CancellationToken.IsCancellationRequested 屬性

定義

取得是否已要求取消這個語彙基元。Gets whether cancellation has been requested for this token.

public:
 property bool IsCancellationRequested { bool get(); };
public bool IsCancellationRequested { get; }
member this.IsCancellationRequested : bool
Public ReadOnly Property IsCancellationRequested As Boolean

屬性值

如果已為這個語彙基元要求取消,則為 true;否則為 falsetrue if cancellation has been requested for this token; otherwise, false.

範例

以下是一個簡單的範例,它會執行伺服器進程,直到 IsCancellationRequested 屬性傳回 true 為止。The following is a simple example that executes a server process until the IsCancellationRequested property returns true.

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,以控制對解除標記的存取。The example instantiates a CancellationTokenSource object, which controls access to the cancellation token. 然後,它會定義兩個執行緒程式。It then defines two thread procedures. 第一個是定義為集區的 lambda 運算式,當按下 "C" 鍵時,會呼叫 CancellationTokenSource.Cancel,將解除標記設定為已取消的狀態。The first is defined as a lambda expression that pools the keyboard and, when the "C" key is pressed, calls CancellationTokenSource.Cancel to set the cancellation token to the cancelled state. 第二個是參數化的方法,ServerClass.StaticMethod,它會執行迴圈,直到 @no__t 1 屬性 true 為止。The second is a parameterized method, ServerClass.StaticMethod, that executes a loop until the IsCancellationRequested property is true.

然後,主執行緒會啟動兩個執行緒並封鎖,直到執行 ServerClass.StaticMethod 方法的執行緒終止為止。The main thread then starts the two threads and blocks until the thread that executes the ServerClass.StaticMethod method terminates.

備註

這個屬性會指出是否已針對此標記要求取消,方法是透過一開始在已取消的狀態下建立的權杖,還是在權杖的相關 CancellationTokenSource 上呼叫 CancelThis property indicates whether cancellation has been requested for this token, either through the token initially being constructed in a canceled state, or through calling Cancel on the token's associated CancellationTokenSource.

如果此屬性 true,則只會保證已要求取消。If this property is true, it only guarantees that cancellation has been requested. 它不保證每個已註冊的處理常式都已完成執行,也不會將取消要求傳播到所有已註冊的處理常式。It does not guarantee that every registered handler has finished executing, nor that cancellation requests have finished propagating to all registered handlers. 可能需要額外的同步處理,特別是在同時取消相關物件的情況下。Additional synchronization may be required, particularly in situations where related objects are being canceled concurrently.

適用於

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