Potential sync issues with Invoke?

I am trying to read value from control in worker thread. 

    public void worker()
    {
        while (true)
        {
            ewh.WaitOne();

            int index = -1;
            this.Invoke((MethodInvoker)delegate()
            {
                index = this.comboBoxSource.SelectedIndex;
            });

            // using index here

As I understand Invoke is launched asynchronously. Am I right that there is no guarantee at the point where I use index it Invoke will finish its work? If so, how can I make Invoke as blocking operation?

Jon Skeet
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As I understand Invoke is launched asynchronously.

No, Invoke is synchronous, in that it will block until the delegate has completed in the UI thread. It's unfortunate that this isn't clearly documented in Control.Invoke(Delegate). The other overload (Control.Invoke(Delegate, object[]) states that it's the implementation of ISynchronizeInvoke.Invoke which is clearer:

Unlike BeginInvoke, this method operates synchronously, that is, it waits until the process completes before returning. Exceptions raised during the call are propagated back to the caller.

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