CancellationToken.IsCancellationRequested CancellationToken.IsCancellationRequested CancellationToken.IsCancellationRequested CancellationToken.IsCancellationRequested Property

定义

获取是否已请求取消此标记。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

属性值

如果此令牌已请求取消,则为 true;否则为 falsetrue if cancellation has been requested for this token; otherwise, false.

示例

下面是一个简单的示例, 在IsCancellationRequested属性返回true之前执行服务器进程。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.

该示例实例化CancellationTokenSource一个对象, 该对象控制对取消标记的访问。The example instantiates a CancellationTokenSource object, which controls access to the cancellation token. 然后, 它定义了两个线程过程。It then defines two thread procedures. 第一个定义为用于汇集键盘的 lambda 表达式, 当按下 "C" 键时, 将调用CancellationTokenSource.Cancel以将取消标记设置为 "已取消" 状态。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. 第二个是参数化方法ServerClass.StaticMethod, 它执行循环, IsCancellationRequested直到属性为trueThe second is a parameterized method, ServerClass.StaticMethod, that executes a loop until the IsCancellationRequested property is true.

然后, 主线程将启动两个线程和块, 直到执行ServerClass.StaticMethod方法的线程终止。The main thread then starts the two threads and blocks until the thread that executes the ServerClass.StaticMethod method terminates.

注解

此属性指示是否已为此标记请求取消, 无论是通过最初以已取消状态构造的令牌, 还是通过对关联Cancel CancellationTokenSource的令牌调用。This 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.

如果此属性为true, 则只保证已请求取消。If this property is true, it only guarantees that cancellation has been requested. 它不保证每个已注册的处理程序已完成执行, 也不保证取消请求已完成传播到所有已注册的处理程序。It does not guarantee that every registered handler has finished executing, nor that cancellation requests have finished propagating to all registered handlers. 可能需要更多的同步, 尤其是在同时取消相关对象的情况下。Additional synchronization may be required, particularly in situations where related objects are being canceled concurrently.

适用于

另请参阅