CancellationTokenSource.Cancel 方法
定義
重要
部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。
傳遞取消要求。
多載
| Cancel() |
傳遞取消要求。 |
| Cancel(Boolean) |
傳遞取消要求，並指定如果發生例外狀況時，是否應處理其餘回呼和可取消的作業。 |
Cancel()
傳遞取消要求。
public:
void Cancel();public void Cancel ();member this.Cancel : unit -> unitPublic Sub Cancel ()例外狀況
包含所有由相關聯的 CancellationToken 上已註冊的回呼所擲回例外狀況的彙總例外狀況。
範例
下列範例會使用亂數產生器來模擬從十一個不同檢測讀取 10 個整數值的資料收集應用程式。 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 產生傳遞至 TaskFactory 物件的解除標記的物件。 物件 TaskFactory 接著會將取消權杖傳遞至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。 如果工作尚未取消，則方法的 TaskFactory.ContinueWhenAll 呼叫會擲回例外狀況。
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
相關聯的 CancellationToken 將會收到取消通知，並轉換為傳回 true 的狀態 IsCancellationRequested 。
將會執行向 CancellationToken 註冊的任何回呼或可取消作業。
我們建議取消的作業和回呼註冊， CancellationToken 但不會擲回例外狀況。
Cancel 的這個多載會將擲回的任何例外狀況匯總到 AggregateException ，如此一個擲回例外狀況的回呼將不會防止執行其他已註冊的回呼。
呼叫這個方法的效果與呼叫 Cancel(false) 相同。
另請參閱
適用於
Cancel(Boolean)
傳遞取消要求，並指定如果發生例外狀況時，是否應處理其餘回呼和可取消的作業。
public:
void Cancel(bool throwOnFirstException);public void Cancel (bool throwOnFirstException);member this.Cancel : bool -> unitPublic Sub Cancel (throwOnFirstException As Boolean)參數
- throwOnFirstException
- Boolean
如果應該立即散佈例外狀況則為 true，否則為 false。
例外狀況
包含所有由相關聯的 CancellationToken 上已註冊的回呼所擲回例外狀況的彙總例外狀況。
備註
相關聯的 CancellationToken 將會收到取消通知，並轉換為傳回 true 的狀態 IsCancellationRequested 。
將會執行向 CancellationToken 註冊的任何回呼或可取消作業。 回呼會以 LIFO 順序同步執行。
我們建議取消的作業和回呼註冊， CancellationToken 但不會擲回例外狀況。
如果 為 throwOnFirstException true ，例外狀況會立即傳播至 的呼叫 Cancel ，以防止處理其餘的回呼和可取消的作業。
如果 throwOnFirstException 為 false ，此多載會將擲回的任何例外狀況匯總到 AggregateException ，如此一個擲回例外狀況的回呼將不會防止執行其他已註冊的回呼。