CancellationToken Struktura

Definice

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

Dědičnost

Object

ValueType

CancellationToken

Atributy

ComVisibleAttribute

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 CancellationTokenSource objektu, který generuje token zrušení, který je předán TaskFactory objektu.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. V takovém případě TaskFactory objekt předá token zrušení každému z úloh zodpovědných za shromažďování čtení pro konkrétní instrumentaci.In turn, the TaskFactory object passes the cancellation token to each of the tasks responsible for collecting readings for a particular instrument. TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken)Metoda je volána, 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 nebyla dokončena, protože byla zrušena, TaskFactory.ContinueWhenAll metoda vyvolá výjimku.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.

Poznámky

A CancellationToken umožňuje kooperativní zrušení mezi vlákny, pracovními položkami fondu vláken nebo Task objekty.A CancellationToken enables cooperative cancellation between threads, thread pool work items, or Task objects. Můžete vytvořit token zrušení vytvořením instance CancellationTokenSource objektu, který spravuje tokeny zrušení načtené z jeho CancellationTokenSource.Token Vlastnosti.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 , IsCancellationRequested vlastnost u každé kopie 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

Vlastnosti

Metody

Operátory

Platí pro

Bezpečný přístup z více vláken

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