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TaskScheduler.FromCurrentSynchronizationContext() in .NET

I am getting a runtime exception trying to run the example below.

Unhandled Exception: System.InvalidOperationException: The current SynchronizationContext may not be used as a TaskScheduler.
   at System.Threading.Tasks.SynchronizationContextTaskScheduler..ctor()
   at System.Threading.Tasks.TaskScheduler.FromCurrentSynchronizationContext()
   at TaskDemo.MyForm..ctor() in D:\myStudio\ASPNet\CSharp\CSharp4\MyApp\MyApp\Hello.cs:line 428
   at TaskDemo.SynchronizationContextTaskScheduler() in D:\myStudio\ASPNet\CSharp\CSharp4\MyApp\MyApp\Hello.cs:line 396
   at TaskDemo.Go() in D:\myStudio\ASPNet\CSharp\CSharp4\MyApp\CLRviaCSharp\Hello.cs:line 214
   at ComputeOps.Main() in D:\myStudio\ASPNet\CSharp\CSharp4\MyApp\CLRviaCSharp\Hello.cs:line 23

Code sample:

public class TaskSchedulerTest {

    public void Test() {
        SynchronizationContextTaskScheduler();
    }

    private void SynchronizationContextTaskScheduler() {
        var f = new MyForm();
        System.Windows.Forms.Application.Run();
    }

    private sealed class MyForm : System.Windows.Forms.Form {
        public MyForm() {
            Text = "Synchronization Context Task Scheduler Demo";
            Visible = true; Width = 400; Height = 100;
        }

        private readonly TaskScheduler m_syncContextTaskScheduler =
           TaskScheduler.FromCurrentSynchronizationContext();

        private CancellationTokenSource m_cts;

        protected override void OnMouseClick(System.Windows.Forms.MouseEventArgs e) {
            if (m_cts != null) {    // An operation is in flight, cancel it
                m_cts.Cancel();
                m_cts = null;
            } else {                // An operation is not in flight, start it
                Text = "Operation running";
                m_cts = new CancellationTokenSource();

                // This task uses the default task scheduler and executes on a thread pool thread
                var t = new Task<Int32>(() => Sum(m_cts.Token, 20000), m_cts.Token);
                t.Start();

                // These tasks use the synchronization context task scheduler and execute on the GUI thread
                t.ContinueWith(task => Text = "Result: " + task.Result,
                   CancellationToken.None, TaskContinuationOptions.OnlyOnRanToCompletion,
                   m_syncContextTaskScheduler);

                t.ContinueWith(task => Text = "Operation canceled",
                   CancellationToken.None, TaskContinuationOptions.OnlyOnCanceled,
                   m_syncContextTaskScheduler);

                t.ContinueWith(task => Text = "Operation faulted",
                   CancellationToken.None, TaskContinuationOptions.OnlyOnFaulted,
                   m_syncContextTaskScheduler);
            }
            base.OnMouseClick(e);
        }
    }
}

Any idea?

like image 822
Pingpong Avatar asked Nov 19 '11 10:11

Pingpong


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What is SynchronizationContext in C#?

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1 Answers

put the creation of m_syncContextTaskScheduler into your form constructor .

public MyForm() {
    Text = "Synchronization Context Task Scheduler Demo";
    Visible = true; Width = 400; Height = 100;
    m_syncContextTaskScheduler = TaskScheduler.FromCurrentSynchronizationContext();
}
like image 175
Alex Avatar answered Nov 07 '22 14:11

Alex