CancellationToken Struktura

Definice

Šíří oznámení, že operace by se měly zrušit.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
Dědičnost
CancellationToken
Atributy

Příklady

Následující příklad používá generátor náhodných čísel k emulaci aplikace shromažďování dat, která čte 10 integrálních hodnot z jedenáct různých nástrojů.The following example uses a random number generator to emulate a data collection application that reads 10 integral values from eleven different instruments. Hodnota nula znamená, že měření se pro jeden nástroj nezdařilo. v takovém případě by operace měla být zrušena a žádný celkový význam by neměl být vypočítán.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.

Aby bylo možné zpracovat možnou zrušení operace, příklad vytvoří instanci objektu CancellationTokenSource, který generuje token zrušení, který je předán objektu TaskFactory.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. Objekt TaskFactory v systému předává token zrušení každému z úloh zodpovědných za shromažďování čtení pro určitý nástroj.The TaskFactory object in turn passes the cancellation token to each of the tasks responsible for collecting readings for a particular instrument. Je volána metoda TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken), aby se zajistilo, že se střední hodnota vypočítá až po úspěšném shromáždění všech čtení.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. Pokud úloha není, protože byla zrušena, volání metody TaskFactory.ContinueWhenAll vyvolá výjimku.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.

Poznámky

@No__t_0 umožňuje kooperativní zrušení mezi vlákny, pracovními položkami fondu vláken nebo objekty Task.A CancellationToken enables cooperative cancellation between threads, thread pool work items, or Task objects. Token zrušení vytvoříte vytvořením objektu CancellationTokenSource, který spravuje tokeny zrušení načtené z jeho vlastnosti CancellationTokenSource.Token.You create a cancellation token by instantiating a CancellationTokenSource object, which manages cancellation tokens retrieved from its CancellationTokenSource.Token property. Pak předáte token zrušení do libovolného počtu vláken, úkolů nebo operací, které by měly obdržet upozornění na zrušení.You then pass the cancellation token to any number of threads, tasks, or operations that should receive notice of cancellation. Token se nedá použít k inicializaci zrušení.The token cannot be used to initiate cancellation. Když vlastnící objekt volá CancellationTokenSource.Cancel, vlastnost IsCancellationRequested na každé kopii tokenu zrušení je nastavena na true.When the owning object calls CancellationTokenSource.Cancel, the IsCancellationRequested property on every copy of the cancellation token is set to true. Objekty, které obdrží oznámení, mohou reagovat jakýmkoli způsobem.The objects that receive the notification can respond in whatever manner is appropriate.

Další informace a příklady kódu naleznete v tématu zrušení ve spravovaných vláknech.For more information and code examples see Cancellation in Managed Threads.

Konstruktory

CancellationToken(Boolean)

Inicializuje CancellationToken.Initializes the CancellationToken.

Vlastnosti

CanBeCanceled

Zjistí, zda je tento token schopný ve zrušeném stavu.Gets whether this token is capable of being in the canceled state.

IsCancellationRequested

Vrátí, zda byl pro tento token požadován zrušení.Gets whether cancellation has been requested for this token.

None

Vrací prázdnou CancellationToken hodnotu.Returns an empty CancellationToken value.

WaitHandle

Získá WaitHandle, která je signalizována při zrušení tokenu.Gets a WaitHandle that is signaled when the token is canceled.

Metody

Equals(CancellationToken)

Určuje, zda je aktuální instance CancellationToken rovna zadanému tokenu.Determines whether the current CancellationToken instance is equal to the specified token.

Equals(Object)

Určuje, zda je aktuální instance CancellationToken rovna zadanému Object.Determines whether the current CancellationToken instance is equal to the specified Object.

GetHashCode()

Slouží jako funkce hash pro CancellationToken.Serves as a hash function for a CancellationToken.

Register(Action)

Zaregistruje delegáta, který bude volán při zrušení tohoto CancellationToken.Registers a delegate that will be called when this CancellationToken is canceled.

Register(Action, Boolean)

Zaregistruje delegáta, který bude volán při zrušení tohoto CancellationToken.Registers a delegate that will be called when this CancellationToken is canceled.

Register(Action<Object>, Object)

Zaregistruje delegáta, který bude volán při zrušení tohoto CancellationToken.Registers a delegate that will be called when this CancellationToken is canceled.

Register(Action<Object>, Object, Boolean)

Zaregistruje delegáta, který bude volán při zrušení tohoto CancellationToken.Registers a delegate that will be called when this CancellationToken is canceled.

ThrowIfCancellationRequested()

Vyvolá OperationCanceledException, pokud u tohoto tokenu bylo požadováno zrušení.Throws a OperationCanceledException if this token has had cancellation requested.

UnsafeRegister(Action<Object>, Object)

Zaregistruje delegáta, který se volá, když se tato CancellationToken zruší.Registers a delegate that is called when this CancellationToken is canceled.

Operátory

Equality(CancellationToken, CancellationToken)

Určuje, zda jsou dvě instance CancellationToken stejné.Determines whether two CancellationToken instances are equal.

Inequality(CancellationToken, CancellationToken)

Určuje, zda se dvě instance CancellationToken neshodují.Determines whether two CancellationToken instances are not equal.

Platí pro

Bezpečný přístup z více vláken

Všechny veřejné a chráněné členy CancellationToken jsou bezpečné pro přístup z více vláken a mohou být použity souběžně z více vláken.All public and protected members of CancellationToken are thread-safe and may be used concurrently from multiple threads.

Viz také