two CancellationToken instances are not equal.

Aplica-se a

Acesso thread-safe

Todos os membros públicos e protegidos da CancellationToken são thread-safe e podem ser usados simultaneamente de vários threads.All public and protected members of CancellationToken are thread-safe and may be used concurrently from multiple threads.

Veja também