Question

Hi i am trying to make the Elapsed event of the Timer.Timer class fire on my main thread.
I am restricted to VS 2008, .net 3.5…
In this post:
Do C# Timers elapse on a separate thread?
it is stated that using a SynchronizingObject will make the handler execute on the thread that owns the object.

So I tried this:

class MyTimer
{
  private readonly Timer timer;

  public MyTimer(ISynchronizeInvoke synchronizingObject)
  {
    Console.Out.WriteLine(Thread.CurrentThread.ManagedThreadId);
    timer = new Timer(1000);
    timer.SynchronizingObject = synchronizingObject;
    timer.Elapsed +=
      delegate
        {
          timer.Stop();
          Thread.Sleep(2000);
          Console.Out.WriteLine(Thread.CurrentThread.ManagedThreadId);
          timer.Start();

        };
    timer.Start();
  }
}

class Program
{
  static void Main(string[] args)
  {
    ISynchronizeInvoke syncObject = new Control();
    var mytimer = new MyTimer(syncObject);

    Console.ReadKey();
  }
}

But the output is: 1,4,4,4,4…

Why is that? How do i make the Elapsed handler execute on the mainthread.

I tried using SynchronizingObject for an event
but that didn’t help either:

  public static ElapsedEventHandler Wrap(ElapsedEventHandler original, ISynchronizeInvoke synchronizingObject) 
  {
    return (sender, args) =>
    {
      if (synchronizingObject.InvokeRequired)
      {
        synchronizingObject.Invoke(original, new object[] { sender, args });
      }
      else
      {
        original(sender, args);
      }
    };
  }

and:

timer.Elapsed += Wrap(
      delegate
        {
          timer.Stop();
          Thread.Sleep(200);
          Console.Out.WriteLine(Thread.CurrentThread.ManagedThreadId);
          timer.Start();
        }, 
        synchronizingObject);

But still no success… everytime InvokeRequired is false…

forcing debug into the invoke causes a invalidoperation: “Invoke or BeginInvoke cannot be called on a control until the window handle has been created.”

last resort would be to look into:
http://www.codeproject.com/Articles/12082/A-DelegateQueue-Class?msg=3655119#xx3655119xx
but is that really necessary? or is there some simpler solution?

Answer 1

I found a solution using DispatcherTimer
and Dispatcher.Run() to start the message pump in a new thread. To stop the dispatcher and exit the service smoothly i used

if (_currentDispatcher != null) _currentDispatcher.InvokeShutdown();
_thread.Join();