CancellationToken CancellationToken CancellationToken CancellationToken Struct

定义

传播有关应取消操作的通知。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
继承
CancellationTokenCancellationTokenCancellationTokenCancellationToken
属性

示例

下面的示例使用随机数生成器来模拟数据收集应用程序, 该应用程序从第11个不同乐器读取10个整数值。The following example uses a random number generator to emulate a data collection application that reads 10 integral values from eleven different instruments. 如果值为零, 则指示度量值对一个检测失败, 在这种情况下, 应取消该操作, 而不应计算整体平均值。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.

为了处理可能取消的操作, 此示例实例化一个CancellationTokenSource对象, 该对象生成一个传递TaskFactory给对象的取消标记。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. TaskFactory对象反过来将取消标记传递给负责收集特定检测的读取的每个任务。The TaskFactory object in turn passes the cancellation token to each of the tasks responsible for collecting readings for a particular instrument. 调用TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken)方法以确保仅在成功收集所有读数后计算平均值。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. 如果任务未被取消, 则调用TaskFactory.ContinueWhenAll方法将引发异常。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.

注解

启用CancellationToken线程、线程池工作项或Task对象之间的协作取消。A CancellationToken enables cooperative cancellation between threads, thread pool work items, or Task objects. 可以通过实例化CancellationTokenSource对象来创建取消标记, 该对象管理从其CancellationTokenSource.Token属性检索的取消标记。You create a cancellation token by instantiating a CancellationTokenSource object, which manages cancellation tokens retrieved from its CancellationTokenSource.Token property. 然后, 将取消标记传递给应接收取消通知的任意数量的线程、任务或操作。You then pass the cancellation token to any number of threads, tasks, or operations that should receive notice of cancellation. 标记无法用于启动取消。The token cannot be used to initiate cancellation. 当拥有对象调用CancellationTokenSource.Cancel时, 取消标记的每个副本上的IsCancellationRequested属性都设置为trueWhen the owning object calls CancellationTokenSource.Cancel, the IsCancellationRequested property on every copy of the cancellation token is set to true. 接收通知的对象可以采用任何适当的方式进行响应。The objects that receive the notification can respond in whatever manner is appropriate.

有关详细信息和代码示例, 请参阅托管线程中的取消For more information and code examples see Cancellation in Managed Threads.

构造函数

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

初始化 CancellationTokenInitializes the CancellationToken.

属性

CanBeCanceled CanBeCanceled CanBeCanceled CanBeCanceled

获取此标记是否能处于已取消状态。Gets whether this token is capable of being in the canceled state.

IsCancellationRequested IsCancellationRequested IsCancellationRequested IsCancellationRequested

获取是否已请求取消此标记。Gets whether cancellation has been requested for this token.

None None None None

返回一个空 CancellationToken 值。Returns an empty CancellationToken value.

WaitHandle WaitHandle WaitHandle WaitHandle

获取在取消标记时收到信号的 WaitHandleGets a WaitHandle that is signaled when the token is canceled.

方法

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

确定当前的 CancellationToken 实例是否等于指定的 ObjectDetermines whether the current CancellationToken instance is equal to the specified Object.

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

确定当前的 CancellationToken 实例是否等于指定的标记。Determines whether the current CancellationToken instance is equal to the specified token.

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

作为 CancellationToken 的哈希函数。Serves as a hash function for a CancellationToken.

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

注册一个将在取消此 CancellationToken 时调用的委托。Registers a delegate that will be called when this CancellationToken is canceled.

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

注册一个将在取消此 CancellationToken 时调用的委托。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)

注册一个将在取消此 CancellationToken 时调用的委托。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)

注册一个将在取消此 CancellationToken 时调用的委托。Registers a delegate that will be called when this CancellationToken is canceled.

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

如果已请求取消此标记,则引发 OperationCanceledExceptionThrows 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)

注册一个在取消此 CancellationToken 时调用的委托。Registers a delegate that is called when this CancellationToken is canceled.

操作员

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

确定两个 CancellationToken 实例是否相等。Determines whether two CancellationToken instances are equal.

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

确定两个 CancellationToken 实例是否不相等。Determines whether two CancellationToken instances are not equal.

适用于

线程安全性

的所有公共和受保护CancellationToken的成员都是线程安全的, 可从多个线程并发使用。All public and protected members of CancellationToken are thread-safe and may be used concurrently from multiple threads.

另请参阅