Question

Why does the following code executes WebRequests after 5 secs when the UI Thread isn’t being blocked anymore? Thread.Sleep is in the UI Thread while both Instantiation and Invocation of WebRequests occurring inside a Thread from ThreadPool.

Loaded += (sender, args) => {

    for (int i = 0; i < 5; i++) {

        ThreadPool.QueueUserWorkItem(state => {
            var request = WebRequest.CreateHttp("http://google.com");
            request.BeginGetResponse(ar => Debug.WriteLine("Request finished"), null);
        });

        Thread.Sleep(1000);
    }

};

What code should I write in order to execute a WebRequest in a background thread while the UI Thread is blocked?

EDIT:
…to be more specific. Why is this request being executed after 10 seconds since is in a background thread?

Loaded += (sender, args) => {

    ThreadPool.QueueUserWorkItem(state => {
        var request = WebRequest.CreateHttp("http://google.com");
        request.BeginGetResponse(ar => Debug.WriteLine("Request finished"), null);
    });
    Thread.Sleep(10000);

};

Answer 1

I asked almost the exact same question here (which I’ll close now that I found yours):
DownloadStringAsync requires UI thread?

The answer is that ALL network code is ultimately marshaled to the UI thread in Silverlight before version 5. Unfortunately, even when I build against Silverlight 5, I’m still getting the same issue, so I’m still investigating…