CancellationToken 結構

定義

命名空間:

System.Threading

組件:

System.Runtime.dll

Source:

CancellationToken.cs

傳播通知，表示應該取消作業。

public value class CancellationToken : IEquatable<System::Threading::CancellationToken>

public readonly struct CancellationToken : IEquatable<System.Threading.CancellationToken>

type CancellationToken = struct

Public Structure CancellationToken
Implements IEquatable(Of CancellationToken)

繼承

Object

ValueType

CancellationToken

實作

IEquatable<CancellationToken>

範例

下列範例會使用亂數產生器來模擬資料收集應用程式，以從十一個不同的檢測讀取 10 個整數值。 值為零表示一個檢測的度量失敗，在此情況下應該取消作業，而且不應該計算整體平均數。

為了處理作業的可能取消，此範例會具現化 CancellationTokenSource 物件，該物件會產生傳遞至 TaskFactory 物件的解除標記。 接著， TaskFactory 物件會將解除標記傳遞給負責收集特定檢測讀數的每個工作。 系統會 TaskFactory.ContinueWhenAll<TAntecedentResult,TResult>(Task<TAntecedentResult>[], Func<Task<TAntecedentResult>[],TResult>, CancellationToken) 呼叫 方法，以確保只有在成功收集所有讀數之後，才會計算平均值。 如果工作因為取消而尚未完成，方法 TaskFactory.ContinueWhenAll 會擲回例外狀況。

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.

備註

啟用 CancellationToken 執行緒、執行緒集區工作專案或 Task 物件之間的合作式取消。 您可以藉由具 CancellationTokenSource 現化 物件來建立取消權杖，以管理從其 CancellationTokenSource.Token 屬性擷取的取消權杖。 接著，您會將取消權杖傳遞至任何數目的執行緒、工作或作業，這些執行緒、工作或作業應該會收到取消通知。 權杖無法用來起始取消。 當擁有物件呼叫 CancellationTokenSource.Cancel 時， IsCancellationRequested 解除標記的每個複本上的 屬性都會設定為 true 。 接收通知的物件可以適當地回應。

如需詳細資訊和程式碼範例，請參閱 Managed 執行緒中的取消。

建構函式

CancellationToken(Boolean)

初始化 CancellationToken。

屬性

CanBeCanceled	取得這個語彙基元是否能夠處於已取消狀態。
IsCancellationRequested	取得是否已要求取消這個語彙基元。
None	傳回空的 CancellationToken 值。
WaitHandle	取得取消語彙基元時所發出的 WaitHandle 信號。

方法

Equals(CancellationToken)	判斷目前的 CancellationToken 執行個體與指定的語彙基元是否相等。
Equals(Object)	判斷目前的 CancellationToken 執行個體與指定的 Object 是否相等。
GetHashCode()	做為 CancellationToken 的雜湊函式。
Register(Action)	註冊委派，當取消這個 CancellationToken 時將會呼叫該委派。
Register(Action, Boolean)	註冊委派，當取消這個 CancellationToken 時將會呼叫該委派。
Register(Action<Object,CancellationToken>, Object)	註冊取消此 CancellationToken 時將會呼叫的委派。
Register(Action<Object>, Object)	註冊委派，當取消這個 CancellationToken 時將會呼叫該委派。
Register(Action<Object>, Object, Boolean)	註冊委派，當取消這個 CancellationToken 時將會呼叫該委派。
ThrowIfCancellationRequested()	如果已要求取消這個語彙基元，則擲回 OperationCanceledException。
UnsafeRegister(Action<Object,CancellationToken>, Object)	註冊取消此 CancellationToken 時將會呼叫的委派。
UnsafeRegister(Action<Object>, Object)	註冊取消此 CancellationToken 時要呼叫的委派。

運算子

Equality(CancellationToken, CancellationToken)	判斷兩個 CancellationToken 執行個體是否相等。
Inequality(CancellationToken, CancellationToken)	判斷兩個 CancellationToken 執行個體是否不相等。

執行緒安全性

的所有公用和受保護成員 CancellationToken 都是安全線程，而且可以從多個執行緒同時使用。

另請參閱

• 取消
• 工作取消