Use async/await pattern for remote resource requests

[jt000]

In an ASP.NET application there are a limited number of request threads available. When request threads are all used up, then any future requests will be denied (i.e. a DOS attack). A way to mitigate this is to release a thread while I/O operations are occurring allowing re-use of the thread & push an operation back onto the thread pool when the I/O operation completes.

For example, instead of...

        static string GetGoogleHomepage()
        {
            var request = (HttpWebRequest) WebRequest.Create("http://www.google.com");

            var response = request.GetResponse();

            var s = new StringWriter();
            var buffer = new byte[1024];
            using (var stream = response.GetResponseStream())
            {
                int length;
                while ((length = stream.Read(buffer, 0, 1024)) != 0)
                {
                    s.Write(Encoding.UTF8.GetString(buffer, 0, length));
                }
            }

            s.Flush();
            return s.ToString();
        }

... use the async await pattern to allow other requests to re-use the threads while awaiting IO requests...

        static async Task<string> GetGoogleHomepageAsync()
        {
            var request = (HttpWebRequest)WebRequest.Create("http://www.google.com");

            var response = await request.GetResponseAsync();

            var s = new StringWriter();
            var buffer = new byte[1024];
            using (var stream = response.GetResponseStream())
            {
                int length;
                while ((length = await stream.ReadAsync(buffer, 0, 1024)) != 0)
                {
                    await s.WriteAsync(Encoding.UTF8.GetString(buffer, 0, length));
                }
            }

            await s.FlushAsync();
            return s.ToString();
        }

This can be re-used in the synchronous calls to prevent repetitious code and to prevent build breaks by using the Result property (though, don't use this in the async methods since it blocks a thread).

        static string GetGoogleHomepage()
        {
            return GetGoogleHomepageAsync().Result;
        }

For more information on async\await, see http://msdn.microsoft.com/en-us/library/hh191443.aspx