Additionally, I think it’s the case that when we use this.Invoke, we actually automatically put ourselves in a thread-safe situation. The Invoke method executes the method on the control’s thread, which I think means that even if you have 20 different threads simultaneously use this.Invoke, they will all get executed sequentially and safely. However, again I admit that I’m not an expert on the subject. Nevertheless, I’ve never run into a problem with the method used in the above code, so I feel pretty good about it being a safe/good way to handle the textbox update.

I’m always open to learn new things, so if anyone has additional light to shed, please do.

-Doug

One point about preventing the exception when closing the form before the worker thread completes: Microsoft appears to acknowledge that this is expected behavior, if I’m reading the following page correctly.

They say: “An exception might be thrown if the thread that should process the message is no longer active.”

http://msdn.microsoft.com/en-us/library/zyzhdc6b.aspx

So, perhaps the best thing to do is put the this.Invoke call inside a try {} block. I haven’t tested that, but I’d imagine it might work.

-Doug

I use C# 2010 Express, and I noticed couple of things different from this example which was done in VC#2008:
- using a direct call populateTextBox(count.ToString()); in workerFunction method using new thread doesn’t yield “funky” results; instead, it gives “InvalidOperationException” saying ‘textBox1′ cannot be “accessed from a thread other than the thread it was created on.”
- the output of “wrong way” to execute worker function is different than one described here( At the end of 15 seconds the UI becomes responsive again and you see a “15″ in the text box.). Instead, at the end of 15 seconds, you see the whole series “1 2 3 4 (…) 15″ appear at once.

As per Frank’s concern, I found placing lock around worker function seem to make the problem go away. I am not at all sure if this is a legitimate solution, since removing the lock doesn’t necessarily bring the problem back; I’d love to see some1 answer his/my question someday.

Thanks again Doug

Just a quick Thanks!! for posting your article. After digging through the C# 4.0 Nutshell book and numerous examples on the ‘net, yours is the first example that is straightforward, understandable, and actually worked when I used it as an example in my thread-to-UI update code. Jim

If you start the “worker in a new thread” and close the form BEFORE it has completed, the application crashes.

Any idea on how to deal with this situation?

void populateTextBox(string text)
{
lock(this)
{
textBox1.Text = textBox1.Text + ” ” + text;
}
}