How can I make a background worker thread set to Single Thread Apartment?

Question

I am creating an automated test running application. In this part of the application, I am working on a polling server. It works by constantly polling the web server to de

Answer 1

This is not possible, BGW uses a threadpool thread. TP threads are always MTA, it cannot be changed. You will have to use a regular Thread, call SetApartmentState() before you start it. This thread also should pump a message loop, call Application.Run().

Maybe you ought to consider calling this code from the UI thread. Because in all likelihood, the COM server is running its methods on the UI thread anyway. Marshaling calls from a worker thread to the STA thread that created the COM server is automatic, COM takes care of it.

Or take the bull by the horns and marshal yourself. You can create your own STA thread to give the server a happy home. You'll find code in this post, be sure to create the COM object in your Initialize() override.

Answer 2

I have not tested it, but if you invoke the WinForms Form, you should be back to the UI thread and most of the stuff should work again.

BackgroundWorker bgw = new BackgroundWorker();
bgw.DoWork += new DoWorkEventHandler(this.bgw_DoWork);
bgw.RunWorkerAsync();

private void bgw_DoWork(object sender, DoWorkEventArgs e)
{
    // Invoke the UI thread
    // "this" is referring to the Form1, or what ever your form is
    this.Invoke((MethodInvoker)delegate
    {
        Clipboard.GetText();
        // etc etc
    });
}

Answer 3

BackgroundWorker uses by default a ThreadPool thread, but you can override this behavior. First you need to define a custom SynchronizationContext:

public class MySynchronizationContext : SynchronizationContext
{
    public override void Post(SendOrPostCallback d, object state)
    {
        Thread t = new Thread(d.Invoke);
        t.SetApartmentState(ApartmentState.STA);
        t.Start(state);
    }
}

And override the default SynchronizationContext, like this, before you use your BackgroundWorker:

   AsyncOperationManager.SynchronizationContext = new MySynchronizationContext();

NOTE: this can have performance effects on the rest of your application, so you might want to restrict the new Post implementation (for example using the state or d parameters).

Answer 4

I used +Conrad de Wet's idea and it worked great!

There is one small issue with that code though, you have to close the "this.Invoke....." like with a });

Here is Conrad de Wet's code with this fix:

    BackgroundWorker bgw = new BackgroundWorker();
    bgw.DoWork += new DoWorkEventHandler(this.bgw_DoWork);
    bgw.RunWorkerAsync();>

    private void bgw_DoWork(object sender, DoWorkEventArgs e)
    {
        // Invoke the UI thread
        // "this" is referring to the Form1, or what ever your form is
        this.Invoke((MethodInvoker)delegate
        {
            Clipboard.GetText();
            // etc etc
        });
    }

Answer 5

You normally set it by defining attributre [STAThread()] on the entry point (e.g. Static Main).