CancellationToken.IsCancellationRequested 屬性

定義

命名空間:

System.Threading

組件:

System.Runtime.dll

來源:

CancellationToken.cs

取得是否已要求取消這個語彙基元。

public:
 property bool IsCancellationRequested { bool get(); };

public bool IsCancellationRequested { get; }

member this.IsCancellationRequested : bool

Public ReadOnly Property IsCancellationRequested As Boolean

屬性值

Boolean

如果已為這個語彙基元要求取消，則為 true；否則為 false。

範例

以下是執行伺服器進程的簡單範例，直到 IsCancellationRequested 屬性傳 true 回 為止。

using System;
using System.Threading;

public class ServerClass
{
   public static void StaticMethod(object obj)
   {
      CancellationToken ct = (CancellationToken)obj;
      Console.WriteLine("ServerClass.StaticMethod is running on another thread.");

      // Simulate work that can be canceled.
      while (!ct.IsCancellationRequested) {
         Thread.SpinWait(50000);
      }
      Console.WriteLine("The worker thread has been canceled. Press any key to exit.");
      Console.ReadKey(true);
   }
}

public class Simple
{
   public static void Main()
   {
      // The Simple class controls access to the token source.
      CancellationTokenSource cts = new CancellationTokenSource();

      Console.WriteLine("Press 'C' to terminate the application...\n");
      // Allow the UI thread to capture the token source, so that it
      // can issue the cancel command.
      Thread t1 = new Thread(() => { if (Console.ReadKey(true).KeyChar.ToString().ToUpperInvariant() == "C")
                                     cts.Cancel(); } );

      // ServerClass sees only the token, not the token source.
      Thread t2 = new Thread(new ParameterizedThreadStart(ServerClass.StaticMethod));
      // Start the UI thread.

      t1.Start();

      // Start the worker thread and pass it the token.
      t2.Start(cts.Token);

      t2.Join();
      cts.Dispose();
   }
}
// The example displays the following output:
//       Press 'C' to terminate the application...
//
//       ServerClass.StaticMethod is running on another thread.
//       The worker thread has been canceled. Press any key to exit.

Imports System.Threading

Public Class ServerClass
   Public Shared Sub StaticMethod(obj As Object)
      Dim ct AS CancellationToken = CType(obj, CancellationToken)
      Console.WriteLine("ServerClass.StaticMethod is running on another thread.")

      ' Simulate work that can be canceled.
      While Not ct.IsCancellationRequested
         Thread.SpinWait(50000)
      End While
      Console.WriteLine("The worker thread has been canceled. Press any key to exit.")
      Console.ReadKey(True)
   End Sub
End Class

Public Class Simple
   Public Shared Sub Main()
      ' The Simple class controls access to the token source.
      Dim cts As New CancellationTokenSource()

      Console.WriteLine("Press 'C' to terminate the application..." + vbCrLf)
      ' Allow the UI thread to capture the token source, so that it
      ' can issue the cancel command.
      Dim t1 As New Thread( Sub()
                               If Console.ReadKey(true).KeyChar.ToString().ToUpperInvariant() = "C" Then
                                  cts.Cancel()
                               End If
                            End Sub)

      ' ServerClass sees only the token, not the token source.
      Dim t2 As New Thread(New ParameterizedThreadStart(AddressOf ServerClass.StaticMethod))

      ' Start the UI thread.
      t1.Start()

      ' Start the worker thread and pass it the token.
      t2.Start(cts.Token)

      t2.Join()
      cts.Dispose()
   End Sub
End Class
' The example displays the following output:
'       Press 'C' to terminate the application...
'
'       ServerClass.StaticMethod is running on another thread.
'       The worker thread has been canceled. Press any key to exit.

此範例會具現化 CancellationTokenSource 物件，以控制取消權杖的存取。 接著會定義兩個執行緒程式。 第一個會定義為集區鍵盤的 Lambda 運算式，當按下 「C」 鍵時，呼叫 CancellationTokenSource.Cancel 以將解除標記設定為已取消的狀態。 第二個是參數化方法 ServerClass.StaticMethod ，它會執行迴圈，直到 IsCancellationRequested 屬性為 true 為止。

主執行緒接著會啟動兩個執行緒並封鎖，直到執行方法的 ServerClass.StaticMethod 執行緒終止為止。

備註

這個屬性工作表示是否已要求取消此權杖，不論是透過一開始建構為已取消狀態的權杖，還是透過在權杖的相關聯 CancellationTokenSource 上呼叫 Cancel 來建構。

如果此屬性為 true ，則只會保證已要求取消。 它不保證每個已註冊的處理常式都已完成執行，也不會保證取消要求已完成傳播至所有已註冊的處理常式。 可能需要其他同步處理，特別是在同時取消相關物件的情況下。

另請參閱

• 取消
• 工作取消