Task.Wait Method (CancellationToken)

 

Waits for the Task to complete execution. The wait terminates if a cancellation token is canceled before the task completes.

Namespace:   System.Threading.Tasks
Assembly:  mscorlib (in mscorlib.dll)

public void Wait(
	CancellationToken cancellationToken
)

Parameters

cancellationToken
Type: System.Threading.CancellationToken

A cancellation token to observe while waiting for the task to complete.

Exception Condition
OperationCanceledException

The cancellationToken was canceled.

ObjectDisposedException

The task has been disposed.

AggregateException

The task was canceled. The AggregateException.InnerExceptions collection contains a TaskCanceledException object.

-or-

An exception was thrown during the execution of the task. The AggregateException.InnerExceptions collection contains information about the exception or exceptions.

The Wait(CancellationToken) method creates a cancelable wait; that is, it causes the current thread to wait until one of the following occurs:

  • The task completes.

  • The cancellation token is canceled. In this case, the call to the Wait(CancellationToken) method throws an OperationCanceledException.

System_CAPS_noteNote

Canceling the cancellationToken cancellation token has no effect on the running task unless it has also been passed the cancellation token and is prepared to handle cancellation. Passing the cancellationToken object to this method simply allows the wait to be canceled.

The following example illustrates the simple use of a cancellation token to cancel waiting for a task's completion. A task is launched, calls the CancellationTokenSource.Cancel method to cancel any of the token source's cancellation tokens, and then delays for five seconds. Note that the task itself has not been passed the cancellation token and is not cancelable. The application thread calls the task's Task.Wait method to wait for the task to complete, but the wait is canceled once the cancellation token is cancelled and an OperationCanceledException is thrown. The exception handler reports the exception and then sleeps for six seconds. As the output from the example shows, that delay allows the task to complete in the TaskStatus.RanToCompletion state.

using System;
using System.Threading;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      CancellationTokenSource ts = new CancellationTokenSource();

      Task t = Task.Run( () => { Console.WriteLine("Calling Cancel...");
                                 ts.Cancel();
                                 Task.Delay(5000).Wait();
                                 Console.WriteLine("Task ended delay...");
                               });
      try {
         Console.WriteLine("About to wait for the task to complete...");
         t.Wait(ts.Token);
      }
      catch (OperationCanceledException e) {
         Console.WriteLine("{0}: The wait has been canceled. Task status: {1:G}",
                           e.GetType().Name, t.Status);
         Thread.Sleep(6000);
         Console.WriteLine("After sleeping, the task status:  {0:G}", t.Status);
      }
      ts.Dispose();
   }
}
// The example displays output like the following:
//    About to wait for the task to complete...
//    Calling Cancel...
//    OperationCanceledException: The wait has been canceled. Task status: Running
//    Task ended delay...
//    After sleeping, the task status:  RanToCompletion

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 5.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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