Question

How could I call the onCompleteCallBack method on the same thread the SomeAsyncMethod was called ?

public void SomeAsycMethod ( Action<object> onCompleteCallBack )
{
    // get the current thread 
    /* var ThisThread = Thread.CurrentThread. */

    Task.Factory.StartNew( () =>
    {
        Thread.Sleep( 1000 );// do some work;

        // lastly call the onCompleteCallBack on 'ThisThread'
        onCompleteCallBack( "some result" );

        // I am looking for something like:
        /* ThisThread.Invoke("some result"); */
    });
}

Answer 1

While you can’t guarantee you callback will be called on the same thread, you can guarantee it will be called in the same Synchronization Context (assuming one exists in the original call).

public void SomeAsycMethod ( Action<object> onCompleteCallBack )
{
    // get the current context
    var context = SynchronizationContext.Current;

    Task.Factory.StartNew( () =>
    {
        Thread.Sleep( 1000 );// do some work;

        // lastly call the onCompleteCallBack on 'ThisThread'
        onCompleteCallBack( "some result" );

        // I am looking for something like:
        context.Post(s => onCompleteCallBack ("some result"), null); 
    });
}

For example, in a Windows Forms or WPF program, the above will make sure that the callback is called on the GUI thread (via the message loop or dispatcher, accordingly). Similarly for ASP.NET context.

Having said that, I agree with Justin Harvey in that returning a Task<T> will probably be a better design.